Serratia infections: from military experiments to current practice. Clin Microbiol Rev. 2011;24:755-791. [PMID: 21976608 DOI: 10.1128/cmr.00017-11]

Exploration of the feasibility of clinical application of phage treatment for multidrug-resistant Serratia marcescens-induced pulmonary infection

Serratia marcescens (S. marcescens) commonly induces refractory infection due to its multidrug-resistant nature. To date, there have been no reports on the application of phage treatment for S. marcescens infection. This study was conducted to explore the feasibility of phage application in treating refractory S. marcescens infection by collaborating with a 59-year-old male patient with a pulmonary infection of multidrug-resistant S. marcescens. Our experiments included three domains: i) selection of the appropriate phage, ii) verification of the efficacy and safety of the selected phage, iii) confirmation of phage-bacteria interactions. Our results showed that phage Spe5P4 is appropriate for S. marcescens infection. Treatment with phage Spe5P4 showed good efficacy, manifested as amelioration of symptoms, hydrothorax examinations, and chest computed tomography findings. Phage treatment did not worsen hepatic and renal function, immunity-related indices, or indices of routine blood examination. It did not induce or deteriorate drug resistance of the involved antibiotics. Importantly, no adverse events were reported during the treatment or follow-up periods. Thus, phage treatment showed satisfactory safety. Finally, we found that phage treatment did not increase the bacterial load, cytotoxicity, virulence, or phage resistance of S. marcescens, indicating satisfactory phage-bacteria interactions between Spe5P4 and S. marcescens, which are useful for the future application of phage Spe5P4 against S. marcescens. This work provides evidence and a working basis for further application of phage Spe5P4 in treating refractory S. marcescens infections. We also provided a methodological basis for investigating clinical application of phage treatment against multidrug-resistant bacterial infections in the future.

Warming exacerbates the effects of pesticides on the soil collembolan gut microbiome and antibiotic resistome

In the context of global climate warming, studies have yet to fully clarify how pollutants affect the gut microbiome and antibiotic resistance genes (ARGs) in nontarget soil fauna. This study investigates the interactive effects of pesticide exposure (imidacloprid) and elevated temperature on the gut bacterial community and ARGs in the model soil collembolan Folsomia candida. Our results demonstrate warming exacerbates the toxicity of imidacloprid in collembolans. While exposure to both warming and pesticide significantly altered the gut microbial composition of F. candida, impairing microbial metabolic diversity and potential host defense mechanisms, it also increased collembolan mortality. This combined exposure significantly enhanced the abundance and diversity of ARGs in the collembolan gut. A notable correlation between ARGs and mobile genetic elements (MGEs) underscores the potential risk of ARG transmission. Co-occurrence network analysis identified 52 bacterial genera as potential ARG hosts. Additionally, pure-culture exposure experiments with the isolated bacterium Serratia liquefaciens revealed the adaptability of ARG hosts to pesticide and warming stress plays an important role in driving the observed increase in ARGs. In conclusion, this study highlights the synergistic effects of climate warming and pesticide contamination on nontarget soil organisms, emphasizing the potential long-term risks to soil ecosystem health and stability.

Proteomic profile of multidrug-resistant Serratia marcescens under meropenem challenge

Serratia marcescens is an opportunistic bacterium implicated in the prevalence of serious nosocomial infections and increased outbreaks in Intensive Care Units (ICUs) and Neonatal Intensive Care Units (NICUs). S. marcescens strains are resistant to several antimicrobial classes and express numerous virulence factors that promote pathogenicity. In the present study, the proteomic profile of the multidrug-resistant (MDR) S. marcescens clinical isolate challenged with the antimicrobial meropenem was evaluated. The proteins obtained were analyzed using liquid chromatography coupled with tandem mass spectrometry (LC-MSE). A total of 199 induced proteins were identified revealing that multidrug-resistant S. marcescens promotes increasing of proteins related to energy metabolism and efflux pump and decreases synthesis of proteins related to oxidative stress response and cell mobility upon meropenem challenge, shedding some light on the relationship between expressed proteins and bacterial pathogenicity after antimicrobial induction.

Genomic and phenotypic insights into Serratia interaction with plants from an ecological perspective

We investigated the plant growth-promoting potential of two endophytic strains of Serratia marcescens, namely SmCNPMS2112 and SmUFMG85, which were isolated from the roots of the same maize (Zea mays) plant. The strains were evaluated in vitro for their ability to produce siderophores and indoleacetic acid, form biofilm, solubilize iron phosphate (Fe-P) and Araxá rock phosphate (RP), mineralize phytate, and for their ability to adhere and colonize host roots. Additionally, their plant growth-promoting potential was tested in vivo under greenhouse conditions using millet grown in soil under two fertilization schemes (triple superphosphate, TSP, or commercial rock phosphate, cRP). Both strains improved at least five physiological traits of millet or P content in soil. In order to elucidate the genetic basis of the plant growth-promoting ability of these strains, their genomes were compared. While both genomes exhibited a similar overall functional profile, each strain had unique features. SmCNPMS2112 contained genes related to arsenic and aromatic hydrocarbons degradation, whereas SmUFMG85 harbored genes related to rhamnolipid biosynthesis and chromium bioremediation. Also, we observe a unique repertoire of genes related to plant growth-promotion (PGP) in the SmUFMG85 genome, including oxalate decarboxylase (OxdC), associated with the catabolism of oxalic acid, and aerobactin siderophore (lucD) in the genome of SmCNPMS2112. The alkaline phosphatase was observed on two strains, but acid phosphatase was exclusive to SmUFMG85. Eighteen secondary metabolic gene clusters, such as those involved in the biosynthesis of macrolides and bacillomycin, among others, occur in both strains. Moreover, both genomes contained prophages, suggesting that viral-mediated horizontal gene transfer may be a key mechanism driving genomic variability in the endophytic environment. Indeed, the most genes unique and accessory of SmUFMG85 and SmCNPMS2112 were localized in genomic islands, highlighting genome plasticity and its underlying drivers. To investigate the ecological distribution of plant-interaction traits in the genus Serratia, the genomes of SmUFMG85 and SmCNPMS2112 strains were compared with those of other 19 Serratia strains of different species, which were isolated from different environments. We observe that many features for PGP are present in all genomes, regardless of niche, for instance: formation of flagella, fimbriae and pili, chemotaxis, biosynthesis of siderophores, indole-3-acetic acid (IAA) and volatile organic (VOC) and inorganic (VIC) compounds, such as acetoin and HCN. Also, all the analyzed genomes show an antimicrobial resistance repertoire of genes that confer resistance to several antibiotics belonging to the groups of aminoglycosides and quinolones, for instance. Also, from a niche partitioning perspective, secretion system preference and the ability to produce exopolysaccharides involved in biofilm formation are among the features that vary the most among strains, and most likely influence niche adaptation in Serratia spp., even though only the latter seems to be a feature specifically associated with virulence in the analyzed strains. Our results show that populations of bacteria sharing the same niche can present significant physiological and genomic differences, and reveal the intraspecific metabolic plasticity that underlie plant-bacteria interactions. Also, this study reveals the potential of two Serratia marcescens strains as bioinoculants in agriculture. Considering that Serratia spp. are regarded as low risk biological agents, despite the fact that they can be associated with human disease, we suggest that strain biosafety be evaluated using a combination of genome and phenotypic analyses, as presented herein.

Genomic insights into pigmented Serratia marcescens strains isolated from patients in northeast Mexico

Serratia marcescens (SM) is an opportunistic pathogen associated with outbreaks in immunocompromised hosts. While SM is commonly isolated from clinical and environmental sources, prodigiosin production is typically associated with environmental strains rather than clinical isolates. Here, we report the genome sequences of three pigmented SM clinical isolates -HU1848, HU2225, and HU2228- and examine their genomic and phenotypic characteristics. Phylogenetic analysis using 1103 finished public SM genomes revealed that these isolates cluster more closely with environmental SM strains than with those typically associated with clinical settings. Notably, despite their environmental-like genomic background, these isolates harbor multiple virulence genes implicated in colonization and resistance to fertilizers, as well as antimicrobial resistance genes for chloramphenicol, fosfomycin, and tetracycline. MIC determination showed susceptibility to aminoglycosides and fluoroquinolones. Additionally, we observed that the phenolic compound methyl gallate modulates pigment production and motility. The absence of AHL biosynthetic genes in these pigmented strains challenges previous associations between quorum sensing and prodigiosin biosynthesis. These findings suggest that certain SM strains with environmental-like genetic features can persist in clinical settings, underscoring the need to further investigate their potential role in nosocomial infections.

The Effects of Sampling Sites, Collection Time, and Refrigerated Storage Duration on Microbiota of Raw Milk From a Chinese Dairy Farm: An Exploratory Study

Raw milk is the primary material for all dairy products, making it imperative to characterize and monitor its microbial composition to ensure product quality. To investigate microbial contamination from pasture to processing facilities and establish microbial traceability systems, eighty-seven raw milk samples were collected from a dairy farm in Shijiazhuang of China in August. The raw milk samples were categorized into three experimental groups based on: sampling sites along the production chain (manual milking, buffer tank, filter, refrigeration tank, milk truck, and plant factory), sampling time (before dawn, morning, noon, and afternoon), and refrigeration storage (0-72 h at 12 h intervals). The microbiota were evaluated by 16S rRNA sequencing. The results identified Pseudomonas, Lactobacillus, and Prevotella as the predominant bacterial genera across all sampling conditions. The α-diversity (Shannon and Chao1) and β-diversity analysis jointly revealed significant differences in microbial communities of raw milk samples. Specifically, raw milk collected from milk truck showed distinct bacterial communities compared with upstream collecting points, while morning-collected samples showed marked compositional differences from other time points. These findings were consistently supported by cluster heatmap analysis. In addition, the relative abundance of Pseudomonas in raw milk decreased but Lactococcus and Serratia increased with refrigerated time (P < 0.05). This inverse relationship was further evidenced in cooccurrence network showing a strong negative correlation between Lactococcus, Serratia, and Pseudomonas. These results indicated where and when (after being transported to milk truck and in the morning) we need to alert owing to potential contamination in raw milk. Our results also suggested that psychrotrophic bacteria in raw milk should be paid attention, especially Pseudomonas during early refrigerated storage and Serratia during late refrigerated storage.

Co-exposure to polystyrene nanoplastics and mercury synergistically exacerbates toxicity in rare minnow (Gobiocypris rarus) compared to individual exposures

Nanoplastics (NPs) and mercury (Hg) are ubiquitous pollutants that co-occur in aquatic ecosystems. However, the interaction between NPs and Hg, particularly whether NPs affect the accumulation and in vivo biotransformation of Hg in aquatic organisms, remains unclear. The toxicity of NPs and mercuric chloride (HgCl2), both individually and in combination at environmentally relevant concentrations, on rare minnow (Gobiocypris rarus) were investigated in this study. The results demonstrated that NPs increased total Hg accumulation by 33.33 % but had limited effects on methylmercury (MeHg) content and its proportional distribution in muscle tissue compared to single Hg exposure. Both NPs and Hg induced significant growth inhibition, intestinal damage, oxidative stress, and inflammatory responses in rare minnow, with endpoint-specific effect patterns. Moreover, NPs and Hg dramatically altered gut microbiota composition and co-occurrence networks, with NPs inducing more metabolic pathway changes than Hg. Notably, combined exposure exacerbated almost all toxic effects in rare minnow compared to individual exposures, indicating synergistic interactions between NPs and Hg. These findings highlight the need to consider co-existing contaminants when evaluating NP toxicity.

Investigation and control of two consecutive Serratia marcescens outbreaks linked to reusable LigaSure devices in an operating room

BACKGROUND

Serratia marcescens is an opportunistic gram-negative bacterium that is commonly associated with sudden outbreaks of various healthcare-associated infections in healthcare settings. This study describes two consecutive mini-outbreaks of S. marcescens in an operating room following laparoscopic sleeve gastrectomy procedures.

METHODS

Between December 16 and 26, 2020, five patients who underwent sleeve gastrectomy at a university hospital were re-admitted with clinical symptoms. An investigation by the infection control team was conducted to identify the source. Environmental and instrument samples were collected, and antimicrobial susceptibility testing was performed. Molecular typing using pulsed-field gel electrophoresis (PFGE) was conducted to assess the genetic relatedness of the isolates. Infection control interventions were implemented during the outbreak.

FINDINGS

During this period, four of the five patients tested positive for S. marcescens. A total of 31 surveillance samples were collected, isolates from the handle of one LigaSure and the grasper of another were also positive for S. marcescens. PFGE revealed two distinct clones, indicating two separate outbreaks. Four of the six isolates from samples of patients and environment were the same, while two isolates belonging to another clone were collected from the blood samples of patients. After discontinuation of the reused LigaSure devices and implementation of strict infection control measures, no new cases were reported.

CONCLUSION

The two consecutive S. marcescens outbreaks were linked to the reuse of inadequately sterilized LigaSure devices. The implementation of targeted infection control measures successfully halted further transmission.

Infection characteristics among Serratia marcescens capsule lineages

Serratia marcescens is a healthcare-associated pathogen that can cause severe infections, including bacteremia and pneumonia. The capsule polysaccharide of S. marcescens is a bacteremia fitness determinant, and previous work defined capsule locus (KL) diversity within the species. Strains belonging to KL1 and KL2 capsule clades produce sialylated polysaccharides and represent the largest subpopulation of isolates from clinical origin. In this study, the contribution of these and other S. marcescens capsules to infection was determined in animal and cellular models. Using a murine model of primary bacteremia, clinical isolates of multiple KL types demonstrated capsule-dependent colonization of the spleen, liver, and kidney following tail vein inoculation. Similar results were observed using a bacteremic pneumonia model, in that all tested strains of clinical origin demonstrated a requirement for capsule in both the primary lung infection site and for bloodstream dissemination to secondary organs. Finally, the capsule from each KL clade was examined for the ability to resist internalization by bone marrow-derived macrophages. Only the sialylated KL1 and KL2 clade strains exhibited capsule-dependent inhibition of internalization, including KL2 capsule produced in a heterologous background. Together, these findings indicate that lineage-specific resistance to macrophage phagocytosis may enhance survival and antibacterial defenses of clinically adapted S. marcescens.

IMPORTANCE

Bacteremia occurs when the host immune system fails to contain bacterial bloodstream replication following an initial inoculation event from either an internal or external source. Capsule polysaccharides play a protective role for Serratia marcescens during bacteremia, but there is abundant genetic diversity at the capsule-encoding locus within the species. This study compares the infection characteristics of S. marcescens isolates belonging to five capsule types and defines the contributions to infection fitness for each. By characterizing the differences in capsule dependence and infection potential between S. marcescens strains, efforts to combat these life-threatening infections can be focused toward identifying strategies that target the most critical genetic lineages of this important opportunistic pathogen.

Identification of Bacterial Oligopeptidase B Inhibitors from Microbial Natural Products: Molecular Insights, Docking Studies, MD Simulations, and ADMET Predictions

Background/Objectives: The increasing threat of antibiotic resistance and the declining efficiency of traditional drug discovery pipelines highlight the urgent need for novel drug targets and effective enzyme inhibitors against infectious diseases. Oligopeptidase B (OPB), a serine protease with trypsin-like specificity that processes low-molecular-weight peptides and oligopeptides, is present in bacteria and certain parasites but absent in mammals. This unique distribution makes OPB an attractive and selective target for antimicrobial drug development. Methods: Three-dimensional models of OPB from Serratia marcescens and Stenotrophomonas maltophilia, previously identified by our research group, were constructed via homology modeling using the best available OPB template from the RCSB Protein Data Bank. The S. marcescens OPB model was subjected to high-throughput virtual screening (HTVS) against the Natural Products Atlas (npatlas) database. Top-ranking compounds were further evaluated using Glide standard precision (SP) and extra precision (XP) docking protocols. Binding affinities were refined using molecular mechanics with generalized born and surface area (MM-GBSA) calculations. Molecular dynamics (MD) simulations assessed binding stability, while absorption distribution metabolism excretion and toxicity (ADMET) profiling evaluated drug-likeness and pharmacokinetic properties. Results: Ten natural product compounds demonstrated stronger binding affinities than antipain, a well-known oligopeptide-based protease inhibitor, as indicated by their more favorable MM-GBSA scores of -60.90 kcal/mol (S. marcescens) and -27.07 kcal/mol (S. maltophilia). Among these, dichrysobactin and validamycin E consistently exhibited favorable binding profiles across both OPB models. MD simulations confirmed the stability of their interactions with OPB active sites, maintaining favorable binding conformations throughout the simulation period. ADMET analysis suggested that while both compounds show promise, lead optimization is required to enhance their drug-like characteristics. Conclusions: This study identifies dichrysobactin and validamycin E as promising OPB inhibitors with potential antimicrobial activity. These findings support their further development as selective and potent agents against bacterial pathogens, including resistant strains, and underscore the need for experimental validation to confirm their efficacy and safety.

Microbiological Surveillance and Antimicrobial Susceptibility Observations on Peritoneal Dialysis-Associated Peritonitis in an Outpatient German Reference Center

Background: Peritonitis is a relevant complication in peritoneal dialysis (PD). The initial empirical antibiotic therapy depends on the center-specific distribution of microorganisms and the microbial susceptibility profiles. However, data on the locoregional germ spectrum in Germany are insufficient regarding the current recommended empirical antibiotic regimens of either cefepime as monotherapy or the combination of cefazolin and ceftazidime. Methods: This retrospective single-center study of routine clinical patient data analyzes the range of infecting organisms causing PD-associated peritonitis and their corresponding antimicrobial resistances during the 2015 to 2022 timeframe. We used Ordinary Least-Squares regression to model trends in the detection of microbiological spectrum samples. The 'reporting of studies conducted using observational routinely collected health data' (RECORD) statement was acknowledged. Results: There were 80 documented peritonitis episodes with 99 causal etiologies sampled. Of those, eighty-seven were bacterial, three were fungi (3%), eight had no microbial growth (8%), and one more had missing data. The largest group of microorganisms detected were Gram-positive bacteria (N = 56, 56.6%), predominantly sampled as Staphylococcacea, Enterococcaceae, and Streptococcaceae (Staphylococcus aureus, 14.1%). Gram-negative bacteria were found in 31.3% of samples (N = 31), predominantly Enterobacteriaceae (Escherichia coli, 9%). In total, 34 different microorganisms were identified. On one occasion, methicillin-resistant Staphylococcus epidermidis and one sample of multi-resistant Serratia marcescens were identified. Methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci were not detected. Fungi were found in three peritonitis episodes. Regression analyses did not indicate changes in the general microbiological spectrum during the observational timeframe. The center-specific peritonitis rates were below the recommended rates of the International Society for Peritoneal Dialysis for all years studied. Conclusions: The recommended empiric therapy was suitable at our center, with a few exceptions for non-specific pathogens and for those with β-lactamases or enterococci. When there is no clinical response to empiric therapy, alternative antibiotics should be considered accordingly. The retrospective data are limited to the reported outcome measures.

Genetic basis of carbapenem-resistant clinical Serratia marcescens in Japan

OBJECTIVE

To investigate the genetic basis of carbapenem resistance in clinical Serratia marcescens isolates collected from patients in Japan between 1994 and 2016. A total of 5135 clinical isolates of S. marcescens were recovered from different medical centres across Japan, identified in central laboratories, and tested for antimicrobial agents using the broth microdilution method.

METHODS

All the isolates that showed intermediate or resistant phenotypes for at least one carbapenem antibiotic were confirmed by antimicrobial susceptibility testing and for carbapenemase production by the modified carbapenem inactivation method. Furthermore, full genetic characterization was performed by whole genome sequencing for all the isolates.

RESULTS

Based on our findings, 27 isolates (0.53%) exhibited resistance to ertapenem and/or meropenem. Among these, 10 isolates were phenotypically confirmed as carbapenemase producers using the modified carbapenem inactivation method test. The isolates were resistant to a wide range of antibiotics including β-lactams (48.1%-100%), two fluoroquinolones (77.8%-88.9%), tigecycline and minocycline (70.4% each), and sulfamethoxazole-trimethoprim (55.6%). Whole-genome sequencing was conducted on all carbapenem-resistant strains, uncovering blaIMP in eight isolates, comprising seven with blaIMP-1 and one with blaIMP-11, alongside multiple antimicrobial resistance determinants. Importantly, the phylogenomic comparison with international S. marcescens isolates revealed genetic relatedness and potential cross-border transmission events.

CONCLUSIONS

Our findings underscore the importance of enhanced surveillance and infection control measures to mitigate the dissemination of multidrug-resistant pathogens, emphasizing the need for international collaboration and coordinated efforts to address antimicrobial resistance on a global scale.

Interaction of Serratia proteamaculans with Integrins Activates Invasion-Promoting Signaling Pathways

The opportunistic bacteria Serratia proteamaculans are able to penetrate human cells. It was previously shown that the bacterial surface protein OmpX promotes bacterial adhesion. In addition, infection with bacteria that synthesize the OmpX protein enhances the expression of EGFR and β1 integrin involved in the invasion of S. proteamaculans. Therefore, this work was aimed at determining the mechanism of interaction of S. proteamaculans with receptors of eukaryotic cells. Both integrin-linked kinase (ILK) and EGFR tyrosine kinase have been shown to be involved in the invasion of these bacteria. During infection, EGFR is first phosphorylated at Tyr845, which is carried out by c-Src kinase transmitting a signal from nearby receptors. The S. proteamaculans invasion depends on c-Src and focal adhesion kinase (FAK), which can both transmit a signal between β1 integrin and EGFR and participate in cytoskeletal rearrangements. These bacteria have been shown to interact with integrin not through the RGD binding site, and integrin binding to the RGD peptide enhances adhesion, invasion, and expression of α5 and β1 integrin subunits in response to infection. On the other hand, bacterial adhesion and increased expression of integrins during infection are caused by OmpX. Thus, OmpX interacts with integrins, and the participation of the α5 and β1 integrin subunits in the S. proteamaculans invasion allows us to assume that the receptor of OmpX is α5β1 integrin.

Detection of a novel SME-6 Carbapenemase in Serratia ureilytica in Germany

BACKGROUND

Carbapenem resistance in Serratia species is occasionally mediated by the serine carbapenemase Serratia marcescens enzymes (SMEs). During microbiological diagnostics, we identified a carbapenem-resistant Serratia ureilytica isolate in which resistance was not mediated by any known SME variants or other characterized carbapenemases.

OBJECTIVES

To identify and characterize the underlying resistance mechanism in a carbapenem-resistant Serratia ureilytica isolate that lacks known SME variants or other characterized carbapenemases.

METHODS

Antimicrobial susceptibility testing (AST) was performed using Vitek, gradient strips, broth microdilution, and disc diffusion methods. WGS was performed to identify the resistance mechanisms. Growth curve analysis and RT-qPCR were performed at 30°C and 37°C.

RESULTS

WGS identified a novel SME variant, SME-6, which differed from a known variant, SME-2, by two amino acids (G117R and G147E). AST showed carbapenem resistance at 30°C but susceptibility at 37°C. Growth curve analysis showed a shorter lag phase at 30°C compared with 37°C, and RT-qPCR showed a ∼3-fold higher blaSME expression at 30°C.

CONCLUSIONS

To the best of our knowledge, this study reports the first identification of SME-6 and the first detection of an SME-type carbapenemase in Germany. Resistance was found to be temperature-dependent, with faster growth and higher SME-6 expression at lower temperatures contributing to the phenotype. These findings suggest SME variants may be underdiagnosed using current diagnostic protocols, highlighting the need for adjustments to improve detection of temperature-sensitive resistance mechanisms.

Complete genome sequence of psychrobacter sp. KFRI-CH2-11: A psychrotolerant bacterium with probiotic, biofortification, and antimicrobial potential for the dairy and meat industries

This dataset provides the complete genome sequence of Psychrobacter sp. KFRI-CH2-11, isolated from Korean fermented anchovy, Myeolchi-jeotgal. Genomic analysis identified genes involved in Vitamin B12 biosynthesis, carbohydrate metabolism, CRISPR-Cas defense systems, and antioxidant activity, underscoring the strain's potential for use in food biotechnology. Additional genes linked to antibiotic resistance and bioremediation suggest adaptability in diverse environments, particularly cold-chain storage in the dairy and meat industry. PathogenFinder analysis confirmed the absence of pathogenicity-associated genes, validating the strain's suitability as a probiotic and biofortifying agent in food products.

An Outbreak of Serratia marcescens in a Cardiothoracic Surgery Unit Associated with an Infected Solution of Pre-Prepared Syringes

Background/Objectives: The aim of the present study is to report an outbreak of bloodstream infections caused by Serratia marcescens in patients undergoing postoperational procedures in the Cardiothoracic Department and to describe the epidemiological investigations and control measures undertaken. A cluster of bacteremia due to Serratia marcescens was identified in blood cultures from postoperative patients in the Cardiothoracic Surgery Department in November 2023. Methods: Active surveillance by the hospital's prevention and control team was initiated. Interviews with nurses and sanitary personnel and reviews of the most common procedures, such as hand washing, bladder catheterization, and intravenous catheter care, were performed. Culturing samples from hospital personnel, postoperative patients, and the environment, including pressure transducers, tap water, soap, therapeutic solutions, antiseptics, respirators, and various intravenous preparations, were drawn up. Overall, 225 samples were collected, including 149 blood cultures, and these were all sent to the Hospital's Microbiology Laboratory. Results: Twenty-three out of forty-seven postoperative patients had positive blood cultures for Serratia marcescens. All the postoperative patients involved in the outbreak received cefepime according to antimicrobial susceptibility testing. Three pre-prepared flushing syringes were found to be positive for Serratia marcescens as well. The Cardiothoracic Department was kept under surveillance with hand hygiene measures, infusion preparation, medical device use, and cleaning procedures reviewed by the infection's prevention and control team. Conclusions: Undoubtedly, nosocomial outbreaks represent an important health issue regarding morbidity, mortality, and costs. Timely interventions by the hospital's infection prevention and control team may be life-saving under these circumstances.

Infection characteristics among Serratia marcescens capsule lineages

Serratia marcescens is a healthcare-associated pathogen that can cause severe infections including bacteremia and pneumonia. The capsule polysaccharide of S. marcescens is a bacteremia fitness determinant and previous work defined capsule locus (KL) diversity within the species. Strains belonging to KL1 and KL2 capsule clades produce sialylated polysaccharides and represent the largest subpopulation of isolates from clinical origin. In this study, the contribution of these and other S. marcescens capsules to infection was determined in animal and cellular models. Using a murine model of primary bacteremia, clinical isolates of multiple KL types demonstrated capsule-dependent colonization of spleen, liver, and kidney following tail vein inoculation. Similar results were observed using a bacteremic pneumonia model, in that all tested strains of clinical origin demonstrated a requirement for capsule in both the primary lung infection site and for bloodstream dissemination to secondary organs. Finally, capsule from each KL clade was examined for the ability to resist internalization by bone marrow-derived macrophages. Only the sialylated KL1 and KL2 clade strains exhibited capsule-dependent inhibition of internalization, including KL2 capsule produced in a heterologous background. Together these findings indicate that lineage-specific resistance to macrophage phagocytosis may enhance survival and antibacterial defenses of clinically-adapted S. marcescens.

Development of a qPCR assay to identify and differentiate insect-associated strains of the Serratia marcescens complex

The Serratia marcescens complex contains important opportunistic pathogens of humans and vertebrate animals, as well as insects and other invertebrates. To date, the methods used for the identification of species within the genus Serratia, including PCR assays, have poor discriminatory power and may require further molecular typing or genomic sequence analysis to determine clinical relevance. We developed a duplex TaqMan probe-based quantitative real-time PCR (qPCR) assay targeting the chiP gene, which is involved in chitin degradation and transport, and the ureD gene, which is involved in urease production. This allowed us to simultaneously identify all members of the S. marcescens complex (chiP positive) and differentiate those most likely to act as insect pathogens (chiP and ureD positive). We applied our assay to identify potentially entomopathogenic members of the S. marcescens complex in the context of a conservation program for the critically endangered insect Dryococelus australis and found it to be a useful aid for rapid and accurate detection of infection with S. marcescens complex strains in insects and determination of their clinical relevance. By targeting 2 genes likely to be virulence factors, this assay may also be of use for research investigating the pathogenesis of entomopathogenic Serratia spp.

A lysis less ordinary: The bacterial Type 10 Secretion System

Bacteria have evolved several different biochemical pathways to either export proteins of all shapes and sizes out of the cell cytoplasm, or to secrete those proteins into the extracellular environment. Many bacterial protein secretion systems have evolutionary links to systems used by bacteriophage to move macromolecules across membranes. The Type 10 Secretion System (T10SS) was identified in gram-negative bacteria and comprises genes that bear striking sequence similarities to those found within phage lysis cassettes. The minimum components of a T10SS are an integral membrane holin-like protein together with a peptidoglycan hydrolase. Here, we review recent research in Serratia spp., Salmonella spp, Yersinia spp, and gram-positive Clostridioides spp., and consider the evidence for different T10SS mechanisms ranging from a controlled release of proteins into the environment, to stochastic altruistic lysis of specialised populations of cells.

Competitive behaviors in Serratia marcescens are coordinately regulated by a lifestyle switch frequently inactivated in the clinical environment

Opportunistic bacterial pathogens must compete with other bacteria and switch between host- and environment-adapted states. Type VI secretion systems (T6SSs) occur widely in gram-negative bacteria and can efficiently kill neighboring competitors. We determined the distribution of T6SSs across the genus Serratia and observed that a highly conserved antibacterial T6SS is differentially active between closely related clinical isolates of Serratia marcescens. By combining genomic and experimental approaches, we identified a genus-core two-component system, BetR-Reg1-Reg2, that controls T6SS activity and exhibits frequent inactivating mutations, exclusively in S. marcescens isolates of clinical origin. This regulatory system controls a number of lifestyle-related traits at transcriptional and post-translational levels, including T6SS activity, antibiotic production, motility, and adhesion, with loss of BetR increasing virulence in an in vivo infection model. Our data support a model whereby this system represents a conserved, modular switch from sessile to pioneering and aggressive behavior, which is subject to selection pressure in clinical environments.

Pathogenicity of Serratia marcescens strains as biological control agent: Implications for sustainable pest management

The escalating demand for sustainable and eco-friendly pest management strategies has raised interest in harnessing the pathogenic potential of microorganisms. Serratia marcescens, a Gram-negative bacterium, has emerged as a potential biological control agent for sustainable pest management. This review critically examines the history, biology, identification, and pathogenicity of S. marcescens strain with their potential application in pest management. The diverse mechanisms employed by the strain to exert control over pests, including the production of metabolites and the induction of systemic resistance in plants, are examined. The review also summarizes the ecological significance and global distribution of S. marcescens associated with the use of S. marcescens in biological control strategies. Furthermore, the usage efficacy of S. marcescens over other conventional chemicals is discussed. A comprehensive understanding of the pathogenic potential of S. marcescens strains as biological control agents is crucial for developing effective and sustainable pest management strategies. This review consolidates current research advances on S. marcescens, and provides insights into the prospects and challenges of using S. marcescens for integrated pest management.

A national outbreak of Serratia marcescens complex: investigation reveals genomic population structure but no source, Norway, June 2021 to February 2023

We report a national outbreak of Serratia marcescens complex type 755 (ct755) in Norway, with 74 cases identified between June 2021 and February 2023. Careful reviews of patient journals and interviews were performed, involving 33 hospitals throughout Norway. All available clinical isolates of S. marcescens collected between January 2021 and February 2023 (n = 455, including cases) from all involved hospitals were whole genome sequenced. Cases displayed a pattern of opportunistic infections, as usually observed with S. marcescens. No epidemiological links, common exposures or common risk factors were identified. The investigation pointed to an outbreak source present in the community. We suspect a nationally distributed product, possibly a food product, as the source. Phylogenetic analysis revealed a highly diverse bacterial population containing multiple distinct clusters. The outbreak cluster ct755 stands out as the largest and least diverse clone of a continuum, however a second cluster (ct281) also triggered a separate outbreak investigation. This report highlights challenges in the investigation of outbreaks caused by opportunistic pathogens and suggests that the presence of identical strains of S. marcescens in clinical samples is more common than previously recognised.

Chronic bacterial infections exert metabolic costs in Drosophila melanogaster

Bacterial infections can substantially impact host metabolic health as a result of the direct and indirect demands of sustaining an immune response and of nutrient piracy by the pathogen itself. Drosophila melanogaster and other insects that survive a sublethal bacterial infection often carry substantial pathogen burdens for the remainder of life. In this study, we asked whether these chronic infections exact metabolic costs for the host, and how these costs scale with the severity of chronic infection. We infected D. melanogaster with four bacterial species (Providencia rettgeri, Serratia marcescens, Enterococcus faecalis and Lactococcus lactis) and assayed metabolic traits in chronically infected survivors. We found that D. melanogaster carrying chronic infections were uniformly more susceptible to starvation than uninfected controls, and that sensitivity to starvation escalated with higher chronic pathogen burden. We observed some evidence for greater depletion of triglyceride and glycogen stores in D. melanogaster carrying chronic bacterial loads, although this varied among bacterial species. Chronically infected flies exhibit sustained upregulation of the immune response, which we hypothesized might contribute to the metabolic costs. Consistent with this prediction, genetic activation of the major innate immune signaling pathways depleted metabolic stores and increased starvation sensitivity even in the absence of infection. These results demonstrate that even sublethal infections can have substantial health and fitness consequences for the hosts, arising in part from pathogen-induced immune activation, and that the consequences scale quantitatively with the severity of infection.

A Bioassay That Yields Quantifiable Symptoms of Cucurbit Yellow Vine Disease Caused by Serratia marcescens

Cucurbit yellow vine disease (CYVD), which is caused by the gram-negative bacterium Serratia marcescens and transmitted by squash bugs (Anasa tristis DeGeer), is a devastating disease of cucurbit crops that is emerging rapidly in the eastern half of the United States. The lack of a robust pathogenicity assay for CYVD in the laboratory has hampered functional tests using genomic sequences to investigate the biology of this phytopathogen. In this study we developed and validated a bioassay that yielded consistent and quantifiable CYVD symptoms on squash in the laboratory. We compared inoculation by wounding with a multipronged floral pin frog to inoculation by injection in which a needle was moved in and out of the stem multiple times in each of multiple piercings to mimic the feeding behavior of squash bugs. We found that inoculation by needle injection of ≥108 CFU/ml of S. marcescens into the stem of squash (Cucurbita pepo) plants at the cotyledon growth stage reproducibly induced CYVD symptoms, whereas injecting 106 or 107 CFU/ml did not. Additionally, we found that S. marcescens induced symptoms on all of the squash cultivars tested, and induced symptoms that have not been previously reported, including stem elongation and leaf cupping. In short, through our injection approach of mimicking the natural process of S. marcescens transmission by squash bug feeding, we obtained robust and quantifiable CYVD symptoms. This laboratory bioassay provides a crucial tool for investigating the biology and pathology of this emerging pathogen and for plant breeding screens aimed at combatting CYVD.

Profiling the Enterobacterales Community Isolated from Retail Foods in England

Enterobacterales include foodborne pathogens of importance to public health and are often targeted in food surveillance programs as both safety and hygiene indicators. Furthermore, Enterobacterales are important in the context of antimicrobial resistance dissemination, also impacting infection treatment efficacy. In this study, the prevalence and characteristics of Enterobacterales in UK retail foods were examined. From 110 retail food samples, 253 Enterobacterales were recovered, with 16S rRNA sequencing revealing a diverse species community, including enteropathogens; the most common were Proteus mirabilis and Escherichia coli (18% each). Antimicrobial resistance was common, with 160/253 (63%) isolates being resistant to at least 1 antimicrobial. Resistance to all tested antimicrobials was observed. Thirteen percent of isolates were multidrug resistant, including 2 isolates each resistant to 8 or 9 of 9 antimicrobials tested. Klebsiella isolates possessed relatively higher levels of antimicrobial resistance to other species. Hafnia, Kluyvera, and Proteus isolates produced significantly higher biofilm biomass than Klebsiella (p = 0.038, 0.028, and 0.042, respectively) or Escherichia (p = 0.001, 0.008, and 0.001, respectively). Simultaneous curli fimbriae and cellulose production was noted in 7% of isolates at 37 °C, but not at 15 °C. This research demonstrates a high diversity of Enterobacterales within UK retail foods, alongside notable antimicrobial resistance phenotypes in enteropathogenic species, highlighting the need for effective surveillance and interventions.

Targeted therapies in HER2-positive breast cancer with receptor-redirected Arazyme-linker-Herceptin as a novel fusion protein

BACKGROUND

Targeted treatment of different types of cancers through highly expressed cancer cell surface receptors by fusion proteins is an efficient method for cancer therapy. The HER2 receptor is a member of the tyrosine kinase receptors family, which plays a notable role in breast cancer tumor development. About 25-30% of breast cancers overexpress human epidermal growth factor receptor 2 (HER2).

METHODS

In this study, we evaluated the particulars of a designed recombinant protein formed by HER2-specific Mab Herceptin linked with Arazyme on a HER2-overexpressing breast cancer cell line (SKBR3). Arazyme, a metalloprotease produced by Serratia proteamaculans was fused to the variable area of light and heavy chains of the Herceptin. The cytotoxic assay of the Arazyme-linker-Herceptin in the SKBR3 and MDA-MB-468 cells was evaluated by the MTT and flow cytometry techniques. The Caspase‑3 activity determination and adhesion assay were performed to evaluate the antitumor activity of the Arazyme-linker-Herceptin against SKBR3 cells. Furthermore, RT-PCR was used to measure the expression levels of the Bcl-2, Bax, MMP2, MMP9, and RIP3 genes.

RESULTS

The Arazyme-linker-Herceptin showed higher cytotoxicity in SKBR3 cells compared to MDA-MB-468 cells. In addition, flow cytometry results revealed that the Arazyme-linker-Herceptin can significantly induce apoptosis in the HER2-overexpressing breast cancer cell line (SKBR3), which was confirmed by Bax upregulation and the decrease in adhesion of tumor cells and MMP2/MMP9.

CONCLUSION

The findings of this study demonstrated that the Arazyme-linker-Herceptin induced apoptosis and decreased metastatic genes in SKBR3 cells; however, further research is required to confirm the effectiveness of the fusion protein.

Brodie's abscess of the calcaneus due to Serratia marcescens

Brodie's abscess is a subacute or chronic osteomyelitis characterised by an intraosseous abscess. It may present months to years after the inciting event. Staphylococcus aureus is the most common causative organism of Brodie's abscess, while Gram-negative bacteria are uncommon causative organisms. A combination of culture-directed antibiotics and surgical debridement is key to successful management. This case report describes a patient with a history of minor trauma preceding the development of Brodie's abscess of the calcaneus caused by Serratia marcescens This was managed successfully with surgical debridement, followed by oral antibiotics.

Microbial richness and air chemistry in aerosols above the PBL confirm 2,000-km long-distance transport of potential human pathogens

The existence of viable human pathogens in bioaerosols which can cause infection or affect human health has been the subject of little research. In this study, data provided by 10 tropospheric aircraft surveys over Japan in 2014 confirm the existence of a vast diversity of microbial species up to 3,000 m height, which can be dispersed above the planetary boundary layer over distances of up to 2,000 km, thanks to strong winds from an area covered with massive cereal croplands in Northeast (NE) Asia. Microbes attached to aerosols reveal the presence of diverse bacterial and fungal taxa, including potential human pathogens, originating from sewage, pesticides, or fertilizers. Over 266 different fungal and 305 bacterial genera appeared in the 10 aircraft transects. Actinobacteria, Bacillota, Proteobacteria, and Bacteroidetes phyla dominated the bacteria composition and, for fungi, Ascomycota prevailed over Basidiomycota. Among the pathogenic species identified, human pathogens include bacteria such as Escherichia coli, Serratia marcescens, Prevotella melaninogenica, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus saprophyticus, Cutibacterium acnes, Clostridium difficile, Clostridium botulinum, Stenotrophomonas maltophilia, Shigella sonnei, Haemophillus parainfluenzae and Acinetobacter baumannii and health-relevant fungi such as Malassezia restricta, Malassezia globosa, Candida parapsilosis and Candida zeylanoides, Sarocladium kiliense, Cladosporium halotolerans, and Cladosporium herbarum. Diversity estimates were similar at heights and surface when entrainment of air from high altitudes occurred. Natural antimicrobial-resistant bacteria (ARB) cultured from air samples were found indicating long-distance spread of ARB and microbial viability. This would represent a novel way to disperse both viable human pathogens and resistance genes among distant geographical regions.

Classification of a novel Serratia species, isolated from a wound swab in North Rhine-Westphalia: Proposal of Serratia sarumanii sp. nov

Novel, white-pigmented, Gram-negative bacterial strains (K-M0706T, K-M0228, K-M0252, K-M0260) were isolated from clinical samples. With a similarity of up to 69.7 % to Serratia nevei S15T and up to 63.8 % to Serratia marcescens ATCC 13880T, as determined by digital DNA-DNA hybridization, the strains were assigned as novel species of the genus Serratia. The species can easily be differentiated from the red colored Serratia marcescens sensu stricto by its white phenotype. Discrimination between this strain and Serratia nevei is possible due to alpha-glucosidase activity and O/129-resistance, as shown for strain K-M0706T. The major fatty acids were determined as myristate, palmitate, cis-9,10-methylenehexadecanoate, linoleate, and (all cis-9,10)-methyleneoctadecanoate. These phenotypical and genomic data support the assignment of a novel species within the genus Serratia, named S. sarumanii due to its pathogenicity and white phenotype, with strain K-M0706T as the type strain.

Microbial agents for the control of ticks Rhipicephalus microplus

Ticks are ectoparasites responsible for the transmission of various pathogens to vertebrates. They represent one of the major threats to livestock production worldwide due to their impact on the health, production and welfare of livestock destined for human consumption. The development of resistance to the main families of ixodicides used for their control has led to the search for new alternatives, where microbial control is an option. The use of microbial control agents against the tick Rhipicephalus microplus is reviewed in this paper. Bacteria such as Bacillus thuringiensis, Serratia marcescens and Staphylococcus spp. the nematodes Steinernema spp. and Heterorhabditis spp. as well as the fungi Metarhizium anisopliae and Beauveria bassiana are the most studied organisms for use as biological control agents against ticks. Laboratory, stable and field trials with free-living and parasitised ticks have shown that microbial agents can control both susceptible and ixodicide-resistant tick populations. However, multidisciplinary studies using novel tools like genomics, transcriptomics and proteomics should be carried out to understand the virulence factors which microbial agents use to induce pathogenesis and virulence in ticks. In addition, applied research will be carried out with the aim of improving techniques for large-scale application, as well as the improvement of cultivation, storage, formulation and application methods.

High Prevalence of Antibiotic Resistance in Traditionally Fermented Foods as a Critical Risk Factor for Host Gut Antibiotic Resistome

This study aimed to assess the suitability of fermented food interventions to replenish damaged gut microbiota. Metagenomic assessment of published sequencing data found that fermented food interventions led to a significant increase in the gut antibiotic resistome in healthy human subjects. Antibiotic resistome and viable antibiotic-resistant (AR) bacteria were further highly prevalent in retail kimchi and artisan cheeses by metagenomic and culture analyses. Representative AR pathogens of importance in nosocomial infections, such as Klebsiella pneumoniae, Serratia marcescens, and vancomycin-resistant Enterococcus (VRE), as well as commensals and lactic acid bacteria, were characterized; some exhibited an extremely high minimum inhibitory concentration (MIC) against antibiotics of clinical significance. Exposing fermented food microbiota to representative antibiotics further led to a boost of the corresponding antibiotic and multidrug-resistance gene pools, as well as disturbed microbiota, including the rise of previously undetectable pathogens. These results revealed an underestimated public health risk associated with fermented food intervention at the current stage, particularly for susceptible populations with compromised gut integrity and immune functions seeking gut microbiota rescue. The findings call for productive intervention of foodborne AR via technology innovation and strategic movements to mitigate unnecessary, massive damages to the host gut microbiota due to orally administered or biliary excreted antibiotics.

Umbelliferone modulates the quorum sensing and biofilm of Gram - ve bacteria: in vitro and in silico investigations

In last two decades, the world has seen an exponential increase in the antimicrobial resistance (AMR), making the issue a serious threat to human health. The mortality caused by AMR is one of the leading causes of human death worldwide. Till the end of the twentieth century, a tremendous success in the discovery of new antibiotics was seen, but in last two decades, there is negligible progress in this direction. The increase in AMR combined with slow progress of antibiotic drug discovery has created an urgent demand to search for newer methods of intervention to combat infectious diseases. One of such approach is to look for biofilm and quorum sensing (QS) inhibitors. Plants are excellent source of wide class compounds that can be harnessed to look for the compounds with such properties. This study proves a broad-spectrum biofilm and QS inhibitory potential of umbelliferone. More than 85% reduction in violacein production Chromobacterium violaceum 12472 was found. All tested virulent traits of Pseudomonas aeruginosa PAO1 and Serratia marcescens MTCC 97 were remarkably inhibited that ranged from 56.62% to 86.24%. Umbelliferone also successfully prevented the biofilm of test bacteria at least by 67.68%. Umbelliferone interacted at the active site of many proteins of QS circuit, which led to the mitigation of virulent traits. The stable nature of complexes of umbelliferone with proteins further strengthens in vitro results. After examining the toxicological profile and other drug-like properties, umbelliferone could be potentially developed as new drug to target the infections caused by Gram - ve bacteria.Communicated by Ramaswamy H. Sarma.

A Rare Infection Post Hyaluronic Acid Injection in the Trochanter: Case Report and Literature Review

Filler injection has become a commonplace aesthetic procedure. Although the incidence of infection following filler injections is typically low, ranging between 0.04% and 0.2%, the potential consequences can be serious. In this manuscript, we present the case of a 29-year-old female patient who presented to our emergency department after receiving a hyaluronic acid filler injection in the trochanteric area at a private center. She developed signs and symptoms shortly after the procedure, including bilateral hip pain and a fever that persisted for 3 days. Despite initial antibiotic and pain medication treatment, the patient's condition continued to worsen. Incision and drainage were performed, and pus culture revealed profuse Extended Spectrum Beta-Lactamase (ESBL)-producing Serratia marcescens. The patient experienced clinical improvement following the incision and drainage procedure and initiation of antibiotics sensitive to the pathogen. Although rare, S. marcescens infection following filler injections has been reported in 2 previous cases. Therefore, early recognition of infection signs and symptoms is crucial to mitigate the severity of consequences and improve outcomes. Aggressive surgical and medical interventions, such as incision and drainage, debridement, and appropriate antibiotic therapy, may be necessary to achieve a successful outcome.

Level of Evidence 5

The Balance between Protealysin and Its Substrate, the Outer Membrane Protein OmpX, Regulates Serratia proteamaculans Invasion

Serratia are opportunistic bacteria, causing infections in plants, insects, animals and humans under certain conditions. The development of bacterial infection in the human body involves several stages of host-pathogen interaction, including entry into non-phagocytic cells to evade host immune cells. The facultative pathogen Serratia proteamaculans is capable of penetrating eukaryotic cells. These bacteria synthesize an actin-specific metalloprotease named protealysin. After transformation with a plasmid carrying the protealysin gene, noninvasive E. coli penetrate eukaryotic cells. This suggests that protealysin may play a key role in S. proteamaculans invasion. This review addresses the mechanisms underlying protealysin's involvement in bacterial invasion, highlighting the main findings as follows. Protealysin can be delivered into the eukaryotic cell by the type VI secretion system and/or by bacterial outer membrane vesicles. By cleaving actin in the host cell, protealysin can mediate the reversible actin rearrangements required for bacterial invasion. However, inactivation of the protealysin gene leads to an increase, rather than decrease, in the intensity of S. proteamaculans invasion. This indicates the presence of virulence factors among bacterial protealysin substrates. Indeed, protealysin cleaves the virulence factors, including the bacterial surface protein OmpX. OmpX increases the expression of the EGFR and β1 integrin, which are involved in S. proteamaculans invasion. It has been shown that an increase in the invasion of genetically modified S. proteamaculans may be the result of the accumulation of full-length OmpX on the bacterial surface, which is not cleaved by protealysin. Thus, the intensity of the S. proteamaculans invasion is determined by the balance between the active protealysin and its substrate OmpX.

Nosocomial outbreak caused by disinfectant-resistant Serratia marcescens in an adult intensive care unit, Hungary, February to March 2022

In 2022, an outbreak with severe bloodstream infections caused by Serratia marcescens occurred in an adult intensive care unit (ICU) in Hungary. Eight cases, five of whom died, were detected. Initial control measures could not stop the outbreak. We conducted a matched case-control study. In univariable analysis, the cases were more likely to be located around one sink in the ICU and had more medical procedures and medications than the controls, however, the multivariable analysis was not conclusive. Isolates from blood cultures of the cases and the ICU environment were closely related by whole genome sequencing and resistant or tolerant against the quaternary ammonium compound surface disinfectant used in the ICU. Thus, S. marcescens was able to survive in the environment despite regular cleaning and disinfection. The hospital replaced the disinfectant with another one, tightened the cleaning protocol and strengthened hand hygiene compliance among the healthcare workers. Together, these control measures have proved effective to prevent new cases. Our results highlight the importance of multidisciplinary outbreak investigations, including environmental sampling, molecular typing and testing for disinfectant resistance.

The ICU environment contributes to the endemicity of the "Serratia marcescens complex" in the hospital setting

Serratia marcescens is an opportunistic pathogen historically associated with sudden outbreaks in intensive care units (ICUs) and the spread of carbapenem-resistant genes. However, the ecology of S. marcescens populations in the hospital ecosystem remains largely unknown. We combined epidemiological information of 1,432 Serratia spp. isolates collected from sinks of a large ICU that underwent demographic and operational changes (2019-2021) and 99 non-redundant outbreak/non-outbreak isolates from the same hospital (2003-2019) with 165 genomic data. These genomes were grouped into clades (1-4) and subclades (A and B) associated with distinct species: Serratia nematodiphila (1A), S. marcescens (1B), Serratia bockelmannii (2A), Serratia ureilytica (2B), S. marcescens/Serratia nevei (3), and S. nevei (4A and 4B). They may be classified into an S. marcescens complex (SMC) due to the similarity between/within subclades (average nucleotide identity >95%-98%), with clades 3 and 4 predominating in our study and publicly available databases. Chromosomal AmpC β-lactamase with unusual basal-like expression and prodigiosin-lacking species contrasted classical features of Serratia. We found persistent and coexisting clones in sinks of subclades 4A (ST92 and ST490) and 4B (ST424), clonally related to outbreak isolates carrying blaVIM-1 or blaOXA-48 on prevalent IncL/pB77-CPsm plasmids from our hospital since 2017. The distribution of SMC populations in ICU sinks and patients reflects how Serratia species acquire, maintain, and enable plasmid evolution in both "source" (permanent, sinks) and "sink" (transient, patients) hospital patches. The results contribute to understanding how water sinks serve as reservoirs of Enterobacterales clones and plasmids that enable the persistence of carbapenemase genes in healthcare settings, potentially leading to outbreaks and/or hospital-acquired infections.IMPORTANCEThe "hospital environment," including sinks and surfaces, is increasingly recognized as a reservoir for bacterial species, clones, and plasmids of high epidemiological concern. Available studies on Serratia epidemiology have focused mainly on outbreaks of multidrug-resistant species, overlooking local longitudinal analyses necessary for understanding the dynamics of opportunistic pathogens and antibiotic-resistant genes within the hospital setting. This long-term genomic comparative analysis of Serratia isolated from the ICU environment with isolates causing nosocomial infections and/or outbreaks within the same hospital revealed the coexistence and persistence of Serratia populations in water reservoirs. Moreover, predominant sink strains may acquire highly conserved and widely distributed plasmids carrying carbapenemase genes, such as the prevalent IncL-pB77-CPsm (pOXA48), persisting in ICU sinks for years. The work highlights the relevance of ICU environmental reservoirs in the endemicity of certain opportunistic pathogens and resistance mechanisms mainly confined to hospitals.

Calcium-induced structural transitions are central to the folding, function, and processing of serratiopeptidase zymogen into mature form

Serratia marcescens is an emerging health-threatening, gram-negative opportunistic pathogen associated with a wide variety of localized and life-threatening systemic infections. One of the most crucial virulence factors produced by S. marcescens is serratiopeptidase, a 50.2-kDa repeats-in-toxin (RTX) family broad-specificity zinc metalloprotease. RTX family proteins are functionally diverse exoproteins of gram-negative bacteria that exhibit calcium-dependent structural dynamicity and are secreted through a common type-1 secretion system (T1SS) machinery. To evaluate the impact of various divalent ligands on the folding and maturation of serratiopeptidase zymogen, the protein was purified and a series of structural and functional investigations were undertaken. The results indicate that calcium binding to the C-terminal RTX domain acts as a folding switch, triggering a disordered-to-ordered transition in the enzyme's conformation. Further, the auto-processing of the 16-amino acid N-terminal pro-peptide results in the maturation of the enzyme. The binding of calcium ions to serratiopeptidase causes a highly cooperative conformational transition in its structure, which is essential for the enzyme's activation and maturation. This conformational change is accompanied by an increase in solubility and enzymatic activity. For efficient secretion and to minimize intracellular toxicity, the enzyme needs to be in an unfolded extended form. The calcium-rich extracellular environment favors the folding and processing of zymogen into mature serratiopeptidase, i.e., the holo-form required by S. marcescens to establish infections and survive in different environmental niches.

Opportunistic Pathogens in Drinking Water Distribution Systems-A Review

In contrast to "frank" pathogens, like Salmonella entrocolitica, Shigella dysenteriae, and Vibrio cholerae, that always have a probability of disease, "opportunistic" pathogens are organisms that cause an infectious disease in a host with a weakened immune system and rarely in a healthy host. Historically, drinking water treatment has focused on control of frank pathogens, particularly those from human or animal sources (like Giardia lamblia, Cryptosporidium parvum, or Hepatitis A virus), but in recent years outbreaks from drinking water have increasingly been due to opportunistic pathogens. Characteristics of opportunistic pathogens that make them problematic for water treatment include: (1) they are normally present in aquatic environments, (2) they grow in biofilms that protect the bacteria from disinfectants, and (3) under appropriate conditions in drinking water systems (e.g., warm water, stagnation, low disinfectant levels, etc.), these bacteria can amplify to levels that can pose a public health risk. The three most common opportunistic pathogens in drinking water systems are Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. This report focuses on these organisms to provide information on their public health risk, occurrence in drinking water systems, susceptibility to various disinfectants, and other operational practices (like flushing and cleaning of pipes and storage tanks). In addition, information is provided on a group of nine other opportunistic pathogens that are less commonly found in drinking water systems, including Aeromonas hydrophila, Klebsiella pneumoniae, Serratia marcescens, Burkholderia pseudomallei, Acinetobacter baumannii, Stenotrophomonas maltophilia, Arcobacter butzleri, and several free-living amoebae including Naegleria fowleri and species of Acanthamoeba. The public health risk for these microbes in drinking water is still unclear, but in most cases, efforts to manage Legionella, mycobacteria, and Pseudomonas risks will also be effective for these other opportunistic pathogens. The approach to managing opportunistic pathogens in drinking water supplies focuses on controlling the growth of these organisms. Many of these microbes are normal inhabitants in biofilms in water, so the attention is less on eliminating these organisms from entering the system and more on managing their occurrence and concentrations in the pipe network. With anticipated warming trends associated with climate change, the factors that drive the growth of opportunistic pathogens in drinking water systems will likely increase. It is important, therefore, to evaluate treatment barriers and management activities for control of opportunistic pathogen risks. Controls for primary treatment, particularly for turbidity management and disinfection, should be reviewed to ensure adequacy for opportunistic pathogen control. However, the major focus for the utility's opportunistic pathogen risk reduction plan is the management of biological activity and biofilms in the distribution system. Factors that influence the growth of microbes (primarily in biofilms) in the distribution system include, temperature, disinfectant type and concentration, nutrient levels (measured as AOC or BDOC), stagnation, flushing of pipes and cleaning of storage tank sediments, and corrosion control. Pressure management and distribution system integrity are also important to the microbial quality of water but are related more to the intrusion of contaminants into the distribution system rather than directly related to microbial growth. Summarizing the identified risk from drinking water, the availability and quality of disinfection data for treatment, and guidelines or standards for control showed that adequate information is best available for management of L. pneumophila. For L. pneumophila, the risk for this organism has been clearly established from drinking water, cases have increased worldwide, and it is one of the most identified causes of drinking water outbreaks. Water management best practices (e.g., maintenance of a disinfectant residual throughout the distribution system, flushing and cleaning of sediments in pipelines and storage tanks, among others) have been shown to be effective for control of L. pneumophila in water supplies. In addition, there are well documented management guidelines available for the control of the organism in drinking water distribution systems. By comparison, management of risks for Mycobacteria from water are less clear than for L. pneumophila. Treatment of M. avium is difficult due to its resistance to disinfection, the tendency to form clumps, and attachment to surfaces in biofilms. Additionally, there are no guidelines for management of M. avium in drinking water, and one risk assessment study suggested a low risk of infection. The role of tap water in the transmission of the other opportunistic pathogens is less clear and, in many cases, actions to manage L. pneumophila (e.g., maintenance of a disinfectant residual, flushing, cleaning of storage tanks, etc.) will also be beneficial in helping to manage these organisms as well.

Detection of clinical Serratia marcescens isolates carrying blaKPC-2 in a hospital in China

Serratia marcescens is an opportunistic and nosocomial pathogen found in the intensive care unit (ICU), but its antimicrobial resistance (AMR) is rarely addressed. Here, we reported two blaKPC-2-positive S. marcescens strains, SMBC31 and SMBC50, recovered from the ICU of a hospital in Zhengzhou, China. The minimum inhibitory concentration (MIC) was determined using the broth microdilution method, while S1-PFGE was employed to demonstrate plasmid size approximation. Complete genome sequences were obtained through Illumina NovaSeq 6000 and Oxford Nanopore Technologies. Both strains exhibit resistance to meropenem and harbor the blaKPC-2 and blaSRT-1 resistance genes. The plasmid pSMBC31-39K in strain SMBC31 and pSMBC50-107K in strain SMBC50 were identified as carrying the blaKPC-2 gene. Notably, both of these plasmids were successfully transferred to Escherichia coli strain J53. Phylogenetic analysis based on plasmid sequences revealed that pSMBC31-39K exhibited high homology with plasmids found in Aeromonas caviae, Citrobacter sp., and Pseudomonas aeruginosa, while pSMBC50-107K showed significant similarity to those of E. coli and Klebsiella pneumoniae. Notably, the coexistence of blaKPC-2 and blaSRT-1 was observed in all 94 KPC-2-producing S. marcescens strains by mining all genomes available under the GenBank database, which were mainly isolated from hospitalized patients. The emergence of multidrug-resistant S. marcescens poses significant challenges in treating clinical infections, highlighting the need for increased surveillance of this pathogen.

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Biological characterization and complete genome analysis of the newly isolated Serratia liquefaciens phage vB_SlqS_ZDD2

A novel lytic phage named vB_SlqS_ZDD2 was isolated from hospital sewage using the double-layer agar method with Serratia liquefaciens ATCC 27592 as the host. BLASTn analysis showed that the genome sequence of phage vB_SlqS_ZDD2 did not resemble any other phages in the NCBI database. Phenotype and phylogeny analysis indicated that this phage might be a new member of the class Caudoviricetes. Phage vB_SlqS_ZDD2 has a dsDNA genome of 49,178 bp with 55% GC content and has 73 open reading frames. This phage exhibited strong lytic activity and a wide range of pH (3-12) and temperature tolerance (below 70℃).

Microbial Community Changes in Silkworms Suspected of Septicemia and Identification of Serratia sp

Diseases that occur in silkworms include soft rot, hardening disease, digestive diseases, and sepsis. However, research on the causes of bacterial diseases occurring in silkworms and the resulting changes in the microbial community is lacking. Therefore, we examined the morphological characteristics of sepsis and changes in the microbial community between silkworms that exhibit a unique odor and healthy silkworms; thus, we established a relationship between disease-causing microorganisms and sepsis. After producing a 16S rRNA amplicon library for samples showing sepsis, we obtained information on the microbial community present in silkworms using next-generation sequencing. Compared to that in healthy silkworms, in silkworms with sepsis, the abundance of the Firmicutes phylum was significantly reduced, while that of Proteobacteria was increased. Serratia sp. was dominant in silkworms with sepsis. After bacterial isolation, identification, and reinfection through the oral cavity, we confirmed this organism as the disease-causing agent; its mortality rate was 1.8 times higher than that caused by Serratia marcescens. In summary, we identified a new causative bacterium of silkworm sepsis through microbial community analysis and confirmed that the microbial community balance was disrupted by the aberrant proliferation of certain bacteria.

Research on carbon and nitrogen removal of tetramethylammonium hydroxide containing wastewater by combined anaerobic/integrated fixed film activated sludge process

Tetramethylammonium hydroxide (TMAH) is widely used as a developer and etchant in the thin-film transistor liquid crystal display industry, which is the main component of developer wastewater with low C/N ratio. This study investigated TMAH degradation by combined anaerobic/integrated fixed film activated sludge (A/IFAS) process, especially for nitrogen removal. Effects of process condition on the TMAH degradation were studied, including dissolved oxygen concentration in IFAS reactor and the temperature of anaerobic reactor. Especially, the nitrogen removal was studied through the monitoring of intermediate products during TMAH biodegradation. The results indicated that lower the anaerobic treatment temperature can provide more available organic matters to enhance the denitrification in the subsequent IFAS reactor. Less oxygen supply in the IFAS reactor contributed to simultaneous nitrification and denitrification. Removal efficiency of total organic carbon and total nitrogen was up to 95.8% and 80.7%, when the temperature of anaerobic treatment was controlled at 30 °C with the DO kept at 0.7 mg/L. It indicated that A/IFAS process was efficient in carbon and nitrogen removal for TMAH degradation. The results also confirmed intermediate products of TMAH biodegradation can be used as the electron donor during denitrification, including trimethylamine, dimethylamine and methylamine. Illumina MiSeq sequencing showed that Proteobacteria was the dominant phylum contribute to nitrogen removal. Compared to sludge flocs in IFAS reactor, richer community and higher microbial diversity were observed in the biofilm.

Outbreak of Invasive Serratia marcescens among Persons Incarcerated in a State Prison, California, USA, March 2020-December 2022

Serratia marcescens is an environmental gram-negative bacterium that causes invasive disease in rare cases. During 2020-2022, an outbreak of 21 invasive Serratia infections occurred in a prison in California, USA. Most (95%) patients had a history of recent injection drug use (IDU). We performed whole-genome sequencing and found isolates from 8 patients and 2 pieces of IDU equipment were closely related. We also identified social interactions among patients. We recovered S. marcescens from multiple environmental samples throughout the prison, including personal containers storing Cell Block 64 (CB64), a quaternary ammonium disinfectant solution. CB64 preparation and storage conditions were suboptimal for S. marcescens disinfection. The outbreak was likely caused by contaminated CB64 and propagated by shared IDU equipment and social connections. Ensuring appropriate preparation, storage, and availability of disinfectants and enacting interventions to counteract disease spread through IDU can reduce risks for invasive Serratia infections in California prisons.

Increased Proteolytic Activity of Serratia marcescens Clinical Isolate HU1848 Is Associated with Higher eepR Expression

Serratia marcescens is a global opportunistic pathogen. In vitro cytotoxicity of this bacterium is mainly related to metalloprotease serralysin (PrtS) activity. Proteolytic capability varies among the different isolates. Here, we characterized protease production and transcriptional regulators at 37°C of two S. marcescens isolates from bronchial expectorations, HU1848 and SmUNAM836. As a reference strain the insect pathogen S. marcescens Db10 was included. Zymography of supernatant cultures revealed a single (SmUNAM836) or double proteolytic zones (HU1848 and Db10). Mass spectrometry confirmed the identity of PrtS and the serralysin-like protease SlpB from supernatant samples. Elevated proteolytic activity and prtS expression were evidenced in the HU1848 strain through azocasein degradation and qRT-PCR, respectively. Evaluation of transcriptional regulators revealed higher eepR expression in HU1848, whereas cpxR and hexS transcriptional levels were similar between studied strains. Higher eepR expression in HU1848 was further confirmed through an in vivo transcriptional assay. Moreover, two putative CpxR binding motifs were identified within the eepR regulatory region. EMSA validated the interaction of CpxR with both motifs. The evaluation of eepR transcription in a cpxR deletion strain indicated that CpxR negatively regulates eepR. Sequence conservation suggests that regulation of eepR by CpxR is common along S. marcescens species. Overall, our data incorporates CpxR to the complex regulatory mechanisms governing eepR expression and associates the increased proteolytic activity of the HU1848 strain with higher eepR transcription. Based on the global impact of EepR in secondary metabolites production, our work contributes to understanding virulence factors variances across S. marcescens isolates.

Recurrent Serratia marcescens osteomyelitis eight years after a contaminated open fracture: a case report and review of the literature

Background

Serratia marcescens (S. marcescens) is an unusual cause of osteomyelitis. Infection may develop following open trauma, intravenous drug abuse, or in the presence of hardware, but osteoarticular infections outside of this context are atypical in the absence of immunodeficiency. Rarely, a chronic indolent infection may develop after open trauma with disease recurrence years after the initial injury.

Case Description

We present the case of a 16-year-old male with extensive left lower extremity osteomyelitis secondary to S. marcescens eight years after an open fracture to this leg was complicated by an infection with the same organism. Suboptimal therapy of his initial infection may have contributed to persistent, latent disease before recurrence years later. Evaluation for immunodeficiency was negative and he responded well to ciprofloxacin antibiotic therapy.

Conclusions

S. marcescens infection may complicate open fractures, and, if not adequately treated, a chronic, indolent infection may result, with disease recurrence years later. We stress the importance of adequate therapy for infectious complications following open fractures and discuss virulence factors of S. marcescens that may allow this organism to evade the immune system and survive subclinically within a host. The optimal therapy of S. marcescens osteomyelitis is not established and further studies are needed to best guide the therapeutic approach.

Fernández-de-Bobadilla M, Serrano-Tomás MI, Sánchez-Díaz AM, Avendaño-Ortiz J, Coque TM, Ruiz-Garbajosa P, del Campo R, Cantón R. A long-term survey of Serratia spp. bloodstream infections revealed an increase of antimicrobial resistance involving adult population

Serratia spp. is a well-recognized pathogen in neonates; however, limited data are available in adults. We studied microbiological and clinical characteristics of Serratia spp. causing bloodstream infections (BSI) in our institution (January 2005-July 2020). Overall, 141 BSI episodes affecting 139 patients were identified and medical records reviewed. Antimicrobial susceptibility was recovered from our informatics system and 118 isolates from 116 patients were available for further microbiological studies. Whole genome sequencing (WGS) was completed in 107 isolates. Incidence of Serratia BSI was 0.3/1000 overall admissions (range 0.12-0.60), with maximum prevalence (27 episodes, 19.1%) during 2017-2018. Relevant patients' clinical characteristics were 71.9% ≥60 years (n = 100), with high comorbidity rates (49%, ≥2), 23 (74.2%) of them died within 1 month of the BSI episode. WGS identified all isolates as Serratia marcescens when Kraken bioinformatics taxonomic tool was used despite some which were identified as Serratia nematodiphila (32/118) or Serratia ureilytica (5/118) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Nevertheless, when using MASH distance, Serratia nevei (63/107), S. ureilytica (38/107), and S. marcescens (6/107) were assigned. Carbapenemase (blaVIM-1) and extended-spectrum β-lactases (ESBL) (blaSHV-12) genes were found in seven and three isolates, respectively, one of them expressing both genes. The worldwide-disseminated IncL/M scaffold plasmid was identified in six VIM producers. Four genotypes were established based on their virulence factors and resistome. Serratia spp. emerged as a relevant nosocomial pathogen causing BSI in elderly patients in our hospital, particularly in recent years with a remarkable increase in antibiotic resistance. ESBL and carbapenemases production related to plasmid dissemination are particularly noteworthy.IMPORTANCESerratia spp. is the third most frequent pathogen involved in outbreaks at neonatal facilities and is primarily associated with bacteremia episodes. In this study, we characterized all causing bloodstream infection (BSI) in patients admitted to our hospital during a 16-year period (2005-2020). Despite having no neonatal intensive care unit in our hospital, this study revealed that Serratia spp. is a relevant pathogen causing BSI in elderly patients with high comorbidity rates. A significant increase of antimicrobial resistance was detected over time, particularly in 2020 and coinciding with the coronavirus disease (COVID-19) pandemic and nosocomial spread of multidrug-resistant Serratia spp. isolates. extended-spectrum β-lactases and carbapenemases genes associated with plasmid dissemination, typically detected in other Enterobacterales species, were also identified, reinforcing the role of Serratia spp. in the antimicrobial resistance landscape. Additionally, this work highlights the need to reclassify the species of Serratia, since discrepancies were observed in the identification when using different tools.

A Rare Presentation of Serratia marcescens Endocarditis

Serratia marcescens is uncommon and rarely causes bacterial endocarditis. It can follow a rapid and progressive course with high mortality. Here, we present the case of a 27-year-old gentleman with bacterial endocarditis secondary to S. marcescens who was successfully treated medically.

А Rare Case of an Infected, Ruptured Popliteal Artery Aneurysm Occurring Following Surgical Treatment for Panaritium

We present a successful case of treating an infected popliteal aneurysm in a 71-year-old man who arrived at the emergency department in a septic state, reporting a three-week history of fever, lethargy, general malaise, and pain and swelling in the right popliteal fossa. Previously diagnosed with a sizable right popliteal aneurysm, the patient had undergone endovascular treatment using a Viabahn (WL Gore & Associates, Flagstaff, USA) endoprosthesis two months earlier. His fever and malaise emerged a week following minor surgery for a toe infection (panaritium) on the right foot, leading to subsequent necrotic lymphangitis on the dorsum of the same foot. A PET/CT scan strongly indicated an infection within the aneurysmal sac, while a CT angiography confirmed the integrity of the stent graft without any leaks but revealed a ruptured aneurysm. Urgent surgical intervention was necessary. An extra-anatomical autovenous bypass was conducted, followed by an aneurysm and endograft removal. Subsequently, a vacuum-assisted closure (VAC) system was employed to manage the infected wound post sac extraction. The surgical procedure went smoothly without complications, and following a course of antibiotics, the patient recovered well, eventually being discharged after 50 days.

Divergent genetic landscapes drive lower levels of AmpC induction and stable de-repression in Serratia marcescens compared to Enterobacter cloacae

The chromosomally encoded AmpC beta-lactamase is widely distributed throughout the Enterobacterales. When expressed at high levels through transient induction or stable de-repression, resistance to ceftriaxone, a commonly used antibiotic, can develop. Recent clinical guidance suggests, based on limited evidence, that resistance may be less likely to develop in Serratia marcescens compared to the better-studied Enterobacter cloacae and recommends that ceftriaxone may be used if the clinical isolate tests susceptible. We sought to generate additional data relevant to this recommendation. AmpC de-repression occurs predominantly because of mutation in the ampD peptidoglycan amidohydrolase. We find that, in contrast to E. cloacae, where deletion of ampD results in high-level ceftriaxone resistance (with ceftriaxone MIC = 96 µg/mL), in S. marcescens deletion of two amidohydrolases (ampD and amiD2) is necessary for AmpC de-repression, and the resulting ceftriaxone MIC is 1 µg/mL. Two mechanisms for this difference were identified. We find both a higher relative increase in ampC transcript level in E. cloacae ΔampD compared to S. marcescens ΔampDΔamiD2, as well as higher in vivo efficiency of ceftriaxone hydrolysis by the E. cloacae AmpC enzyme compared to the S. marcescens AmpC enzyme. We also observed higher relative levels of transient AmpC induction in E. cloacae vs S. marcescens when exposed to ceftriaxone. In time-kill curves, this difference translates into the survival of E. cloacae but not S. marcescens at clinically relevant ceftriaxone concentrations. In summary, our findings can explain the decreased propensity for on-treatment ceftriaxone resistance development in S. marcescens, thereby supporting recently issued clinical guidance.