Isolation and characterization of cytotoxic, aggregative Citrobacter freundii

Shiga Toxin: Emerging Producer Strains, Prophylactic Approaches, and Application in Cancer Therapy

Shiga toxin-producing Escherichia coli is the most prevalent bacterial strain responsible for Shiga toxin-related infections. While Shiga toxin is inherently toxic, it has potential therapeutic applications as a component of anticancer drugs. Despite its association with infections and harmful effects on human health, Shiga toxin is being explored as a viable element in drug delivery systems targeting cancer cells. The findings indicate that the production of mutated bacteria containing Shiga toxin is an effective preventive strategy for immunization against these toxins. Furthermore, the B subunit of Shiga toxin shows promise for imaging cancer cells, opening new paths for therapeutic interventions.

First identification and genomic features of multidrug-resistant Citrobacter freundii ST669 strain isolated from a domesticated duck in Bangladesh

Objectives

Citrobacter freundii is a prevalent source of nosocomial infections and a well-known cause of diarrheal diseases. In recent years, it has also become increasingly resistant to various antimicrobials. In this study, we screened and characterized a multidrug-resistant (MDR) C. freundii isolate obtained from a domesticated diseased duck to better understand the genetic features, molecular epidemiology, and underlying factors linked to the antimicrobial resistance genes (ARGs) and virulence factor genes (VFGs) of the isolate.

Methods

The C. freundii BAU_TM8 strain was isolated using culturing, staining, biochemical, polymerase chain reaction, and Matrix-assisted laser desorption/ionization-time of flight methods. The MDR properties of the strain were determined by a disk diffusion test. The genomic sequence of C. freundii BAU_TM8 was performed using the Illumina NextSeq2000 platform. The ARGs, VFGs, and genomic functional characteristics of the C. freundii BAU_TM8 strain were identified using several open-source databases.

Results

The sequence type of this strain was ST669, and the pathogenicity index of the strain was 0.919. Moreover, the strain had an estimated genome length of 5,797,806 bp, harboring 62 contigs, a G + C content of 54.32 %, and five contig L50s with an N50 value of 443,947 bp. Using phylogenetic analysis, this strain was closely related to two strains isolated from human and environmental samples in the USA and China despite huge geographical distances. The C. freundii BAU_TM8 strain consisted of 40 AGRs encoding resistance to 19 antimicrobial categories, e.g., fluoroquinolones, macrolides, folate pathway antagonists, aminoglycosides, tetracyclines, cephalosporins, and others. According to the phenotypic assay and genome sequence, the sensitivity and specificity of resistance profiles of the strain were 100 % and 20 %, respectively. Moreover, the virulence factor database detected 66 VFGs in this strain. This strain contained 1581 subsystems, having 33 % subsystem coverage and 2275 genes encoding amino acid derivatives, carbohydrate metabolism, protein metabolism, cofactors, vitamins, prosthetic groups, pigments, respiration, motility and chemotaxis, stress response, DNA metabolism, nucleosides and nucleotides, and others.

Conclusions

To the best of our knowledge, this is the first WGS report of C. freundii from a domesticated duck in Bangladesh. The ubiquitous occurrence of ARGs and VFGs in the C. freundii BAU_TM8 strain detected in this study highlights the growing concern about antimicrobial resistance in humans, animals, and environments.

Red pandas with different diets and environments exhibit different gut microbial functional composition and capacity

The red panda (Ailurus fulgens) is a distinctive mammal known for its reliance on a diet primarily consisting of bamboo. The gut microbiota and overall health of animals are strongly influenced by diets and environments. Therefore, conducting research to explore the taxonomical and functional variances within the gut microbiota of red pandas exposed to various dietary and environmental conditions could shed light on the dynamic complexities of their microbial communities. In this study, normal fecal samples were obtained from red pandas residing in captive and semi-free environments under different dietary regimes and used for metabolomic, 16S rRNA, and metagenomic sequencing analysis, with the pandas classified into four distinct cohorts according to diet and environment. In addition, metagenomic sequencing was conducted on mucus fecal samples to elucidate potential etiological agents of disease. Results revealed an increased risk of gastrointestinal diseases in red pandas consuming bamboo shoots due to the heightened presence of pathogenic bacteria, although an increased presence of microbiota-derived tryptophan metabolites appeared to facilitate intestinal balance. The red pandas fed bamboo leaves also exhibited a decrease in gut microbial diversity, which may be attributed to the antibacterial flavonoids and lower protein levels in leaves. Notably, red pandas residing in semi-free environments demonstrated an enriched gut microbial diversity. Moreover, the occurrence of mucus secretion may be due to an increased presence of species associated with diarrhea and a reduced level of microbiota-derived tryptophan metabolites. In summary, our findings substantiate the influential role of diet and environment in modulating the gut microbiota of red pandas, offering potential implications for improved captive breeding practices.

Colistin heteroresistance in Citrobacter freundii clinical isolates from Republic of Korea

We investigated colistin heteroresistance in Citrobacter freundii isolates from Korean hospitals. Using population analysis profiling (PAP), we detected colistin heteroresistance in 31.3% of isolates. Among these, ST217 was the most prevalent clone (58.5%), particularly within colistin-heteroresistant isolates (80.0%). Interestingly, the second most common clone, ST248, was not found in heteroresistant isolates. We identified amino acid changes in PhoQ, PmrA, and PmrB, along with mRNA overexpression in pmrB and arnD. Colistin monotherapy showed no efficacy, but a combination of colistin and ciprofloxacin successfully eradicated all five isolates, even at 0.5 × minimum inhibitory concentrations. This study underscores the high prevalence of colistin heteroresistance in C. freundii isolates, limiting the effectiveness of colistin monotherapy. Combining colistin with ciprofloxacin may offer a viable treatment option for C. freundii infections.

Characterization of cytotoxic Citrobacter braakii isolated from human stomach

Citrobacter braakii (C. braakii) is an anaerobic, gram-negative bacterium that has been isolated from the environment, food, and humans. Infection by C. braakii has been associated with acute mucosal inflammation in the intestine, respiratory tract, and urinary tract. However, the pathogenesis of C. braakii in the gastric mucosa has not yet been clarified. In this study, the bacterium was detected in 35.5% (61/172) of patients with chronic gastritis (CG) and was closely associated with the severity of mucosal inflammation. Citrobacter braakii P1 isolated from a patient with CG exhibited urease activity and acid resistance. It contained multiple secretion systems, including a complete type I secretion system (T1SS), T5aSS and T6SS. We then predicted the potential pilus-related adhesins. Citrobacter braakii P1 diffusely adhered to AGS cells and significantly increased lactate dehydrogenase (LDH) release; the adhesion rate and LDH release were much lower in HEp-2 cells. Strain P1 also induced markedly increased mRNA and protein expression of IL-8 and TNF-α in AGS cells, and the fold increase was much higher than that in HEp-2 cells. Our results demonstrate proinflammatory and cytotoxic role of C. braakii in gastric epithelial cells, indicating the bacterium is potentially involved in inducing gastric mucosa inflammation.

Identification and drug resistance of pathogen of ulcerative skin disease and its immune responses and protective efficacy after vaccination in a giant spiny frog, Quasipaa spinosa

OBJECTIVE

In order to explore the pathogen of the ulcerative skin disease in giant spiny frog (Quasipaa spinosa), and to provide theoretical basis for the prevention and control of the disease in practical production, this study was carried out to isolate and identify the pathogenic bacteria from the sick frogs suffering from rotting skin disease and to carry out the immunization test of the inactivated vaccine.

METHODS

Physiological and biochemical characterization, and molecular biology of the pathogenic bacteria were identified, and drug screening and immunization responses were also carried out.

RESULTS

The dominant bacterium QS01 was isolated from the lesions of diseased giant spiny frogs, which was confirmed to be the causative agent of the rotting skin disease of giant spiny frogs by artificial regression infection test. Based on the fact that the pathogen is a gram-negative short bacterium, its phenotypic characteristics and 16S rRNA and gyrB gene sequences were analyzed, and the bacterium was determined to be Citrobacter freundii. The results of the drug sensitivity test showed that the bacterium was sensitive to 11 antibiotics, including Enrofloxacin, Fleroxacin and Ciprofloxacin, including three non-polluting drugs such as Florfenicol, Roxithromycin and Thiamphenicol, as well as three Chinese herbal medicines such as Rheum officinale Baill, Coptis chinensis Franch and Scutellaria baicalensis Georgi. Most non-specific immune responses could go to recovery in 24h. The frogs were vaccinated with QS01 formaldehyde inactivated vaccine by injection, immersion and spraying, and the serum antibody potency of the three immunized groups with the average potency reached the peak at the 20th d after immunization, and the serum antibody potency of the injected immunized group was at the highest ratio of 1:64-128 (101.6), while the immersed group and the spraying group attained the ratio of 1:16-32 (20.2) and 1:16-32 (16) respectively, and lasted until the 30th d. The control group that was not immunized had the highest serum antibody potency of 1:16-32 (20.2) and 1:16-32 (16), and continued until the 30th d. The control group that was not immunized was not immunized. The serum antibody potency of the unimmunized control group was 1:2 to 2(2). The immunoprotection rates after takedown were 100 %, 85.71 % and 71.43 %, respectively.

CONCLUSION

C. freundii is the pathogen of the disease in this farm, and the vaccination by immersion and spraying can effectively prevent and control the rotting skin disease in frogs. These results revealed pathogenicity of C. freundii and its activation of host immune response, which will provide a scientific reference for the aquaculture and disease prevention in Q. spinosa culture.

Propolis Silver Nanoparticles as an Adjuvant in Immunization of Rats with Citrobactor Freundii Antigens

This study aimed to examine the impact of Citrobacter freundii killed whole cell sonicated antigen (KWCSAg) alone and in combination with propolis nanoparticles on humoral immunoglobulin (IgG) and cellular immune responses of rats. The ELISA interleukin 4 (IL4) and IgG, delayed-type hypersensitivity (DTH) skin test, and phagocytosis activity tests were used in this study. In total, 45 rats were divided into five groups of 9 rats. The first group received a 1,000 μg\ml dose of KWCSAg-CF. The second group received an injection of 1,000 μg/ml of KWCSAg-CF antigen and 30 mg/ml of propolis AgNPs. The third group received an injection of 1,000 μg/ml of KWCSAg-CF antigen along with 10 mg/ml of propolis AgNPs. The fourth group was subjected to 30 mg/ml of propolis AgNPs. One ml of phosphate-buffered saline (pH 7.2) was injected into the fifth group (the negative control group). The rats received booster injections of the same antigens after 14 days. Blood was obtained from them to detect immunoglobulin and interleukin 4 (IL-4) on days 21, 28, 32, 46, 50, and 60 following the injection. The second group showed the most significant rise in IL-4 and IgG concentration, followed by the third group, the first group, and the fourth group, compared to the negative control group (fifth group). In all immunized groups, the DTH test results demonstrated an increase in the means of induration with significant differences (P<0.05) of the concentrated antigen after 24 and 48 h, and subsequently a decrease after 72 h, compared to the negative control group. At 48 h after the concentrated antigen was indurated, the second group displayed the most significant increase in diameter.

Phenotypic and Genotypic Characteristics of Antimicrobial Resistance in Citrobacter freundii Isolated from Domestic Ducks (Anas platyrhynchos domesticus) in Bangladesh

Antimicrobial resistance (AMR) in Citrobacter freundii poses a serious challenge as this species is one of the sources of nosocomial infection and causes diarrheal infections in humans. Ducks could be the potential source of multidrug-resistant (MDR) C. freundii; however, AMR profiles in C. freundii from non-human sources in Bangladesh have remained elusive. This study aimed to detect C. freundii in domestic ducks (Anas platyrhynchos domesticus) in Bangladesh and to determine their phenotypic and genotypic antibiotic susceptibility patterns. A total of 150 cloacal swabs of diseased domestic ducks were screened using culturing, staining, biochemical, polymerase chain reaction (PCR), and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) to detect C. freundii. Phenotypic and genotypic antibiotic susceptibility patterns were done by the disk diffusion method and PCR, respectively. In total, 16.67% (25/150) of the samples were positive for C. freundii. C. freundii isolates showed a range of 20% to 96% resistance to cefotaxime, gentamicin, levofloxacin, ciprofloxacin, cotrimoxazole, tetracycline, ampicillin, and cephalexin. More than 60% of the isolates were phenotypically MDR, and the index of multiple antibiotic resistance ranged from 0.07 to 0.79. Genes encoding resistance to beta-lactams [bla_TEM-1-88% (22/25), bla_CMY-2-56% (14/25), bla_CMY-9-8% (2/25), and bla_CTX-M-14-20% (5/25)], sulfonamides [sul1-52% (13/25), sul2-24% (6/25)], tetracyclines [tetA-32% (8/25) and tetB-4% (1/25)], aminoglycosides [aacC4-16% (4/25)], and fluoroquinolones [qnrA-4% (1/25), qnrB-12% (3/25), and qnrS-4% (1/25)] were detected in the isolated C. freundii. To the best of our knowledge, this is the first study in Bangladesh to detect MDR C. freundii with their associated resistance genes from duck samples. We suggest addressing the burden of diseases in ducks and humans and associated AMR issues using the One Health approach.

Multidrug resistance-encoding gene in Citrobacter freundii isolated from healthy laying chicken in Blitar District, Indonesia

Background and Aim: The increasing prevalence of resistance (MDR) of Enterobacteriaceae in Indonesia has caused concern regarding human health. Citrobacter freundii reportedly targets the gastrointestinal tract of animals and is a common cause of foodborne diseases associated with diarrhea, peritonitis, meningitis, brain abscess, bacteremia, and urinary tract infection. This study aimed to estimate the prevalence of MDR and the presence of Class 1 integron-encoding genes in C. freundii isolates obtained from cloacal swabs of healthy laying chickens in Blitar district, Indonesia. Materials and Methods: One hundred and sixty-five cloacal swab samples were collected from 33 farms in Blitar over a period of 4 months. Standard microbiological techniques such as bacterial culture in MacConkey agar, Simmons citrate agar, and triple sugar iron agar and biochemical tests such as the indole test were performed to identify the isolates. The antibiotic sensitivity patterns of C. freundii isolates were determined by the disk diffusion method, and MDR-encoding genes (Class 1 integron) were detected by polymerase chain reaction (PCR). Results: Out of 165 cloacal swab samples, 7 (4.24%) were positive for C. freundii. Citrobacter freundii was highly resistant to erythromycin (71.43%) and moderately to streptomycin, tetracycline, and trimethoprim-sulfamethoxazole (all 42.86%); however, it showed low resistance to ampicillin (28.57%). All isolates were found to exhibit MDR. Only 1 (14.29%) of the seven C. freundii isolates harbored a Class 1 integron gene. This study revealed that Class 1 integron-encoding genes have a low prevalence in C. freundii isolated from healthy laying chickens in Blitar, Indonesia. Conclusion: Poultry animals can play a role in the transmission of resistance genes to humans due to the MDR of Enterobacteriaceae, including C. freundii in the intestines.

Assessment of Performance, Microbial Community, Bacterial Food Quality, and Gene Expression of Whiteleg Shrimp (Litopenaeus vannamei) Reared under Different Density Biofloc Systems

Biofloc shrimp culture, as a way of improving shrimp production, gains worldwide consideration. However, the effects of the biofloc system on shrimp culture at high densities could be a challenge. Here, this study is aimed at identifying a better stocking density of whiteleg shrimp (Litopenaeus vannamei) between two intensive biofloc systems of 100 and 300 org./m2. Achieving that was done by comparing growth performance, water quality, feed utilization, microbial loads from water and shrimps, and gene expression of growth, stress, and immune-related genes. Shrimp postlarvae with a mean weight of 35.4 ± 3.7 mg were reared in six indoor cement tanks (36 m3 total capacity each) at two stocking densities (3 replicates each) for a rearing period of 135 days. Better final weight, weight gain, average daily weight gain, specific growth rate, biomass increase percentage, and survival rate were associated with lower density (100/m2), whereas high-density showed significantly higher total biomass. Better feed utilization was found in the lower density treatment. Lower density treatment enhanced water quality parameters, including higher dissolved oxygen and lower nitrogenous wastes. Heterotrophic bacterial count in water samples was recorded as 5.28 ± 0.15 and 5.11 ± 0.28 log CFU/ml from the high- and low-density systems, respectively, with no significant difference. Beneficial bacteria such as Bacillus spp. were identified in water samples from both systems, still, the Vibrio-like count was developed in the higher density system. Regarding shrimp food bacterial quality, the total bacterial count in the shrimp was recorded as 5.09 ± 0.1 log CFU/g in the 300 org./m2 treatment compared to 4.75 ± 0.24 log CFU/g in the lower density. Escherichia coli was isolated from the shrimps in a lower density group while Aeromonas hydrophila and Citrobacter freundii were associated with shrimps from a higher density system. Immune-related genes including prophenoloxidase, superoxide dismutase (SOD), and lysozyme (LYZ) expressions were all significantly higher expressed in the shrimp from the lower density treatment. Toll receptor (LvToll), penaiedin4 (PEN4), and stress-related gene (HSP 70) showed a decreased gene expression in the shrimp raised in the lower density. Significant upregulation of growth-related gene (Ras-related protein-RAP) expression was associated with the lower stocking density system. In conclusion, the current study found that applying high stocking density (300 org./m2) contributes negatively to performance, water quality, microbial community, bacterial food quality, and gene expression of immune, stress, and growth-related genes when compared with the lower stocking density system (100 org./m2) under biofloc system.

Citrobacter freundii, a natural associate of the Colorado potato beetle, increases larval susceptibility to Bacillus thuringiensis

BACKGROUND

We assume that certain representatives of gut microflora mediate immune changes during dysbiosis, accelerating septicemia caused by Bacillus thuringiensis.

RESULTS

Co-introduction of Citrobacter freundii with Bacillus thuringiensis var. tenebrionis (morrisoni) (Bt) led to an increase in Colorado potato beetle (CPB) larval mortality to 69.0% (1.3-5×) and a synergistic effect was observed from day 1 to day 6. Ultrathin sections of the CPB midgut showed autophagosome formation and partial destruction of gut microvilli under the influence of Bt, which was accompanied by pronounced hypersecretion of the endoplasmic reticulum with apocrine vesicle formation and oncotic changes in cells under the action of C. freundii. The destruction of gut tissues was accompanied by suppression of detoxification processes under the action of the bacteria and a decrease (2.8-3.5×) in the concentration of lipid oxidation products during Bt infection. In the first hours post combined treatment, we registered a slight increase in the total hemocyte count (THC) especially a predomination (1.4×) of immune-competent plasmatocytes. Oral administration of symbiotic and entomopathogenic bacteria to the CPB larvae significantly decreased the THC (1.4×) after 24 h and increased (1.1-1.5×) the detoxifying enzymes level in the lymph. These changes are likely to be associated with the destruction of hemocytes and the need to remove the toxic products of reactive oxygen species.

CONCLUSION

The obtained results indicate that feeding of C. freundii and B. thuringiensis to the CPB larvae is accompanied by tissue changes that significantly affect the cellular and humoral immunity of the insect, increasing its susceptibility to Bt. © 2022 Society of Chemical Industry.

The pathogenic characterization of Citrobacter freundii and its activation on immune related genes in Macrobrachium nipponense

Out breaks of mass mortalities occurred in Macrobrachium nipponense farms in Jintan county, Jiangsu Province. The bacterial isolates from M. nipponense exhibited the same phenotypic traits and biochemical characteristics, and were identified as Citrobacter freundii according to biochemical characteristics and molecular identification. The infection test revealed that the strain YG2 was pathogenic to M. nipponense, and the half lethal dose (LD₅₀) was 3.35 × 10⁵ CFU/mL at 7 d post-infection. Detection of virulence genes indicated that YG2 was positive for cfa, ureG, ureF, ureE, ureD, viaB, ompX, and LDH. Furthermore, the results of extracellular enzyme analysis revealed that the strain can produce protease, amylase, lecithin, urease, and hemolysin. Antibiotic resistance results showed that the isolate was resistant to ampicillin, cefazolin, cephalothin, cefoxitin, aboren, doxycycline, neomycin, penicillin, erythromycin, and vancomycin. The expression level of MyD88, α2M, CDSP, and Relish were detected in hepatopancreas, hemolymph, gills and intestine tissues by quantitive real-time PCR (qRT-PCR), and clear transcriptional activation of these genes were observed in M. nipponense after C. freundii infection. These results revealed pathogenicity of C. freundii and its activation of host immune response, which will provide a scientific reference for the breeding and disease prevention in M. nipponense culture.

Submarine Outfalls of Treated Wastewater Effluents are Sources of Extensively- and Multidrug-Resistant KPC- and OXA-48-Producing Enterobacteriaceae in Coastal Marine Environment

The rapid and ongoing spread of carbapenemase-producing Enterobacteriaceae has led to a global health threat. However, a limited number of studies have addressed this problem in the marine environment. We investigated their emergence in the coastal waters of the central Adriatic Sea (Croatia), which are recipients of submarine effluents from two wastewater treatment plants. Fifteen KPC-producing Enterobacteriaceae (nine Escherichia coli, four Klebsiella pneumoniae and two Citrobacter freundii) were recovered, and susceptibility testing to 14 antimicrobials from 10 classes showed that four isolates were extensively drug resistant (XDR) and two were resistant to colistin. After ERIC and BOX-PCR typing, eight isolates were selected for whole genome sequencing. The E. coli isolates belonged to serotype O21:H27 and sequence type (ST) 2795, while K. pneumoniae isolates were assigned to STs 37 and 534. Large-scale genome analysis revealed an arsenal of 137 genes conferring resistance to 19 antimicrobial drug classes, 35 genes associated with virulence, and 20 plasmid replicons. The isolates simultaneously carried 43–90 genes encoding for antibiotic resistance, while four isolates co-harbored carbapenemase genes blaKPC-2 and blaOXA-48. The blaOXA-48 was associated with IncL-type plasmids in E. coli and K. pneumoniae. Importantly, the blaKPC-2 in four E. coli isolates was located on ~40 kb IncP6 broad-host-range plasmids which recently emerged as blaKPC-2 vesicles, providing first report of these blaKPC-2-bearing resistance plasmids circulating in E. coli in Europe. This study also represents the first evidence of XDR and potentially virulent strains of KPC-producing E. coli in coastal waters and the co-occurrence of blaKPC-2 and blaOXA-48 carbapenemase genes in this species. The leakage of these strains through submarine effluents into coastal waters is of concern, indicating a reservoir of this infectious threat in the marine environment.

Combinations of Peptide-Protein Extracts from Native Probiotics Suppress the Growth of Multidrug-Resistant Staphylococcus aureus and Citrobacter freundii via Membrane Perturbation and Ultrastructural Changes

The occurrence of multidrug-resistant pathogens in the food chain causes health problems in humans, thus, research for novel antimicrobials to combat their growth is of interest. This study evaluates the antimicrobial potential of several combinations of peptide-protein extracts (PCs) consisting of peptide extracts from three native probiotic strains, Lactiplantibacillus plantarum UTNGt2, Lactococcus lactis UTNGt28, and L. plantarum UTNGt21A, alone or in combination with EDTA (ethylenediaminetetraacetic acid) against multidrug-resistant Staphylococcus aureus ATCC1026 and Citrobacter freundii UTNB3Sm1. Based on the antimicrobial assay, among the 19 tested PCs, two (PC11 and PC17) produced a greater zone of inhibition against both pathogens in vitro. Time-killing assays indicated the rapid death of S. aureus after exposure to PC11 and PC17, while C. freundii was rapidly inhibited by PC11 and PC1 (UTNGt2 only), suggesting that the inhibitory action is pathogen and dose-dependent of a particular molecule present in the extract. A marginal inhibitory effect was observed when the peptides were combined with EDTA. Transmission electron microscopy (TEM) revealed the structural membrane damage of both target strains upon interaction with individual peptide extracts. Different degrees of cell deformation, condensed cytoplasm, membrane blebbing, and ghost cell formation with visibly broken cell walls were observed in S. aureus. Likewise, the separation of the cytoplasmic membrane from the outer membrane, ghost cells, along with ovoid and deformed cells with undulated cell walls were observed for C. freundii. Furthermore, scanning electronic microscopy (SEM) analysis revealed different wrinkled and deformed cells covered by debris. A leakage of aromatic molecules was detected for both pathogens, indicating that PCs disrupted the cell wall integrity, inducing cell death. Given their inhibitory action and capacity to induce damage of the cytoplasmic membrane, the selected PCs may serve to slow bacterial growth in vitro; further research is required to prove their efficiency ex vitro to battle against food poisoning and subsequent human infection.

Pathological, Immunological, and Hematological Parameters Associated with Experimental Infection of Citrobacter Freundii in Rabbits

Citrobacter freundii is one of the most important nosocomial opportunistic pathogens, which causes sepsis, as well as different gross and histopathological lesions in various internal organs in humans and animals, especially dogs and fish. This study aimed to investigate the hematological parameters, immunological responses, and pathological effects of the infection induced by the virulent strain of C. freundii on rabbits. A total of 42 rabbits (local breed; male and female), with a mean weight of 1.5-2 kg, were housed under controlled environmental conditions (20±2°C, 14:10 h light: dark cycle) and allowed ad libitum access to food and water. After two weeks of adaption, the rabbits were divided randomly into three groups of 14 animals per group. Group one (G1) received 3×10⁸ CFU/ml of the virulent isolate (intraperitoneally [IP]) of C. freundii. Group two (G2) was injected subcutaneously (SC) with 3×10⁸ CFU/ml of the virulent strain of C. freundii, while group three was IP injected with phosphate buffer saline and considered a negative control group. Results showed the variable gross pathological effects which included hemorrhage, edema, and congestion of visceral organs. Furthermore, the microscopic lesions showed pneumonia due to inflammatory cells infiltration, mainly neutrophils, macrophages, plasmacytes, and lymphocytes, severe interstitial and intra-alveolar edema, extensive pulmonary hemorrhage, emphysema, and atelectasis. The recorded data from the liver samples revealed hepatitis which was characterized by perivascular and periportal leukocyte cuffing, marked centrilobular with periportal necrosis, extensive hepatic edema, and periportal edema in addition to extensive fibrosis in interlobular septa and periportal fibrosis with severe interstitial hemorrhage. In the kidneys, there were severe renal edema, mixed inflammatory exudation, mainly neutrophils, macrophages, plasmacytes, lymphocytes, fibroblast infiltration in renal parenchyma and renal cortex, extensive renal hemorrhage, edema, as well as fibrosis and severe renal tubular necrosis. In addition, enteritis appeared in the intestine with mucosal edema, especially in lamina propria; moreover, necrosis of entire villi, epithelial necrosis, mucosal and submucosal hemorrhage, and fibrosis were observed. The present study revealed a significant increase in total leukocytes count and the concentration of TNF-α in the infected groups. To the best of the authors' knowledge, this study is considered the first attempt aimed to detect the pathological effects of C. freundii on visceral organs in rabbits. It is concluded that this bacterium could induce a significant pathological, hematological, and immunological changes in the infected animals.

Antimicrobial Resistance and Molecular Characterization of Citrobacter spp. Causing Extraintestinal Infections

Objectives

This prospective study was carried out to investigate molecular characteristics and antimicrobial susceptibility patterns of Citrobacter spp. from extraintestinal infections.

Methods

Forty-six clinical Citrobacter spp. isolates were isolated from hospital patients with extraintestinal infections and analyzed by multilocus sequence typing (MLST) using seven housekeeping genes. Antimicrobial susceptibility testing was performed by disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) recommendations. Adhesion and cytotoxicity to HEp-2 cells were assessed.

Results

The 46 clinical Citrobacter spp. isolates were typed into 38 sequence types (STs), 9 of which belonged to four clonal complexes (CCs). None of the isolates shared the same ST or CCs with isolates from other countries or from other parts of China. Over half of the isolates were multidrug-resistant (MDR), with 17/26 C. freundii, 5/6 C. braakii, and 3/14 C. koseri isolates being MDR. Moreover, four isolates were carbapenem resistant with resistance to imipenem or meropenem. Among eight quinolone resistant C. freundii, all had a mutation in codon 59 (Thr59Ile) in quinolone resistance determining region of the gyrA gene. Only a small proportion of the isolates were found to be highly cytotoxic and adhesive with no correlation to sample sources.

Conclusions

There was a diverse range of Citrobacter isolates causing extraintestinal infections and a high prevalence of MDR.

The Changing Face of the Family Enterobacteriaceae (Order: "Enterobacterales"): New Members, Taxonomic Issues, Geographic Expansion, and New Diseases and Disease Syndromes

The family Enterobacteriaceae has undergone significant morphogenetic changes in its more than 85-year history, particularly during the past 2 decades (2000 to 2020). The development and introduction of new and novel molecular methods coupled with innovative laboratory techniques have led to many advances. We now know that the global range of enterobacteria is much more expansive than previously recognized, as they play important roles in the environment in vegetative processes and through widespread environmental distribution through insect vectors. In humans, many new species have been described, some associated with specific disease processes. Some established species are now observed in new infectious disease settings and syndromes. The results of molecular taxonomic and phylogenetics studies suggest that the current family Enterobacteriaceae should possibly be divided into seven or more separate families. The logarithmic explosion in the number of enterobacterial species described brings into question the relevancy, need, and mechanisms to potentially identify these taxa. This review covers the progression, transformation, and morphogenesis of the family from the seminal Centers for Disease Control and Prevention publication (J. J. Farmer III, B. R. Davis, F. W. Hickman-Brenner, A. McWhorter, et al., J Clin Microbiol 21:46-76, 1985, https://doi.org/10.1128/JCM.21.1.46-76.1985) to the present.

Bacterial and heavy metal contamination in selected commonly sold herbal medicine in Blantyre, Malawi

Background

There has been an increase in use of herbal medicine worldwide. It is either used as a stand-alone or complementary therapy to conventional medicine due to past good experience, poverty and family traditions. In Malawi, there are no regulations governing the supply, acquisition, marketing and quality enforcement of herbal medicine. This compromises its safety thereby exposing consumers to avoidable bacteria and heavy metals leading to various adverse health effects.

Methods

Cross-sectional laboratory experiments were conducted to determine bacterial and heavy metal contamination of herbal medicine commonly sold in Blantyre, Malawi. A total of 47 samples which were in three formulations namely liquid, powder and tablet were used in the experiments. 29 samples were used for bacterial limit tests and 18 samples were used for heavy metal analysis. Bacterial contamination was determined by streak plate method and biochemical tests while heavy metals were determined by atomic absorption spectroscopy. Descriptive statistics and t-tests were calculated using Microsoft excel and SPSS software programs.

Results

Twenty out of the 29 samples (68.9%) were contaminated with Bacillus, coagulase negative Staphylococcus, Klebsiella, Enterobacter, Citrobacter and other-Coliform bacterial species. Most isolated microorganism was Citrobacter spp. (30%), followed by Bacillus spp. (25%). Out of 20 contaminated samples, 75% were contaminated with coliforms. From these 75% which were contaminated with coliforms, 93.3% of them exceeded WHO regulatory limit (103 CFU/g for enterobacteria). Although liquid samples had the highest level of bacterial contaminants, the count was not statistically different from other formulations (P = 0.058). For heavy metals, lead and cadmium were detected and 67% of the samples had lead levels exceeding regulatory limits.

Conclusion

Levels of bacterial and lead contamination in herbal medicine from Blantyre markets are far above acceptable limits set by WHO and Canadian guidelines. The use of these herbal medicines is a major risk to the health of consumers.

Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669-Potential Zoonotic Pathogens Isolated from Spotted Turtles

Antimicrobial resistance (AMR) is one of the biggest challenges of the 21st century, and biofilm formation enables bacteria to resist antibiotic at much higher concentrations than planktonic cells. Earlier, we showed that the Gram-negative Aeromonas hydrophila RIT668 and Citrobacter portucalensis RIT669 (closely related to C. freundii NBRC 12681) from infected spotted turtles (Clemmys guttata), formed biofilms and upregulated toxin expression on plastic surfaces, and were predicted to possess multiple antibiotic resistance genes. Here, we show that they each resist several antibiotics in the planktonic phase, but were susceptible to neomycin, and high concentrations of tetracycline and cotrimoxazole. The susceptibility of their biofilms to neomycin and cotrimoxazole was tested using the Calgary device. For A. hydrophila, the minimum inhibitory concentration (MIC) = 500-1000, and the minimum biofilm eradication concentration (MBEC) > 1000 μg/mL, using cotrimoxazole, and MIC = 32.3-62.5, and MBEC > 1000 μg/mL, using neomycin. For C. freundii MIC = 7.8-15.6, and, MBEC > 1000 μg/mL, using cotrimoxazole, and MIC = 7.8, and MBEC > 1000 μg/mL, using neomycin. Both A. hydrophila and C. portucalensis activated an acyl homoserine lactone (AHL) dependent biosensor, suggesting that quorum sensing could mediate biofilm formation. Their multidrug resistance in the planktonic form, and weak biofilm eradication even with neomycin and cotrimoxazole, indicate that A. hydrophila and C. portucalensis are potential zoonotic pathogens, with risks for patients living with implants.

Citrobacter freundii Activation of NLRP3 Inflammasome via the Type VI Secretion System

Citrobacter freundii is a significant cause of human infections, responsible for food poisoning, diarrhea, and urinary tract infections. We previously identified a highly cytotoxic and adhesive C. freundii strain CF74 expressing a type VI secretion system (T6SS). In this study, we showed that in mice-derived macrophages, C. freundii CF74 activated the Nucleotide Oligomerization Domain -Like Receptor Family, Pyrin Domain Containing 3(NLRP3) inflammasomes in a T6SS-dependent manner. The C. freundii T6SS activated the inflammasomes mainly through caspase 1 and mediated pyroptosis of macrophages by releasing the cleaved gasdermin-N domain. The CF74 T6SS was required for flagellin-induced interleukin 1β release by macrophages. We further show that the T6SS tail component and effector, hemolysin co-regulation protein-2 (Hcp-2), was necessary and sufficient to trigger NLRP3 inflammasome activation. In vivo, the T6SS played a key role in mediating interleukin 1β secretion and the survival of mice during C. freundii infection in mice. These findings provide novel insights into the role of T6SS in the pathogenesis of C. freundii.

Adherence to Human Colon Cells by Multidrug Resistant Enterobacterales Strains Isolated From Solid Organ Transplant Recipients With a Focus on Citrobacter freundii

Enterobacteria species are common causes of hospital-acquired infections, which are associated with high morbidity and mortality rates. Immunocompromised patients such as solid organ transplant (SOT) recipients are especially at risk because they are frequently exposed to antibiotics in the course of their treatments. In this work, we used a collection of 106 Escherichia coli, 78 Klebsiella pneumoniae, 25 Enterobacter spp., and 24 Citrobacter spp. multidrug resistant strains isolated from transplant patients (hepatic, renal or renal/pancreatic) in order to examine their ability to adhere in vitro to HT-29 human colon cells, and to determine if some adhesive characteristics are associated with prevalence and persistence of these strains. A total of 33 E. coli (31%), 21 K. pneumoniae (27%), 7 Enterobacter spp. (28%), and 5 Citrobacter spp. (21%), adhered to the colon epithelial cells. Two main adherence patterns were observed in the four species analyzed, diffuse adherence, and aggregative adherence. Under transmission electronic microscopy (TEM), most bacteria lacked visible fimbria on their surface, despite their strong adherence to epithelial cells. None of the strains studied was able to induce any cytotoxic effect on HT-29 cells although some of them strongly colonizing both cells and glass coverslips at high density. Some of the strains failed to adhere to the epithelial cells but adhered strongly to the cover-slide, which shows that microscopy studies are mandatory to elucidate the adherence of bacteria to epithelial cells in vitro, and that quantitative assays using colony forming unit (CFUs) counting need to be supplemented with pictures to determine definitively if a bacterial strain adheres or not to animal cells in vitro. We report here, for the first time, the aggregative adherence pattern of two multidrug resistant (MDR) Citrobacter freundii strains isolated from human patients; importantly, biofilm formation in Citrobacter is totally dependent on the temperature; strong biofilms were formed at room temperature (RT) but not at 37°C, which can play an important role in the colonization of hospital surfaces. In conclusion, our results show that there is a great variety of adhesion phenotypes in multidrug-resistant strains that colonize transplanted patients.

Expression of a Shiga-Like Toxin during Plastic Colonization by Two Multidrug-Resistant Bacteria, Aeromonas hydrophila RIT668 and Citrobacter freundii RIT669, Isolated from Endangered Turtles (Clemmys guttata)

Aeromonas hydrophila RIT668 and Citrobacter freundii RIT669 were isolated from endangered spotted turtles (Clemmys guttata). Whole-genome sequencing, annotation and phylogenetic analyses of the genomes revealed that the closest relative of RIT668 is A. hydrophila ATCC 7966 and Citrobacter portucalensis A60 for RIT669. Resistome analysis showed that A. hydrophila and C. freundii harbor six and 19 different antibiotic resistance genes, respectively. Both bacteria colonize polyethylene and polypropylene, which are common plastics, found in the environment and are used to fabricate medical devices. The expression of six biofilm-related genes—biofilm peroxide resistance protein (bsmA), biofilm formation regulatory protein subunit R (bssR), biofilm formation regulatory protein subunit S (bssS), biofilm formation regulator (hmsP), toxin-antitoxin biofilm protein (tabA) and transcriptional activator of curli operon (csgD)—and two virulence factors—Vi antigen-related gene (viaB) and Shiga-like toxin (slt-II)—was investigated by RT-PCR. A. hydrophila displayed a > 2-fold increase in slt-II expression in cells adhering to both polymers, C. freundii adhering on polyethylene displayed a > 2-fold, and on polypropylene a > 6-fold upregulation of slt-II. Thus, the two new isolates are potential pathogens owing to their drug resistance, surface colonization and upregulation of a slt-II-type diarrheal toxin on polymer surfaces.

Lineage, Antimicrobial Resistance and Virulence of Citrobacter spp

Citrobacter spp. are opportunistic human pathogens which can cause nosocomial infections, sporadic infections and outbreaks. In order to determine the genetic diversity, in vitro virulence properties and antimicrobial resistance profiles of Citrobacter spp., 128 Citrobacter isolates obtained from human diarrheal patients, foods and environment were assessed by multilocus sequence typing (MLST), antimicrobial susceptibility testing and adhesion and cytotoxicity testing to HEp-2 cells. The 128 Citrobacter isolates were typed into 123 sequence types (STs) of which 101 were novel STs, and these STs were divided into five lineages. Lineages I and II contained C. freundii isolates; Lineage III contained all C. braakii isolates, while Lineage IV and V contained C. youngae isolates. Lineages II and V contained more adhesive and cytotoxic isolates than Lineages I, III, and IV. Fifty-one of the 128 isolates were found to be multidrug-resistant (MDR, ≥3) and mainly distributed in Lineages I, II, and III. The prevalence of quinolone resistance varied with Lineage III (C. braakii) having the highest proportion of resistant isolates (52.6%), followed by Lineage I (C. freundii) with 23.7%. Seven qnrB variants, including two new alleles (qnrB93 and qnrB94) were found with Lineage I being the main reservoir. In summary, highly cytotoxic MDR isolates from diarrheal patients may increase the risk of severe disease.

Preharvest Transmission Routes of Fresh Produce Associated Bacterial Pathogens with Outbreak Potentials: A Review

Disease outbreaks caused by the ingestion of contaminated vegetables and fruits pose a significant problem to human health. The sources of contamination of these food products at the preharvest level of agricultural production, most importantly, agricultural soil and irrigation water, serve as potential reservoirs of some clinically significant foodborne pathogenic bacteria. These clinically important bacteria include: Klebsiella spp., Salmonella spp., Citrobacter spp., Shigella spp., Enterobacter spp., Listeria monocytogenes and pathogenic E. coli (and E. coli O157:H7) all of which have the potential to cause disease outbreaks. Most of these pathogens acquire antimicrobial resistance (AR) determinants due to AR selective pressure within the agroecosystem and become resistant against most available treatment options, further aggravating risks to human and environmental health, and food safety. This review critically outlines the following issues with regards to fresh produce; the global burden of fresh produce-related foodborne diseases, contamination between the continuum of farm to table, preharvest transmission routes, AR profiles, and possible interventions to minimize the preharvest contamination of fresh produce. This review reveals that the primary production niches of the agro-ecosystem play a significant role in the transmission of fresh produce associated pathogens as well as their resistant variants, thus detrimental to food safety and public health.

Petting Zoo Animals as an Emerging Reservoir of Extended-Spectrum β-Lactamase and AmpC-Producing Enterobacteriaceae

Extended spectrum beta-lactamases and AmpC-producing Enterobacteriaceae (ESBL/AmpC-E) have become a great concern in both human and veterinary medicine. One setting in which this risk could be particularly prominent is petting zoos, in which humans, especially children, directly and indirectly interact with the animals. Yet, while the zoonotic transmission of various Enterobacteriaceae has been reported previously in petting zoos, reports on ESBL/AmpC-E shedding in this setting is currently lacking, despite the high potential risk. To fill this knowledge gap, we conducted a prospective cross-sectional study to explore the prevalence, molecular epidemiology, and risk for shedding of ESBL/AmpC-E in petting zoos. We performed a prospective cross-sectional study in eight petting zoos. Altogether, we collected 381 fecal and body-surface samples from 228 animals, broth-enriched them, and then plated them onto CHROMagar ESBL-plates for ESBL/AmpC-E isolation. Next, we identified the isolated species and tested their susceptibility to various antibiotics using the Vitek-2 system, determined bacterial relatedness by multilocus sequence typing (MLST), and identified ESBL/AmpC genes by using PCR and sequencing. Finally, we asked petting zoo owners and veterinarians to complete questionnaires, which we then analyzed to evaluate risk factors for ESBL/AmpC-E shedding. We found that ESBL/AmpC-E shedding is an important, currently oversighted risk in petting zoos, as the overall shedding rate was 12% (35 isolates, including 29% ESBL-producers, 34% AmpC-producers, and 37% ESBL and AmpC-producers). The isolated bacteria included Enterobacter cloacae (55%), Escherichia coli (31%), and Citrobacter freundii (14%), with diverse ESBL genes. MLST revealed diverse sequence types (STs), including the highly virulent Enterotoxigenic ST656 and the Uropathogenic ST127 E. coli strains, indicating complex epidemiology with inter-animal bacterial transmission. Shedding was associated with petting permission and antibiotic treatment in the petting zoo (OR = 7.34), which were identified as risk factors for ESBL/AmpC shedding. Our findings highlight petting zoos as a source for antibiotic-resistant ESBL/AmpC-producing bacteria, including highly virulent, disease-associated MDR E. coli strains. As this risk has not been previously described in detail, it calls for the implementation of infection control and active surveillance programs in petting zoos and raises the need for a comprehensive guideline to restrain this emerging concern.

Citrobacter freundii Foodborne Disease Outbreaks Related to Environmental Conditions in Yazd Province, Iran

BACKGROUND

The aim of this study was to assess associations of Citrobacter freundii foodborne outbreaks with environmental factors in various regions of Yazd Province, Iran, 2012-2016.

METHODS

The public health surveillance data were used for one period of five years reported foodborne disease outbreaks in various regions of the Province. Multilevel regression statistical method was used to analyze associations of climatic and demographic variables with outbreaks. Significant associations were tested using likelihood ratio tests.

RESULTS

Results showed a significant association between C. freundii outbreaks and air dust conditions, age groups and various regional cities.

CONCLUSION

The current study revealed necessity of etiologic agent identification for use in foodborne disease outbreak guidance in future outbreaks. Systemic surveillance schemes can help prevent and control similar scenarios using reports of environmental effects on foodborne disease outbreaks.

Comparative genomics analysis of pTEM-2262, an MDR plasmid from Citrobacter freundii, harboring two unclassified replicons

AIM

To genetically characterize the multidrug-resistance (MDR) plasmid pTEM-2262 that could not be classified into any known incompatibility group from the clinical Citrobacter freundii isolate 2262.

MATERIALS & METHODS

The repA or repB deletion mutants of pTEM-2262 were constructed using the scarless Cas9-assisted recombineering system. Comparative genomic analysis of pTEM-2262 and the other four previously sequenced plasmids belonging to the same incompatibility group were performed.

RESULTS

pTEM-2262, a conjugative plasmid, harbored two unclassified replicons, repA and repB, while repB was not essential for pTEM-2262 replication. In five analyzed plasmids, their conserved backbones primarily integrated massive accessory modules at two 'hotspots' that were located between orf597 and orf504, and between orf393 and orf405. All the antibiotic resistance genes of pTEM-2262 were clustered in the MDR region with a complex mosaic structure.

CONCLUSION

This study thoroughly investigates the detailed structure and genomic comparison of this unknown incompatibility group for the first time.

Clonal Background, Resistance Gene Profile, and Porin Gene Mutations Modulate In Vitro Susceptibility to Imipenem-Relebactam in Diverse Enterobacteriaceae

Treatment options for carbapenem-resistant Enterobacteriaceae (CRE) are limited. While Klebsiella pneumoniae strains harboring bla_KPC account for most CRE, recent evidence points to increasing diversification of CRE. We determined whether the CRE species and antibiotic resistance genotype influence the response to relebactam (REL), a novel beta-lactamase inhibitor with class A/C activity, combined with imipenem-cilastatin (IMI). We carried out broth microdilution testing with IMI alone or in the presence of 4 μg/ml REL against 154 clinical isolates collected at a New York City hospital with a high prevalence of organisms carrying bla_KPC, including Enterobacter spp. (n = 96), K. pneumoniae (n = 44), Escherichia coli (n = 1), Serratia marcescens (n = 9), and Citrobacter spp. (n = 4). Resistance gene profiles and the presence of major porin gene disruptions were ascertained by whole-genome sequencing. Addition of REL decreased the IMI MIC to the susceptible range (≤1 μg/ml) against 88% of isolates. However, S. marcescens IMI-REL MICs were 4- to 8-fold higher than those for other organisms. Most bla_KPC-positive isolates had IMI-REL MICs of ≤1 μg/ml (88%), including isolates of Enterobacter cloacae ST171 (93%) and K. pneumoniae ST258 (82%). Nineteen isolates had IMI-REL MICs of ≥2 μg/ml, among which 84% harbored bla_KPC and one was bla_NDM-1 positive. Isolates with IMI-REL MICs of ≥2 μg/ml versus those with MICs of ≤1 μg/ml were significantly more likely to demonstrate disruption of at least one porin gene (42% versus 19%; P = 0.04), although most S. marcescens isolates (67%) had intact porin genes. In conclusion, while REL reduced IMI MICs in a majority of diverse CRE isolates, including high-risk clones, chromosomal factors had an impact on IMI-REL susceptibilities and may contribute to elevated MICs for S. marcescens.

Proteins of generalist and specialist pathogens differ in their amino acid composition

Pathogens differ in their host specificities, with species infecting a unique host (specialist pathogens) and others having a wide host range (generalists). Molecular determinants of pathogen's host range remain poorly understood. Secreted proteins of generalist pathogens are expected to have a broader range of intermolecular interactions (i.e., higher promiscuity) compared with their specialist counterparts. We hypothesize that this increased promiscuity of generalist secretomes may be based on an elevated content of primitive amino acids and intrinsically disordered regions, as these features are known to increase protein flexibility and interactivity. Here, we measure the proportion of primitive amino acids and percentage of intrinsically disordered residues in secreted, membrane, and cytoplasmic proteins from pathogens with different host specificity. Supporting our prediction, there is a significant general enrichment for primitive amino acids and intrinsically disordered regions in proteins from generalists compared to specialists, particularly among secreted proteins in prokaryotes. Our findings support our hypothesis that secreted proteins' amino acid composition and disordered content influence the pathogens' host range.

Genetic Diversity, Multidrug Resistance, and Virulence of Citrobacter freundii From Diarrheal Patients and Healthy Individuals

Objectives:Citrobacter freundii is a frequent cause of nosocomial infections and a known cause of diarrheal infections, and has increasingly become multidrug resistant (MDR). In this study, we aimed to determine the genetic diversity, the antimicrobial resistance profiles and in vitro virulence properties of C. freundii from diarrheal patients and healthy individuals. Methods: 82 C. freundii isolates were obtained from human diarrheal outpatients and healthy individuals. Multilocus Sequence Typing (MLST) of seven housekeeping genes was performed. Antimicrobial susceptibility testing was carried out using the disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) recommendations. Adhesion and cytotoxicity to HEp-2 cells were assessed. PCR and sequencing were used to identify bla_CTX-M, bla_SHV, bla_TEM, qnrA, qnrB, qnrS, qnrC, qnrD, aac(6')-Ib-cr, and qepA genes. Results: The 82 C. freundii isolates were divided into 76 sequence types (STs) with 65 STs being novel, displaying high genetic diversity. Phylogenetic analysis divided the 82 isolates into 5 clusters. All 82 isolates were sensitive to imipenem (IPM), but resistant to one or more other 16 antibiotics tested. Twenty-six isolates (31.7%) were multidrug resistant to three or more antibiotic classes out of the 10 distinct antibiotic classes tested. Five MDR isolates, all of which were isolated from 2014, harbored one or more of the resistance genes, bla_TEM-1, bla_CTX-M-9, aac(6')-Ib-cr, qnrS1, qnrB9, and qnrB13. All 11 qnrB-carrying C. freundii isolates belonged to cluster 1, and one C. freundii isolate carried a new qnrB gene (qnrB92). Six isolates showed strong cytotoxicity to HEp-2 cells, one of which was multidrug resistant. Conclusions:C. freundii isolates from human diarrheal outpatients and healthy individuals were diverse with variation in sequence types, antibiotic resistance profiles and virulence properties.

Characterization of KPC-Encoding Plasmids from Enterobacteriaceae Isolated in a Czech Hospital

Ten Enterobacteriaceae isolates collected in a Czech hospital carried blaKPC-positive plasmids of different sizes (∼30, ∼45, and ∼80 kb). Sequencing revealed three types of plasmids (A to C) with the Tn4401a transposon. Type A plasmids comprised an IncR backbone and a KPC-2-encoding multidrug resistance (MDR) region. Type B plasmids were derivatives of type A plasmids carrying an IncN3-like segment, while type C plasmids were IncP6 plasmids sharing the same KPC-2-encoding MDR region with type A and B plasmids.

Characterization of the Complete Nucleotide Sequences of IncA/C2 Plasmids Carrying In809-Like Integrons from Enterobacteriaceae Isolates of Wildlife Origin

A total of 18 Enterobacteriaceae (17 from gulls and 1 from a clinical sample) collected from Australia, carrying IncA/C plasmids with the IMP-encoding In809-like integrons, were studied. Seven plasmids, being representatives of different origins, plasmid sizes, replicon combinations, and resistance genes, were completely sequenced. Plasmid pEc158, identified in a clinical Escherichia coli ST752 isolate, showed extensive similarity to type 2 IncA/C₂ plasmids. pEc158 carried none of the bla_CMY-2-like region or ARI-B and ARI-A regions, while it contained a hybrid transposon structure. The six remaining plasmids, which were of wildlife origin, were highly similar to each other and probably were fusion derivatives of type 1 and type 2 A/C₂ plasmids. The latter plasmids contained an ARI-B region and hybrid transposon structures. In all plasmids, hybrid transposon structures containing In809-like integrons were inserted 3,434 bp downstream of the rhs2 start codon. In all cases, the one outermost 38-bp inverted repeat (IR) of the transposon was associated with the Tn1696 tnp module, while the other outermost 38-bp IR of the transposon was associated with either a Tn6317-like module or a Tn21 mer module. However, the internal structure of the transposon and the resistance genes were different in each plasmid. These findings indicated that, for the specific periods of time and settings, different IncA/C₂ plasmid types carrying In809-like elements circulated among isolates of wildlife and clinical origins. Additionally, they provided the basis for speculations regarding the reshuffling of IncA/C₂ plasmids with In809-like integrons and confirmed the rapid evolution of IncA/C₂ plasmid lineages.

Circulation of blaKPC-3-Carrying IncX3 Plasmids among Citrobacter freundii Isolates in an Italian Hospital

Colonizations due to carbapenem-resistant Enterobacteriaceae (CRE) are a source of antimicrobial resistance transmission in health care settings. Eleven Citrobacter freundii strains producing KPC-3 carbapenemase were isolated from rectal swabs during a 3-year surveillance program. bla_KPC-3-carrying plasmids were found to belong to the IncX3 group in 9 of the 11 strains, and complete nucleotide sequences were obtained for 2 of them. Our results highlight the possible role of C. freundii as reservoir of resistance genes.

Antimicrobial Resistance and Cytotoxicity of Citrobacter spp. in Maanshan Anhui Province, China

Objectives:Citrobacter spp. especially Citrobacter freundii, is frequently causing nosocomial infections, and increasingly becoming multi-drug resistant (MDR). In this study, we aimed to determine the genetic diversity and relationships of Citrobacter spp. from diarrheal patients and food sources, their antimicrobial resistance profiles and in vitro virulence properties.

Methods: Sixty two Citrobacter isolates, including 13 C. freundii, 41 C. youngae and eight C. braakii isolates, were obtained from human diarrheal patients and food sources. Multilocus Sequence Typing (MLST) of seven housekeeping genes and antimicrobial susceptibility testing using the broth microdilution method according to CLSI recommendations were carried out. Adhesion and cytotoxicity to HEp-2 cells were performed. PCR and sequencing were used to identify bla_CTX−M, bla_SHV, bla_TEM and qnr genes.

Results: The 62 isolates were divided into 53 sequence types (STs) with all STs being novel, displaying high genetic diversity. ST39 was a predominant ST shared by 5 C. youngae strains isolated from four foods and a diarrheal patient. All isolates were resistant to cefoxitin, and sensitive to imipenem, meropenem and amikacin. The majority of Citrobacter isolates (61.3%) were MDR of three or more antibiotics out of the 22 antibiotics tested. Two C. freundii isolates each carried the bla_TEM−1 gene and a variant of qnrB77. Three Citrobacter isolates each carried qnrS1 and aac(6')-Ib-cr genes. Seven isolates that showed strong cytotoxicity to HEp-2 cells were MDR.

Conclusions:Citrobacter spp. from human and food sources are diverse with variation in virulence properties and antibiotic resistance profiles. Food may be an important source of Citrobacter species in transmission to humans. C. freundii and C. youngae are potential foodborne pathogens.

Emergence of a multidrug-resistant Citrobacter freundii ST8 harboring an unusual VIM-4 gene cassette in Poland

OBJECTIVES

The growing incidence of multidrug-resistant (MDR) bacteria is an emerging challenge in modern medicine. The utility of carbapenems, which are considered 'last-line' agents, is being diminished by the growing incidence of various resistance mechanisms in Gram-negative bacteria. A molecular investigation was performed of an MDR carbapenem-resistant Citrobacter freundii of sequence type 8 (ST8) isolated from a hematology patient with acute myeloid leukemia.

METHODS

Multilocus sequence typing and analysis of the nucleotide sequence of the class I integron were performed using PCR and Sanger sequencing. Transformation of the resistance plasmid isolated following the alkaline lysis method was performed using chemically competent E. coli TOP10.

RESULTS

Molecular analysis of the carbapenem-resistant C. freundii revealed the presence of the VIM-4 isoenzyme located on the ∼55-kb transferable resistance plasmid. Interestingly, the bla_VIM-4 gene was inserted into an unusual gene cassette containing a 169-bp direct repeat of the 3' segment of the bla_VIM-4 gene.

CONCLUSIONS

All unusual gene cassettes containing VIM-DR (direct repeat) described thus far have been harbored by non-fermenters, i.e., Acinetobacter and Pseudomonas, underscoring the importance of resistance determinant mobility, which may go even beyond genus, family, and order boundaries. Great efforts need to be taken to explore pathways of resistance to 'last-resort' antimicrobials, especially among clinically relevant pathogens.

Cronobacter sakazakii ATCC 29544 Autoaggregation Requires FliC Flagellation, Not Motility

Cronobacter sakazakii is an opportunistic nosocomial and foodborne pathogen that causes severe infections with high morbidity and mortality rates in neonates, the elderly, and immunocompromised individuals. Little is known about the pathogenesis mechanism of this pathogen and if there are any consequences of C. sakazakii colonization in healthy individuals. In this study, we characterized the mechanisms of autoaggregation in C. sakazakii ATCC 29544 (CS29544). Autoaggregation in CS29544 occurred rapidly, within 30 min, and proceeded to a maximum of 70%. Frameshift mutations in two flagellum proteins (FlhA and FliG) were identified in two nonautoaggregating CS29544 clonal variant isolates. Strategic gene knockouts were generated to determine if structurally intact and functional flagella were required for autoaggregation in CS29544. All structural knockouts (ΔflhA, ΔfliG, and ΔfliC) abolished autoaggregation, whereas the functional knockout (ΔmotAB) did not prevent autoaggregation. Complementation with FliC (ΔfliC/cfliC) restored autoaggregation. Autoaggregation was also disrupted by the addition of exogenous wild-type CS29544 filaments in a dose-dependent manner. Finally, filament supercoils tethering neighboring wild-type CS29544 cells together were observed by transmission electron microscopy. In silico analyses suggest that direct interactions of neighboring CS29544 FliC filaments proceed by hydrophobic bonding between the externally exposed hypervariable regions of the CS29544 FliC flagellin protein. Further research is needed to confirm if flagella-mediated autoaggregation plays a prominent role in C. sakazakii pathogenesis.

Characterization of Five Podoviridae Phages Infecting Citrobacter freundii

Citrobacter freundii causes opportunistic infections in humans and animals, which are becoming difficult to treat due to increased antibiotic resistance. The aim of this study was to explore phages as potential antimicrobial agents against this opportunistic pathogen. We isolated and characterized five new virulent phages, SH1, SH2, SH3, SH4, and SH5 from sewage samples in Tunisia. Morphological and genomic analyses revealed that the five C. freundii phages belong to the Caudovirales order, Podoviridae family, and Autographivirinae subfamily. Their linear double-stranded DNA genomes range from 39,158 to 39,832 bp and are terminally redundant with direct repeats between 183 and 242 bp. The five genomes share the same organization as coliphage T7. Based on genomic comparisons and on the phylogeny of the DNA polymerases, we assigned the five phages to the T7virus genus but separated them into two different groups. Phages SH1 and SH2 are very similar to previously characterized phages phiYeO3-12 and phiSG-JL2, infecting, respectively, Yersinia enterocolitica and Salmonella enterica, as well as sharing more than 80% identity with most genes of coliphage T7. Phages SH3, SH4, and SH5 are very similar to phages K1F and Dev2, infecting, respectively, Escherichia coli and Cronobacter turicensis. Several structural proteins of phages SH1, SH3, and SH4 were detected by mass spectrometry. The five phages were also stable from pH 5 to 10. No genes coding for known virulence factors or integrases were found, suggesting that the five isolated phages could be good candidates for therapeutic applications to prevent or treat C. freundii infections. In addition, this study increases our knowledge about the evolutionary relationships within the T7virus genus.

The clonal relationship among the Citrobacter freundii isolated from the main hospital in Kermanshah, west of Iran

BACKGROUND AND OBJECTIVES

Citrobacter freundii is an opportunistic pathogen causing nosocomial infections and resistant to various antibiotics. We aimed to determine the clonal relationship of C. freundii isolates using Pulsed-Field Gel Electrophoresis (PFGE).

MATERIALS AND METHODS

Fifty clinical isolates of C. freundii were collected from the main hospital in Kermanshah. After antibiotic susceptibility testing and screening for extended-spectrum beta lactamase (ESBL), all isolates were genotyped by PFGE. The DNA fragment patterns were analysed using Gelcompar II version 6.6 software. The Dice coefficient was used to calculate similarities for cluster analysis.

RESULTS

The PFGE results of 12 (24%) and 38 (76%) ESBL positive and negative isolates, respectively, produced 39 clusters (X_1-39) with different genotype patterns. The X₁ and X₂ clusters were the major clusters, each contained 3 isolates from different hospital wards. However, the majority of isolates showed a high genotypic diversity.

CONCLUSION

Results revealed the genotypic diversity of C. freundii isolates indicating the various sources for the bacterial isolates. However, the presence of isolates with similar genotypes indicates the common origin for these strains and may reflect the strain dissemination within the hospital wards, in particular in infectious ward and intensive care unit.

Topological distortion and reorganized modular structure of gut microbial co-occurrence networks in inflammatory bowel disease

The gut microbiome plays a key role in human health, and alterations of the normal gut flora are associated with a variety of distinct disease states. Yet, the natural dependencies between microbes in healthy and diseased individuals remain far from understood. Here we use a network-based approach to characterize microbial co-occurrence in individuals with inflammatory bowel disease (IBD) and healthy (non-IBD control) individuals. We find that microbial networks in patients with IBD differ in both global structure and local connectivity patterns. While a “core” microbiome is preserved, network topology of other densely interconnected microbe modules is distorted, with potent inflammation-mediating organisms assuming roles as integrative and highly connected inter-modular hubs. We show that while both networks display a rich-club organization, in which a small set of microbes commonly co-occur, the healthy network is more easily disrupted by elimination of a small number of key species. Further investigation of network alterations in disease might offer mechanistic insights into the specific pathogens responsible for microbiome-mediated inflammation in IBD.

Experiences from the 2014 outbreak of bluetongue in Greece

Objective of this paper was to review relevant work and to present a general account of the bluetongue outbreak, which occurred in Greece in 2014. In total, 2895 outbreaks of the disease have been reported by the veterinary authorities of Greece; sheep, goats and cattle were affected with officially reported morbidity rates of 11.0%, 2.0% and 3.5%, respectively. No vaccinations were allowed and conservative measures were implemented to attempt to limit the disease, which at the end had expanded throughout the country. In field investigations, a significantly higher bluetongue morbidity rate (27.5%) in sheep has been reported. During that work, clinical anaemia was encountered, which was characterised as macrocytic, hypochromic, regenerative and non-haemolytic. Other investigations, which are reviewed in this paper, have described an outbreak of Citrobacter freundii-associated enteritis in newborn kids, offspring of goats subclinically infected with Bluetongue virus, increased rate of early embryonic deaths, reduced conception rates, increased incidence risk of mastitis and reduced milk yield in herds of subclinically-infected cattle and detection of the virus from hunter-harvested tissue samples of roe-deer. In 2015, vaccines against the disease have been licenced; vaccinations started in May 2015. Then, in 2015, only one outbreak of the disease was confirmed, which could have been the result of a combination of reasons acting concurrently to prevent further cases.

KPC-Like Carbapenemase-Producing Enterobacteriaceae Colonizing Patients in Europe and Israel

In a 2008-2011 survey, 17,945 patients in 18 hospital units in Europe and Israel were screened for carriage of Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae, resulting in identification of 124 positive patients. The isolates were dominated by Klebsiella pneumoniae sequence type 258 (ST258) KPC-2 and ST512 KPC-3, mainly from Greece and Italy, respectively, whereas Israeli isolates were of diverse species, clones, and KPC variants. Various blaKPC platforms were observed, among which IncFIIK-FIBK plasmids with blaKPC-2/-3 genes in the Tn4401a transposon prevailed.

The Type VI Secretion System Modulates Flagellar Gene Expression and Secretion in Citrobacter freundii and Contributes to Adhesion and Cytotoxicity to Host Cells

The type VI secretion system (T6SS) as a virulence factor-releasing system contributes to virulence development of various pathogens and is often activated upon contact with target cells. Citrobacter freundii strain CF74 has a complete T6SS genomic island (GI) that contains clpV, hcp-2, and vgr T6SS genes. We constructed clpV, hcp-2, vgr, and T6SS GI deletion mutants in CF74 and analyzed their effects on the transcriptome overall and, specifically, on the flagellar system at the levels of transcription and translation. Deletion of the T6SS GI affected the transcription of 84 genes, with 15 and 69 genes exhibiting higher and lower levels of transcription, respectively. Members of the cell motility class of downregulated genes of the CF74ΔT6SS mutant were mainly flagellar genes, including effector proteins, chaperones, and regulators. Moreover, the production and secretion of FliC were also decreased in clpV, hcp-2, vgr, or T6SS GI deletion mutants in CF74 and were restored upon complementation. In swimming motility assays, the mutant strains were found to be less motile than the wild type, and motility was restored by complementation. The mutant strains were defective in adhesion to HEp-2 cells and were restored partially upon complementation. Further, the CF74ΔT6SS, CF74ΔclpV, and CF74Δhcp-2 mutants induced lower cytotoxicity to HEp-2 cells than the wild type. These results suggested that the T6SS GI in CF74 regulates the flagellar system, enhances motility, is involved in adherence to host cells, and induces cytotoxicity to host cells. Thus, the T6SS plays a wide-ranging role in C. freundii.

Genetic characterization of atypical Citrobacter freundii

The ability of a bacterial population to survive in different niches, as well as in stressful and rapidly changing environmental conditions, depends greatly on its genetic content. To survive such fluctuating conditions, bacteria have evolved different mechanisms to modulate phenotypic variations and related strategies to produce high levels of genetic diversity. Laboratories working in microbiological diagnosis have shown that Citrobacter freundii is very versatile in its colony morphology, as well as in its biochemical, antigenic and pathogenic behaviours. This phenotypic versatility has made C. freundii difficult to identify and it is frequently confused with both Salmonella enterica and Escherichia coli. In order to determine the genomic events and to explain the mechanisms involved in this plasticity, six C. freundii isolates were selected from a phenotypic variation study. An I-CeuI genomic cleavage map was created and eight housekeeping genes, including 16S rRNA, were sequenced. In general, the results showed a range of both phenotypes and genotypes among the isolates with some revealing a greater similarity to C. freundii and some to S. enterica, while others were identified as phenotypic and genotypic intermediary states between the two species. The occurrence of these events in natural populations may have important implications for genomic diversification in bacterial evolution, especially when considering bacterial species boundaries. In addition, such events may have a profound impact on medical science in terms of treatment, course and outcomes of infectious diseases, evading the immune response, and understanding host-pathogen interactions.

Evaluation of the virulence markers in the clinical isolates of citrobacter species: the first report from India

BACKGROUND

Citrobacter, a gram negative bacillus, is emerging as one of the major pathogens in hospital settings, with a potential to cause serious infections. Virulence markers are the factors which enhance the survival ability of the micro-organisms. Among the gram negative bacilli, these have been extensively studied in Escherichia coli. To the best of our knowledge as per internet search, we report that this study has been done for the first time in India on Citrobacter.

AIMS

An investigation was done to determine the ability of Citrobacter in producing virulence markers like the ability to survive the serum bactericidal activity, the resistance to the intracellular killing in the Polymorphonuclear Leucocytes (PMNLs) and the Cell Surface Hydrophobicity (CSH).

SETTINGS AND DESIGN

This prospective study was conducted in the Department of Microbiology of a tertiary care hospital in Aligarh, India, for a period of one year and six months.

MATERIAL AND METHODS

A total of 105 clinical isolates and 20 control isolates from healthy subjects were identified as having Citrobacter spp. by using standard biochemical tests and they were studied for the presence of virulence markers like the ability to survive the serum bactericidal activity, the resistance to the intracellular killing in the Polymorphonuclear Leucocytes (PMNLs) and the cell surface hydrophobicity. The statistical analysis which was used: The standard deviations and the p-values were calculated for comparison.

RESULTS

Out of the 105 clinical isolates of Citrobacter which were studied, 86.6% isolates were resistant to 100% serum after 180 minutes of incubation and intracellular killing in PMNL was demonstrated in 17% strains. The Salt Aggregation Test (SAT) for the cell surface hydrophobicity was positive in 17.1% strains at different concentrations of ammonium sulphate. The presence of more than one virulence marker was present in 71.4% of the clinical isolates while in the control isolates.

CONCLUSIONS

The presence of the virulence markers in Citrobacter demonstrated its pathogenic potential. Its invasiveness and ability to disseminate can be studied by identifying these markers.

Outbreak of Citrobacter freundii carrying VIM-1 in an Italian Hospital, identified during the carbapenemases screening actions, June 2012

OBJECTIVE

The identification of patients colonized or infected with carbapenemase-producing Enterobacteriaceae (CPE), in order to control and prevent the global spread of multidrug-resistant (MDR) pathogens.

METHODS

From June 1 to June 15, 2012, eight Citrobacter freundii strains with reduced susceptibility to carbapenems were isolated from rectal swabs of hospitalized patients during active screening following the detection of a Klebsiella pneumoniae carbapenemase (KPC) -positive patient on the ward. All isolates were analyzed phenotypically and molecularly by PCR and sequencing. Genotype clustering was performed by multilocus sequence typing (MLST) analysis.

RESULTS

The isolates showed high rates of multidrug resistance profile. A phenotypic assay for carbapenemase production suggested the presence of metallo-β-lactamase (MBL). The blaVIM-1 gene was detected in all imipenem-resistant C. freundii isolates. MLST showed that the C. freundii isolates shared the same sequence type (ST). Phylogenetic analysis revealed a strict relationship with an ST5C. freundii isolate from a diarrhea patient in China.

CONCLUSIONS

Our findings showed that the active surveillance program for CPE was useful, not only for the detection of KPC-producers, but also to identify and control the spread of other MDR pathogens that could expand the spectrum of circulating MDR pathogens.