Current concepts on the virulence mechanisms of meticillin-resistant Staphylococcus aureus

Prevalence and antimicrobial resistance of gram-positive pathogens in Lebanon: The need for surveillance and stewardship

Background

Resistance in Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), poses a significant healthcare challenge globally. However, data on these organisms in Lebanon remain limited. This retrospective study aimed to assess the prevalence and antimicrobial resistance patterns of Staphylococcus aureus (S. aureus), coagulase-negative Staphylococci (CoNS), and Enterococcus spp. in clinical infections at the Lebanese Hospital Geitaoui - UMC from 2017 to 2023.

Methods

A total of 2676 isolates were collected from urine, blood, respiratory specimens, and other infection sites. Bacterial identification was performed following WHO clinical bacteriology procedures, utilizing gram staining, catalase and coagulase tests, and biochemical assays. Antimicrobial susceptibility testing was conducted using the Kirby-Bauer disk diffusion method and minimum inhibitory concentration (MIC) analysis, interpreted according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Statistical analyses were performed using SPSS® version 24, with significance set at p < 0.05.

Results

CoNS were the most prevalent (42.83 %), followed by Enterococcus spp. (28.81 %) and S. aureus (28.36 %). Blood cultures had the highest isolation rates (29.04 %), predominantly CoNS (76.45 %). Enterococcus spp. dominated urinary tract infections (85.01 %), while S. aureus was prevalent in wound/surgical site infections (59.23 %). Gender-specific trends showed CoNS and S. aureus more in males, while Enterococcus spp. infections were more common in females.

Conclusion

This study provides valuable insights into the prevalence and resistance patterns of Gram-positive pathogens in a Lebanese hospital setting. The findings highlight the need for continuous surveillance and stringent antibiotic stewardship to combat antimicrobial resistance effectively.

Molecular Dynamics Simulation Studies of Beta-Glucogallin and Dihydro Dehydro Coniferyl Alcohol from Syzygium cumini for its Antimicrobial Activity on Staphylococcus aureus

With the escalating threat of antimicrobial resistance (AMR), discovering novel therapeutic agents against resistant pathogens like Staphylococcus aureus is crucial. This study explores phytochemicals from Syzygium cumini for their potential efficacy against AMR S. aureus infections, elucidating their mechanisms through in silico methods. We investigated 83 compounds from S. cumini, sourced from PubMed, using rigorous docking analysis against the ATP binding domain AgrC of S. aureus with AMdock with Autodock Vina v1.5.2. Drug-likeness predictions were assessed using SwissADME v2023 and Pass online v2.0. Molecular dynamics (MD) simulations identified promising compounds, focusing on stability and interaction dynamics. Beta-Glucogallin (BEG) and Dihydro Dehydro Coniferyl alcohol (DIH) emerged as significant hits. MD simulations with GROMACS v2020.6 revealed stable BEG and DIH complexes with AgrC, forming six hydrogen bonds with six key amino acids (Arg-303, Asp-338, Glu-342, Glu-384, Lys-389, Gly-396), indicating strong and stable bonding. The binding affinities for DIH and BEG are -73.474 ± 11.104 kJ/mol and -6.319 ± 18.823 kJ/mol with 4BXI, respectively. Our findings highlight BEG and DIH as promising candidates against AMR S. aureus infections, showing favourable binding affinities and stable interactions with AgrC. This study underscores the importance of natural products in combating AMR and demonstrates the utility of computational methodologies in drug discovery. Further experimental validation is warranted to fully exploit these phytochemicals' therapeutic potential.

Molecular characterization of methicillin-resistant Staphylococcus aureus: Dissemination of multidrug-resistant community-associated MRSA and emergence of LA-MRSA, in a healthcare setting

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a significant cause of healthcare-associated infections (HAIs). In this study, we aimed to characterize the MRSA isolates obtained from HAIs.

METHODS

A total of 200 clinical and 13 nasal MRSA isolates were collected and tested. The samples were analyzed for SCCmec typing by using multiplex PCR. Microtiter for biofilm formation were performed and molecular typing for the samples were performed for spa and agr typing.

RESULTS

The isolates showed 100 % sensitivity to vancomycin and linezolid, while 92.5 % were multidrug-resistant. Strong biofilm-forming ability was observed in 47 % of the isolates. SCC mec typing identified 52.5 % of the isolates as classical hospital-associated MRSA or HA-MRSA (SCC mec type III), 23.5 % as community-associated MRSA or CA-MRSA (type IV and V), and 16.5 % as non-typeable, with 7.5 % having multiple SCCmec types.

CONCLUSION

Comparison of HA and CA-MRSA traits revealed that both groups had multidrug resistance, but HA-MRSA was distinguished by its strong capacity for biofilm formation, whereas CA-MRSA was marked by a high count of toxin gene. Our study, to the best of our awareness, documents the presence of LA-MRSA (SCCmec V- t127-agr III) causing HAIs in Indian patients for the first time.

Molecular Characteristics of Community-Acquired Methicillin-Resistant Staphylococcus aureus, Hospital-Acquired MRSA Isolates, and PVL in one of the Indian hospitals

Community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) strains are increasingly replacing hospital-acquired MRSA (HA-MRSA) strains in hospitalized patients leading to poor clinical outcomes. Hence, this study aimed to characterize clinical isolates of MRSA (HA-MRSA and CA-MRSA) and to understand their clonal origin. A total of 400 consecutive S. aureus clinical isolates were collected from the clinical bacteriology lab of a tertiary care hospital. All the isolates were screened for MRSA by cefoxitin disc diffusion test and mecA PCR, followed by SCCmec typing, antibiotic susceptibility testing, Panton Valentine Leukocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE). Of the total 400 isolates, 134 categorized MRSA by cefoxitin, while 129 as mecA positive by PCR, of which 117 could be characterized into SCCmec types. SCCmecI and II were present in 1 isolate each, SCCmecIII in 36 (31%) representing HA-MRSA, While SCCmecIV in 51 (44%), and SCCmecV in 28 (24%) isolates representing CA-MRSA. Of all SCCmecIII isolates, 70% were multidrug resistant (MDR) while 59% of SCCmecIV and 29% of SCCmecV isolates were MDR. PVL (CA-MRSA virulence factor) positivity in mecIII, IV, V isolates was 9%, 31%, 46% respectively. PFGE typing showed MRSA clones of multiple origins. In conclusion, study showed the evolving epidemiology of HA-MRSA and CA-MRSA. CA-MRSA constituted the majority of clinical isolates amongst both community and hospital MRSA isolates. Various MDR clones of mecIV and mecV were circulating and replacing mecIII in hospital settings. SCCmecIV isolates were predominant and evolved as MDR, however, PVL was significantly associated with CA-MRSA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-024-01195-9.

Disease-Inspired Design of Biomimetic Tannic Acid-Based Hybrid Nanocarriers for Enhancing the Treatment of Bacterial-Induced Sepsis

This study explored the development of novel biomimetic tannic acid-based hybrid nanocarriers (HNs) for targeted delivery of ciprofloxacin (CIP-loaded TAH-NPs) against bacterial-induced sepsis. The prepared CIP-loaded TAH-NPs exhibited appropriate physicochemical characteristics and demonstrated biocompatibility and nonhemolytic properties. Computational simulations and microscale thermophoresis studies validated the strong binding affinity of tannic acid (TA) and its nanoformulation to human Toll-like receptor 4, surpassing that of the natural substrate lipopolysaccharide (LPS), suggesting a potential competitive inhibition against LPS-induced inflammatory responses. CIP released from TAH-NPs displayed a sustained release profile over 72 h. The in vitro antibacterial activity studies revealed that CIP-loaded TAH-NPs exhibited enhanced antibacterial efficacy and efflux pump inhibitory activity. Specifically, they showed a 3-fold increase in biofilm eradication activity against MRSA and a 2-fold increase against P. aeruginosa compared to bare CIP. Time-killing assays demonstrated complete bacterial clearance within 8 h of treatment with CIP-loaded TAH-NPs. In vitro DPPH scavenging and anti-inflammatory investigations confirmed the ability of the prepared hybrid nanosystem to neutralize reactive oxygen species (ROS) and modulate LPS-induced inflammatory responses. Collectively, these results suggest that CIP-loaded TAH-NPs may serve as an innovative nanocarrier for the effective and targeted delivery of antibiotics against bacterial-induced sepsis.

Piperine, a phytochemical prevents the biofilm city of methicillin-resistant Staphylococcus aureus: A biochemical approach to understand the underlying mechanism

Methicillin-resistant Staphylococcus aureus (MRSA), a drug-resistant human pathogen causes several nosocomial as well as community-acquired infections involving biofilm machinery. Hence, it has gained a wide interest within the scientific community to impede biofilm-induced MRSA-associated health complications. The current study focuses on the utilization of a natural bioactive compound called piperine to control the biofilm development of MRSA. Quantitative assessments like crystal violet, total protein recovery, and fluorescein-di-acetate (FDA) hydrolysis assays, demonstrated that piperine (8 and 16 μg/mL) could effectively compromise the biofilm formation of MRSA. Light and scanning electron microscopic image analysis confirmed the same. Further investigation revealed that piperine could reduce extracellular polysaccharide production by down-regulating the expression of icaA gene. Besides, piperine could reduce the cell-surface hydrophobicity of MRSA, a crucial factor of biofilm formation. Moreover, the introduction of piperine could interfere with microbial motility indicating the interaction of piperine with the quorum-sensing components. A molecular dynamics study showed a stable binding between piperine and AgrA protein (regulator of quorum sensing) suggesting the possible meddling of piperine in quorum-sensing of MRSA. Additionally, the exposure to piperine led to the accumulation of intracellular reactive oxygen species (ROS) and potentially heightened cell membrane permeability in inhibiting microbial biofilm formation. Besides, piperine could reduce the secretion of diverse virulence factors from MRSA. Further exploration revealed that piperine interacted with extracellular DNA (e-DNA), causing disintegration by weakening the biofilm architecture. Conclusively, this study suggests that piperine could be a potential antibiofilm molecule against MRSA-associated biofilm infections.

mecA and fdh: markers of pathogenicity and commensalism in Staphylococcus epidermidis of pediatric origin from Pakistan

Staphylococcus epidermidis is an opportunistic bacterial pathogen. The study screened isolates of S. epidermidis of pediatric origin for genetic markers of discriminatory potential. 103 isolates (n = 75 clinical; n = 28 community) were screened for methicillin resistance (mecA), formate dehydrogenase (fdh) and an array of virulence factors through multiplex PCR and Congo red assay. The isolates were typed in four distinct categories, based on the presence of selected virulent factors. The type A clinical isolates carrying icaADBC operon (n = 22; 29.3%, P = 0.117) were not significantly differentiating the origin of isolates. The type B clinical isolates representing methicillin resistant S. epidermidis (MRSE) (n = 73; 97.3%, P < 0.00001) and the type C clinical isolates lacking formate dehydrogenase fdh (n = 62; 82.6%, P < 0.00001) were having significant discriminatory potential of clinical isolates, respectively. All type D community isolates were carrying fdh (n = 28; 100%, P < 0.00001). MecA and fdh are significant differential markers of pathogenicity and commensalism in S. epidermidis of pediatric origin.

Quinoline-2-one derivatives as promising antibacterial agents against multidrug-resistant Gram-positive bacterial strains

This study describes the discovery of a variety of quinoline2-one derivatives with significant antibacterial action vs a spectrum of multidrug-resistant Gram-positive bacterial strains, especially methicillin-resistant Staphylococcus aureus (MRSA). Compounds 6c, 6l, and 6o exhibited significant antibacterial activity versus the Gram-positive bacterial pathogens evaluated. In comparison to the reference daptomycin, compound 6c demonstrated the most effective activity among the assessed derivatives, with MIC concentrations of 0.75 μg/mL versus MRSA and VRE and 2.50 μg/mL against MRSE. We also reported on these compounds' biofilm and dihydrofolate reductase inhibitory activities. Compound 6c showed the greatest antibiofilm action in a dose-dependent way and a substantial decrease of biofilm development in the MRSA ACL51 strain at concentrations of 0.5, 0.25, and 0.12 MIC, with reductions of 79%, 55%, and 38%, consecutively, whereas the corresponding values for vancomycin were 20%, 12%, and 9%. These findings imply that these quinoline compounds could be used to develop a new category of antibiotic representatives to prevent Gram-positive drug-resistant bacterial strains.

Methicillin-resistant Staphylococcus aureus-associated orbital cellulitis: a case series

PURPOSE

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) orbital cellulitis (OC) has drawn increasing clinical and public health concern. We present a case series of MRSA OC encountered at four Australian tertiary institutions.

METHODS

A multi-centre retrospective case series investigating MRSA OC in Australia from 2013 to 2022. Patients of all ages were included.

RESULTS

Nine cases of culture-positive non-multi-resistant MRSA (nmMRSA) OC were identified at four tertiary institutions across Australia (7 male, 2 female). Mean age was 17.1 ± 16.7 years (range 13-days to 53-years), of which one was 13 days old, and all were immunocompetent. Eight (88.9%) patients had paranasal sinus disease, and seven (77.8%) had a subperiosteal abscess. Four (44.4%) had intracranial extension, including one (11.1%) case which was also complicated by superior sagittal sinus thrombosis. Empirical antibiotics, such as intravenous (IV) cefotaxime alone or IV ceftriaxone and flucloxacillin, were commenced. Following identification of nmMRSA, targeted therapy consisting of vancomycin and/or clindamycin was added. Nine (100%) patients underwent surgical intervention. Average hospital admission was 13.7 ± 6.9 days (range 3-25 days), with two patients requiring intensive care unit (ICU) admission due to complications related to their orbital infection. All patients had favourable prognosis, with preserved visual acuity and extraocular movements, following an average follow-up period of 4.6 months (range 2-9 months).

CONCLUSION

NMMRSA OC can follow an aggressive clinical course causing severe orbital and intracranial complications across a wide demographic. However, early recognition, initiation of targeted antibiotics and surgical intervention when required can effectively manage these complications and achieve favourable visual outcomes.

Association of Antibacterial Susceptibility Profile with the Prevalence of Genes Encoding Efflux Proteins in the Bangladeshi Clinical Isolates of Staphylococcus aureus

Expelling antibiotic molecules out of the cell wall through multiple efflux pumps is one of the potential mechanisms of developing resistance against a wide number of antibiotics in Staphylococcus aureus. The aim of this study was to investigate the association between the antibiotic susceptibility profile and the prevalence of different efflux pump genes i.e., norA, norB, norC, mepA, sepA, mdeA, qacA/B, and smr in the clinical isolates of S. aureus. Sixty clinical isolates were collected from a tertiary level hospital in Bangladesh. The disc diffusion method using ten antibiotics of different classes was used to discern the susceptibility profile. polymerase chain reaction (PCR) was employed to observe the resistance patterns and to detect the presence of plasmid and chromosomal encoded genes. Among the clinical isolates, 60% (36 out of 60) of the samples were Methicillin-resistant Staphylococcus aureus (MRSA), whereas 55% (33 out of 60) of the bacterial samples were found to be multi-drug resistant. The bacteria showed higher resistance to vancomycin (73.33%), followed by ciprofloxacin (60%), cefixime (53.33%), azithromycin (43.33%), and amoxicillin (31.67%). The prevalence of the chromosomally-encoded efflux genes norA (91.67%), norB (90%), norC (93.33%), mepA (93.33%), sepA (98.33%), and mdeA (93.33%) were extremely high with a minor portion of them carrying the plasmid-encoded genes qacA/B (20%) and smr (8.33%). Several genetic combinations of efflux pump genes were revealed, among which norA + norB + norC + mepA + sepA + mdeA was the most widely distributed combination among MRSA and MSSA bacteria that conferred resistance against ciprofloxacin and probably vancomycin. Based on the present study, it is evident that the presence of multiple efflux genes potentiated the drug extrusion activity and may play a pivotal role in the development of multidrug resistance in S. aureus.

An emerging Panton-Valentine leukocidin-positive CC5-meticillin-resistant Staphylococcus aureus-IVc clone recovered from hospital and community settings over a 17-year period from 12 countries investigated by whole-genome sequencing

BACKGROUND

A novel Panton-Valentine leukocidin (PVL)-positive meticillin-resistant Staphylococcus aureus (MRSA) clonal complex (CC)5-MRSA-IVc ('Sri Lankan' clone) was recently described from Sri Lanka. Similar isolates caused a recent Irish hospital outbreak.

AIM

To investigate the international dissemination and diversity of PVL-positive CC5-MRSA-IVc isolates from hospital and community settings using whole-genome sequencing (WGS).

METHODS

Core-genome single nucleotide polymorphism (cgSNP) analysis, core-genome multi-locus sequence typing (cgMLST) and microarray-based detection of antimicrobial-resistance and virulence genes were used to investigate PVL-positive CC5-MRSA-IVc (N = 214 including 46 'Sri Lankan' clone) from hospital and community settings in 12 countries over 17 years. Comparators included 29 PVL-positive and 23 PVL-negative CC5/ST5-MRSA-I/II/IVa/IVc/IVg/V.

RESULTS

Maximum-likelihood cgSNP analysis grouped 209/214 (97.7%) CC5-MRSA-IVc into Clade I; average of 110 cgSNPs between isolates. Clade III contained the five remaining CC5-MRSA-IVc; average of 92 cgSNPs between isolates. Clade II contained seven PVL-positive CC5-MRSA-IVa comparators, whereas the remaining 45 comparators formed an outlier group. Minimum-spanning cgMLST analysis revealed a comparably low average of 57 allelic differences between all CC5/ST5-MRSA-IVc. All 214 CC5/ST5-MRSA-IVc were identified as 'Sri Lankan' clone, predominantly spa type t002 (186/214) with low population diversity and harboured a similar range of virulence genes and variable antimicrobial-resistance genes. All 214 Sri Lankan clone isolates and Clade II comparators harboured a 9616-bp chromosomal PVL-encoding phage remnant, suggesting both arose from a PVL-positive meticillin-susceptible ancestor. Over half of Sri Lankan clone isolates were from infections (142/214), and where detailed metadata were available (168/214), most were community associated (85/168).

CONCLUSIONS

Stable chromosomal retention of pvl may facilitate Sri-Lankan clone dissemination.

Staphylococcus aureus is able to generate resistance to novel lipoglycopeptide antibiotic gausemycin A

Gausemycin A is the first member of the novel lipoglycopeptides family produced by Streptomyces roseoflavus INA-Ac-5812. Gausemycin A has a pronounced bactericidal activity against methicillin-resistant Staphylococcus aureus. However, the ability of S. aureus to be resistant to gausemycin A has not been investigated yet. Using serial passaging, we have obtained the resistant variant S. aureus 5812R, which is 80 times more resistant compared to the parent strain. Susceptibility testing of S. aureus 5812R revealed the acquisition of cross-resistance to daptomycin, cefazolin, tetracycline, and gentamicin, while the resistance to vancomycin, nisin, and ramoplanin was absent. Whole genome sequencing revealed single nucleotide polymorphism (SNP) and deletions in S. aureus 5812R, among which are genes encoding efflux pump (sepA), the two-component Kdp system (kdpE), and the component of isoprenoid biosynthesis pathway (hepT). Phenotypically, S. aureus 5812R resembles a small-colony variant, as it is slow-growing, forms small colonies, and is deficient in pigments. Profiling of fatty acids (FA) composition constituting the cytoplasmic membrane of S. aureus 5812R revealed the prevalence of anteiso-branched FA, while straight FA was slightly less present. The evidence also showed that the gausemycin A-resistant strain has increased expression of the cls2 gene of the cardiolipin synthase. The performed checkerboard assay pointed out that the combination of gausemycin A and ciprofloxacin showed a synergistic effect against S. aureus 5812R.

“Omic” Approaches to Bacteria and Antibiotic Resistance Identification

The quick and accurate identification of microorganisms and the study of resistance to antibiotics is crucial in the economic and industrial fields along with medicine. One of the fastest-growing identification methods is the spectrometric approach consisting in the matrix-assisted laser ionization/desorption using a time-of-flight analyzer (MALDI-TOF MS), which has many advantages over conventional methods for the determination of microorganisms presented. Thanks to the use of a multiomic approach in the MALDI-TOF MS analysis, it is possible to obtain a broad spectrum of data allowing the identification of microorganisms, understanding their interactions and the analysis of antibiotic resistance mechanisms. In addition, the literature data indicate the possibility of a significant reduction in the time of the sample preparation and analysis time, which will enable a faster initiation of the treatment of patients. However, it is still necessary to improve the process of identifying and supplementing the existing databases along with creating new ones. This review summarizes the use of “-omics” approaches in the MALDI TOF MS analysis, including in bacterial identification and antibiotic resistance mechanisms analysis.

Comparative Genomics Identifies Features Associated with Methicillin-Resistant Staphylococcus aureus (MRSA) Transmission in Hospital Settings

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious public health concern in the United States. Patients colonized and/or infected can transmit MRSA to healthcare workers and subsequent patients However, the components of this transmission chain are just becoming evident, including certain patient factors, specific patient-healthcare worker interactions, and microbial factors. We conducted a comparative genomic analysis of 388 isolates from four hospitals in three states: Maryland, California, and New York. Isolates from nasal surveillance or clinical cultures were categorized as high, moderate, or low transmission surrogate outcomes based on the number of times the species was identified on the gloves or gowns of healthcare providers. The comparative analyses included a single gene, multigene, and core genome phylogenetic analysis, as well as a genome-wide association analysis to identify molecular signatures associated with the observed transmission surrogate outcomes, geographic origin, or sample source of isolation. Based on the phylogenetic analysis, 95% (n = 372) of the MRSA isolates were from four well-described genomic clades, with most of the isolates being part of the USA300 containing clade (n = 187; 48%). Genome-wide association studies also identified genes that were exclusive or prevalent among specific geographic locations. The identified genes provide insights into the transmission dynamics of MRSA isolates providing additional insights into the basis of the geographical differences of MRSA for molecular diagnostics. IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is considered a serious threat to public health and contributes to the dissemination of S. aureus in both the healthcare and community setting. Transmission of MRSA between patients via healthcare worker (HCW) has been described. However, what is not understood are the genetic determinants that contribute to the transmission of MRSA from patients to HCWs. In this study, we demonstrated that certain genes may be associated with transmission in the hospital setting.

α-hemolysin of Staphylococcus aureus impairs thrombus formation

BACKGROUND

Toxins are key virulence determinants of pathogens and can impair the function of host immune cells, including platelets. Insights into pathogen toxin interference with platelets will be pivotal to improve treatment of patients with bacterial bloodstream infections.

MATERIALS AND METHODS

In this study, we deciphered the effects of Staphylococcus aureus toxins α-hemolysin, LukAB, LukDE, and LukSF on human platelets and compared the effects with the pore forming toxin pneumolysin of Streptococcus pneumoniae. Activation of platelets and loss of platelet function were investigated by flow cytometry, aggregometry, platelet viability, fluorescence microscopy, and intracellular calcium release. Thrombus formation was assessed in whole blood.

RESULTS

α-hemolysin (Hla) is known to be a pore-forming toxin. Hla-induced calcium influx initially activates platelets as indicated by CD62P and αIIbβ3 integrin activation, but also induces finally alterations in the phenotype of platelets. In contrast to Hla and pneumolysin, S. aureus bicomponent pore-forming leukocidins LukAB, LukED, and LukSF do not bind to platelets and had no significant effect on platelet activation and viability. The presence of small amounts of Hla (0.2 µg/ml) in whole blood abrogates thrombus formation indicating that in systemic infections with S. aureus the stability of formed thrombi is impaired. Damage of platelets by Hla was not neutralized by intravenous immune globulins.

CONCLUSION

Our findings might be of clinical relevance for S. aureus induced endocarditis. Stabilizing the aortic-valve thrombi by inhibiting Hla-induced impairment of platelets might reduce the risk for septic (micro-)embolization.

Synergistic interactions between artocarpin-rich extract, lawsone methyl ether and ampicillin on anti-MRSA and their antibiofilm formation

Artocarpin-rich extract (ARE) was prepared using a green technology and standardized to contain 49·6% w/w artocarpin, while lawsone methyl ether was prepared using a green semi-synthesis. ARE, LME and ampicillin exhibited weak anti-MRSA activity with the MICs of 31·2-62·5 µg/ml. Based on the checkerboard assay, the synergistic interaction between ARE (0·03 µg/ml) and LME (0·49 µg/ml) against four MRSA isolates were observed with the fractional inhibitory concentration index (FICI) value of 0·008, while those of ARE (1·95-7·81 µg/ml) and ampicillin (0·49 µg/ml) as well as LME (0·49-1·95 µg/ml) and ampicillin (0·49 µg/ml) were 0·016-0·257. The time kill confirmed the synergistic interactions against MRSA with different degrees. The combination of ARE and LME as well as its combinations with ampicillin altered the membrane permeability of MRSA, which led to release of the intracellular materials. In addition, each compound inhibited the biofilm formation of standard MRSA (DMST 20654) and the clinical isolate (MRSA 1096). These findings suggested that cocktails containing ARE and LME might be used to overcome problems associated with MRSA. Additionally, the results implied that combination of either ARE or LME with available conventional antibiotic agents might be effective in countering these perilous pathogens.

The Microbial Profile and Resistance Pattern of Pathogens Isolated From Long COVID Pneumonia Patients and Their Correlation to Clinical Outcome: Our Experience From a Tertiary Care Hospital

Background

Coronavirus disease 2019 (COVID-19) patients with persistent symptoms for at least four weeks in spite of being reverse transcriptase-polymerase chain reaction (RTPCR) negative for COVID infection are defined as long COVID (wherein pulmonary involvement is seen in a significant proportion of cases). The history of prolonged use of corticosteroids, broad-spectrum antibiotics, and associated comorbid conditions in these patients increases the possibility of infection with multidrug-resistant microbial strains. It may lead to a grave prognosis, hence appropriate microbiological evaluation and management at the earliest can have a better outcome.

Methods

A retrospective observational study was carried out among long COVID patients admitted to the Kalinga Institute of Medical Sciences, Bhubaneswar, Odisha, India, a tertiary care hospital. Eighty-four patients admitted to the ICU or non-ICU ward in the hospital from April to October 2021 were included in the study. Antibiotics, as prescribed by our hospital antibiotic policy, were administered wherever required and were subsequently changed according to culture and sensitivity reports of the samples (sputum, endotracheal aspirates, or blood). An analysis of the antibiotic sensitivity patterns of the pathogens isolated was performed. The outcome after optimum medical management was assessed for survivors, discharge, or death.

Results

Out of the total of 84 patients, 41 samples (sputum, endotracheal aspirates or blood) were collected and sent for culture, of which 32 (78.1%) were found to be culture positive for pathogens. Among the pathogens isolated, there were 22 (69%) drug-resistant and 10 (31%) sensitive organisms. Among the 22 resistant pathogen isolates, 18 were Gram-negative species, the most common species being Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumanii; two were Gram-positive species, one each from Staphylococcus aureus and Enterococcus faecalis, and three were Candida tropicalis. Of five deaths reported among 22 cases with resistant isolates, extensively drug-resistant (XDR), multi-drug resistance (MDR), and pan drug resistance (PDR) strains were detected in three, one, and one cases, respectively, and were harboured by K. pneumoniae, P. aeruginosa, and A. baumanii. Of the total eight deaths, there were two deaths among the 43 patients who received an empiric antibiotic in the wards, and six deaths were reported in the ICU. Despite raised biomarkers of inflammation, comorbid illnesses, renal impairment, and immunocompromised states, there was 91% survival and discharge, which was statistically significant (p-value = 0.00).

Conclusion

To conclude, K. pneumoniae, P. aeruginosa, A. baumanii, C. tropicalis, S. aureus, and E. faecalis were the most commonly isolated organisms among long COVID pneumonia cases, of which some were MDR, PDR and XDR strains. Early microbiological evaluation with targeted, proper antimicrobial usage along with optimized medical management and, wherever needed, critical care support in the ICU may lead to a better prognostic outcome in those groups of patients.

In Vitro Antibacterial Experiments of Qixingjian Decoction and Its Synergistic Interaction with Oxacillin against Clinical Isolates of Methicillin-Resistant Staphylococcus aureus

Background

With the widespread use and abuse of antimicrobial drugs, the problem of bacterial resistance is becoming increasingly prominent. The clinical detection rate of drug-resistant bacteria is increasing year by year, so there is an urgent need to develop new antimicrobial drugs. Qixingjian Decoction (QXJT) is a formula commonly used in Chinese medicine for the treatment of sepsis caused by acute purulent infections of the face, hands, and feet. There are many compounds with antimicrobial effects that are available, but little is known about their mode of action. In this study, we mainly evaluated the antimicrobial activity of QXJT and explored its synergistic interaction with oxacillin (OX) and the mechanism of its antimicrobial activity.

Methods

The antimicrobial activity of QXJT against methicillin-resistant Staphylococcus aureus (MRSA) was determined by the microdilution method, the broth macrodilution method, and the time-kill curve method. The main compounds in QXJT were analyzed by ultra-performance liquid chromatography. The synergistic interaction of QXJT and oxacillin (OX) was determined by checkerboard assay, and the antimicrobial mechanism of QXJT, OX, and QXJT + OX was evaluated by transmission electron microscopy (TEM) technique. The expression of MRSA superantigen virulence factors (sea, seb, and tst), and drug resistance gene (mecA) was detected to provide a new strategy for new antibiotic drugs.

Results

QXJT exhibited antimicrobial activity against both clinical isolates of MRSA, MICs ranging from 18.75 to 37.5 mg/mL. Active substances such as Scutellarein, Scutellarin, Apigenin, and Wogonin 7-O-glucuronide were detected in the phytochemical analysis that may be associated with the antimicrobial activity of QXJT. The synergistic effect of QXJT and OX was determined by checkerboard assay (FICI = 0.5), and TEM images showed that QXJT could cause the disruption of MRSA cell wall, and QXJT + OX could produce greater disruption of MRSA cell wall, elucidating the synergistic effect of the two together on cell wall disruption by microscopic mechanisms. Our study shows that the combination of QXJT and OX can inhibit the expression of MRSA virulence factor, reduce the virulence of MRSA, and have no significant effect on the expression of MRSA resistance gene mecA.

Conclusion

The results of this study provide scientific experimental data for the traditional application of QXJT and initially explore the mechanism of action of QXJT combined with OX.

Draft Genome Sequences of 12 Panton-Valentine Leucocidin-Positive and Multidrug-Resistant Methicillin-Resistant Staphylococcus aureus Strains Isolated from an Intensive Care Unit in Pakistan

Methicillin-resistant Staphylococcus aureus (MRSA) is a pathogenic bacterium responsible for difficult-to-treat staphylococcal infections due to multidrug resistance. Twelve Panton-Valentine leucocidin (PVL)-positive and multidrug-resistant clinical MRSA isolates from hospitals in Pakistan were sequenced and annotated to investigate genetic markers associated with antimicrobial resistance, virulence, and biofilm formation.

3D-QSAR Studies of 1,2,4-Oxadiazole Derivatives as Sortase A Inhibitors

Sortase A (SrtA) is an enzyme that catalyzes the attachment of proteins to the cell wall of Gram-positive bacterial membrane, preventing the spread of pathogenic bacterial strains. Here, one class of oxadiazole compounds was distinguished as an efficient inhibitor of SrtA via the "S. aureus Sortase A" substrate-based virtual screening. The current study on 3D-QSAR was done by utilizing preparation of the structure in the Schrödinger software suite and an assessment of 120 derivatives with the crystal structure of 1,2,4-oxadiazole which was extracted from the PDB data bank. The docking operation of the best compound in terms of pMIC (pMIC = 2.77) was done to determine the drug likeliness and binding form of 1,2,4-oxadiazole derivatives as antibiotics in the active site. Using the kNN-MFA way, seven models of 3D-QSAR were created and amongst them, and one model was selected as the best. The chosen model based on q 2 (pred_r 2) and R 2 values related to the sixth factor of PLS illustrates better and more acceptable external and internal predictions. Values of crossvalidation (pred_r 2), validation (q 2), and F were observed 0.5479, 0.6319, and 179.0, respectively, for a test group including 24 molecules and the training group including 96 molecules. The external reliability outcomes showed that the acceptable and the selective 3D-QSAR model had a high predictive potential (R 2 = 0.9235) which was confirmed by the Y-randomization test. Besides, the model applicability domain was described successfully to validate the estimation of the model.

Antimicrobial resistance determinants are associated with Staphylococcus aureus bacteraemia and adaptation to the healthcare environment: a bacterial genome-wide association study

Staphylococcus aureus is a major bacterial pathogen in humans, and a dominant cause of severe bloodstream infections. Globally, antimicrobial resistance (AMR) in S. aureus remains challenging. While human risk factors for infection have been defined, contradictory evidence exists for the role of bacterial genomic variation in S. aureus disease. To investigate the contribution of bacterial lineage and genomic variation to the development of bloodstream infection, we undertook a genome-wide association study comparing bacteria from 1017 individuals with bacteraemia to 984 adults with asymptomatic S. aureus nasal carriage. Within 984 carriage isolates, we also compared healthcare-associated (HA) carriage with community-associated (CA) carriage. All major global lineages were represented in both bacteraemia and carriage, with no evidence for different infection rates. However, kmers tagging trimethoprim resistance-conferring mutation F99Y in dfrB were significantly associated with bacteraemia-vs-carriage (P=10-8.9-10-9.3). Pooling variation within genes, bacteraemia-vs-carriage was associated with the presence of mecA (HMP=10-5.3) as well as the presence of SCCmec (HMP=10-4.4). Among S. aureus carriers, no lineages were associated with HA-vs-CA carriage. However, we found a novel signal of HA-vs-CA carriage in the foldase protein prsA, where kmers representing conserved sequence allele were associated with CA carriage (P=10-7.1-10-19.4), while in gyrA, a ciprofloxacin resistance-conferring mutation, L84S, was associated with HA carriage (P=10-7.2). In an extensive study of S. aureus bacteraemia and nasal carriage in the UK, we found strong evidence that all S. aureus lineages are equally capable of causing bloodstream infection, and of being carried in the healthcare environment. Genomic variation in the foldase protein prsA is a novel genomic marker of healthcare origin in S. aureus but was not associated with bacteraemia. AMR determinants were associated with both bacteraemia and healthcare-associated carriage, suggesting that AMR increases the propensity not only to survive in healthcare environments, but also to cause invasive disease.

Staphylococcus singaporensis sp. nov., a new member of the Staphylococcus aureus complex, isolated from human clinical specimens

Staphylococcus argenteus and Staphylococcus schweitzeri are the newest members of the Staphylococcus aureus complex. The number of clinical reports attributed to these new S. aureus complex members is limited. In a retrospective clinical laboratory study conducted over a 4-month period investigating the prevalence of S. argenteus and S. schweitzeri, a total of 43 isolates were selected. Phylogeny based on core-gene multilocus sequence typing (MLST) analysis confirmed that 37 were S. argenteus but a genetically distinct clade of six isolates was identified. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses further supported the classification of these six isolates as a separate species. When compared to S. aureus complex reference genomes, the ANI values were ≤94 % and the dDDH values were <53 %. Based on the seven-gene S. aureus MLST scheme, the six isolates belong to five novel allelic profiles (ST6105, ST6106, ST6107, ST6108 and ST109). Their clinical infection features were similar to S. aureus. Skin and soft tissue infections presented in four out of the six cases. Routine clinical diagnostic identification using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and biochemical profiling does not differentiate these new members from the rest of the complex. Genotypic analysis suggests that the six isolates belong to a novel species, Staphylococcus singaporensis sp. nov. with isolate SS21^T (=DSM 111408^T=NCTC14419^T) designated as the type strain.

Characterization of methicillin-resistant Staphylococcus aureus strains colonizing the nostrils of Spanish children

OBJECTIVE

To characterize the Staphylococcus aureus strains colonizing healthy Spanish children.

METHODS

Between March and July 2018, 1876 Spanish children younger than 14 years attending primary healthcare centers were recruited from rural and urban areas. Staphylococcus aureus colonization of the anterior nostrils was analyzed. MecA and mecC genes, antibiotic susceptibility, and genotyping according to the spa were determined in all strains, and the following toxins were examined: Panton-Valentine leucocidin (pvl), toxic shock syndrome toxin (tst), and exfoliative toxins (eta, etb, etd). Multilocus sequence typing (MLST) and staphylococcal cassette chromosome (SCCmec) typing were performed on methicillin-resistant Staphylococcus aureus (MRSA) strains, as well as pulsed-field gel electrophoresis (PFGE).

RESULTS

619 strains were isolated in 1876 children (33%), and 92% of them were sent for characterization to the Spanish National Centre of Microbiology (n = 572). Twenty (3.5%) of these strains were mecA-positive. Several spa types were detected among MRSA, being t002 the most frequently observed (30%), associating with SCCmec IVc. Among MSSA, 33% were positive for tst, while only 0.73% were positive for pvl. The 20 MRSA strains were negative for pvl, and 6 (30%) harbored the tst gene.

CONCLUSIONS

methicillin-resistant Staphylococcus aureus nasal colonization in Spanish children is rare, with t002 being the most observed spa type, associated with SCCmec IVc. None of the MRSA strains produced pvl, but up to 30% of S. aureus strains were positive for tst.

Genomic Investigation of Methicillin-Resistant Staphylococcus aureus ST113 Strains Isolated from Tertiary Care Hospitals in Pakistan

Methicillin-resistant Staphylococcus aureus (MRSA) is a multi-drug resistant and opportunistic pathogen. The emergence of new clones of MRSA in both healthcare settings and the community warrants serious attention and epidemiological surveillance. However, epidemiological data of MRSA isolates from Pakistan are limited. We performed a whole-genome-based comparative analysis of two (P10 and R46) MRSA strains isolated from two provinces of Pakistan to understand the genetic diversity, sequence type (ST), and distribution of virulence and antibiotic-resistance genes. The strains belong to ST113 and harbor the SCCmec type IV encoding mecA gene. Both the strains contain two plasmids, and three and two complete prophage sequences are present in P10 and R46, respectively. The specific antibiotic resistance determinants in P10 include two aminoglycoside-resistance genes, aph(3’)-IIIa and aad(6), a streptothrin-resistance gene sat-4, a tetracycline-resistance gene tet(K), a mupirocin-resistance gene mupA, a point mutation in fusA conferring resistance to fusidic acid, and in strain R46 a specific plasmid associated gene ant(4’)-Ib. The strains harbor many virulence factors common to MRSA. However, no Panton-Valentine leucocidin (lukF-PV/lukS-PV) or toxic shock syndrome toxin (tsst) genes were detected in any of the genomes. The phylogenetic relationship of P10 and R46 with other prevailing MRSA strains suggests that ST113 strains are closely related to ST8 strains and ST113 strains are a single-locus variant of ST8. These findings provide important information concerning the emerging MRSA clone ST113 in Pakistan and the sequenced strains can be used as reference strains for the comparative genomic analysis of other MRSA strains in Pakistan and ST113 strains globally.

Genotypic Characterization of Clinical Isolates of Staphylococcus aureus from Pakistan

In this study, we compared pulsed-field gel electrophoretic (PFGE), multilocus sequence typing (MLST), Staphylococcal cassette chromosome mec (SCCmec), spa typing, and virulence gene profiles of 19 Panton–Valentine leucocidin (PVL)-positive, multidrug-, and methicillin-resistant clinical Staphylococcus aureus (MRSA) isolates obtained from a hospital intensive care unit in Pakistan. The isolates exhibited 10 pulsotypes, contained eight adhesin genes (bbp, clfA, clfB, cna, fnbA, fnbB, map-eap, and spa), 10 toxin genes (hla, hlb, hld, hlg, pvl, sed, see, seg, seh, and tst), and two other virulence genes (cfb, v8) that were commonly present in all isolates. The spa-typing indicated seven known spa types (t030, t064, t138, t314, t987, t1509, and t5414) and three novel spa types. MLST analysis indicated eight ST types (ST8, ST15, ST30, ST239, ST291, ST503, ST772, and ST1413). All isolates belonged to the agr group 1. Most of the isolates possessed SCCmec type III, but some isolates had it in combination with types SCCmec IV and V. The presence of multidrug-resistant MRSA isolates in Pakistan indicates poor hygienic conditions, overuse of antibiotics, and a lack of rational antibiotic therapy that have led to the evolution and development of hypervirulent MRSA clones. The study warrants development of a robust epidemiological screening program and adoption of effective measures to stop their spread in hospitals and the community.

Regulation of virulence and β-lactamase gene expression in Staphylococcus aureus isolates: cooperation of two-component systems in bloodstream superbugs

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA)-bloodstream infections (BSI) are predominantly seen in the hospital or healthcare-associated host. Nevertheless, the interactions of virulence factor (VFs) regulators and β-lactam resistance in MRSA-BSI are unclear. This study aims to characterize the molecular relationship of two-component systems of VFs and the expression of the β-lactamase gene in MRSA-BSI isolates. In this study, 639 samples were collected from BSI and identified by phenotypic methods. We performed extensive molecular characterization, including SCCmec type, agr type, VFs gene profiles determinations, and MLST on isolates. Also, a quantitative real-time PCR (q-RT PCR) assay was developed for identifying the gene expressions.

RESULTS

Ninety-one (91) S. aureus and 61 MRSA (67.0%) strains were detected in BSI samples. The presence of VFs and SCCmec genes in MRSA isolates were as follows: tst (31.4%), etA (18.0%), etB (8.19%), lukS-PVL (31.4%), lukF-PV (18.0%), lukE-lukD (16.3%), edin (3.2%), hla (16.3%), hlb (18.0%), hld (14.7%), hlg (22.9%), SCCmecI (16.3%), SCCmecII (22.9%), SCCmecIII (36.0%), SCCmecIV (21.3%), and SCCmecV (16.3%). Quantitative real-time PCR showed overexpression of mecRI and mecI in the toxigenic isolates. Moreover, RNAIII and sarA genes were the highest expressions of MRSA strains. The multi-locus sequence typing data confirmed a high prevalence of CC5, CC8, and CC30. However, ST30, ST22, and ST5 were the most prevalent in the resistant and toxigenic strains.

CONCLUSION

We demonstrated that although regulation of β-lactamase gene expressions is a significant contributor to resistance development, two-component systems also influence antibiotic resistance development in MRSA-BSI isolates. This indicates that resistant strains might have pathogenic potential. We also confirmed that some MLST types are more successful colonizers with a potential for MRSA-BSI.

Growth and Stress Tolerance Comprise Independent Metabolic Strategies Critical for Staphylococcus aureus Infection

Staphylococcus aureus is an important pathogen that leads to high morbidity and mortality. Although S. aureus produces many factors important for pathogenesis, few have been validated as playing a role in the pathogenesis of S. aureus pneumonia. To gain a better understanding of the genetic elements required for S. aureus pathogenesis in the airway, we performed an unbiased genome-wide transposon sequencing (Tn-seq) screen in a model of acute murine pneumonia. We identified 136 genes important for bacterial survival during infection, with a high proportion involved in metabolic processes. Phenotyping 80 individual deletion mutants through diverse in vitro and in vivo assays demonstrated that metabolism is linked to several processes, which include biofilm formation, growth, and resistance to host stressors. We further validated the importance of 23 mutations in pneumonia. Multivariate and principal-component analyses identified two key metabolic mechanisms enabling infection in the airway, growth (e.g., the ability to replicate and form biofilms) and resistance to host stresses. As deep validation of these hypotheses, we investigated the role of pyruvate carboxylase, which was important across multiple infection models and confirmed a connection between growth and resistance to host cell killing. Pathogenesis is conventionally understood in terms of the host-pathogen interactions that enable a pathogen to neutralize a host’s immune response. We demonstrate with the important bacterial pathogen S. aureus that microbial metabolism influences key traits important for in vivo infection, independent from host immunomodulation.

The ClpXP Protease Contributes to Staphylococcus aureus Pneumonia

Staphylococcus aureus is a leading cause of pneumonia. We show here that the ClpXP protease involved in protein turnover is important for pathogenesis in a murine model of acute pneumonia. Staphylococcus aureus lacking this protease is attenuated in vivo, being rapidly cleared from the airway and leading to decreased immune cell influx and inflammation. Characterization of defined mutations in vitro identified defects in intracellular survival and protection against neutrophil killing. Our results further expand on what is known about ClpXP in the pathogenesis of S. aureus to include the respiratory tract.

Staphylococcus aureus and its Effects on the Prognosis of Bronchiectasis

Bronchiectasis, which is an abnormal and irreversible dilation of one or several bronchial segments, causes significant morbidity and impaired quality of life to patients, mainly as the result of recurrent and chronic respiratory infections. Staphylococcus aureus is a microorganism known for its high infectious potential related to the production of molecules with great pathogenic power, such as enzymes, toxins, adhesins, and biofilm, which determine the degree of severity of systemic symptoms and can induce exacerbated immune response. This review highlighted the clinical significance of S. aureus colonization/infection in bronchiectasis patients, since little is known about it, despite its increasing frequency of isolation and potential serious morbidity.

In Silico Evaluation of Human Cathelicidin LL-37 as a Novel Therapeutic Inhibitor of Panton-Valentine Leukocidin Toxin of Methicillin-Resistant Staphylococcus aureus

Incidence of drug resistance in clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) is attributed to its diverse repertoire of virulence factors. Of these virulence determinants, Panton-Valentine Leukocidin (PVL) has been experimentally validated as a prospective drug target due to its conspicuous and comprehensive role in nosocomial infections. This study encompassed an in silico approach to elucidate the antimicrobial potentiality of human cathelicidin LL-37 against PVL toxin of MRSA. Molecular docking studies of LL-37 and its segments with the PVL toxin subunits LukS and LukF were carried out using PatchDock server and the results were refined using FireDock server. The paramount ligand-receptor combination was selected and analyzed based on diverse parametric attributes and compared with the commercial inhibitors of PVL viz. Andrimid, Beclobrate, Beta-sitosterol, Diathymosulfone, and Probucol to determine the most potent inhibitor among them. Our results elucidated that the interaction of LL-37 with the LukS subunit of PVL toxin (minimum global energy of -61.82 kcal/mol) depicted 34 molecular interactions, while the commercial PVL inhibitors depicted fewer and insubstantial interactions. SWISS-ADME (Absorption, Distribution, Metabolism, and Excretion) and ToxinPred analysis of LL-37 further corroborated its null potency of toxicity in systemic milieu. The results obtained may credit this study as basis for the development of LL-37 as a potential inhibitor against virulent MRSA toxins, thereby exalting the treatment regimes for nosocomial infections in health care facilities worldwide.

Strain Background, Species Frequency, and Environmental Conditions Are Important in Determining Pseudomonas aeruginosa and Staphylococcus aureus Population Dynamics and Species Coexistence

Bacterial communities in the environment and in infections are typically diverse, yet we know little about the factors that determine interspecies interactions. Here, we apply concepts from ecological theory to understand how biotic and abiotic factors affect interaction patterns between the two opportunistic human pathogens Pseudomonas aeruginosa and Staphylococcus aureus, which often cooccur in polymicrobial infections. Specifically, we conducted a series of short- and long-term competition experiments between P. aeruginosa PAO1 (as our reference strain) and three different S. aureus strains (Cowan I, 6850, and JE2) at three starting frequencies and under three environmental (culturing) conditions. We found that the competitive ability of P. aeruginosa strongly depended on the strain background of S. aureus, whereby P. aeruginosa dominated against Cowan I and 6850 but not against JE2. In the latter case, both species could end up as winners depending on conditions. Specifically, we observed strong frequency-dependent fitness patterns, including positive frequency dependence, where P. aeruginosa could dominate JE2 only when common (not when rare). Finally, changes in environmental (culturing) conditions fundamentally altered the competitive balance between the two species in a way that P. aeruginosa dominance increased when moving from shaken to static environments. Altogether, our results highlight that ecological details can have profound effects on the competitive dynamics between coinfecting pathogens and determine whether two species can coexist or invade each others' populations from a state of rare frequency. Moreover, our findings might parallel certain dynamics observed in chronic polymicrobial infections.IMPORTANCE Bacterial infections are frequently caused by more than one species, and such polymicrobial infections are often considered more virulent and more difficult to treat than the respective monospecies infections. Pseudomonas aeruginosa and Staphylococcus aureus are among the most important pathogens in polymicrobial infections, and their cooccurrence is linked to worse disease outcome. There is great interest in understanding how these two species interact and what the consequences for the host are. While previous studies have mainly looked at molecular mechanisms implicated in interactions between P. aeruginosa and S. aureus, here we show that ecological factors, such as strain background, species frequency, and environmental conditions, are important elements determining population dynamics and species coexistence patterns. We propose that the uncovered principles also play major roles in infections and, therefore, proclaim that an integrative approach combining molecular and ecological aspects is required to fully understand polymicrobial infections.

Prevalence and association of Panton-Valentine Leukocidin gene with the risk of sepsis in patients infected with Methicillin Resistant Staphylococcus aureus

BACKGROUND

Panton-Valentine Leukocidin (PVL), is one of the virulence gene expressed by Methicillin Resistant Staphylococcus aureus (MRSA) and is known to be associated with severe form of community acquired MRSA infection. The aim of this study is to investigate its prevalence in our setting and patient's clinical outcome.

METHODS

A cross sectional study involve retrospective record review were done involving 90 MRSA positive isolates between November 2016 and October 2017. Multiplex PCR was performed to detect femA, mecA and PVL genes. Clinical presentation and outcomes of patients were reviewed and presented as descriptive analysis.

RESULTS

All of the 90 MRSA isolates included in this study were positive for femA and mecA genes following PCR. PVL gene was detected in 20% (n = 18) of the isolates of which 61.1% (n = 11) were community acquired infections and 38.8% (n = 7) were hospital acquired. Case distribution from community acquired infections include patients with skin and soft tissue infections (33.3%, n = 6), infected diabetic foot ulcers (16.7%, n = 3), and one patient each (5.5%, n = 1) for community acquired pneumonia and meningitis. Half of the PVL positive MRSA cases (50%, n = 9) were having sepsis and four of them succumbed to death due to severe infection.

CONCLUSION

This study shows a high prevalence of PVL positive MRSA infection in our population. Skin and soft tissue infections accounting for the major sources. In addition, the presence of the PVL gene is associated with increased risk for developing sepsis.

Prevalence and Molecular Genetics of Methicillin-Resistant Staphylococcus aureus Colonization in Nursing Homes in Saudi Arabia

Objective

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main causative agents of nosocomial infections that has posed a major threat to those with compromised immune systems such as nursing home residents. The aim of this study was to determine the rates of MRSA strains and the types of Staphylococcal Cassette Chromosome mec (SCCmec)in nursing homes in Saudi Arabia.

Methods

A total of 188 nasal swabs were collected from the residents and nursing staff in two nursing homes in Riyadh, Saudi Arabia. All MRSA isolates were tested for antimicrobial susceptibility and analyzed for mecA and SCCmec typing by multiplex PCR assay. Detection of the Panton–Valentine leukocidin (PVL) gene was also tested in all positive MRSA isolates by multiplex PCR using specific primers.

Results

Among the 188 collected nasal swabs (105 males and 83 females), MRSA colonization rate was 9.04% (11 (5.85%) females and 6 (5.71%) males). About 47% of MRSA were multidrug resistant (MDR) as acquired resistance to beta-lactam, macrolide, and aminoglycoside antibiotics. However, all the MRSA isolates showed susceptibility to vancomycin, tigecycline, and linezolid. All the MRSA isolates (n = 17) were mecA-positive with the SCCmec IVc (n = 7, 41.18%) as the most common SCCmec type followed by SCCmec V (n = 5, 29.41%) and SCCmec IVa (n = 2, 11.76%). The remaining isolates (n = 3) were nontypeable (17.65%). In addition, the PVL toxin gene was only detected in four of the male samples.

Conclusion

MRSA nasal colonization is a common incident among nursing home residents. The prevalence of community-associated (CA) MRSA (SCCmec IV and V) was more common than hospital-associated (HA) MRSA in our study samples. It is crucial to investigate such rate of incidence, which is a key tool in preventive medicine and would aid in determining health policy and predict emergent outbreaks.

Antimicrobial resistance three ways: healthcare crisis, major concepts and the relevance of biofilms

Worldwide, infections are resuming their role as highly effective killing diseases, as current treatments are failing to respond to the growing problem of antimicrobial resistance (AMR). The social and economic burden of AMR seems ever rising, with health- and research-related organizations rushing to collaborate on a worldwide scale to find effective solutions. Resistant bacteria are spreading even in first-world nations, being found not only in healthcare-related settings, but also in food and in the environment. In this minireview, the impact of AMR in healthcare systems and the major bacteria behind it are highlighted. Ecological aspects of AMR evolution and the complexity of its molecular mechanisms are explained. Major concepts, such as intrinsic, acquired and adaptive resistance, as well as tolerance and heteroresistance, are also clarified. More importantly, the problematic of biofilms and their role in AMR, namely their main resistance and tolerance mechanisms, are elucidated. Finally, some of the most promising anti-biofilm strategies being investigated are reviewed. Much is still to be done regarding the study of AMR and the discovery of new anti-biofilm strategies. Gladly, considerable research on this topic is generated every day and increasingly concerted actions are being engaged globally to try and tackle this problem.

Methicillin-resistant Staphylococcus aureus colonization in HIV patients of Arba Minch province, Ethiopia: Carriage rates, antibiotic resistance, and biofilm formation

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a significant opportunistic pathogen among human immunodeficiency virus (HIV) patients of Ethiopia. This study aimed at delineating the prevalence, antimicrobial resistance, and biofilm-forming potentials of nasally colonized MRSA among HIV patients in the Arba Minch province of Ethiopia. A cross-sectional study was performed in HIV patients who visit anti-retroviral therapy clinic of the Arba Minch Hospital between February and April 2017. Nasal samples were collected and inspected for Staphylococcus following standard procedures. MRSA was identified using cefoxitin disk and antibiotics sensitivity test was performed as per Kirby-Baur disk diffusion method. The formation of biofilm was inspected using both qualitative and quantitative methods. A total of 307 HIV patients were examined. The overall prevalence of S. aureus was found to be 39.7%. The prevalence of MRSA was 20.8%. The rate of nasal colonization of MRSA was relatively higher among females. In bivariate analysis, MRSA colonization was statistically significant in patients with CD₄ count ≤350 (p value = 0.002) and co-trimoxazole prophylaxis (p value = 0.003). Concomitant resistance to erythromycin, tetracycline, and co-trimoxazole were 48.4%, 45.3%, and 39.0%, respectively. Invariably, all MRSA isolates were 100% sensitive to vancomycin. Of the 64 MRSA isolates, 18.7% were considered as multidrug-resistant. The rate of biofilm formation was 34.3%. The results revealed a high prevalence rate in the nasal colonization of MRSA in HIV patients.

Genome Mining and Comparative Pathogenomic Analysis of An Endemic Methicillin-Resistant Staphylococcus Aureus (MRSA) Clone, ST612-CC8-t1257-SCCmec_IVd(2B), Isolated in South Africa

This study undertook genome mining and comparative genomics to gain genetic insights into the dominance of the methicillin-resistant Staphylococcus aureus (MRSA) endemic clone ST612-CC8-t1257-SCCmec_IVd(2B), obtained from the poultry food chain in South Africa. Functional annotation of the genome revealed a vast array of similar central metabolic, cellular and biochemical networks within the endemic clone crucial for its survival in the microbial community. In-silico analysis of the clone revealed the possession of uniform defense systems, restriction-modification system (type I and IV), accessory gene regulator (type I), arginine catabolic mobile element (type II), and type 1 clustered, regularly interspaced, short palindromic repeat (CRISPR)Cas array (N = 7 ± 1), which offer protection against exogenous attacks. The estimated pathogenic potential predicted a higher probability (average Pscore ≈ 0.927) of the clone being pathogenic to its host. The clone carried a battery of putative virulence determinants whose expression are critical for establishing infection. However, there was a slight difference in their possession of adherence factors (biofilm operon system) and toxins (hemolysins and enterotoxins). Further analysis revealed a conserved environmental tolerance and persistence mechanisms related to stress (oxidative and osmotic), heat shock, sporulation, bacteriocins, and detoxification, which enable it to withstand lethal threats and contribute to its success in diverse ecological niches. Phylogenomic analysis with close sister lineages revealed that the clone was closely related to the MRSA isolate SHV713 from Australia. The results of this bioinformatic analysis provide valuable insights into the biology of this endemic clone.

β-Lactam Antibiotics Enhance the Pathogenicity of Methicillin-Resistant Staphylococcus aureus via SarA-Controlled Lipoprotein-Like Cluster Expression

β-Lactam antibiotics are widely applied to treat infectious diseases. However, certain poor disease outcomes caused by β-lactams remain poorly understood. In this study, we have identified a cluster of lipoprotein-like genes (lpl, sa2275–sa2273) that is upregulated in the major clinically prevalent MRSA clones in response to subinhibitory concentrations of β-lactam induction. The major highlight of this work is that β-lactams stimulate the expression of SarA, which directly binds to the lpl cluster promoter region and upregulates lpl expression in MRSA. Deletion of lpl significantly decreases proinflammatory cytokine levels in vitro and in vivo. The β-lactam-induced Lpls enhance host inflammatory responses by triggering the Toll-like-receptor-2-mediated expressions of interleukin-6 and tumor necrosis factor alpha. The β-lactam-induced Lpls are important virulence factors that enhance MRSA pathogenicity. These data elucidate that subinhibitory concentrations of β-lactams can exacerbate the outcomes of MRSA infection through induction of lpl controlled by the global regulator SarA.

Methicillin-resistant Staphylococcus aureus (MRSA) resists nearly all β-lactam antibiotics that have a bactericidal activity. However, whether the empirically used β-lactams enhance MRSA pathogenicity in vivo remains unclear. In this study, we showed that a cluster of lipoprotein-like genes (lpl, sa2275 to sa2273 [sa2275–sa2273]) was upregulated in MRSA in response to subinhibitory concentrations of β-lactam induction. The increasing expression of lpl by β-lactams was directly controlled by the global regulator SarA. The β-lactam-induced Lpls stimulated the production of interleukin-6 and tumor necrosis factor alpha in RAW 264.7 macrophages. The lpl deletion mutants (N315Δlpl and USA300Δlpl) decreased the proinflammatory cytokine levels in vitro and in vivo. Purified lipidated SA2275-his proteins could trigger a Toll-like-receptor-2 (TLR2)-dependent immune response in primary mouse bone marrow-derived macrophages and C57BL/6 mice. The bacterial loads of N315Δlpl in the mouse kidney were lower than those of the wild-type N315. The β-lactam-treated MRSA exacerbated cutaneous infections in both BALB/c and C57BL/6 mice, presenting increased lesion size; destroyed skin structure; and easily promoted abscess formation compared with those of the untreated MRSA. However, the size of abscesses caused by the β-lactam-treated N315 was negligibly different from those caused by the untreated N315Δlpl in C57BL/6 TLR2^−/− mice. Our findings suggest that β-lactams must be used carefully because they might aggravate the outcome of MRSA infection compared to inaction in treatment.

YpdA, a putative bacillithiol disulfide reductase, contributes to cellular redox homeostasis and virulence in Staphylococcus aureus

The intracellular redox environment of Staphylococcus aureus is mainly buffered by bacillithiol (BSH), a low molecular weight thiol. The identity of enzymes responsible for the recycling of oxidized bacillithiol disulfide (BSSB) to the reduced form (BSH) remains elusive. We examined YpdA, a putative bacillithiol reductase, for its role in maintaining intracellular redox homeostasis. The ypdA mutant showed increased levels of BSSB and a lower bacillithiol redox ratio vs. the isogenic parent, indicating a higher level of oxidative stress within the bacterial cytosol. We showed that YpdA consumed NAD(P)H; and YpdA protein levels were augmented in response to stress. Wild type strains overexpressing YpdA showed increased tolerance to oxidants and electrophilic agents. Importantly, YpdA overexpression in the parental strain caused an increase in BSH levels accompanied by a decrease in BSSB concentration in the presence of stress, resulting in an increase in bacillithiol redox ratio vs. the vector control. Additionally, the ypdA mutant exhibited decreased survival in human neutrophils (PMNs) as compared with the parent, while YpdA overexpression protected the resulting strain from oxidative stress in vitro and from killing by human neutrophils ex vivo. Taken together, these data present a new role for YpdA in S. aureus physiology and virulence through the bacillithiol system.

S. epidermidis strains from artisanal cheese made from unpasteurized milk in Poland - Genetic characterization of antimicrobial resistance and virulence determinants

In Poland artisanal cheese production is an important local economic activity. Artisanal cheese is usually produced using raw cow's milk, animal rennet and salt, without the addition of starter cultures. Coagulase negative staphylococci (CoNS) are often present in artisanal cheeses. Pathogenic potential of some CoNS species, especially S. epidermidis, suggests that they could correspond to emerging pathogens. The identified risk factors correspond to virulence, antibiotic resistance and biofilm formation. Therefore, we aimed to characterize S. epidermidis isolated along the artisanal raw milk production chain. Seventy artisanal cheeses samples from unpasteurized cow milk purchased in Podlasie and Warmia and Mazury region in Poland, were included in this study. A total of 26 S. epidermidis isolates were obtained. Most of them were antimicrobial resistant, such as to penicillin (84,6%), clindamycin (46,2%), tetracycline (42,3%), erythromycin (42,3%) and cefoxitin (26,9%). Only one isolate was susceptible to all antibiotics used in the study. All methicillin resistant S. epidermidis strains (26,9%) harbored mecA gene. Isolates, phenotypic resistant to tetracycline, harbored at least one tetracycline resistance determinant on which tet(M) was most frequent. Moreover, all tetracycline resistant strains harbored Tn916-Tn1545-like integrase family gene. In the erythromycin resistant isolates, the macrolide resistance genes ermC, ermB or msrA/B were present. Seven strains demonstrated a strong ability to form biofilm and moderate and weak biofilm was demonstrated by 4 strains, whereas 11 of S. epidermidis isolates were found to be unable to form a biofilm. All strains producing strong biofilm harbored the icaD gene which occurred independently or in combination with the icaA. Insertion element IS256, was identified in 15,4% of S. epidermidis strains, all of which were multidrug resistant. Arginine Catabolic Mobile Element (ACME) was identified in 13 of the 26 examined strains (50%). Most common was ACME type I (26,9%), followed by type III (15,4%) and type II (7,7%). Our data indicate that S. epidermidis are widely present in artisanal cheeses from raw whole cow milk in Poland. Many isolated strains containing more virulence factors and antibiotic resistant and carry mobile genetic elements which represent a potential source of resistance transmission to bacteria in humans.

In Vitro Inhibition of Staphylococcus aureus subsp. aureus (ATCC® 6538™) by Artemether-Lumefantrine Tablets: A Comparative Study of Three Dosage Strengths

Purpose:

Antibiotics are progressively failing in the fight against infections due to S. aureus because the bacterium has an outstanding ability to acquire multi-antibiotic resistance and become resistant to most antibiotics. Multi-drug resistant S. aureus poses a major threat to the foundation upon which standard antibacterial chemotherapy stands, hence the need to consider non-antibiotic solutions to manage invasive bacterial infections. This study investigated the inhibitory activities of three dosage strengths of artemether-lumefantrine tablets against Staphylococcus aureus subsp. aureus (ATCC® 6538™) and determined the minimum concentrations of the tablets that are able to completely inhibit growth of the bacterium in vitro.

Methods:

The agar dilution and broth macrodilution techniques were used to determine the susceptibility of the Staphylococcus aureus subsp. aureus (ATCC® 6538™) strain to artemether-lumefantrine 20/120mg, 40/240mg and 80/480mg tablets.

Results:

The most active inhibitor was artemether-lumefantrine 80/480mg tablet with a minimum inhibitory concentration value of 2.5mg/mL while artemether-lumefantrine 20/120mg and 40/240mg tablets exhibited moderate but equal activities against the test strain.

Conclusions:

The study has revealed that artemether-lumefantrine, an antimalarial drug, also has anti-staphylococcal properties and inhibits S. aureus in vitro. This study presents the first report on the in vitro activity of artemether-lumefantrine tablet against S. aureus and suggests the need to consider it as an alternative in the treatment of staphylococcus infections.

MLSB-Resistant Staphylococcus aureus in Central Greece: Rate of Resistance and Molecular Characterization

The aim of the present study was to determine the rate and mechanisms of resistance to macrolides, lincosamides, and streptogramin B (MLS_B) antibiotics of Staphylococcus aureus collected in Central Greece. Of the 2,893 S. aureus collected during 2012-2017, 1,161 isolates (40.2%) exhibited resistance to at least one of the MLS_B agents. The rate of erythromycin resistance was statistically significantly higher in methicillin-resistant S. aureus (MRSA) (58.6%) than in methicillin-sensitive S. aureus (MSSA) isolates (20.7%) (p = 0.002). Two hundred seventy-five representative MLS_B-resistant S. aureus, including 81 MSSA and 194 MRSA isolates, were further studied. Thirty-eight MSSA isolates carried ermC, 26 MSSA were positive for ermA, whereas 17 isolates carried msrA gene. Among MRSA, the ermA gene was identified in the majority of the isolates (n = 153). Thirty-seven MRSA isolates carried ermC; three isolates carried msrA, whereas the remaining MRSA was positive for two genes (ermA and ermC). Phylogenetic analysis showed that ST225, which belongs to CC5, was the most prevalent, accounting for 137 MRSA isolates. Higher genetic diversity was found in the group of MSSA isolates, which comprised of 13 sequence types. Whole-genome sequencing data showed that all ermA-positive S. aureus, with the exception of one ST398 isolate, harbored the ermA-carrying Tn554 transposon integrated into their chromosomes. Furthermore, Illumina sequencing followed by polymerase chain reaction screening identified that ermC, which was identified in a polyclonal population of MSSA and MRSA isolates, was carried by small plasmids, like pNE131. These findings highlighted the important role of high-risk clones and of mobile elements carrying resistance genes in the successful dissemination of MLS_B-resistant staphylococci.

Antibiotic resistance: a rundown of a global crisis

The advent of multidrug resistance among pathogenic bacteria is imperiling the worth of antibiotics, which have previously transformed medical sciences. The crisis of antimicrobial resistance has been ascribed to the misuse of these agents and due to unavailability of newer drugs attributable to exigent regulatory requirements and reduced financial inducements. Comprehensive efforts are needed to minimize the pace of resistance by studying emergent microorganisms, resistance mechanisms, and antimicrobial agents. Multidisciplinary approaches are required across health care settings as well as environment and agriculture sectors. Progressive alternate approaches including probiotics, antibodies, and vaccines have shown promising results in trials that suggest the role of these alternatives as preventive or adjunct therapies in future.

Healthcare-associated transmission of Panton-Valentine leucocidin positive methicillin-resistant Staphylococcus aureus: the value of screening asymptomatic healthcare workers

Background

Three patients hospitalised in the coronary care unit of a general district hospital (England, UK) were tested positive for Panton-Valentine leucocidin methicillin-resistant Staphylococcus aureus colonisation during their routine weekly screening for methicillin-resistant Staphylococcus aureus (MRSA). The isolates were indistinguishable and all three patients have previously had negative screening tests. The outbreak investigation team considered exploring the possibility of PVL-MRSA transmission from members of staff to the patients and potentially between members of staff.

Method

As part of the investigations, healthcare workers on coronary care unit and intensive care unit were screened for MRSA carriage.

Results

Among 134 screened healthcare workers, five staff members (3.7%) were MRSA colonised. Among these isolates, four were Panton-Valentine leukocidin positive. However, only two healthcare workers had an indistinguishable isolate with the isolate identified among the colonised patients. Decolonisation treatment was offered to all colonised patients and healthcare workers.

Conclusion

In low MRSA prevalence settings, healthcare workers may be a reservoir of MRSA and an important potential source of transmission to patients. Screening and decolonisation of colonised healthcare workers may provide a valuable strategy in managing linked hospital acquisitions and reduce the risk of occupationally acquired complications. MRSA mass screen of healthcare workers should be considered in transmission with a strain that has a potentially increased virulence, such as Panton-Valentine leucocidin methicillin-resistant Staphylococcus aureus.

Molecular characteristics of antimicrobial resistance and virulence determinants of Staphylococcus aureus isolates derived from clinical infection and food

BACKGROUND

Staphylococcus aureus (S. aureus) is an important human etiologic agent. An investigation of the characteristics of common genotypes of S. aureus relating to pathogenicity and antibiotic resistance may provide a foundation to prevent infection.

METHODS

This study collected 275 S. aureus isolates from Zhengzhou city in China, including 148 isolates from patient samples and 127 isolates from ready-to-eat food samples. Antimicrobial susceptibility testing was performed using the broth dilution method. Molecular characteristics of antimicrobial resistance, virulence, and genotypes were identified by polymerase chain reaction (PCR).

RESULTS

In total, 34.18% (94/275) of S. aureus isolates were MRSA. Compared with food isolates, clinical isolates had significantly higher antibiotic resistance rates, carrying resistance genes such as acc(6')/aph(2'), aph(3')-III, ermA, and ermB and virulence genes such as tetM, sea, seb, pvl, and etb. MRSA-t030-agrI-SCCmecIII and MSSA-t002-agrII were the most common strain types among clinical strains, and MRSA-t002-agrII-SCCmecIII and MSSA-t002-agrII were the most common strain types among food strains. Additionally, some strains in the agr group were also spa type-specific, suggesting that there may be phenotypic consistency.

CONCLUSION

Clinical isolates contained higher numbers of resistance genes and demonstrated higher antibiotic resistance, while 2 source strains exhibited high toxicity. These results indicate that bacteria with different origins may have undergone different evolutionary processes. As resistance and virulence factors in food bacteria can be transmitted to humans, food handlers should strictly follow hygienic measures during food production to ensure the safety of human consumers.

Synergistic Effects of Influenza and Staphylococcus aureus Toxins on Inflammation Activation and Cytotoxicity in Human Monocytic Cell Lines

In patients with influenza, morbidity and mortality are strongly influenced by infections with Staphylococcus aureus producing high amounts of certain toxins. Here we tested the impact of influenza virus on the pro-inflammatory and cytotoxic actions of a panel of S. aureus virulence factors, including Panton-Valentine Leucocidin (PVL), phenol-soluble modulin α1 (PSMα1) and 3 (PSMα3), α-hemolysin (Hla), and cell wall components, i.e., heat-killed S. aureus (HKSA) and protein A. We initially screened for potential synergic interactions using a standardized in vitro model in influenza-infected continuous human monocytic cell lines. Then we tested the identified associations using an ex vivo model in influenza-infected human monocytes freshly isolated from blood. Co-exposure to influenza virus and HKSA, PVL, PSMα1, and PSMα3 increased NF-κB/AP-1 pathway activation in THP1-XBlue cells, and co-exposure to influenza virus and PVL increased cytotoxicity in U937 cells. In monocytes isolated from blood, the synergy between influenza virus and HKSA was confirmed based on cytokine production (TNF-α, IL-1β, IL-6), and co-exposure to influenza virus and Hla-increased cytotoxicity. Our findings suggest that influenza virus potentiates the pro-inflammatory action of HKSA and contributes to the cytotoxicity of Hla on monocytes. Synergic interactions identified in the cell-line model must be cautiously interpreted since few were relevant in the ex vivo model.