Methicillin-resistant S. Aureus Isolates Research Articles

Australian Group on Antimicrobial Resistance (AGAR) Australian Staphylococcus aureus Surveillance Outcome Program (ASSOP) Bloodstream Infection Annual Report 2023.

From 1 January to 31 December 2023, fifty-seven institutions across Australia participated in the Australian Staphylococcus aureus Surveillance Outcome Program (ASSOP). The aim of ASSOP 2023 was to determine the proportion of Staphylococcus aureus bacteraemia (SAB) isolates in Australia that were antimicrobial resistant, with particular emphasis on methicillin resistance, and to characterise the methicillin-resistant S. aureus (MRSA) molecular epidemiology. A total of 3,422 SAB episodes were reported, of which 77.0% were community-onset. Overall, 16.1% of S, aureus were methicillin resistant. The 30-day all-cause mortality associated with methicillin-resistant SAB was 14.8%, which was not significantly different to the 16.5% all-cause mortality associated with methicillin-susceptible SAB (p = 0.44). With the exception of the β-lactams and erythromycin, antimicrobial resistance in methicillin-susceptible S, aureus (MSSA) was infrequent. However, in addition to the β-lactams, approximately 33% of MRSA were resistant to ciprofloxacin; 30% to erythromycin; 13% to tetracycline; 13% to gentamicin; and 3% to co-trimoxazole. Two New South Wales daptomycin-resistant MRSA, with minimum inhibitory concentrations (MICs) of 3.0 and 4.0 mg/L, were identified as ST22-IV, with a V351E mprF mutation, and ST45-V with a T345I mprF mutation respectively. Three daptomycin-resistant MSSA were identified. One from Tasmania, with a daptomycin MIC of 1.5 mg/L, identified as ST9295 with a L341I mprF mutation; one from New South Wales, with a daptomycin MIC of 3.0 mg/L, identified as ST97 with a L776S mprF mutation; and one from Western Australia, with a daptomycin MIC of 2.0 mg/L, identified as ST5. No previously reported mutations in known loci were detected in the Western Australian isolate. When applying the European Committee on Antimicrobial Susceptibility Testing breakpoints, teicoplanin resistance was detected in three MSSA isolates and one MRSA isolate. Vancomycin or linezolid resistance was not detected. Resistance to non-β-lactam antimicrobials was largely attributable to the healthcare-associated MRSA (HA-MRSA) clone ST22-IV [2B] (EMRSA-15), and the community-associated MRSA (CA-MRSA) clone ST45-V [5C2&5] which has acquired resistance to multiple antimicrobials including ciprofloxacin, clindamycin, erythromycin, gentamicin, and tetracycline. ST22-IV [2B] (EMRSA-15) was the predominant HA-MRSA clone in Australia. Overall, 85% of methicillin-resistant SAB were caused by community-associated MRSA (CA-MRSA) clones. Although polyclonal, approximately 70.3% of CA-MRSA clones were characterised as ST93-IV [2B] (Queensland clone); ST5-IV [2B]; ST1-IV [2B]; ST45-V [5C2&5]; ST30-IV [2B]; ST8-IV [2B]; ST6-IV [2B]; ST97-IV [2B]; and ST953-IV [2B]. As CA-MRSA is well established in the Australian community, it is important to monitor antimicrobial resistance patterns in community- and healthcare-associated SAB as this information will guide therapeutic practices in treating S, aureus bacteraemia.

Occurrence, Multidrug Resistance, SCCmec Typing of Methicillin-Resistant Staphylococcus aureus from Farmed Eggs and Environment.

A comparative cross-sectional study was conducted on farmed eggs (n: 480) and environmental samples (n: 72; feed, water, and poultry droppings) from twenty-four deep litter and caged poultry layer farms across Punjab, India. The study noted a significantly higher occurrence of Staphylococcus aureus (31.67%; 95% CI 26.37-36.96%) and methicillin-resistant S. aureus (MRSA) (32.5%, 95% CI 23-43.3%) in deep litter farms (P < 0.05). The logistic regression analysis revealed while the odds of presumptive MRSA from egg isolates were high (Odds ratio: 2.714; 95% CI 1.172, 6.284) in deep litter, conversely, resistance against ceftriaxone (0.279; 95% CI 0.129, 0.605), tetracycline (0.227; 95% CI 0.104, 0.497), and erythromycin (0.46; 95% CI 0.218, 0.973) was low. The multi-drug resistance was high and nearly equal; 68.53%, and 72.22% in deep litter and cage systems respectively. Additionally, around 89.65% and 77.7% of MRSA from deep litter and cage systems had multiple antibiotic resistance index > 0.2 respectively. Among the resistance genes under study, the odds of mecA and tetL were 2.417 and 8.029 times higher in deep litter. The hierarchical clustering of MRSA isolates based on the antibiogram profile depicted the formation of a large number of cluster solutions with a mix of isolates from both systems. The SCCmec typing revealed a predominance of type V in both the systems (34.4%; deep litter and 33.3%; cage), with a scarce distribution of other types and subtypes viz., deep litter: types III; 13.7%, IVc; 6.8%, II; 6.8%, IVa, and IVb; 3.4% and cage system: types III and IVc; 11.1%. To, the best of our knowledge current study is the first-ever comprehensive study on comparative occurrence, AMR profile, molecular characterization, and typing of MRSA from farmed eggs and environment from India.

Revealing inducible clindamycin resistance in methicillin-resistant S aureus : A vital diagnostic imperative for effective treatment.

The World Health Organization added methicillin-resistant S aureus (MRSA) to the list of "priority pathogens," given its capacity to cause life-threatening infections. Clindamycin is a preferred treatment for non-complicated S aureus-induced skin and soft tissue infections. Its good tissue penetration and oral absorption make it suitable for outpatient therapy. However, the emergence of inducible and constitutive (MLS B ) resistance led to clinical challenges, primarily due to the potential oversight of inducible resistance in routine antimicrobial sensitivity testing. This cross-sectional study was conducted at a tertiary care hospital during 2020-2022. A total of 158 MRSA isolates from various clinical specimens were analyzed. The Kirby-Bauer disk diffusion method using cefoxitin disk and D-test were used to identify MRSA and detect inducible clindamycin resistance (ICR), respectively. Among the 158 MRSA isolates, 34.17% showed constitutive clindamycin resistance (MLS B c), while 22.15% displayed ICR (MLS B i). In addition, 10.13% of isolates demonstrated the MS phenotype, clindamycin, and erythromycin susceptibility, with 53 (33.54%) isolates susceptible to both antibiotics. The relative risk of clindamycin treatment failure was 7.66 times higher if the D-test was not used. To prevent clindamycin treatment failures, the D-test must be implemented to detect ICR in MRSA isolate. Neglecting simple and cost-effective tests may lead to inaccurate susceptibility reporting, jeopardizing treatment success.

Molecular characterization of Staphylococcus aureus from nasal samples of healthy pet cats.

The objective of this study was to characterize Staphylococcus aureus (S. aureus) isolates recovered from the nasal samples of healthy pet cats in Algiers province. A total of 138 nasal swabs were collected. Antimicrobial susceptibility was conducted using the disk-diffusion method and the VITEK-2 susceptibility system. Whole genome sequencing (WGS) was performed to identify multiple-locus sequence typing (MLST), antimicrobial and virulence genes. S. aureus isolates were detected in 23 cats. Among these, 11 were methicillin-resistant S. aureus (MRSA) (one isolate/sample). Three sequence types (ST6, ST5, and ST1) were identified in MRSA, with the predominance of ST6 (n=7). Seven distinct STs (ST398, ST97, ST15, ST7, ST291, ST5043 and a new ST, (ST9219)) were detected in methicillin-sensitive S. aureus (MSSA). All MRSA isolates harbored the mecA gene and SCCmec-type-IVa. MRSA exhibited resistance to tetracycline (n=3/tet(L) and tet(M); n=1/tet(K)), kanamycin-tobramycin (n=3/ant(4')-Ia), amikacin-kanamycin (n=1/aph(3')-IIIa), and erythromycin-clindamycin (n=1/erm(C)). Seven S. aureus isolates were multidrug-resistant. All the isolates were negative for lukS/lukF-PV and tst-1 genes, while 20 isolates were IEC-positive. This study revealed a diversity of genetic lineages in S. aureus strains isolated from nasal samples of pet cats, including multidrug-resistant and toxigenic strains. The presence of IEC-positive S. aureus suggests possible human-animal transmission.

Genetic characteristics and antimicrobial resistance of Staphylococcus aureus isolates from pig farms in Korea: emergence of cfr-positive CC398 lineage

BackgroundLivestock-associated Staphylococcus aureus (LA-SA) has gained global attention because of its ability to colonize farm animals and transmit to the environment and humans, leading to symptomatic infections and the spread of antimicrobial resistance (AMR). In the last decade, numerous studies have reported a high prevalence of S. aureus clonal complex (CC) 398 in pig farms.ResultsIn this study, 163 S. aureus isolates were collected from healthy pigs (n = 110), farm environments (n = 42), and farm workers (n = 11), and their AMR profiles and epidemiological characteristics were analyzed. We identified 51 (31.3%) methicillin-resistant S. aureus (MRSA) and 112 (68.7%) methicillin-susceptible S. aureus (MSSA), with 161 (98.8%) isolates belonging to the CC398 lineage. The highest prevalence of spa type t571 was observed among the CC398 isolates. All 47 sequence type (ST) 398 MRSA isolates carried staphylococcal cassette chromosome mec (SCCmec) V, while four ST541 isolates carried SCCmec IV. High levels of resistance to commonly used antibiotics, including phenicols, quinolones, lincosamides, macrolides, aminoglycosides, and tetracyclines, have been observed on Korean pig farms. Notably, 21 cfr-positive CC398 isolates (four ST541-SCCmec IV MRSA and 17 ST398 MSSA) displaying increased resistance to linezolid were identified in healthy pigs.ConclusionsIn summary, these findings suggest that the multidrug-resistant CC398 S. aureus lineage predominantly colonizes healthy pigs and farm environments in Korea. The emergence of cfr-positive S. aureus at human-animal interfaces presents a significant threat to food safety and public health.

Prevalence and antibiotic resistance of Staphylococcus aureus in wound infections: a hospital study in Hawassa, Ethiopia.

Wound infections are common nosocomial infections associated with increased morbidity and mortality. Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA), is a major cause of hospital-acquired wound infections. This study aimed to determine the burden and antimicrobial susceptibility pattern of S. aureus and MRSA, among patients with wound infections at Hawassa University Comprehensive Specialized Hospital (HUCSH), Hawassa, Ethiopia. A hospital-based cross-sectional study was conducted on 246 admitted patients with wound infections at HUCSH from April to August 2021. Wound swabs were aseptically collected and cultured for bacterial isolation and drug susceptibility testing. Data were analyzed using SPSS version 20, and descriptive statistics were computed. Among the 246 clinical specimens analyzed, S. aureus was isolated from 57 (23.2%), of which 5 (8.8%) were identified as MRSA. All S. aureus strains were sensitive to linezolid. The highest resistance was observed for penicillin (52 strains, 91.2%), and 24.6% of S. aureus strains were found to be multidrug resistant. All MRSA strains were isolated from patients with no history of past wound infection, and all of them were sensitive to vancomycin. This study identified S. aureus (23.2%) and MRSA (8.8%) along with their antimicrobial resistance among patients with wound infections at HUCSH. A substantial proportion (24.6%) of S. aureus exhibited multidrug resistance. However, all MRSA isolates were sensitive to vancomycin. Continuous drug resistance monitoring (drug surveillance) is crucial to manage and prevent resistance spread in the hospital.

Investigations of Antibiotic Susceptibilities of S. aureus Strains Isolated from Various Clinical Samples

Objective: Staphylococcus aureus (S. aureus) is a critical microorganism that causes a range of infections with high morbidity and mortality rates, including skin and soft tissue infections, urinary tract infections, endocarditis, pneumonia, septic arthritis, osteomyelitis, and sepsis in both community and healthcare settings. The objective of this study was to ascertain the antimicrobial resistance rates of methicillin-resistant S. aureus (MRSA) and Methicillin-susceptible S. aureus (MSSA) isolates derived from a range of clinical samples submitted to the Medical Microbiology Laboratory of our hospital and to examine the resistance profile specific to our hospital. Methodology: The study included 229 S. aureus isolates collected between 2022 and 2023. The isolates were identified through the application of conventional methods and the MALDI-TOF-MS system (VITEK MS, bioMerieux France). The antimicrobial susceptibility of the isolates was determined by the BD Phoenix automated system (Becton Dickinson, USA) in accordance with the criteria set forth by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Results: The MRSA rate in the one-year period was 25.77%. When the distribution of S. aureus isolates was analyzed, it was determined that blood cultures were the most common clinical specimens from which S. aureus was isolated. Resistance to glycopeptides and linezolid was determined in MRSA isolates, albeit at a low rate. No resistance to glycopeptide and linezolid was detected in MSSA isolates. MSSA isolates were found to have a more sensitive profile to other antibiotics than MRSA isolates. The highest resistance rate was detected against penicillin with 100% and 87.06% in MRSA and MSSA isolates, respectively. In addition, the most sensitive antibiotics were determined to be glycopeptide, linezolid, daptomycin, and aminoglycoside. Conclusion: In conclusion, knowing the resistance profiles of S. aureus isolates in our hospital, will guide empirical treatment. Furthermore, the implementation of effective infection control measures and a cautious approach to antibiotic use will contribute to the management of MRSA infections.

Prevalence and factors associated with human colonisation and vancomycin minimum inhibitory concentration of &lt;em&gt;Staphylococcus aureus&lt;/em&gt; in Colombo, Sri Lanka

Introduction: Staphylococcus aureus is known to cause a wide variety of diseases of varying severity in humans. The objectives of this study were to determine the prevalence of S. aureus and methicillin resistant S. aureus (MRSA) colonisation, assess factors associated with MRSA colonisation, identify antibiotic susceptibility patterns of MRSA isolates, determine distribution of vancomycin minimum inhibitory concentrations (MIC) of S. aureus and factors associated with high vancomycin MIC values (≥2 µg/ml). Methods: A descriptive cross sectional study was conducted among 341 participants aged 18 to 84 years selected randomly from the Colombo district from 11th December 2018 to 10th April 2019. Samples were collected from the nose, axilla, groin of participants and identification and sensitivity testing of S. aureus were performed based on standard operation procedures given in the Laboratory manual in microbiology published by the Sri Lanka College of Microbiologists (2011). Results: Prevalence of S. aureus and MRSA colonisation in the sample population was 34.6% and 13.78% respectively. All MRSA isolates were susceptible to linezolid. MRSA susceptibility to gentamicin (86%), co-trimoxazole (88 %), and chloramphenicol (80%) was high. Erythromycin had the lowest susceptibility (20%). Inducible clindamycin resistance was demonstrated in 31% of isolates. Meat consumption and consumption of antibiotics within the previous six months showed a significant association with MRSA colonisation. Vancomycin MIC of S. aureus ranged from ≤ 0.5 to 2 µg/ml. Conclusion: As prevalence of MRSA colonisation is 13.78%, more attention should be paid when managing patients with suspected S. aureus infections presenting from the community. Further research on associated factors and environmental triggers are warranted with a larger sample size and different study design to formulate national regulations and guidelines.

Modulatory effects of sub-MIC concentrations silver nanoparticles on virulence factor gene expression in Staphylococcus aureus

BackgroundSilver nanoparticles (AgNPs) exhibit a dose-dependent anti-bacterial effect, and it was aimed in this study to investigate the impact of sub-minimum inhibitory concentration (MIC) doses of AgNPs on the expression of virulence genes in Staphylococcus aureus (S. aureus). MethodsMinimum inhibitory concentration (MIC) values for AgNPs were determined for 183 S. aureus isolates. Gene expression was assessed in 14 isolates with sea and seb genes treated with AgNPs at a sub-MIC dose of 1 μg/ml. Accordingly, these strains were exposed to 1 μg/ml doses of AgNPs, and gene expression levels of sea, seb, and agr were assessed using quantitative RT-PCR after 4- and 12-hour post-AgNPs inoculation at 37 °C. The impact of AgNPs on the virulence factors of S. aureus was investigated over different time points, focusing on methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates. ResultsAnalysis revealed significant reductions in gene expression levels of seb and agr after 4 h post-AgNPs treatment in the MSSA group (p < 0.05), with further decreases observed at 12 h for sea, seb, and agr genes (p < 0.0001). MRSA isolates exhibited significant declines in sea and agr gene expression levels at both time points (p < 0.0001). However, no significant changes were observed in seb gene expression among MRSA isolates. Fold-change analysis indicated time-dependent effects of AgNP treatment on gene expression, highlighting substantial alterations in gene expression levels over time, particularly in seb and agr genes. ConclusionThese results show that sub-MIC levels of AgNPs greatly decrease the gene expression of important virulence factors in MSSA and MRSA strains, indicating their promise as treatments for S. aureus infections, particularly at 12 h post-treatment. The differential response between MSSA and MRSA isolates highlights the importance of strain variation in antimicrobial strategies.

Unraveling the genetic basis of antibiotic resistance in Staphylococcus aureus: Focus on mecA and PVL Genes

Background Staphylococcus aureus infections, including Methicillin-Resistant S. aureus (MRSA) and Methicillin-Sensitive S. aureus (MSSA), present significant challenges in healthcare due to rising antimicrobial resistance. This study evaluates the genetic basis of antibiotic resistance in S. aureus, focusing on key resistance-associated genes mecA and PVL. Methods A total of 568 clinical specimens were analyzed for the presence of S. aureus. Demographic data were collected to assess age-dependent prevalence. Antimicrobial susceptibility testing was conducted to evaluate resistance patterns. The prevalence of the mecA and PVL genes was determined using molecular techniques. Results S. aureus was identified in 37.9% of cases, with the highest prevalence (60-79 age group). All S. aureus isolates showed 100% resistance to penicillin. Multidrug-resistant (MDR) strains accounted for 84.19% of isolates, with a significant presence of extensively drug-resistant (XDR) strains. The mecA gene was prevalent in 82.79% of MRSA isolates, indicating its strong association with methicillin resistance. Additionally, 41.86% of all S. aureus isolates were positive for the PVL gene, highlighting its widespread distribution. Conclusions The high prevalence of mecA and PVL genes in S. aureus strains underscores the challenges in managing these infections. These findings emphasize the necessity for judicious antibiotic use and enhanced collaborative efforts to combat antimicrobial resistance. Understanding the genetic basis of resistance can inform more effective diagnostic, therapeutic, and preventive strategies, ultimately improving patient outcomes in S. aureus infections.

Design, Synthesis, and Anticancer and Antibacterial Activities of Quinoline-5-Sulfonamides.

A series of new unique acetylene derivatives of 8-hydroxy- and 8-methoxyquinoline- 5-sulfonamide 3a-f and 6a-f were prepared by reactions of 8-hydroxy- and 8-methoxyquinoline- 5-sulfonyl chlorides with acetylene derivatives of amine. A series of new hybrid systems containing quinoline and 1,2,3-triazole systems 7a-h were obtained by reactions of acetylene derivatives of quinoline-5-sulfonamide 6a-d with organic azides. The structures of the obtained compounds were confirmed by 1H and 13C NMR spectroscopy and HR-MS spectrometry. The obtained quinoline derivatives 3a-f and 6a-f and 1,2,3-triazole derivatives 7a-h were tested for their anticancer and antimicrobial activity. Human amelanotic melanoma cells (C-32), human breast adenocarcinoma cells (MDA-MB-231), and human lung adenocarcinoma cells (A549) were selected as tested cancer lines, while cytotoxicity was investigated on normal human dermal fibroblasts (HFF-1). All the compounds were also tested against reference strains Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 and representatives of multidrug-resistant clinical isolates of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis. Only the acetylene derivatives of 8-hydroxyquinoline-5-sulfonamide 3a-f were shown to be biologically active, and 8-hydroxy-N-methyl-N-(prop-2-yn-1-yl)quinoline-5-sulfonamide (3c) showed the highest activity against all three cancer lines and MRSA isolates. Its efficacies were comparable to those of cisplatin/doxorubicin and oxacillin/ciprofloxacin. In the non-cancer HFF-1 line, the compound showed no toxicity up to an IC50 of 100 µM. In additional tests, compound 3c decreased the expression of H3, increased the transcriptional activity of cell cycle regulators (P53 and P21 proteins), and altered the expression of BCL-2 and BAX genes in all cancer lines. The unsubstituted phenolic group at position 8 of the quinoline is the key structural fragment necessary for biological activity.

Unmasking a looming crisis: Escalating MIC of last resort drugs against MRSA isolates from a tertiary care hospital in Central India

PurposeThe Centers for Disease Control and Prevention has classified methicillin-resistant S aureus (MRSA) as a serious public health threat. The escalating minimum inhibitory concentration (MIC) of standard anti-methicillin-resistant S aureus (MRSA) drugs within the susceptible range, known as "MIC creep," jeopardizes their effectiveness against MRSA infections, posing additional challenges in managing MRSA infections. This cross-sectional study was conducted in a tertiary care hospital in Central India to assess the susceptibility trends of clinical MRSA isolates against commonly used anti-MRSA drugs and to observe MIC creep, if any, over three years (2020–2022). MethodsThe study included 158 non-repetitive clinical MRSA isolates. The MICs of vancomycin, teicoplanin, and linezolid were determined in MRSA strains using agar dilution, while the MIC of daptomycin was performed by broth microdilution. MIC creep was assessed by calculating MIC50, MIC90, Modal MIC, G-mean MIC, and susceptible and resistant percentages for the fiscal years 2020, 2021, and 2022. ResultsOf the 158 MRSA isolates, none were resistant to vancomycin, teicoplanin, and daptomycin, but two showed resistance to linezolid (LRSA). However, fifteen isolates showed intermediate resistance to vancomycin (VISA), and five showed intermediate resistance to teicoplanin (TISA). MIC of these anti-MRSA drugs increased in 2021 and 2022 compared to 2020. G-mean MIC for vancomycin, teicoplanin, and linezolid in MRSA strains increased significantly over the study period, while daptomycin MIC remained relatively stable, with a slight increase in 2021 and 2022. There was a high resistance rate for clindamycin, doxycycline, and chloramphenicol among VISA, TISA, and LRSA isolates compared to MRSA. ConclusionsDuring the three years of the study, “MIC creep” was observed in vancomycin, teicoplanin, and linezolid and, to some extent, for daptomycin in MRSA strains. The recovery of VISA, TISA, and linezolid-resistant MRSAs is worrisome, suggesting possible MRSA treatment failure and being a forerunner of resistant strains.

Machine learning assisted identification of antibiotic-resistant Staphylococcus aureus strains using a paper-based ratiometric sensor array

Staphylococcus aureus, a versatile human pathogen, significantly impacts global health causing a broad spectrum of medical conditions that range from minor skin infections to life-threatening diseases. The clinical importance of S. aureus is underscored by its resistance to multiple antibiotics and formation of biofilms, providing protection against antimicrobials and immune responses. To date, the identification of antimicrobial-resistant (AMR) S. aureus strains, such as methicillin-resistant S. aureus (MRSA) and vancomycin-intermediate S. aureus (VISA), requires time-consuming and expensive methodologies, including culture-based, molecular, and phenotypic techniques. Previously, we developed a paper-based ratiometric sensor array composed of fluorescent sensor dyes (3-hydroxyflavone derivatives) pre-adsorbed on paper microzone plates. Combined with machine learning algorithms such as neural networks, this sensor effectively discriminated 16 bacterial species and determined their Gram status. In this study, we evaluate its ability to distinguish antibiotic-resistant S. aureus strains and their biofilms. Our results demonstrate that the sensor array, in conjunction with LDA and neural networks, successfully differentiated three common laboratory MRSA strains from three methicillin-susceptible S. aureus (MSSA) strains with 82.5% accuracy. Furthermore, using support vector machines, this sensor was able to distinguish and categorically classify MRSA, MSSA, and VISA clinical isolates with 97.5% accuracy. Remarkably, beyond distinguishing planktonic cultures, this sensor array demonstrated a formidable capability to discriminate AMR S. aureus biofilms, achieving over 80% accuracy. Combined, the results of this study highlight the paper-based sensor array’s significant potential as a robust diagnostic tool to accurately, rapidly, and easily identify drug-resistant S. aureus strains in clinically relevant settings.

Unraveling the genetic basis of antibiotic resistance in Staphylococcus aureus: Focus on mecA and PVL Genes

Background Staphylococcus aureus infections, including Methicillin-Resistant S. aureus (MRSA) and Methicillin-Sensitive S. aureus (MSSA), present significant challenges in healthcare due to rising antimicrobial resistance. This study evaluates the genetic basis of antibiotic resistance in S. aureus, focusing on key resistance-associated genes mecA and PVL. Methods A total of 568 clinical specimens were analyzed for the presence of S. aureus. Demographic data were collected to assess age-dependent prevalence. Antimicrobial susceptibility testing was conducted to evaluate resistance patterns. The prevalence of the mecA and PVL genes was determined using molecular techniques. Results S. aureus was identified in 37.9% of cases, with the highest prevalence (60-79 age group). All S. aureus isolates showed 100% resistance to penicillin. Multidrug-resistant (MDR) strains accounted for 84.19% of isolates, with a significant presence of extensively drug-resistant (XDR) strains. The mecA gene was prevalent in 82.79% of MRSA isolates, indicating its strong association with methicillin resistance. Additionally, 41.86% of all S. aureus isolates were positive for the PVL gene, highlighting its widespread distribution. Conclusions The high prevalence of mecA and PVL genes in S. aureus strains underscores the challenges in managing these infections. These findings emphasize the necessity for judicious antibiotic use and enhanced collaborative efforts to combat antimicrobial resistance. Understanding the genetic basis of resistance can inform more effective diagnostic, therapeutic, and preventive strategies, ultimately improving patient outcomes in S. aureus infections.

Role of parC Mutations at Position 84 on High-Level Delafloxacin Resistance in Methicillin-Resistant Staphylococcus aureus.

High-level delafloxacin-resistant (H-L DLX-R) Staphylococcus aureus isolates (minimum inhibitory concentration ≥1 mg/L) associated with mutations affecting position 84 of ParC have emerged. We aimed to elucidate the role of these mutations as a mechanism of H-L DLX resistance in methicillin-resistant S. aureus (MRSA) isolates recovered from blood cultures. Susceptibility to DLX was determined in 75 MRSA isolates by E-test, and an rt-PCR was developed to detect mutations affecting position 84 of ParC to screen a further 185 MRSA isolates. The genomes of 48 isolates, including all DLX-R isolates or with alterations at position 84, and also a subset of DLX-susceptible isolates were analyzed. Among the 75 isolates studied, 77.34% were DLX-susceptible and only 4 H-L DLX-R isolates were found. Seven (3.8%) isolates with alterations at position 84 of ParC were detected by rt-PCR. Genomic analysis showed that 89.9% (8/9) of isolates with the substitution E84K/G in ParC, together with other mutations in gyrA and parC, were H-L DLX-R. However, the E84K substitution in ParC alone or with other alterations was found in two isolates without H-L DLX-R. Alterations at position 84 of ParC are rare but play a key role in H-L DLX resistance in MRSA but only when other alterations in GyrA are present.

Large-Scale S. aureus Screening with Molecular Epidemiology; the Role of MSSA and Community MRSA in Hospital Transmissions

Background: The frequency of Staphylococcus aureus transmission in hospitals is unknown: symptomatic infection may occur months after transmission and colonization, and infection prevention efforts rely on indirect measurements, rather than direct detection of transmission events. We implemented a hospital-based S. aureus screening program, combined with whole genome sequencing of S. aureus surveillance and clinical cultures and data extracted from the electronic health record, to identify S. aureus clonal complex-, patient- and location-specific factors associated with S. aureus transmission in our health system. Methods: Screening S. aureus cultures were obtained at admission by nasal swab for adults admitted to Medicine, Transplant, Oncology and intensive care, and weekly by swab of nares, axilla and groin for children admitted to intensive care and Oncology at NYU Langone Health in New York City. All methicillin-resistant S. aureus (MRSA) from screening and clinical (blood, wound, sputum) cultures and all methicillin-susceptible S. aureus (MSSA) from screening and blood cultures underwent whole genome sequencing. Isolates from distinct patients with &lt; 2 0 single nucleotide pair differences were considered genetically related. Electronic health data was extracted for descriptive statistics and for spatiotemporal plots to assess plausible transmissions. We used REDCap electronic data capture tools hosted at NYU Grossman School of Medicine and SAS software for data analysis to evaluate S. aureus transmissions between November 2022 and November 2023. Results: We analyzed 8,567 S. aureus isolates: including 6,552 screening cultures, 1,008 blood cultures, and 1,007 clinical cultures. We found 424 plausible S. aureus hospital transmissions using sequencing and electronic health data. Screening cultures identified 75% of transmissions that would have otherwise been missed with blood and clinical cultures alone. The majority of positive screening cultures isolated MSSA, but the proportion of transmissions due to MSSA differed by age. In children, MSSA colonization accounted for 62% of transmissions. In adults, only 15% of transmissions were due to MSSA colonization, whereas MRSA colonization accounted for 56% of transmissions. Analysis of adult MRSA isolates by clonal complex found that 45% of transmissions were due to CC8, higher than the 17% among isolates agnostic of transmissions. Emergency departments and the neonatal intensive care unit had the highest number of transmissions. Patients involved in transmissions had longer lengths of stay and frequent hospitalizations. Conclusions: A S. aureus screening program, coupled with genome sequencing and electronic health data, can identify patient group, hospital locations and clonal complexes that are at high risk for S. aureus transmissions.

Genomic characterization of Staphylococcus aureus isolated from patients admitted to intensive care units of a tertiary care hospital: epidemiological risk of nasal carriage of virulent clone during admission.

We conducted a molecular epidemiological study of Staphylococcus aureus using whole-genome sequence data and clinical data of isolates from nasal swabs of patients admitted to the intensive care unit (ICU) of Hiroshima University hospital. The relationship between isolate genotypes and virulence factors, particularly for isolates that caused infectious diseases during ICU admission was compared with those that did not. The nasal carriage rates of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in patients admitted to the ICU were 7.0% and 20.1%, respectively. The carriage rate of community-acquired (CA)-MRSA was 2.3%, accounting for 32.8% of all MRSA isolates. Whole-genome sequencing analysis of the MRSA isolates indicated that most, including CA-MRSA and healthcare-associated (HA)-MRSA, belonged to clonal complex (CC) 8 [sequence type (ST) 8] and SCCmec type IV. Furthermore, results for three disease foci (pneumonia, skin and soft tissue infection, and deep abscess) and the assessment of virulence factor genes associated with disease conditions [bacteremia, acute respiratory distress syndrome (ARDS), disseminated intravascular coagulopathy (DIC), and septic shock] suggested that nasal colonization of S. aureus clones could represent a risk for patients within the ICU. Particularly, MRSA/J and MSSA/J may be more likely to cause deep abscess infection; ST764 may cause ventilation-associated pneumonia, hospital-acquired pneumonia and subsequent bacteremia, and ARDS, and tst-1-positive isolates may cause DIC onset.IMPORTANCENasal colonization of MRSA in patients admitted to the intensive care unit (ICU) may predict the development of MRSA infections. However, no bacteriological data are available to perform risk assessments for Staphylococcus aureus infection onset. In this single-center 2-year genomic surveillance study, we analyzed all S. aureus isolates from nasal swabs of patients admitted to the ICU and those from the blood or lesions of in-patients who developed infectious diseases in the ICU. Furthermore, we identified the virulent clones responsible for causing infectious diseases in the ICU. Herein, we report several virulent clones present in the nares that are predictive of invasive infections. This information may facilitate the design of preemptive strategies to identify and eradicate virulent MRSA strains, reducing nosocomial infections within the ICU.

Antimicrobial Resistance Patterns of Outpatient Staphylococcus aureus Isolates

Oral non-β-lactam antibiotics are commonly used for empirical therapy of Staphylococcus aureus infections, especially in outpatient settings. However, little is known about potential geographic heterogeneity and temporal trends in the prevalence of S aureus resistance to non-β-lactams in the US. To characterize the spatiotemporal trends of resistance to non-β-lactam antibiotics among community-onset S aureus infections, including regional variation in resistance rates and geographical heterogeneity in multidrug resistance. This cross-sectional study used data from Veterans Health Administration clinics collected from adult outpatients with S aureus infection in the conterminous 48 states and Washington, DC, from January 1, 2010, to December 31, 2019. Data were analyzed from January to November 2023. Resistance to lincosamides (clindamycin), tetracyclines, sulfonamides (trimethoprim-sulfamethoxazole [TMP-SMX]), and macrolides. Spatiotemporal variation of S aureus resistance to these 4 classes of non-β-lactam antibiotics, stratified by methicillin-resistant S aureus (MRSA) and methicillin-sensitive S aureus (MSSA), and subdivided by regions of the US (Northeast, Midwest, South, and West). Trend tests and bivariate mapping were used to determine significant changes in resistant proportions over time and identify counties where rates of resistance to multiple non-β-lactams were high. A total of 382 149 S aureus isolates from 268 214 unique outpatients (mean [SD] age, 63.4 [14.8] years; 252 910 males [94.29%]) were analyzed. There was a decrease in the proportion of MRSA nationwide, from 53.6% in 2010 to 38.8% in 2019. Among MRSA isolates, we observed a significant increase in tetracycline resistance (from 3.6% in 2010 to 12.8% in 2019; P for trend < .001) and TMP-SMX resistance (from 2.6% in 2010 to 9.2% in 2019; P for trend < .001), modest and not significant increases in clindamycin resistance (from 24.2% in 2010 to 30.6% in 2019; P for trend = .34), and a significant decrease in macrolide resistance (from 73.5% in 2010 to 60.2% in 2019; P for trend < .001). Among MSSA isolates, significant upward trends in clindamycin, tetracyclines, and TMP-SMX resistance were observed. For example, tetracycline resistance increased from 3.7% in 2010 to 9.1% in 2019 (P for trend < .001). Regional stratification over time showed that the Northeast had slightly higher rates of clindamycin resistance but lower rates of tetracycline resistance, while the South had notably higher rates of resistance to tetracyclines and TMP-SMX, particularly among MRSA isolates. Bivariate mapping at the county scale did not indicate clear regional patterns of shared high levels of resistance to the 4 classes of antimicrobials studied. In this study of outpatient S aureus isolates, MRSA became less common over the 10-year period, and MRSA isolates were increasingly resistant to tetracyclines and TMP-SMX. Geographic analysis indicated no spatial overlap in counties with high rates of resistance to both tetracyclines and TMP-SMX. Examining the regional spatial variation of antibiotic resistance can inform empirical therapy recommendations and help to understand the evolution of S aureus antibiotic resistance mechanisms.

Phenotypic and genotypic characterization of methicillin and vancomycin-resistant Staphylococcus aureus isolated from human clinical samples in Kerman hospitals, Iran

Today, methicillin-resistant S. aureus (MRSA) isolates are widely spread in both communities and hospitals, causing high morbidity and mortality worldwide. However, the emergence of vancomycin resistance among MRSA isolates has been perceived as a formidable threat to therapeutic management. Therefore, the present study aimed to determine the frequency and antibiotic susceptibility of MRSA and vancomycin-resistant S. aureus (VRSA) strains in Kerman hospitals in Iran. A total of 455 human clinical samples were collected from Kerman hospitals. The samples were examined for the presence of S. aureus and the isolates were tested for their susceptibility to antibiotics by disk diffusion method. MRSA and VRSA isolates were detected by a combination of phenotypic and genotypic methods. Sixty-five coagulase-positive S. aureus strains were isolated, and the higher isolation rate was from wound samples (47.7%) compared with blood (18.5%), respiratory tract secretions (10.8%), urine (10.8%), body fluids (9.2%), abscess (1.5%), and cerebrospinal fluids (1.5%). The isolates exhibited high resistance toward tetracycline (69.2%). Thirty-four isolates (52.3%) were categorized as MRSA (phenotypically resistant to cefoxitin). mecA gene was amplified in 97.1% of MRSA strains. Moreover, only one MRSA strain was resistant to vancomycin (MIC=128), and this isolate carried the vanA gene. The frequency of MRSA was not significantly associated with gender, age, sample type, and sampling locality (p&gt;0.05). Given the alarming rate of resistance among MRSA isolates, monitoring of antibiotic resistance should be performed to reduce treatment failure in patients with staphylococcal infections. Although vancomycin remains a drug of choice for MRSA, our study suggests that its efficacy may be limited by resistance development.

Antibacterial and Antibiofilm Potential of Bacterial Cellulose Hydrogel Containing Vancomycin against Multidrug-Resistant Staphylococcus aureus and Staphylococcus epidermidis.

The present study aimed to evaluate the in vitro antibacterial and antibiofilm activity of bacterial cellulose hydrogel produced by Zoogloea sp. (HYDROGEL) containing vancomycin (VAN) against bacterial strains that cause wound infections, such as multidrug-resistant (MDR) Staphylococcus aureus and Staphylococcus epidermidis. Initially, HYDROGEL was obtained from sugar cane molasses, and scanning electron microscopy (SEM) was performed to determine morphological characteristics. Then, VAN was incorporated into HYDROGEL (VAN-HYDROGEL). The antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was assessed using the broth microdilution method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) against methicillin-sensitive S. aureus (MSSA) ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 33591, S. epidermidis INCQS 00016 (ATCC 12228), five clinical isolates of MRSA, and nine clinical isolates of methicillin-resistant S. epidermidis, following the Clinical and Laboratory Standards Institute (CLSI) guidelines. Additionally, the antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was studied using the time-kill assay. Subsequently, the antibiofilm activity of VAN, HYDROGEL, and VAN-HYDROGEL was evaluated using crystal violet and Congo red methods, as well as SEM analysis. VAN and VAN-HYDROGEL showed bacteriostatic and bactericidal activity against MRSA and methicillin-resistant S. epidermidis strains. HYDROGEL did not show any antibacterial activity. Analysis of the time-kill assay indicated that HYDROGEL maintained the antibacterial efficacy of VAN, highlighting its efficiency as a promising carrier. Regarding antibiofilm activity, VAN and HYDROGEL inhibited biofilm formation but did not demonstrate biofilm eradication activity against methicillin-resistant S. aureus and S. epidermidis strains. However, it was observed that the biofilm eradication potential of VAN was enhanced after incorporation into HYDROGEL, a result also proven through images obtained by SEM. From the methods carried out in this study, it was possible to observe that HYDROGEL preserved the antibacterial activity of vancomycin, aside from exhibiting antibiofilm activity and enhancing the antibiofilm effect of VAN. In conclusion, this study demonstrated the potential of HYDROGEL as a candidate and/or vehicle for antibiotics against MDR bacteria that cause wound infections.