Methicillin-susceptible S. Aureus Research Articles

P-1141. Antibiotic administration for Staphylococcus aureus infections in US children's hospitals, 2015-2023

Abstract Background The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) infections in children has changed. In response to the introduction of new antibiotics published clinical data, treatment strategies have evolved. The objective of this study is to describe the antimicrobial treatment regimens for children hospitalized with this important pathogen.Table 1.Type of Infections by MRSA vs. MSSA Methods A retrospective observational study was performed using the Pediatric Health Information System (PHIS) data, including all patients discharged from a PHIS-member hospital from October 1, 2015 to June 31, 2023. Patients with ICD 10 codes identifying an MRSA or MSSA infection and indicating the type of infection were included (Table 1): bacteremia, endovascular, pneumonia, skin and soft tissue infection (SSTI), osteomyelitis, and myositis. The proportion of anti-staphylococcal antibiotics of interest received by all patients, patients with MRSA infections, and patients with MSSA infections were calculated by year.Figure 1.Percent of Antibiotics Prescribed for All Patients with Staphylococcus aureus Results 21,206 patients met eligibility criteria and were included in the final data set. Infections due to MRSA and MSSA were 9,561 and 11,645, respectively (Table 1). The proportion of patients with S. aureus infections caused by MRSA decreased from 2015 (55%) to 2023 (41%). The most frequent infections were bacteremia (32%), SSTI (27%), and pneumonia (23%, Table 1). The most common antibiotics prescribed for all S. aureus infections in 2015 were clindamycin (53%), vancomycin (49%), and cefazolin (27%) and in 2023 were vancomycin (56%), cefazolin (48%), and ceftriaxone (34%, Figure 1). While vancomycin prescriptions remained consistent over the study period, clindamycin administration decreased 20% (Figure 1). Daptomycin and ceftaroline, the newest MRSA agents, increased from 2% and 3% to 7% and 8%, respectively, of agents prescribed for MRSA infections (Figure 2). For MSSA infections, cefazolin increased in use while oxacillin/nafcillin use remained consistent (Figure 3). Conclusion Clindamycin administration has substantially decreased, likely a result of increased resistance prevalence in both MSSA and MRSA. Cefazolin use increased commensurate with the increasing incidence of MSSA infection. Disclosures Jason G. Newland, MD, MEd, Moderna: Grant/Research Support|Pfizer: Grant/Research Support

P-1257. Cefazolin Dosage Considerations for Methicillin-Susceptible Staphylococcus aureus (MSSA) Central Nervous System Infections: Exploring Optimal Regimens

Abstract Background Historically, cefazolin (CFZ) has not been considered an appropriate agent to treat central nervous system (CNS) infections. Recent studies have shown that standard CFZ dosing achieves concentrations above the epidemiologic cutoff of minimum inhibitory concentration ≤ 2 mg/L for Staphylococcus aureus, but literature describing optimal dosing for CNS infections is lacking. This study aimed to identify CFZ dosing regimens necessary to achieve adequate probability of target attainment (PTA) for treatment of a methicillin-susceptible S. aureus (MSSA) CNS infection. Methods CFZ plasma and cerebral spinal fluid (CSF) pharmacokinetic parameters were obtained from a previous published study. Monte Carlo simulations were performed utilizing PD targets of 40%fT > MIC for intermittent infusions and 100%fT > MIC and 100%fT > 4xMIC for continuous infusions (CI) to determine probability of target attainment (PTA) for seven CFZ dosing regimens at an MIC of 0.5 mg/L, 1 mg/L, and 2 mg/L. Adequate target attainment, defined as ≥ 90% PTA, was evaluated for CFZ dosing regimens ranging from 6-12g/day administered intermittently every 4-8 hours over 30 minutes or as a CI over 24 hours (Table 1). Results The standard intermittent regimen of 2g q8h did not achieve ≥ 90% PTA for any MIC evaluated. Furthermore, no CI regimen achieved ≥ 90% PTA when using the PD target of 100%fT > 4xMIC. All continuous and intermittent regimens achieved ≥ 90% PTA when the MIC remained ≤ 0.5 mg/L. Only the 10 g and 12 g CI regimens achieved ≥ 90% PTA for 100%fT > MIC when the MIC was 1 mg/L while no regimen achieved the desired target when the MIC was 2 mg/L. Conclusion These findings underscore the inadequacy of standard intermittent CFZ regimens in achieving desired PD targets for MSSA CNS infections. Higher total daily doses or CI CFZ is necessary to achieve satisfactory PD targets for MSSA CNS infections. When comparing the same total daily dose administered as an intermittent versus continuous infusion, our results suggest that continuous infusions are more likely to achieve PD target attainment for MSSA CNS infections, particularly when the cefazolin MIC exceeds 0.5 mg/L. Further clinical studies are warranted to evaluate the safety and efficacy of CFZ for CNS infections caused by MSSA. Disclosures All Authors: No reported disclosures

Antibiotic susceptibility and molecular characterization based on whole-genome sequencing of Staphylococcus aureus causing invasive infection in children and women living in Southwest China during 2018–2023

BackgroundStaphylococcus aureus is one of the most common pathogens that colonizes human skin/mucous membranes, where it causes local infection that can progress to invasive infection, resulting in high morbidity and mortality worldwide. This study aimed to investigate the antibiotic susceptibility and molecular characteristics of invasive S. aureus in children and women in Southwest China from 2018 to 2023 to provide novel insights helpful in preventing and treating S. aureus infections.MethodsThe demographic and clinical characteristics of patients with invasive S. aureus infection were collected and analyzed. Next-generation sequencing (NGS) and sequence analysis techniques were used to determine the molecular epidemiological characteristics of the S. aureus isolates, and the microdilution broth method was used for antimicrobial susceptibility testing.ResultsA total of 108 invasive S. aureus isolates, 29 methicillin-resistant S. aureus (MRSA) isolates and 79 methicillin- susceptible S. aureus (MSSA) isolates, were included. The isolates had the highest rate of resistance to PEN, at 91.67%, with all the MRSA isolates being resistant; the next highest resistance was to ERY and CLI, both at 65.74%. A total of 32 STs (including 8 novel STs) were detected and divided into 10 CCs. Moreover, 45 spa types were also detected. The main STs were ST22 (17.59%) and ST59 (15.74%), and the main CCs were CC59 (21.30%) and CC22 (19.44%). The most prevalent spa types were t309 and t437, both at 14.81%, and the SCCmec type could be assigned to two categories: IV (62.07%) and V (34.48%). Among the 29 MRSA isolates tested, CC59-IV-t437 (34.48%) and CC59-V-t437 (13.79%) were the main lineages, and among the 79 MSSA isolates, CC22-t309 (18.99%), CC1-t189 (10.13%), and CC5-t002 (7.60%) were the main lineages. Except for SXT, the resistance rates of the 29 MRSA isolates were greater than those of the MSSA isolates. Most isolates carried common virulence genes, among which the carriage rate of pvl reached 33.33%.ConclusionsThis study provides valuable information, including the prevalence, molecular characteristics and antimicrobial resistance of S. aureus isolates that cause invasive infectious diseases in Southwest China, and the findings may advance the prevention and treatment of S. aureus infections.

Bicarbonate Within: A Hidden Modulator of Antibiotic Susceptibility.

Since its standardization, clinical antimicrobial susceptibility testing (AST) has relied upon a standard medium, Mueller-Hinton Broth/Agar (MHB/A), to determine antibiotic resistance. However, this microbiologic medium bears little resemblance to the host milieu, calling into question the physiological relevance of resistance phenotypes it reveals. Recent studies investigating antimicrobial susceptibility in mammalian cell culture media, a more host-mimicking environment, demonstrate that exposure to host factors significantly alters susceptibility profiles. One such factor is bicarbonate, an abundant ion in the mammalian bloodstream/tissues. Importantly, bicarbonate sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to early-generation β-lactams used for the treatment of methicillin-susceptible S. aureus (MSSA). This "NaHCO3-responsive" phenotype is widespread among US MRSA USA300/CC8 bloodstream and skin and soft tissue infection isolates. Translationally, β-lactam therapy has proven effective against NaHCO3-responsive MRSA in both ex vivo simulated endocarditis vegetation (SEV) and in vivo rabbit infective endocarditis (IE) models. Mechanistically, bicarbonate appears to influence mecA expression and PBP2a production/localization, as well as key elements for PBP2a functionality, including the PBP2a chaperone PrsA, components of functional membrane microdomains (FMMs), and wall teichoic acid (WTA) synthesis. The NaHCO3-responsive phenotype highlights the critical role of host factors in shaping antibiotic susceptibility, emphasizing the need to incorporate more physiological conditions into AST protocols.

Enhanced Killing of Methicillin-Resistant Staphylococcus aureus with Ceftaroline or Vancomycin in Combination with Carbapenems.

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is associated with high rates of treatment failure, even when antibiotics showing in vitro susceptibility are used. Early optimization of therapy is crucial to reduce morbidity and mortality. Building on our previous research on carbapenem therapy for methicillin-susceptible S. aureus (MSSA) bacteremia, we examined the utility of adjunctive carbapenems (ertapenem or meropenem) to enhance the efficacy of ceftaroline or vancomycin for treatment of MRSA. The effectiveness of combination therapy versus monotherapy against MRSA was assessed using checkerboard, time-kill, and human whole blood killing assays, as well as a murine bacteremia model. Additionally, we performed transcriptomic analysis and conducted human platelet and antimicrobial peptide killing assays on MRSA pretreated with subtherapeutic concentrations of ceftaroline and carbapenems. The supernatants from these MRSA were used to treat platelets, and cytotoxicity was assessed via LDH release assays. Although not typically used for MRSA, we identified striking in vitro and in vivo synergy between carbapenems and ceftaroline or vancomycin. MRSA pretreated with subtherapeutic ceftaroline-carbapenem therapy revealed transcriptional shifts indicative of reduced antibiotic resistance, virulence, and host immune evasion. Supernatants from these MRSA also caused less platelet injury compared to monotherapy. Furthermore, MRSA pretreated with ceftaroline and carbapenems demonstrated increased susceptibility to killing by human platelets and the antimicrobial peptide LL-37. The therapeutic success of adjunctive carbapenems appears to be driven by multiple mechanisms, including direct drug-drug synergy with first-line anti-MRSA agents, attenuation of resistance and virulence factors, and enhancement of immune-mediated killing, each warranting further investigation.

Reshaping the Battlefield: A Decade of Clonal Wars Among Staphylococcus aureus in China

BackgroundLong-term comprehensive studies on the genomic epidemiology of both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates are limited in China. Here, we aimed to assess the genomic epidemiological characteristics and population dynamics of S. aureus in China. MethodsWe performed whole-genome sequencing and resistance phenotyping on 3,848 S. aureus isolates from bloodstream infections across 72 hospitals in 22 provinces, from 2011 to 2020 in China. We explored the dynamic trends in the resistance/virulence genes and mobile genetic element profiles across lineages, and conducted time-scaled phylogenetic investigation for prevalent lineages. FindingsThe results revealed 315 different sequence types (STs) among all strains, 205 of which were novel. Significant shifts in MRSA population structure were observed, with ST59 replacing ST239 as the dominant lineage, exhibiting widespread inter-hospital transmission and increasing lineage diversity. In contrast, the composition of predominant MSSA lineages, ST188 (11.21%), ST7 (9.79%), ST22 (9.10%), ST5 (8.56%) and ST398 (7.91%), remained relatively stable over time, with the diversity among MSSA strains consistently preserved at the population level. Phylogenetic reconstruction showed that ST59, ST398, ST22 and ST188 MSSA could evolve into corresponding MRSA lineages through the acquisition of staphylococcal cassette chromosome mec (SCCmec) elements. Moreover, the distribution patterns of resistance and virulence genes closely correlated with different lineages, where the proportion of PVL+ isolates in MRSA is rising. Concurrently, changes in the MRSA population structure led to an overall decrease in the number of resistance and virulence genes, significantly increased antimicrobial sensitivity. InterpretationThe shifting genomic landscape of S. aureus in China underscores the need for tailored antimicrobial stewardship and enhances understanding of its epidemiological trends over the past decade.

Methyl Gallate and Amoxicillin-Loaded Electrospun Poly(vinyl alcohol)/Chitosan Mats: Impact of Acetic Acid on Their Anti-Staphylococcus aureus Activity.

Methyl gallate (MG), a natural phenolic compound, exhibits in vitro synergistic activity with amoxicillin (Amox) against methicillin-resistant Staphylococcus aureus (MRSA), a global health concern. This study developed electrospun nanofibers incorporating MG and Amox into a poly(vinyl alcohol) (PVA)/chitosan (CS) blend to target both methicillin-susceptible S. aureus (MSSA) and MRSA. The formulation was optimized, and the impact of acetic acid on antibacterial activity was evaluated using agar disc diffusion. The final formulation was fabricated and characterized using SEM, FTIR, DSC, swelling, and release behavior analyses to understand its antibacterial efficacy. Results revealed that acetic acid eliminated antibacterial activity, but MG (64 mg/mL) and Amox (2.5 mg/mL) were successfully incorporated into a PVA/CS solution prepared with deionized water. The resulting nanofiber mats featured nanoscale fibers (126 ± 45 nm) with and micron-oval beads. Despite the in vitro synergism, the MG/Amox/PVA/CS mats showed no significant improvement over MG or Amox alone against MRSA, likely due to their physicochemical properties. FTIR and DSC results confirmed molecular interactions between the active compounds and the polymer matrix, which may cause a minimal swelling and low drug release at 24 h. This study offers insights into the potential of MG/Amox-loaded nanofibers for anti-MRSA material development.

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.

The antibacterial and anti-biofilm effects of novel synthetized nitroimidazole compounds against methicillin-resistant Staphylococcus aureus and carbapenem-resistant Escherichia coli and Klebsiella pneumonia in vitro and in silico

The antibiotic resistance and biofilm formation by bacterial pathogens has led to failure in infections elimination. This study aimed to assess the antibacterial and anti-biofilm properties of novel synthesized nitroimidazole compounds (8a–8o). In this study, nitroimidazole compounds were synthesized via the A3 coupling reaction of sample substrates in the presence of copper-doped silica cuprous sulfate (CDSCS). Fifteen and two carbapenemase producing Escherichia coli and Klebsiella pneumonia (CP-E. coli and CP-K. pneumonia, respectively) and one methicillin-resistant Staphylococcus aureus (MRSA) and one methicillin-susceptible S. aureus (MSSA) plus standard strain of each isolate were included. The antibacterial effects of these compounds demonstrated that the lowest minimum inhibitory and bactericidal concentrations (MIC/MBC, respectively) levels corresponded to compound 8g against S. aureus (1/2 µg/mL) and K. pneumonia (8/32 µg/mL) standard and clinical strains and confirmed by in silico assessment. This was comparable to those of metronidazole being 32–128 µg/mL against K. pneumonia and 32–64 µg/mL against S. aureus. In comparison to metronidazole, against CP-E. coli, compounds 8i and 8m had significantly higher antibacterial effects (p < 0.001) and against CP-K. pneumonia, compounds 8a–8j and 8l–8o had significantly higher (p < 0.0001) antibacterial effects. Compound 8g exhibited significantly higher antibacterial effects against MSSA and compounds 8b (p < 0.001), 8c (p < 0.001), 8d (p < 0.001), 8e (p < 0.001) and 8g (p < 0.0001) exerted significantly higher antibacterial effects than metronidazole against MRSA. Moreover, potential anti-biofilm effects was corresponded to compounds 8a, 8b, 8c, 8e, 8f, 8g, 8i, 8k, 8m and 8n. Considering the antibacterial and anti-biofilm effects of novel synthesized compounds evaluated in this study, further assessments is warranted to verify their properties in vivo and clinical trials in the future.

Discordant β-Lactam Susceptibility in Clinical Staphylococcus aureus Isolates: A Molecular and Phenotypical Exploration to Detect the BORSA/MODSA Isolates in Bogotá, Colombia.

Staphylococcus aureus is a human pathogen responsible for a wide range of diseases, such as skin and soft tissue infections, pneumonia, toxic shock syndrome, and urinary tract infections. Methicillin-resistant S. aureus (MRSA) is a well-known pathogen with consistently high mortality rates. Detecting the mecA resistance gene and phenotypical profile to β-lactams allows for the differentiation of MRSA from methicillin-susceptible S. aureus (MSSA) isolates. In this study, we characterized 57 S. aureus clinical isolates for β-lactam susceptibility and mecA presence. We classified 52.63% as MRSA and 45.61% as MSSA. However, some isolates evidenced different oxacillin resistance profiles, such as borderline oxacillin-resistant or modified S. aureus (BORSA/MODSA). The cefazolin inoculum effect (CzIE) was established for these samples, emphasizing the relevance of these isolates as a source of therapeutic failure. We also performed the detection of the Panton-Valentine Leucocidin virulence genes as well as the S. aureus spa-type clonality. As expected, spa-types t002 and t008 were the most prevalent clones, demonstrating the success of well-established clones. These findings emphasize the importance of establishing sensitivity profiles, especially in isolates with poor resistance mechanisms, to determine their prevalence and their impact on public health.

β-Lactam Inoculum Effect in Methicillin-Susceptible Staphylococcus aureus Infective Endocarditis

Infective endocarditis (IE) caused by Staphylococcus aureus is associated with high mortality, approximately 20% to 30%, mostly in the first month, with no improvement in recent decades. Current opinion is that antistaphylococcal penicillin and cefazolin are equally effective in treating methicillin-susceptible S aureus (MSSA) IE, and both are recommended as possible first-line treatments. Most MSSA strains carry the β-lactamase blaZ gene, and some blaZ-positive strains exhibit an inoculum effect, meaning increased minimum inhibitory concentrations at high inoculum. This reduced susceptibility to an antibiotic at high bacterial inoculum may be particularly relevant in IE, where vegetations have very high bacterial densities. To evaluate the association between phenotypic characteristics of S aureus isolates, β-lactam used, and outcome in patients with MSSA IE. This retrospective case series included MSSA cases treated at 3 French university hospitals between February 2016 and February 2022. The study included patients who had clinical isolates available and had definite or possible S aureus IE that involved native or prosthetic valves. Data were analyzed from July 2023 to June 2024. MSSA isolates were tested for the presence of blaZ and for inoculum effects to cefazolin and oxacillin. The association between first-month mortality and the β-lactam used, the presence of blaZ, and the presence of an inoculum effect to the treatment received was evaluated. This study included 216 patients with MSSA IE (median [IQR] age, 65 [49-73] years; 152 [70.4%] male) who were treated with antistaphylococcal penicillin (139 [64.4%]) or cefazolin (77 [35.6%]). One-month mortality of left-sided IE was 44 of 180 patients (24.4%), with no overall difference between patients treated with antistaphylococcal penicillin or cefazolin. However, 1-month mortality was higher in patients infected with blaZ-positive strains than with blaZ-negative strains (38 of 129 [29.5%] vs 6 of 51 [11.8%]; P = .01), and with strains with an inoculum effect to the β-lactam received than with strains without an inoculum effect (25 of 62 [40.3%] vs 13 of 67 [19.4%]; P = .005). On multivariable analysis, the presence of an inoculum effect was independently associated with first-month mortality (HR, 2.84; 95% CI, 1.28-6.30; P = .01). In this case series of MSSA IE, the presence of an inoculum effect to the β-lactam received was a risk factor for death in the first month. Phenotyping MSSA isolates for inoculum effect may guide β-lactam choice and improve outcomes.

Whole genome sequencing-based characterization and determination of quinolone resistance among methicillin-resistant and methicillin-susceptible S. Aureus isolates from patients attending regional referral hospitals in Tanzania

BackgroundThe emergence of multidrug-resistant termed Methicillin-resistant Staphylococcus aureus (MRSA) strain, driven by the acquisition of resistance gene mecA imposes a substantial challenge in the treatment and control of their related infections. Although quinolones have historically been effective against both MRSA and methicillin-susceptible S. aureus (MSSA) strains, the rising resistance to quinolones among S. aureus isolates, particularly in MRSA, has severely curtailed their potency and further narrowed down the therapeutic options. This study aimed to determine the burden of MRSA among isolates, as well as their resistance profile, genotypic characterization, and molecular relatedness through the construction of a phylogenetic tree.Materials and methodsArchived clinical S. aureus isolates from a descriptive, cross-sectional study involving six regional referral hospitals in Dodoma, Songea, Kigoma, Kitete, and Morogoro in the mainland Tanzania and Mnazi Mmoja in Zanzibar were analyzed. Bacterial identification was performed using both classical microbiology and whole genome sequencing on Illumina Nextseq 550 Sequencer. Species identification was done using KmerFinder 3.2, Multilocus Sequence Typing using MLST 2.0, SCCmec typing using SCCmecFinder 1.2, resistance genes using ResFinder 4.1, and phylogenetic relatedness using CSI Phylogeny 1.4.ResultsOut of the 140 isolates analyzed, 69 (49.3%) were identified as MRSA, with 57 (82.6%) exhibiting quinolone resistance. Conversely, 71 isolates were identified as MSSA, and none of them exhibited resistance to quinolones. Spa-typing revealed six spa types, with t355, t1476, and t498 being the most common. Moreover, all (69) MRSA were found to carry SCCmec type IV. The isolates exhibited 14 different sequence types (STs). Notably, ST152 was prevalent among MSSA (50 isolates, 70%), while ST8 was the predominant sequence type among MRSA (58 isolates, 84%). The antimicrobial resistance profile revealed at least three horizontally acquired resistance genes, with blaZ, dfrG, tet(K), and aac (6’)-aph (2’’) genes being highly prevalent.ConclusionThere is a high genetic diversity among the S. aureus isolates existing in Tanzania regional hospitals, with a concerning burden of quinolone resistance among MRSA isolates. The diversity in resistance genes among MRSA lineages emphasizes the necessity for the development of sustainable antimicrobial stewardship and surveillance to support evidence-based guidelines for managing and controlling MRSA infections in both community and hospital settings.

Whole genome sequencing revealed high proportions of ST152 MRSA among clinical Staphylococcus aureus isolates from ten hospitals in Ghana.

Previous studies in Ghana indicated low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and predominance of ST152 methicillin-susceptible S. aureus (MSSA) among clinical isolates. ST152 MRSA clones are associated with severe infections and epidemics. Using whole genome sequencing (WGS), 159 S. aureus isolated from clinical sources (wound, blood, urine, ear, abscess, umbilical cord, eye, vaginal samples, and others) from 10 hospitals across Ghana were investigated. mecA (gene for methicillin resistance) was detected in 38% of the isolates. Panton-Valentine leucocidin toxin (PVL) gene occurred in 65% isolates, with 84% of the MRSA's harboring the PVL gene. ST152 was the major clone, with 74% harboring the mecA gene. Other MRSA clones detected were ST5, ST5204, ST852, and ST1. MSSA clones included ST3249, ST152, ST5, ST1, and ST8. Twenty-three genes encoding resistance to 12 antimicrobial classes were observed with blaZ (97%) being the most prevalent. Other predominant resistance genes included tetK (46%), cat (42%), and dfrG (36%) encoding resistance for tetracyclines, phenicols, and diaminopyrimidine, respectively. Virulence genes for enterotoxins, biofilms, toxic-shock-syndrome toxins, hemolysins, and leukotoxins were also detected. Phylogenetic analysis revealed a shift in the dominant clone from MSSA ST152 to MRSA ST152 over the past decade. The study provides valuable insights into the genomic content of S. aureus from clinical sources in Ghana. The finding of ST152 MRSA in high numbers suggests a shifting epidemiological landscape of these pathogens and continuous surveillance using robust tools like WGS is needed to monitor the rise and spread of these epidemic clones in the country.IMPORTANCESince its emergence in 1959, MRSA has been a significant public health concern, causing infections in both clinical and community settings. Patients with MRSA-related infections experience higher mortality rates due to its ability to evade antimicrobials and immune defenses. In Ghana, understanding the molecular epidemiology of MRSA has been hindered by the lack of appropriate laboratory infrastructure and the limited capacity for molecular data analysis. This study, the largest genomic study of S. aureus in Ghana, addresses this gap by utilizing whole genome sequencing to examine the diversity of circulating S. aureus strains from 10 hospitals. Our findings highlight the predominance of pandemic clones, particularly ST152, and the notable transition of ST152 MSSA to ST152 MRSA over the past decade. The findings from this study supports AMR surveillance efforts in Ghana and emphasize the importance of implementing genomic surveillance using WGS to comprehensively monitor the rise and spread of multi-drug-resitant organisms such as MRSA in the country.

Molecular epidemiology and clinical characteristics of Staphylococcus aureus bacteremia in Japanese adults

IntroductionStaphylococcus aureus bacteremia (SAB), especially when caused by methicillin-resistant S. aureus (MRSA), is of considerable clinical importance. In recent years, the proportion of MRSA among S. aureus has decreased, and a relative increase in the proportion of methicillin-susceptible S. aureus (MSSA) has been observed. It is therefore necessary to consider both MRSA and MSSA when assessing the microbiological and clinical significance of SAB. Materials and methodsWe included SAB cases from the Nara Medical University Hospital between January 2015 and February 2017. We performed drug susceptibility testing, toxicity gene analysis, multilocus sequence typing (MLST), and polymerase chain reaction-based open reading frame typing (POT) of stored strains to integrate clinical and bacteriological characteristics. ResultsThere were 90 cases during the experimental period (42 MRSA and 48 MSSA), with 30-day mortality rates of 19 % for MRSA and 10.4 % for MSSA. Deaths were more frequently complicated by septic shock and disseminated intravascular coagulation. MLST studies showed that ST8, ST764, ST1, and ST15 were prevalent in the MRSA group, whereas ST5, ST188, and ST12 were prevalent in MSSA. Infective endocarditis cases had a long time from onset to the initiation of effective antimicrobials and were all MSSA. MLST and POT results correlated well, and POT appeared to have better discriminatory power. ConclusionsThe severity and mortality of SAB, along with the microbiological characteristics of causative isolates, vary by location and time. Continued studies integrating clinical and microbiological investigations are thus needed.

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.

A silver lining in MRSA treatment: The synergistic action of poloxamer-stabilized silver nanoparticles and methicillin against antimicrobial resistance

BackgroundIncreasing antibiotic resistance in bacterial infections, including drug-resistant strains like methicillin-resistant Staphylococcus aureus (MRSA), necessitates innovative therapeutic solutions. Silver nanoparticles are promising for combating infections, but toxicity concerns emphasize the importance of factors like dosage, size, shape, and surface chemistry. Hence, exploring poloxamer as a stabilizing agent to reduce its toxicity and enhance the antibacterial effect on MRSA is investigated. MethodsSilver nanoparticles stabilized with poloxamer (AgNPs@Pol) were synthesized through the chemical reduction method and characterized using UV–visible spectrophotometer, HR-TEM, DLS, and Zeta potential measurements. Subsequently, the antibacterial activity of AgNPs@Pol alone and in combination with methicillin against MRSA and methicillin-susceptible S. aureus (MSSA) was evaluated using the broth microdilution method. ResultsAgNPs@Pol showed significant efficacy against MRSA and MSSA, achieving a 100 % reduction in colony-forming units (CFU) at 9.7 μg/ml. The minimum inhibitory concentration (MIC) against MRSA and MSSA was 8.6 μg/ml and 4.3 μg/ml, respectively. A synergistic effect was observed when AgNPs@Pol was combined with methicillin. Treatment with AgNPs@Pol increased reactive oxygen species (ROS) production in both strains, contributing to its antibacterial activity. Real-time qPCR analysis indicated the downregulation of genes involved in antimicrobial resistance and cell adhesion in both strains. Further, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay demonstrated low cytotoxicity for AgNPs@Pol against MCF-7, MG-63, and NIH-3T3 cell lines. ConclusionThe developed AgNPs@Pol demonstrated extensive colloidal stability, potent antibacterial activity and synergistic effect with methicillin against MRSA and MSSA. Further studies in primary cells and in vivo models may validate its potential for clinical applications.

Low prevalence of borderline oxacillin resistant Staphylococcus aureus (BORSA) in a tertiary care hospital in South Carolina

Prompt treatment for Staphylococcus aureus bloodstream infections is often dependent on known diagnostic testing modalities to differentiate between methicillin-susceptible S.aureus (MSSA) and methicillin-resistant S.aureus (MRSA). Borderline-oxacillin resistant S. aureus (BORSA), a rare, non-mecA mediated phenotype, has unclear resistance mechanisms but potentially significant consequences as it is frequently misidentified as MSSA but behaves more like MRSA. A retrospective analysis was performed of MSSA bloodstream infections to determine the prevalence of BORSA. Our institution found BORSA prevalence of 0.1%, consistent with literature. Though prevalence is low, due to unclear mechanisms and unreliable detection methods, BORSA may pose a therapeutic and epidemiological threat.

Electrospun Cellulose Acetate/Poly(Vinyl Alcohol) Nanofibers Loaded with Methyl Gallate and Gallic Acid for Anti-Staphylococcus aureus Applications.

Methyl gallate (MG) and gallic acid (GA) are natural compounds with potent activity against methicillin-resistant Staphylococcus aureus (MRSA), a significant global health concern. In this study, MG and GA were incorporated into cellulose acetate (CA) blended with poly(vinyl alcohol) (PVA) to create electrospun nanofibers aimed at combating both methicillin-susceptible S. aureus (MSSA) and MRSA. Key electrospinning parameters-DC voltage, injection flow rate, and syringe tip-collector distance-were optimized, with the best conditions being a 1.5 mL/h flow rate, 30 cm distance, and 20 kV voltage. The resulting nanofiber mats were characterized by SEM, FTIR, DSC, tensile strength testing, contact angle measurement, swelling behavior, and release profiling. Antibacterial properties were assessed using the agar diffusion test. The obtained nanofibers had diameters ranging from 879.33 to 906.13 nm. Among the samples, MG-GA-CA/PVA exhibited the highest tensile strength, good flexibility, and improved stiffness, which was related to enhanced thermal stability and chemical interactions as shown by DSC and FTIR analyses. This formulation also displayed excellent hydrophilicity, swelling properties, and a consistent release profile over 8 to 24 h. Furthermore, MG-GA-CA/PVA showed superior antibacterial activity against both MSSA and MRSA, suggesting its potential as a strong, flexible, and effective anti-S. aureus material.

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 of the Cefazolin Inoculum Effect in Methicillin-Susceptible Staphylococcus aureus Isolates Collected from Kingston Health Sciences Centre.

Background: Staphylococcus aureus is a bacterium that causes serious human infections, including bloodstream infections, pneumonia, deep abscesses, and bone and joint infections. Methicillin-susceptible S. aureus (MSSA) are S. aureus bacteria susceptible to the antibiotic methicillin. Cefazolin is the first-line antibiotic to treat MSSA infections. The cefazolin inoculum effect (CzIE) is a lab phenomenon in which S. aureus is susceptible to cefazolin at a standard bacterial inoculum but develops resistance at a higher cell inoculum. CzIE occurs when the bacteria produce beta-lactamases that degrade cefazolin, preventing the antibiotic from inhibiting cell wall synthesis and allowing bacterial growth. In theory, CzIE may lead to cefazolin treatment failure, but currently, there is insufficient evidence in the literature. Objective: We aimed to determine the prevalence of the CzIE in patients with serious MSSA infections at Kingston Health Sciences Centre (KHSC). Methods: Clinical MSSA isolates from patients with serious infections at KHSC were collected. The MSSA isolates were then tested for CzIE using broth microdilution testing at a standard inoculum (5×10^5 CFU/mL) and a high inoculum (5×10^7 CFU/mL). The CzIE was defined as a ≥ 4-fold increase in minimum inhibitory concentration (MIC) from the standard to the high and with a MIC above the resistant breakpoint of 16 µg/mL. Results: Of the 51 MSSA isolates tested to date, 17 (33%) displayed CzIE, with 13 of the 17 (76%) requiring 64 µg/ml of antibiotic to prevent growth. Conclusion: Our initial testing indicates that the CzIE is common in MSSA infections at KHSC. We will complete testing 100 MSSA isolates for a more precise estimate of CzIE prevalence, which will be followed up with a chart review of the patients to determine if there is a correlation between CzIE and cefazolin treatment failure.