Methicillin-susceptible S. Aureus Research Articles

Investigation of nasal Staphylococcus aureus carriage by real-time PCR in patients receiving hemodialysis treatment

Objectives: Staphylococcus aureus, coagulase-negative staphylococci (CoNS), and methicillin-resistant S. aureus (MRSA), which are significant nosocomial pathogens, have become a growing global problem because their carriage and diseases have become resistant to many antibiotics. This study aimed to investigate and determine the rate of MRSA carriage among patients receiving hemodialysis treatment using molecular methods. Methods: In the 254 hemodialysis patients, the nasal carriage rates, susceptibility and resistance to S. aureus, CoNS and MRSA were examined using culture and real-time PCR methods. Nasal samples from hemodialysis patients were examined using real-time PCR. Microscopic examination was performed using the Gram staining method, and S. aureus was identified using catalase and coagulase. The strains were then tested for antibiotic susceptibility. Staphylococci was isolated from 231 of the 254 patients. Results: S. aureus carriage was detected in 50 patients, MRSA in 16, methicillin-susceptible S. aureus (MSSA) in 33, CoNS in 66, methicillin-resistant CoNS (MR-CoNS) in 38, and methicillin-susceptible CoNS (MS-CoNS) in 28. S. aureus and MRSA strains exhibited 100% susceptibility to nitrofurantoin, and vancomycin. MSSA strains showed the highest susceptibility to chloramphenicol, clindamycin (84.8%), and co-trimoxazole (36.4%). CoNS showed 100% susceptibility to vancomycin, and 16.7% susceptibility to ampicillin. Vancomycin was found to be the most effective antibiotic against S. aureus, CoNS, and MRSA pathogens identified in patients undergoing hemodialysis, whereas penicillin resistance was found. Conclusions: It can be concluded that one of the most effective ways to prevent the formation of antibiotic resistant strains is the hygiene of the hospital and hospital staff. Real-time PCR is very important for analyzing with high sensitivity.

High Prevalence of Panton-valentine Leukocidin-encoding Genes in Methicillin-resistant Staphylococcus aureus Isolated from Inpatients with Invasive Infections at a University Hospital in Southern Brazil.

Staphylococcus aureus is a major cause of a wide diversity of infections in humans, and the expression of Panton-Valentine Leukocidin (PVL) has been associated with severe clinical syndromes. The present study aimed to investigate the prevalence of PVL-encoding genes in S. aureus isolated from clinical samples of inpatients with invasive infections in a teaching hospital in Southern Brazil. Furthermore, phenotypic and genotypic characteristics of bacterial isolates were analyzed. A total of 98 S. aureus isolates recovered from different body sites were characterized according to their antimicrobial susceptibility profile, methicillin-resistance and SCCmec typing, genetic relatedness and occurrence of virulence-encoding genes, such as icaA, lukS-PV/lukF-PV, and tst. Sixty-eight (69.4%) isolates were classified as methicillin-resistant, and among them, four (5.9%) did not harbor the mecA gene. The mecA-harboring methicillin-resistant S. aureus (MRSA) isolates were grouped into SCCmec types I (6.3%), II (64.1%), III (6.3%), IV (15.6%), V (4.7%), and VI (1.6%). One isolate (1.6%) was classified as non-typeable (NT). Seventy isolates (71.4%) were classified as multidrug-resistant. The overall prevalence of virulence-encoding genes was as follows: icaA, 99.0%; tst, 27.5%; and lukS-PV/lukF-PV, 50.0%. The presence of tst gene was significantly higher (p < 0.001) in methicillin-susceptible S. aureus (MSSA) compared to MRSA isolates. The present study reports a high prevalence of multidrug-resistant S. aureus harboring lukS-PV/lukF-PV and tst genes in invasive infections. The continuous monitoring of the antimicrobial susceptibility profile and virulence of S. aureus is an important measure for the control of infections caused by this bacterium.

Phenotypic and Molecular Detection of Biofilm Formation in Methicillin-Resistant Staphylococcus Aureus Isolated from Different Clinical Sources in Erbil City.

Staphylococcus aureus is an important causative pathogen. The production of biofilms is an important factor and makes these bacteria resistant to antimicrobial therapy. the current study aimed to assess the prevalence of resistance to antibacterial agents and to evaluate the phenotypic and genotypic characterization of biofilm formation among S. aureus strains. This study included 50 isolates of Methicillin-resistant S. aureus (MRSA) and Methicillin-Susceptible S. aureus (MSSA). S. aureus was identified by molecular and conventional methods, and antimicrobial resistance was tested with a disc diffusion method. The biofilm formation was performed through the Microtiter plate method. Strains were subjected to PCR to determine the presence of nuc, mecA, icaA, icaB, icaC, and icaD genes. Of the 50 S. aureus isolates, 32(64%) and 18(36%) were MRSA and MSSA, respectively. A large number of MRSA and MSSA isolates showed resistance to Penicillin and Azithromycin, and a lower number of MRSA and MSSA isolates showed resistance to Amikacin Gentamicin. None of the isolates was resistant to Vancomycin. The MRSA strains had significantly higher resistance against antibiotics than MSSA strains (P = 0.0154). All isolates (MRSA and MSSA) were able to produce biofilm with levels ranging from strong (31.25 %), (16.6%) to moderate (53.12%), (50%) to weak (15.6%), (33.3%) respectively. The MRSA strains had a significantly higher biofilm formation ability than the MSSA strains (P = 0.0079). The biofilm-encoding genes were detected among isolates with different frequencies. The majority of S. aureus isolates, 42 (84%), were positive for the icaA. The prevalence rates of the icaB, icaC and icaD genes were found to be 37 (74%), 40 (80%) and 41 (82%), respectively. The prevalence of biofilm encoding genes associated with multidrug resistance in S. aureus strains is high. Therefore, identifying epidemiology, molecular characteristics, and biofilm management of S. aureus infection would be helpful.

Genomic Epidemiology and Phenotypic Characterization of Staphylococcus aureus from a Tertiary Hospital in Tianjin Municipality, Northern China.

Staphylococcus aureus remains a dangerous pathogen and poses a great threat to public health worldwide. The prevalence of the S. aureus clonotype is temporally and geographically variable. The genomic and phenotypic characteristics of S. aureus isolates in Tianjin, which is among the four big municipalities in China, are unclear. In the present study, 201 nonduplicate S. aureus isolates, including 70 methicillin-resistant S. aureus (MRSA) and 131 methicillin-susceptible S. aureus (MSSA), were collected from 2015 to 2021 in a tertiary hospital in Tianjin. Whole-genome sequencing of S. aureus isolates was carried out to investigate bacterial molecular characteristics, genomic phylogeny, antimicrobial resistance (AMR) gene carriage, and virulence factor gene distribution. The antibiotic resistance profiles, hemolytic activities, and biofilm formation abilities of the S. aureus isolates were also determined. In total, 31 distinct sequence types (STs) and 68 spa types were identified. ST59 (15.9%, 32/201) was the predominant clonotype, followed by ST398 (14.9%, 30/201) and several other major STs (ST1, ST5, ST6, ST22, ST25, ST188, and the newly emerging ST5527). ST59 and ST5527 mainly included MRSA isolates, while ST398 and the other major STs mainly included MSSA isolates. The unique characteristics of the S. aureus isolates belonging to the major STs were determined. ST59 isolates exhibited strong hemolytic activity, and ST398 strains had high biofilm formation capacity, while ST5527 isolates presented the greatest AMR. The genomic epidemiology and phenotypic characteristics of S. aureus isolates determined in this study will help in disease control in nosocomial environments. IMPORTANCE Staphylococcus aureus is an important bacterium pathogen in tertiary hospitals, which provide rich medical resources. Tianjin is one of the four municipalities in China with a population of more than 13 million. However, the epidemiology and molecular characteristics of S. aureus isolates in Tianjin are unknown. In this study, the genomic and phenotypic analyses were performed to investigate 201 S. aureus isolates collected from a tertiary hospital in Tianjin over a time span of 6 years. The refined analysis of predominant clones ST59, ST398, the newly emerging clone ST5527, as well as other major clones, will undoubtedly aid in the control and prevention of infections caused by S. aureus in tertiary hospitals.

Increase in methicillin-susceptible Staphylococcus aureus bloodstream infections in Switzerland: a nationwide surveillance study (2008–2021)

PurposeAn increasing burden of Staphylococcus aureus bloodstream infections (BSI), despite a decrease in the percentage of methicillin-resistant S. aureus (MRSA), was described recently in other European countries. The main aim of this study was to analyse recent temporal trends of S. aureus, methicillin-susceptible S. aureus (MSSA) and MRSA BSI for Switzerland as well as the different linguistic regions within Switzerland. An additional aim was to estimate potential differences among patient-based and epidemiological risk factors.MethodsA retrospective observational study was conducted in Switzerland over a period of 14 years (2008–2021). Trends in S. aureus, MSSA and MRSA BSI were analysed by applying linear regression models.ResultsStaphylococcus aureus BSI increased by + 30% from 19.7 to 25.6 cases per 100,000 inhabitants between 2008 and 2021 (P < 0.01) in Switzerland. Thereof, MSSA increased by + 37% from 17.8 to 24.4 cases per 100,000 inhabitants (P < 0.01). MRSA decreased from 1.9 to 1.2 cases per 100,000 inhabitants (P < 0.01), which was driven by decreasing incidence in the French-speaking region. MSSA BSI increased significantly (P < 0.01) in both linguistic regions. A further stratification revealed that incidence increased the most in male patients of the age group ≥ 80 years of the German-speaking region.ConclusionThe increasing health burden of MSSA BSI in Switzerland indicates that not only proportions of resistant microorganisms but also total BSI incidences should be monitored. In addition, data stratification revealed that the increase was mainly driven by an increasing incidence in elderly males of the German-speaking region.

Isolation of pathogenic strains of methicillin-resistant Staphylococcus aureus from mobile phones in a tertiary institution in Ibadan, Nigeria

The health implications of mobile phones emission have been a matter of concern to health practitioners for decades but little or no attention has been given to the mobile phones as potential fomites for pathogens. This study isolated and characterised methicillin-resistant Staphylococcus aureus (MRSA) on mobile phones of students in a tertiary institution in Ibadan, Nigeria. One hundred swab samples were obtained from the surfaces of mobile phones of students in a cross-sectional study conducted between July and August, 2019. Presumptive staphylococci were isolated on mannitol salt agar and identities were confirmed by standard biochemical test and Gram-staining. Antimicrobial susceptibility test was done by disc-diffusion method and mecA or mecALGA251, tsst-1, eta and etb genes screened by PCR technique. Among the 200 presumptive S. aureus isolated, 163 (81.5%) were confirmed as S. aureus exhibiting resistance to ofloxacin (1.8%), gentamicin (3.7%), ceftriaxone (29.4%), ceftazidime (57.7%), cefoxitin (61.3%), cefuroxime (64.4%), erythromycin (85.3%), amoxicillin-clavulanic acid (86.5%) and cloxacillin (92%). Proportion of MRSA and methicillin-susceptible S. aureus (MSSA) were 61.3% and 38.7% respectively with significant difference in their level of antibiotic resistance to the cephalosporins (excluding ceftriaxone), penicillins, erythromycin and ofloxacin (p&lt;0.05). All the MRSA strains were multidrug resistant (MDR) harbouring mecA or mecALGA251 (56.3%), tsst-1 (56.3%), etb (31.3%) and eta (12.5%) genes. This study detected a high proportion of methicillin-resistant, virulent S. aureus as fomites on surfaces of mobile phones among students of a tertiary institution. This is of public health concern and thus requires strong public education to avoid imminent spread and outbreaks.

Serrapeptase impairs biofilm, wall, and phospho-homeostasis of resistant and susceptible Staphylococcus aureus

Staphylococcus aureus biofilms are implicated in hospital infections due to elevated antibiotic and host immune system resistance. Molecular components of cell wall including amyloid proteins, peptidoglycans (PGs), and lipoteichoic acid (LTA) are crucial for biofilm formation and tolerance of methicillin-resistant S. aureus (MRSA). Significance of alkaline phosphatases (ALPs) for biofilm formation has been recorded. Serrapeptase (SPT), a protease of Serratia marcescens, possesses antimicrobial properties similar or superior to those of many antibiotics. In the present study, SPT anti-biofilm activity was demonstrated against S. aureus (ATCC 25923, methicillin-susceptible strain, methicillin-susceptible S. aureus (MSSA)) and MRSA (ST80), with IC50 values of 0.67 μg/mL and 7.70 μg/mL, respectively. SPT affected bacterial viability, causing a maximum inhibition of − 46% and − 27%, respectively. Decreased PGs content at [SPT] ≥ 0.5 μg/mL and ≥ 8 μg/mL was verified for MSSA and MRSA, respectively. In MSSA, LTA levels decreased significantly (up to − 40%) at lower SPT doses but increased at the highest dose of 2 μg/mL, a counter to spectacularly increased cellular and secreted LTA levels in MRSA. SPT also reduced amyloids of both strains. Additionally, intracellular ALP activity decreased in both MSSA and MRSA (up to − 85% and − 89%, respectively), while extracellular activity increased up to + 482% in MSSA and + 267% in MRSA. Altered levels of DING proteins, which are involved in phosphate metabolism, in SPT-treated bacteria, were also demonstrated here, implying impaired phosphorus homeostasis. The differential alterations in the studied molecular aspects underline the differences between MSSA and MRSA and offer new insights in the treatment of resistant bacterial biofilms.Key points• SPT inhibits biofilm formation in methicillin-resistant and methicillin-susceptible S. aureus.• SPT treatment decreases bacterial viability, ALP activity, and cell wall composition.• SPT-treated bacteria present altered levels of phosphate-related DING proteins.Graphical

Molecular Epidemiological Characterization of Staphylococcus aureus and Staphylococcus argenteus Clinical Isolates from a National Tertiary Care Hospital in Myanmar: Co-Isolation of Multiple Clones and Identification of Novel Staphylocoagulase Genotype.

Spread of antimicrobial resistance and virulence factors among Staphylococcus aureus/Staphylococcus argenteus poses a potential public health concern in Myanmar. In this study, a total of 226 clinical isolates of S. aureus (n = 211) and S. argenteus (n = 15) collected in Yangon General Hospital during a two-year period were analyzed for their antimicrobial susceptibility and genetic features. Methicillin-resistant S. aureus (MRSA) accounted for 19% of S. aureus isolates, associated with mostly staphylococcal cassette chromosome mec (SCCmec) type IV, or V. Panton-Valentine leukocidin (PVL) genes were detected in methicillin-susceptible S. aureus (MSSA) at significantly higher rate (39%) than in MRSA (22%). Among MRSA, ST361 (clonal complex [CC] 361), ST772 (CC1), and ST239 (CC8) were frequently identified, while the most common clone in MSSA was ST2990 (CC1), followed by ST121 and CC8 comprising five STs. Novel coagulase gene genotype XVI was identified in four MSSA isolates. All the S. argenteus isolates were assigned to ST2250 and mecA negative, including only one PVL-positive isolate. MSSA and S. argenteus were co-isolated from two patients, while two different MSSA clones were simultaneously identified in eight patients. This study revealed clonal diversity and genetic characteristics of current MRSA/MSSA/S. argenteus clinical isolates in the national tertiary care hospital in Myanmar.

Going Back in Time: Increasing Penicillin Susceptibility among Methicillin-Susceptible Staphylococcus aureus Osteoarticular Infections in Children.

In the late 1940s to 1950s, Staphylococcus aureus isolates first-gained resistance to penicillin. Recently, some centers have described an increase in the proportion of methicillin susceptible S. aureus (MSSA) which are also susceptible to penicillin (PSSA). There are little data on the frequency of PSSA infections in children. We investigated the prevalence of penicillin susceptibility among pediatric MSSA acute hematogenous osteoarticular infection (OAI) isolates. MSSA OAI isolates were obtained through surveillance studies at Texas Children's and St. Louis Children's Hospitals from January 2011 to December 2019. All isolates underwent PCR for blaZ β-lactamase, PVL genes and agr group. All blaZ negative isolates then underwent penicillin MIC determination. blaZ negative isolates with penicillin MIC ≤ 0.125 μg/mL were considered PSSA. Multilocus sequence typing (MLST) was conducted on a subset of isolates. A total of 329 unique isolates were included in the study. The median patient age was 9.2 years (IQR:5.1 to 12.2). Overall, 6.7% of isolates were penicillin susceptible. No PSSA were detected prior to 2015 but increased yearly thereafter. By the final study year, 20.4% of isolates were PSSA (P = 0.001). PSSA were similar to penicillin-resistant MSSA (PR-MSSA) isolates in terms agr group and PVL carriage as well as clinical presentation and outcomes. PSSA were of distinct sequence types compared to PR-MSSA. PSSA appears to be increasing among OAI in U.S. children. Overall, PSSA isolates are associated with a similar clinical presentation as penicillin-resistant isolates. The potential for use of penicillin treatment in PSSA OAI warrants further study.

Impact of specialty on the self-reported practice of using oral antibiotic therapy for definitive treatment of bloodstream infections.

No established guidelines exist regarding the role of oral antibiotic therapy (OAT) to treat bloodstream infections (BSIs), and practices may vary depending on clinician specialty and experience. To assess practice patterns regarding oral antibiotic use for treatment of bacteremia in infectious diseases clinicians (IDCs, including physicians and pharmacists and trainees in these groups) and non-infectious diseases clinicians (NIDCs). Open-access survey. Clinicians caring for hospitalized patients receiving antibiotics. An open-access, web-based survey was distributed to clinicians at a Midwestern academic medical center using e-mail and to clinicians outside the medical center using social media. Respondents answered questions regarding confidence prescribing OAT for BSI in different scenarios. We used χ2 analysis for categorical data evaluated association between responses and demographic groups. Of 282 survey responses, 82.6% of respondents were physicians, 17.4% pharmacists, and IDCs represented 69.2% of all respondents. IDCs were more likely to select routine use of OAT for BSI due to gram-negative anaerobes (84.6% vs 59.8%; P < .0001), Klebsiella spp (84.5% vs 69.0%; P < .009), Proteus spp (83.6% vs 71.3%; P < .027), and other Enterobacterales (79.5% vs 60.9%; P < .004). Our survey results revealed significant differences in selected treatment of Staphylococcus aureus syndromes. Fewer IDCs than NIDCs selected OAT to complete treatment for methicillin-resistant S. aureus (MRSA) BSI due to gluteal abscess (11.9% vs 25.6%; P = .012) and methicillin-susceptible S. aureus (MSSA) BSI due to septic arthritis (13.9% vs 20.9%; P = .219). Practice variation and discordance with evidence for the use of OAT for BSIs exists among IDCs versus NIDCs, highlighting opportunities for education in both clinician groups.

Antibiotic resistance and molecular typing of clinical Staphylococcus aureus isolates from Malaysian military hospital

Objective: To determine the antibiotic resistance profile (ARP) of Staphylococcus (S.) aureus isolates and molecular typing of the methicillin-resistant S. aureus (MRSA) isolates from Tuanku Mizan Armed Forces Hospital (TMAFH), Kuala Lumpur. Methods: The ARP and presence of the pvl gene were determined for 209 S. aureus isolates from clinical specimens. Of these, 123 were methicillin-susceptible S. aureus (MSSA) isolates and 86 were MRSA isolates. All MRSA isolates were characterized using SCCmec typing and spa typing. Descriptive analysis was performed to compare the demographic data with the phenotypic and genotypic variables of the S. aureus isolates. Results: No vancomycin-intermediate and -resistant S. aureus (VISA and VRSA, respectively) were detected among the study isolates. The MSSA isolates showed low resistance rates to all tested antibiotics, were commonly invasive (28/42, 66.7%), and mostly harboured pvl (35/42, 83.3%). Meanwhile, MRSA isolates showed high resistance to penicillin (86/86, 100%), ampicillin (86/86, 100%), sulbactam/ampicillin (86/86, 100%), cefuroxime (81/86, 94.19%), cefoperazone (76/86, 88.37%), azithromycin (56/86, 65.12%), and erythromycin (54/86, 62.79%). The majority of MRSA isolates were of SCCmec type IVh (65/86, 75.58%), spa type t032 (55/85, 63.95%), and grouped into spaCC-t022 (66/85, 77.65%). The t032 type was found to be associated with resistance traits to azithromycin and erythromycin (P<0.05). We also found several spa types that are typically associated with hospital-, community-, and livestock-associated MRSA co-existing in our MRSA population. Conclusions: This study reflected the consistent absence of VISA and VRSA and corroborated the clonal shifting of MRSA isolates in the Malaysian MRSA isolates.

Epidemiology and Antibiogram of Clinical Staphylococcus aureus Isolates from Tertiary Care Hospitals in Dhaka, Bangladesh

Background: This study aimed to investigate the epidemiology and antibiogram of clinical Staphylococcus aureus isolates from three tertiary care hospitals in Dhaka , Bangladesh. Methods: A total of 185 clinical S. aureus isolates were studied from March 2016 to February 2017 and identified by standard microbiological methods and an antibiogram was determined by disc diffusion method. A duplex polymerase chain reaction (PCR) assay was performed on all isolates to detect femA and mecA genes of S. aureus. Results: Among the 185 isolates, all (100%) were positive for the femA gene, 76 (41.1%) were methicillinresistant S. aureus (MRSA), and 109 (58.9%) were methicillin-susceptible S. aureus (MSSA). The highest and the lowest frequency of both MRSA were isolated from pus and urine specimens, respectively. All 185 S. aureus were 100% sensitive to both vancomycin and linezolid and were highly sensitive towards rifampicin (94%), meropenem (87%), gentamicin (85.4%), and cotrimoxazole (82.2%), whereas the highest resistance was against penicillin G (94.6%) followed by amoxicillin/clavulanic acid (82.7%), azithromycin (72.4%), amoxicillin (66.5%), and ciprofloxacin (63.2%). After vancomycin and linezolid, MRSA showed good susceptibility to rifampicin, cotrimoxazole, and gentamicin, while MSSA exhibited high sensitivity toward rifampicin, gentamicin, cefoxitin, meropenem, cloxacillin, ceftriaxone, and cotrimoxazole. Furthermore, MRSA was significantly more resistant to antibiotics than MSSA (P value&lt;0.05), and the majority of S. aureus (81.1%), MRSA (97.4%), and MSSA (69.7%) were multidrug-resistant (MDR). Conclusion: Our findings can guide physicians to provide effective antibiotic therapy, implement monitoring and control strategies to reduce antimicrobial resistance, and prevent the dissemination of MRSA and MDR in the environment.

Genetic characterization of Staphylococcus aureus isolated from Norway rats in Boston, Massachusetts.

Despite the importance of domesticated animals in the generation and transmission of antibiotic-resistant Staphylococcus aureus, the role of wild animals, specifically rodents, in the ecology of S. aureus remains unclear. We recovered and genotyped S. aureus isolates from wild Norway rats (Rattus norvegicus) in Boston, Massachusetts to examine genetic relationships between common human and animal S. aureus isolates in a large US metropolitan area. We collected and necropsied 63 rats from June 2016 to June 2017. Nasal, foot pad, fur, and fecal swabs were collected. Staphylococcus aureus was isolated using culture-based methods and polymerase chain reaction confirmation. S. aureus isolates were spa typed, tested for antibiotic susceptibility, and whole genome sequenced. Assembled sequences were uploaded to the Comprehensive Antibiotic Resistance Database to identify antibiotic resistance elements. A phylogenetic tree was constructed using the neighbor-joining method with the maximum composite likelihood distance in MEGA7. We recovered 164 Gram-positive bacterial isolates from Norway rats. Nineteen isolates from eight individual rats were confirmed as S. aureus (prevalence: 12.9% (8/63)). All S. aureus isolates were methicillin-susceptible S. aureus (MSSA), pvl-negative, and resistant to penicillin. Two isolates displayed resistance to erythromycin. Four different S. aureus spa types were detected (t933, t10751, t18202, and t189). Thirteen unique antibiotic resistance elements were identified, and all isolates shared genes mepR, mgrA, arlR, and S. aureus norA. Phylogenetic analysis if the 19 S. aureus isolates revealed they were genetically similar to four clades of S. aureus with similar resistance gene profiles isolated from both human- and animal-derived S. aureus, as well as formed a distinct phylogenetic cluster composed only of rat isolates. Wild rodents may serve as a reservoir or vector of antibiotic resistance genes in the urban environment with relevance for human and animal health.

In Vivo Pathogenicity of Methicillin-Susceptible Staphylococcus aureus Strains Carrying Panton-Valentine Leukocidin Gene.

Toxin-producing Staphylococcus aureus strains posing a potential risk for public health have long been a topic of scientific research. Effects of Panton-Valentine leukocidin (PVL) on tissue destruction mechanisms and activities of inflammatory cells were presented in animal models of pneumonia and skin infections induced by PVL-producing S. aureus strains. This study aimed to demonstrate the in vivo pathogenicity of PVL-producing S. aureus strains isolated from some foodstuffs, which can be a potential risk to public health. PVL-positive methicillin-susceptible S. aureus (MSSA) strains M1 and YF1B-b isolated from different foodstuffs and a PVL-positive MSSA strain HT480 (positive control) were administered to New Zealand rabbits. Blood samples were harvested three and six hours after the intratracheal inoculation. Lung tissue samples were collected for gross and microscopic exams and immunohistochemical (IHC) demonstration of IL-6, IL8, IL-10, and TNF-α expressions. Serum cytokine levels were also measured by ELISA. The strains isolated from lung tissue samples were confirmed by pulsed-field gel electrophoresis. The development of acute necrotising pneumonia and a significant elevation in IL-6, IL-8, IL-10, and TNF-α expressions demonstrated the significance of foodborne PVL-positive MSSA strains in public health for the first time.

1324. Penicillin-Susceptibility among Staphylococcus aureus Skin-and-Soft-Tissue Infections at a Children’s Hospital

Abstract Background Shortly after its introduction into clinical practice, Staphylococcus aureus isolates gained resistance to penicillin via the acquisition of β-lactamases. By the 1960s, these strains became the dominant staphylococci in clinical practice. However, a number of centers have recently described an increase in the proportion of methicillin susceptible S. aureus (MSSA) which are also susceptible to penicillin (PSSA). In our center we have recently observed the emergence of PSSA in osteoarticular infections. Little data are available regarding the prevalence or impact of PSSA in pediatric skin-and-soft-tissue infections (SSTI). Methods MSSA SSTI isolates were obtained through an ongoing surveillance study at Texas Children’s (TCH) from 1/2017-12/2021. Twenty community-acquired MSSA SSTI isolates were chosen at random from every six-month interval during the study period, for a total of 200 isolates to be screened. All isolates underwent PCR for blaZ β-lactamase, PVL genes and agr group. All blaZ negative isolates then underwent penicillin susceptibility testing using macrobroth dilution. Isolates which were blaZ negative and had a penicillin MIC ≤ 0.125 μg/ml were regarded as PSSA with the remainder regarded as penicillin-resistant MSSA (PR-MSSA). Results During the study period 1701 MSSA SSTI isolates were collected with 200 examined for penicillin susceptibility. The overall median age of subjects was 4.1 years (IQR: 1.6-10.4). PSSA accounted for 9% of isolates during the study period; the annual frequency of PSSA varied from 5-17.5%. PSSA and PR-MSSA cases were similar with respect to age, demographics, anatomic site of infection and rates of prior antibiotic exposure. Subjects with SSTI secondary to PSSA more often had a prior history of SSTI, a diagnosis of abscess and were more often admitted to the hospital (Figure). Among PSSA, 94.4% belonged to agrI and 33.3% were PVL positive. Penicillin-Susceptible S. aureus (PSSA) vs. Penicillin-Resistant Methicillin-Susceptible S. aureus (PR-MSSA) Pediatric SSTI Isolates Comparison of the clinical features of PSSA and PR-MSSA SSTI isolates. PSSA were significantly associated with the diagnosis of abscess as well as hospital admission. Conclusion PSSA account for a small but significant proportion of MSSA SSTI in children. Clinically distinguishing patients with PSSA and PR-MSSA is challenging. However, PSSA SSTI were associated with a greater rate of abscess formation and hospital admission, suggesting a high clinical impact of these infections. Further studies are needed to understand the optimal management of these infections. Disclosures Jonathon C. McNeil, MD, Agency for Healthcare Research and Quality: Grant/Research Support|Allergan: Provided reagents for unrelated research|Nabriva: Site investigator for multicenter clinical trial Kristina G. Hulten, PhD, Me-med: Grant/Research Support|Pfizer: Grant/Research Support Sheldon L. Kaplan, MD, MeMed: Grant/Research Support|Pfizer: Grant/Research Support.

425: RISK FACTORS FOR PERSISTENT S AUREUS BACTEREMIA IN PEDIATRIC PATIENTS: A SINGLE-CENTER COHORT STUDY

Introduction: Staphylococcus aureus is a leading cause of infection-related hospitalization in children and accounts for approximately 23% of pediatric bacteremia. Persistent S. aureus bacteremia (SAB) is associated with worse outcomes, but there is limited understanding of the risk factors for sustained infection in children. Our objective was to identify risk factors associated with persistent SAB in our pediatric population. Methods: This was a single-center study using an established biorepository of children with S. aureus infection. Patients with at least one S. aureus positive blood culture were included. Persistent SAB was defined as positive blood cultures on 2 or more consecutive hospital days and at least 24 hours apart. Characteristics of patients with and without persistent SAB were compared using Fisher’s exact test, Wilcoxon rank sum test, and Wilcoxon rank sum exact test. Results: Of 65 patients included in the study, 38 (58%) had persistent SAB. The median age was 8.7 years, 65% were male (n=42) and 85% were white (n=54). 95% (n=62) had community-onset bacteremia, 64% (n=42) had infection caused by a methicillin-susceptible S. aureus (MSSA) isolate, and 57% (n=57) had another site of infection (e.g., abscess or bone/joint). Only 14% (n=9) of patients required ICU care. Of those, 67% (n=6) were caused by an MRSA isolate. Patients with persistent SAB had shorter duration to culture positivity than those without persistent SAB: 16 hours (IQR, 4-20h) vs. 20 hours (IQR, 16-25h) (p=0.017); and longer time to source control: 43 hours (IQR, 21-66h) vs. 17 hours (IQR,13-22h) (p=0.011). Conclusions: Our findings reveal that persistent SAB is associated with shorter time to culture positivity and longer time to source control, suggesting that a higher and sustained bacterial burden contributes to persistent infection. Interestingly, we found higher rates of persistent SAB (58%) and SAB due to MSSA (64%) than previously reported. This may be due to a combination of factors including an inconsistent definition of persistent bacteremia across studies, regional variability in S. aureus virulence, differences in the racial and ethnic diversity, and potential sampling bias. Further analysis of laboratory values, antibiotic use, chronic and co-occurring conditions of our cohort are warranted and pending.

568. Using Machine Learning to Predict Place-Based Risks for Staphylococcus aureus Infections in Children

Abstract Background Community-onset Staphylococcus aureus (CO-S. aureus) pediatric infections, methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) continue to contribute to the burden of infections seen in the ambulatory setting in the US. Individual risk factors have been identified, but place-based factors and specific geographic locality have not been well-studied. The purpose of this study is to predict place-based factors that contribute to the spread of CO-S. aureus in a major urban area using maximum entropy (MaxEnt), a machine learning technique. Methods Electronic medical records from two pediatric hospitals (2002 to 2016) were retrospectively reviewed. Inclusion criteria: a confirmed S. aureus infection within 48 hours of hospital admission (CO-S. aureus), &amp;lt; 19 years old, and a geo-referenced address within Atlanta’s metropolitan statistical area (MSA). Fourteen place-based factors, at the US Census block group level, were included in the MaxEnt models: &amp;lt; 18 years old, Caucasian, African American, ethnicity, poverty, education attainment, crowding, daycare, kindergarten enrollment, distance to K-12 school, distance to a children’s hospital, distance to a daycare center, and population density. A total of four models (CO-MRSA early, CO-MSSA early, CO-MRSA later, and CO-MSSA later) were run using the MaxEnt software. For each model, 75% and 25% of data was randomly assigned to training and testing groups, respectively. Models were assessed by jack-knife tests. Results 16,124 records met eligibility criteria for MaxEnt models. The training Area Under the Curve (AUC) ranged from 0.771 to 0.837 and the test AUC ranged from 0.769 to 0.804. Population density had the highest contribution in predicting CO-MRSA and CO-MSSA locations, which was confirmed by jack-knife tests. Conclusion By applying MaxEnt to pediatric CO-S. aureus infections in the Atlanta MSA, it was found that higher risks of CO-S. aureus infections may exist in more densely populated areas. MaxEnt can be utilized to identify potential future areas of CO-MRSA and CO-MSSA infections based on estimated or predicted changes to the place-based factors used to build these models. Disclosures Lilly Immergluck, MD, MS, GSK: Clinical Trial- PI|Merck: Vaccine Trial Site- serve as PI|Moderna: Board Member|Novavax: Part of CoVID-19 Phase 3 Trial through US Covid Prevention Network.

Characteristics of Staphylococcus aureus Isolated from Patients in Busia County Referral Hospital, Kenya.

Staphylococcus aureus is an important pathogen associated with hospital, community, and livestock-acquired infections, with the ability to develop resistance to antibiotics. Nasal carriage by hospital inpatients is a risk for opportunistic infections. Antibiotic susceptibility patterns, virulence genes and genetic population structure of S. aureus nasal isolates, from inpatients at Busia County Referral Hospital (BCRH) were analyzed. A total of 263 inpatients were randomly sampled, from May to July 2015. The majority of inpatients (85.9%) were treated empirically with antimicrobials, including ceftriaxone (65.8%) and metronidazole (49.8%). Thirty S. aureus isolates were cultured from 29 inpatients with a prevalence of 11% (10.3% methicillin-susceptible S. aureus (MSSA), 0.8% methicillin resistant S. aureus (MRSA)). Phenotypic and genotypic resistance was highest to penicillin-G (96.8%), trimethoprim (73.3%), and tetracycline (13.3%) with 20% of isolates classified as multidrug resistant. Virulence genes, Panton-Valentine leukocidin (pvl), toxic shock syndrome toxin-1 (tsst-1), and sasX gene were detected in 16.7%, 23.3% and 3.3% of isolates. Phylogenetic analysis showed 4 predominant clonal complexes CC152, CC8, CC80, and CC508. This study has identified that inpatients of BCRH were carriers of S. aureus harbouring virulence genes and resistance to a range of antibiotics. This may indicate a public health risk to other patients and the community.

Distribution of chlorhexidine resistance genes among Staphylococcus aureus clinical isolates: the challenge of antiseptic resistance.

Chlorhexidine is an antiseptic agent which is extensively used to prevent nosocomial infections; however, this could result in reduction of its susceptibility. The aim of this work was to determine chlorhexidine susceptibility among Staphylococcus aureus isolates and to detect qacA/B and smr antiseptic resistance genes among these isolates. Furthermore, we aimed to identify possible risk factors for the reduction of chlorhexidine susceptibility among S. aureus isolates. Various clinical samples were collected from patients with evidence of S. aureus infection. Antimicrobial susceptibilities of identified S. aureus isolates were determined by disk diffusion method. Resistance to methicillin was identified by cefoxitin disk diffusion test besides mecA gene detection by PCR. Chlorhexidine minimum inhibitory concentration (MIC) values were measured by broth microdilution method while qacA/B and smr resistance genes were detected by multiplex PCR. A total percentage of 25.9% of S. aureus isolates showed reduced susceptibility to chlorhexidine. Methicillin resistant S. aureus (MRSA) had a reported percentage of 39.5%, which was significantly higher than the 11.3% reported for methicillin susceptible S. aureus (MSSA), p<0.001. S. aureus isolates were found to harbor qacA/B and smr genes at 23.2% and 7.7% respectively. Risk factors for reduced susceptibility to chlorhexidine included; ICU setting (OR=2.02, 95%CI: 0.3-1.6), prolonged ICU stay (OR=1.7, 95%CI: 0.4-1.1), presence of central vascular catheter (OR=2.3, 95%CI: 0.2-1.9), mechanical ventilation (OR=1.88, 95%CI: 0.4-1.7) and acquisition of qacA/B (OR=15.7, 95%CI: 3.4-12.1) or smr gene (OR=15.7, 95%CI: 3.4-12.1). Our work highlighted the current challenge of antiseptic resistance in our locality. The frequencies of qacA/B and smr genes were significantly higher among MRSA than MSSA isolates. About two thirds of chlorhexidine tolerant isolates displayed an MDR profile. To maintain chlorhexidine efficiency, biocidal stewardship program and ongoing surveillance are essential.

The association between antibiotics and community-associated Staphylococcus aureus colonization in the United States population: Analysis of the National Health and Nutrition Examination Survey (NHANES).

Staphylococcus aureus nasal colonization is a seriously opportunistic infection. However, there is a lack of research of relationship between antibiotics and S aureus colonization in the general population. Through a cross-sectional investigation, this study intends to establish the parameters related to S aureus nasal colonization, specifically the function antibiotics play in colonization. The key information from 2001 to 2004 was abstracted from National Health and Nutrition Examination Survey (NHANES), including information on general demographics, health care status, antibiotic prescription, diabetes, alcohol consumption, and tobacco smoke exposure. The participants colonized with methicillin-susceptible S aureus (MSSA), or methicillin-resistant S aureus (MRSA) were defined as the case group, and the control group was subjects without positive S aureus colonization. Univariate and multivariate logistic regression models were used to identify the variables associated with MSSA and MRSA colonization. The records of 18,607 individuals were included, involving 13,205 cases without S aureus colonization, 5195 cases with MSSA, and 207 cases with MRSA. In the multivariate logistic regression analysis, the risk of MSSA colonization was significantly reduced with fluoroquinolone use (75% risk reduction, P = .02), sulfonamide use (98% risk reduction, P < .01), tetracycline use (81% risk reduction, P < .01) and antibiotic combination therapy (risk reduction 76%, P < .01). Female, race and total household size were strongly associated with MSSA carriage. On the other hand, regarding MRSA colonization, fluoroquinolone use, long-term care, and former smoker were positively associated with MRSA colonization, while high income was negatively associated with MRSA colonization. More proper use of broad-spectrum antibiotics contributes to reducing MSSA colonization. Former smokers should also practice better personal hygiene to limit the possibility of MRSA colonization.