Methicillin-sensitive Staphylococcus Aureus Isolates Research Articles

Clonal Flux and Spread of Staphylococcus aureus Isolated from Meat and Its Genetic Relatedness to Staphylococcus aureus Isolated from Patients in Saudi Arabia.

In this study, we investigated both meat-derived and methicillin-resistant Staphylococcus aureus (MRSA), exploring their genetic relatedness to patient-derived MRSA isolates in Saudi Arabia. We collected 250 meat samples and identified 53 S. aureus isolates, with 79% being methicillin-sensitive Staphylococcus aureus (MSSA) and 21% being MRSA. Moreover, we included 80 clinically confirmed patient-derived MRSA isolates. We identified the most common S. aureus clone in both patients and retail meat. In meat, ST6 and ST97 were the most common clones in 55% of the MRSA isolates, and ST1153 and ST672 were the most common in 21% and 17% of the MSSA isolates. In patients, ST5 and ST6 were the predominant clones in 46% of the S. aureus isolates. CC5/ST5-SCCmecVc-t311 and CC361/ST672-SCCmecV-t3841 were common MRSA clones in both meat and patients. CC97 and CC361 clones were the second most prevalent S. aureus clones in meat and were relatively common in patients. Furthermore, we sequenced and characterized novel S. aureus strains ST8109, ST8110, and ST8111. The genomic similarities between meat- and patient-derived S. aureus isolates suggest that retail meat might be a reservoir for S.aureus and MRSA transmission. Therefore, a structured One Health approach is recommended for S. aureus dissemination, genetic characterization, antibiotic resistance, and impact on human health.

Using Protein Fingerprinting for Identifying and Discriminating Methicillin Resistant Staphylococcus aureus Isolates from Inpatient and Outpatient Clinics.

In hospitals and other clinical settings, Methicillin-resistant Staphylococcus aureus (MRSA) is a particularly dangerous pathogen that can cause serious or even fatal infections. Thus, the detection and differentiation of MRSA has become an urgent matter in order to provide appropriate treatment and timely intervention in infection control. To ensure this, laboratories must have access to the most up-to-date testing methods and technology available. This study was conducted to determine whether protein fingerprinting technology could be used to identify and distinguish MRSA recovered from both inpatients and outpatients. A total of 326 S. aureus isolates were obtained from 2800 in- and outpatient samples collected from King Faisal Specialist Hospital and Research Centre in Riyadh, Saudi Arabia, from October 2018 to March 2021. For the phenotypic identification of 326 probable S. aureus cultures, microscopic analysis, Gram staining, a tube coagulase test, a Staph ID 32 API system, and a Vitek 2 Compact system were used. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), referred to as protein fingerprinting, was performed on each bacterial isolate to determine its proteomic composition. As part of the analysis, Principal Component Analysis (PCA) and a single-peak analysis of MALDI-TOF MS software were also used to distinguish between Methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA. According to the results, S. aureus isolates constituted 326 out of 2800 (11.64%) based on the culture technique. The Staph ID 32 API system and Vitek 2 Compact System were able to correctly identify 262 (80.7%) and 281 (86.2%) S. aureus strains, respectively. Based on the Oxacillin Disc Diffusion Method, 197 (62.23%) of 326 isolates of S. aureus exhibited a cefoxitin inhibition zone of less than 21 mm and an oxacillin inhibition zone of less than 10 mm, and were classified as MRSA under Clinical Laboratory Standards Institute guidelines. MALDI-TOF MS was able to correctly identify 100% of all S. aureus isolates with a score value equal to or greater than 2.00. In addition, a close relationship was found between S. aureus isolates and higher peak intensities in the mass ranges of 3990 Da, 4120 Da, and 5850 Da, which were found in MRSA isolates but absent in MSSA isolates. Therefore, protein fingerprinting has the potential to be used in clinical settings to rapidly detect and differentiate MRSA isolates, allowing for more targeted treatments and improved patient outcomes.

Antimicrobial effect of areca nut ethanol extract against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA)

Background: Developing herbal medicines for antibacterial activity has been challenging in Indonesia. Of the alternative antimicrobials, areca nut (Areca catechu L) has antimicrobial activity since it contains flavonoids, tannins, phenols, alkaloids, saponins, terpenoids, and glycosides. The use of antibiotics in underdeveloped and developing countries is still irrational, and bacterial infection in Indonesia is still a problem to resolve, so searching for new herbal medicines is very important. Staphylococcus aureus is the most common normal flora that causes infection. The two types of Staphylococcus aureus are Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive Staphylococcus aureus (MSSA). The study aimed to determine the efficacy of the antibacterial activity of areca nut ethanol extract against MRSA and MSSA isolates.
 Methods: The research was conducted at the Biomedical Laboratory, Faculty of Medicine and Health Sciences, University of Jambi. Young and old areca nut ethanol extracts were macerated using 96% ethanol. The antibacterial activity test of the ethanol extract was carried out using the Kirby-Bauer disc diffusion method against the isolates of MRSA (clinical isolates) and MSSA (SA 25923/K+, SA 29213/K-).
 Results: The results showed that the phytochemicals of young areca nut extracts contained alkaloids, flavonoids, phenols, and steroids, and old areca nut extracts contained alkaloids, flavonoids, and phenols. The MRSA isolates did not show the activity of the two areca nut ethanol extracts and were also resistant to Ceftadizime, Gentamicin, Ceftriaxone, and Cefoxitin. The MSSA isolates showed strong activity against old areca nut ethanol extract, moderate activity against young areca nut ethanol extract, and resistance to gentamicin. 
 Conclusion: MRSA bacteria are resistant to the ethanol extract of young and old areca nuts, while the ethanol extract of old areca nuts has strong antibacterial activity against MSSA. 
 Keywords: antibacterial, areca seed ethanol extract, MRSA, MSSA

The Emergence of Mupirocin Resistance among Staphylococcus aureus in a Tertiary Care Hospital in South India: The Necessity for Routine Susceptibility Testing

Methicillin-resistant Staphylococcus aureus (MRSA) is difficult to treat, causing considerable morbidity and mortality. Nasal carriage of MRSA can occur both in healthcare workers and patients. Mupirocin is used as a topical agent for the eradication of such isolates. The present study aims to study the prevalence of mupirocin resistance among the MRSA and MSSA (Methicillin-sensitive Staphylococcus aureus) isolates. A total of 148 Staphylococcus aureus isolates were tested. Antibiotic susceptibility testing was done by Kirby Bauer disc diffusion method for amoxicillin, penicillin, cotrimoxazole, clindamycin, mupirocin(5 µg and 200 µg discs for low and high-level resistance), erythromycin, gentamicin and linezolid. MRSA isolates were detected by cefoxitin disc diffusion and Mec A detection by PCR (Polymerase Chain Reaction). MRSA was detected among 44 (29.7%) of the isolates. Among MSSA, good susceptibility was observed for cotrimoxazole 89 (85.5%) and clindamycin 92 (88.4%). An overall mupirocin resistance of 12(8.1%) was observed, with high-level resistance at 4 (2.7%) and low-level resistance at 8 (5.4%).The mupirocin resistance pattern between MRSA and MSSA was not statistically significant (p=0.1833). The emergence of mupirocin resistance highlights the necessity for creating cognizance among clinicians before prescribing mupirocin. In eradicating nasal carriage of MRSA, all the isolates should always be tested for mupirocin susceptibility to prevent the selection and spread of drug-resistant isolates.

Clinical Characteristics and Microbial Profiles of Paediatric Patients with Methicillin-Resistant Staphylococcus aureus Pneumonia in China

Background: Staphylococcus aureus can cause fatal pneumonia. The evolution of bacteria and the overuse of antibiotics have enhanced the drug resistance of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). Objectives: This study aimed to recapitulate the microbiological profile and clinical characteristics of paediatric patients with MRSA. Methods: This retrospective study was conducted to investigate 1372 paediatric patients with S. aureus pneumonia from January 2017 to December 2021. Sputum specimens were collected and processed for performing bacterial culture and drug sensitivity tests. Medical records of patients were reviewed for clinical characteristics and laboratory examination results. Results: The MRSA and MSSA pneumonia mainly occurred in infants; however, comparisons of sex, age, and sampling time between patients with MRSA and MSSA pneumonia showed no significant differences (P > 0.05). The results of drug sensitivity in sputum culture revealed that all MRSA and MSSA isolates were susceptible to vancomycin, tigecycline, linezolid, teicoplanin, and ceftaroline. Methicillin-sensitive Staphylococcus aureus was completely sensitive to rifampicin and oxacillin. Methicillin-resistant Staphylococcus aureus was completely resistant to penicillin and oxacillin, while MSSA was less sensitive to penicillin. Methicillin-resistant Staphylococcus aureus and MSSA both maintained high sensitivity rates to gentamicin, sulfamethoxazole-trimethoprim, levofloxacin, and moxifloxacin, with the exception of clindamycin and erythromycin. According to our results, moreover, the sensitivity of MRSA to gentamicin and sulfamethoxazole-trimethoprim was significantly higher than that of MSSA (P < 0.05). The common symptoms of patients with S. aureus pneumonia were fever, cough, and wheezing. patients with MRSA pneumonia had significantly higher counts of white blood cells (WBCs), C-reactive protein (CRP), and procalcitonin (PCT) than patients with MSSA pneumonia (P < 0.05). Conclusions: The results of antimicrobial sensitivity test in sputum culture of MRSA and MSSA isolates can reflect the sensitivity of antibiotics and guide the use of clinical antibiotics. Infectious biomarkers can reflect the severity of infection and guide prognosis.

Molecular analysis of Panton-Valentine Leucocidin (pvl) gene among MRSA and MSSA isolates.

The present study was conducted in order to determine the frequency of pvl gene among the pathogenic and healthy population isolates of Methicillin Resistant Staphylococcus aureus (MRSA) and Methicillin Sensitive Staphylococcus aureus (MSSA). For this purpose, nasal swab samples were collected from the healthy individuals (to be used as controls, all the samples were collected irrespective of the sex and age factors), the pathogenic samples were collected from different patients suffering from skin &soft tissue infections caused by S. aureus (to be used as test samples).Both of these population samples were analyzed for the presence of pvl gene. S.aureus were identified through conventional microbiological identification procedures. In the case of normal samples, 70 nasal swabs were collected and only 33 (47%) proved to be S. aureus while 20 pathogenic samples were collected and all (100%) were cleared as S. aureus. For further distribution of samples into MRSA and MSSA, antibiotic susceptibility pattern was checked by using the standard protocols of Kirby-Bauer disc diffusion method. Two antibiotic discs Oxacillin (OX: 1ug) and cefoxitin (FOX: 30ug) were used. Among healthy population, MRSA was found to be 79% (n=26) and MSSA were present as 21% (n= 7). Among pathogenic strains 100% MRSA was detected where n= 20. Detection of pvl gene among the MRSA and MSSA isolates was done by using the uniplex PCR followed by gel electrophoresis. MRSA and MSSA of normal healthy population carried 49% and 7% pvl gene respectively. While, pathogenic MRSA samples carried 46% pvl gene among them. Potentially alarming percentage of pvl gene is present among the normal healthy individuals which indicates a future threat and a major health concern.

Molecular Characterization of Methicillin-Sensitive Staphylococcus aureus from the Intestinal Tracts of Adult Patients in China.

Intestinal infections caused by methicillin-sensitive Staphylococcus aureus (MSSA) have posed a great challenge for clinical treatments. In recent years, the intestinal carriage rates of MSSA have risen steadily in hospital settings in China. However, the epidemiology and molecular characteristics of MSSA from the intestinal tracts of Chinese adult patients remain unknown. In the present study, a total of 80 S. aureus isolates, including 64 MSSA and 16 methicillin-resistant Staphylococcus aureus (MRSA), were recovered from 466 fecal swabs in adult patients between 2019 and 2021 in China. The MSSA isolates exhibited high resistance to penicillin (92.2%) and erythromycin (45.3%). In addition, a higher proportion of MSSA isolates (14.1%) were multidrug-resistant (MDR) strains than that of MRSA isolates (1.3%). Among the 64 MSSA isolates, we identified 17 MLST types, of which ST398 and ST15 were the most predominant types. The most frequently detected resistance genes were blaZ (87.5%) and erm(C) (21.9%). The hemolysin genes (hla, hld, hlgA, hlgB, hlgC) were detected in all the MSSA isolates, but the Panton–Valentine leucocidin (pvl) gene was identified in 1.7% of the MSSA isolates. Our findings indicated that the prevalence and antimicrobial resistance of intestinal MSSA was a serious concern among adult patients in China.

Detection of Methicillin Resistance and β-Lactamase Production in Staphylococcus aureus Isolates: A Cross Sectional Study from a Tertiary Care Hospital

Nosocomial infections are proving to be a menace for the whole health care system, with methicillin resistant Staphylococcus aureus (MRSA) being a very notorious causative agent. Along with the role of mecA gene producing penicillin-binding protein (PBP2a), production of beta-lactamase enzyme by Staphylococcus aureus makes the organism resistant to all β-lactam agents. This study aims at phenotypic detection of methicillin resistance and β-Lactamase production in all S. aureus isolates by Cefoxitin disk diffusion test and Penicillin zone-edge test, respectively. In this prospective cross-sectional study, samples were obtained from patients admitted to different departments and were processed according to the standard laboratory protocols. As per the CLSI guidelines, phenotypic detection of resistance to methicillin was done by Cefoxitin Disk Diffusion test, whereas production of beta-lactamase enzyme was phenotypically detected by penicillin zone edge test. Among 179 isolates of S. aureus, 116 (64.8%) were MRSA, whereas the remaining 63 (35.2%) isolates were methicillin-sensitive Staphylococcus aureus (MSSA). Staphylococcus aureus infection among ICU and non-ICU patients were found to be 24(13%) and 155(86.6%) respectively. Among 24 ICU patients, 19 had MRSA infection, whereas among 155 non-ICU patients, 97 had MRSA infection. Out of 63 MSSA isolates, only 2 (3.17%) were found to be sensitive to Penicillin by Zone-edge test, 04 isolates showed presence of β-lactamase production, while remaining 57 isolates were resistant to Penicillin. At the same time, several class of antibiotics were found to be ineffective against these MRSA isolates. Cases of methicillin-resistant and b–lactamase producing Staphylococcus aureus infections are on the rise in our hospital settings.

Biofilm Formation in Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus Strains

Background: The combination of methicillin resistance (MR) and the ability of biofilm formation of Staphylococcus aureus (SA) makes treatment difficult. Biofilm is formed by distinct genetic mechanisms in MRSA and methicillin-sensitive SA (MSSA), and hence, there is difference in the prevalence of biofilms in them. This study investigated the biofilm production in SA and analyzed its correlation with MR. Materials and methods: A total of 261 consecutive Staphylococcus aureus isolated from various clinical samples from January to April 2019 were included in the study. Antibiotic sensitivity was carried out as per Clinical and Laboratory Standards Institute guidelines and cefoxitin disk was used for screening for MR. Total of 147 MSSA and 114 MRSA were taken for further processing. Biofilm formation was determined by tube and microtiter plate methods in all the isolates. The data were analyzed for statistical significance using Microsoft excel software. Results: Resistance to erythromycin, clindamycin, gentamicin, cotrimoxazole, and inducible clindamycin resistance was significantly higher in all the MR Staphylococcus strain including biofilm forming MRSA strains. The biofilm formation was significantly higher in MSSA isolates by both the tube (78.2%) and microtiter plate methods (64.9%). Discussion: Although the antimicrobial resistance was higher in MRSA, the ability to form biofilms was significantly higher in MSSA. Biofilms of MSSA are usually less prevalent than MRSA probably because of the distinct genetic mechanisms involved in the formation of biofilms. The higher biofilm forming ability of MSSA in our study highlights the need for determination of other genes involved in biofilm formation and virulence mechanisms in SA.

Clinical and microbiological pattern of intertrigo

Background: Intertrigo is a common disorder affecting many flexural areas of the body with significant morbidity.
 Objectives: To determine the clinical pattern of intertrigo. To determine bacterial and fungal pathogens associated with intertrigo. To assess the antibacterial and antifungal sensitivity pattern of the responsible organisms.
 Methods: A total number of 230 patients with intertrigo attending dermatology unit were included in the study after ethical clearance. Laboratory investigations were done to identify the etiologic agent and their sensitivity pattern.
 Results: Majority of patients (75%) belonged to 20-60 years of age. Male to female ratio was 1.15:1. Remarkable proportion (52%) presented with the involvement of more than one intertriginous area. The most common site involved was toe web space (63%) in particular 4th toe web space. Of all positive bacterial cultures 45% revealed Staphylococcus aureus (MSSA+MRSA) followed by CNSA (Coagulase negative Staphylococcal aureus), diptheroids and pseudomonas. The majority of MSSA (Methicillin sensitive Staphylococcus aureus) isolates (91%) were sensitive to cloxacillin and MRSA (Methicillin resistant Staphylococcus aureus) to teicoplanin (85%). CNSA isolates showed considerable proportion of sensitivity to vancomycin (37%) and majority of diptheroids isolates were sensitive to penicillin(87%). All isolates (100%) of pseudomonas were sensitive to gentamicin. Of all positive fungal cultures, candida species constituted the majority (35%) followed by fusarium species (33%) and dermatophytes (30%). Overall fusarium species shows high value of MIC50 and MIC90 for itraconazole, fluconazole and ketoconazole. Fluconazole showed very high MIC50 and MIC90 (256 ug/ml) for dermatophytes and fusarium species whereas itraconazole and ketoconazole showed lower MIC for these fungi.
 Conclusion: Intertrigo can affect various intertriginous areas, among which toe web space is the most common region involved. Intertrigo can be caused by a variety of organisms: Staphylococcus aureus and candida species constituted the majority of cases. Majority of MSSA sensitive to cloxacillin and MRSA to teicoplanin. MIC of itraconazole, fluconazole and ketoconazole are high in fusarium species comparing to candida and dermatophytes. However, itraconazole and ketoconazole had lower MIC than dermatophytes and fusarium comparing to fluconazole.

Mupirocin Resistance of Staphylococcus aureus in Clinical Isolates of National Hospital and in the Nasal Carriage of Healthy Undergraduates in Colombo, Sri Lanka

Introduction and Objectives : Mupirocin resistance in Staphylococcus aureus is increasingly reported in many parts of the world. This study was conducted with the objective of describing high-level and low-level mupirocin resistance of S. aureus in clinical isolates and nasal carriage. Materials and Methods : A descriptive study was conducted including 45 nasal isolates of S. aureus collected from healthy university students in Colombo and 249 clinical isolates of S. aureus from the patient specimens in National Hospital of Sri Lanka. All of the confirmed S. aureus strains were tested for methicillin resistance using cefoxitin disc (30μg). S. aureus isolates were considered methicillin-resistant if the diameter of zone of inhibition was 21mm or less (CLSI, 2017). The S. aureus isolates were then tested for mupirocin resistance. Disk diffusion method was utilized with 5μg and 200μg mupirocin discs to determine low-level and high-level resistances respectively. The criterion employed for interpretation of mupirocin resistance was a combination of the widely accepted criterion described by Finlay, Miller, and Poupard (1997) for low-level mupirocin resistance and CLSI (2017) criterion for high-level mupirocin resistance. If both inhibition zone diameters for 5μg disk and 200μg were ≥14mm, the isolate was considered mupirocin sensitive. If 5μg disc displays <14mm and 200 μg disk displayed ≥14mm inhibition zone diameter, the isolate was considered to be mupirocin low level resistant. If there is no inhibition zone in 200μg disk, the isolate was considered as mupirocin high level resistant. Results : From the 45 nasal carriage isolates, 33 (73%) were Methicillin sensitive Staphylococcus aureus (MSSA) and 12 (27%) were Methicillin Resistant Staphylococcus aureus (MRSA). Among the clinical isolates, majority (n=158, 63%) were MRSA while only 91 (37%) MSSA. An overall mupirocin resistance rate of 4.4% among S. aureus was observed. Low-level mupirocin resistance was observed in 3.7% Staphylococcus aureus isolates and high-level mupirocin resistance was observed in 0.7% isolates. Mupirocin low-level and high-level resistance in MRSA isolates were 5.3% and 0.6% respectively. MSSA isolates demonstrated 1.6% (n=2) and 0.8% (n=1) mupirocin low-level and high-level resistances respectively. None of the nasal isolates were resistant to mupirocin while 6% (n=15) mupirocin low-level resistance and 0.8% (n=2) mupirocin high-level resistance was observed in clinical isolates. Conclusion : This initial survey of mupirocin resistance among S. aureus in a country with fairly high usage of mupirocin emphasizes that although the overall mupirocin resistance is relatively low in this population, regular surveillance of mupirocin resistance remains a necessity.

28. Regulation of the Staphylococcal β-lactamase Plays a Major Role in the cefazolin Inoculum Effect

BackgroundCefazolin (Cz) is commonly used to treat methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia. Yet, some MSSA isolates producing the staphylococcal β-lactamase (BlaZ) exhibit the Cz inoculum effect (CzIE), defined as an increase in the minimum inhibitory concentration (MIC) to ≥ 16 µg/mL at high inoculum (107 CFU/mL, HI-MIC). Retrospective clinical data linked the CzIE to increased 30-day mortality and Cz treatment failure in patients with MSSA bacteremia, yet the mechanistic bases of this phenomenon are unknown. We aimed to explore the contribution of blaZ regulation, via BlaR (antibiotic sensor) and BlaI (transcriptional repressor) (Fig 1) to the CzIE by i) in trans expression assays and ii) analysis of their sequences in a set of isolatesFigure 1. Structure of the Staphylococcal bla OperonMethodsThe blaZ genes (with putative promoters) of strains exhibiting and lacking the CzIE (TX0117 and ATCC29213, respectively) were expressed in trans in RN4220 (blaZ neg) using the promotor-less vector pWM401 (Figure 2). We subsequently cloned the blaR and blaI genes of each TX0117 and ATCC29213 upstream of each blaZ allele (Figure 3). The presence of the CzIE was assessed in transformants using broth microdilution at standard (105 CFU/mL, SI-MIC) and high inoculum. We also performed whole-genome sequencing (WGS) in 104 MSSA isolates exhibiting and lacking the CzIE to compare the sequences of BlaZ, BlaR, and BlaI and classified them by allotypes (unique amino acid sequences) using ATCC29213 as reference. Figure 2. In trans expression of blaZ genes from a CzIE+ strain (TX0117) and a CzIE- strain (ATCC29213) in RN4220 Figure 3. In trans expression of the bla Operons from a CzIE+ strain (TX0117) and a CzIE- strain (ATCC29213) in RN4220ResultsExpression of blaZTX0117 and blaZATCC29213 with their native promoters in RN4220 resulted in the CzIE with Cz HI-MICs ≥ 64 µg/mL regardless of the origin of the allele (Table 1). Inclusion of the regulatory elements blaR and blaI from TX0117 (CzIE+) did not change the phenotype. In contrast, addition of blaR and blaI from ATCC29213 (CzIE-) led to a marked decrease in the Cz HI-MIC (Table 1). Sequence analyses of 104 MSSA isolates revealed 10, 17 and 6 BlaZ, BlaR and BlaI allotypes, respectively (Table 2). BlaZ-2 and BlaR-4 were linked to the CzIE in 90% of isolates. Table 1. MIC values of transformans after In trans expression of blaZ genes and bla Operons from a S. aureus CzIE+ strain(TX0117) and a CzIE- strain (ATCC29213) in RN4220 Table 2. BlaZ allotypes of 104 Staphylococcus aureus isolates and their association with the CzIEConclusionOur results suggest that overexpression of blaZ can lead to the CzIE in any MSSA strain. Thus, the regulation of blaZ expression via BlaR and BlaI seem to play a major role in the CzIE. Identification of specific BlaR and BlaI allotypes could predict the presence of the CzIE. Disclosures Cesar A. Arias, M.D., MSc, Ph.D., FIDSA, Entasis Therapeutics (Scientific Research Study Investigator)MeMed (Scientific Research Study Investigator)Merck (Grant/Research Support)

Prevalence of methicillin-sensitive, methicillin-resistant Staphylococcus aureus, and extended-spectrum beta-lactamase-producing Escherichia coli in newborns: a cross-sectional study

Background The prevalence of antimicrobial-resistant bacteria and methicillin-sensitive Staphylococcus aureus (MSSA) in healthy newborns and the role of maternal transmission are scarcely discussed. Objectives The objective of this study was to evaluate the prevalence of MSSA, MRSA, and ESBL among healthy newborns. Additionally, mother-to-newborn transmission rates were investigated as well as antibiotic susceptibility of MSSA, MRSA, and ESBL isolates. Methods Swabs of 658 newborns and their mothers were collected to investigate the presence of MSSA, MRSA, and ESBL. Swabs were taken from the nose and umbilicus immediately after birth. Additional swabs were taken from the nose, perianal area, and umbilicus 3 days after birth. Samples were screened and further characterized using culture and molecular methods. Results Prevalence of MSSA, MRSA, and ESBL colonization was 10.9, 0.5, and 2.6%, respectively. There was no association between the colonization status of the newborn and infections at any time point. Mother-to-newborn transmission rates (confirmed by PFGE) were 53.6% for MSSA/MRSA and 100% for ESBL. Maternal carriage of MSSA, MRSA, or ESBL was a risk factor for colonization of the newborn. Some isolates were resistant to the antibiotics recommended for therapy, including clindamycin and daptomycin for MSSA/MRSA isolates and ertapenem, fosfomycin, and tigecyclin for ESBL isolates. Conclusion No association between infections and the newborns’ colonization status could be detected. Maternal colonization played an important role in newborn colonization, but not every case of colonization could be explained by mother-to-newborn transmission. General screening of pregnant women and healthy newborns in the absence of other risk factors is not necessary. To prevent the possibility of transmission in the healthcare setting, professionals, pregnant women, parents, hospital visitors, and obstetricians should receive regular training on appropriate hygiene measures. With regard to the emergence of resistance to recommended antibiotics, an antibiogram should be conducted before treating MSSA/MRSA/ESBL infections to ensure the efficacy of the antibiotics.

Trimethoprim-Sulfamethoxazole Resistance Patterns Among Methicillin-Resistant Staphylococcus aureus, 2012–2018

Background: Trimethoprim-sulfamethoxazole is commonly used for the treatment of noninvasive methicillin-resistant Staphylococcus aureus (MRSA) infections. Following a report from 2 facilities of increased trimethoprim-sulfamethoxazole resistance among MRSA infections, we assessed changes in resistance nationally and by state. Methods: We reviewed antibiotic susceptibility testing (AST) data for trimethoprim-sulfamethoxazole among S. aureus isolates associated with surgical site infections (SSIs), central-line–associated bloodstream infections (CLABSIs), and catheter-associated urinary tract infections (CAUTIs) from acute-care hospitals reported to the NHSN Device and Procedure Module from 2012 to 2018. We compared the pooled mean percentage of isolates nonsusceptible to trimethoprim-sulfamethoxazole in 2012 and 2018, stratified by MRSA and methicillin-sensitive Staphylococcus aureus (MSSA). Among MRSA isolates, we compared the percentage nonsusceptible to trimethoprim-sulfamethoxazole by healthcare-associated infection (HAI) type and state in 2012 and 2018. States with ≥20 MRSA isolates with AST reported each year were included in the state-level analysis. Results: Overall, 36,587 MRSA isolates and 46,824 MSSA isolates were reported from 2012 to 2018. Moreover, >80% of MRSA and MSSA isolates had trimethoprim-sulfamethoxazole AST reported each year. Nationally, the percentage of trimethoprim-sulfamethoxazole nonsusceptible among MRSA isolates was 3.9% in 2012 compared to 6.5% in 2018 (P < .001), but it was unchanged among MSSA isolates during the same period (1.1% in 2012 vs 1.4% in 2018; P = .08). Among MRSA surgical site infections (SSIs), the proportion of trimethoprim-sulfamethoxazole nonsusceptible isolates was 3.1% in 2012 versus 6.1% in 2018 (P < .001) but did not change significantly for CLABSIs or CAUTIs (Fig. 1). Among the 32 states that met the inclusion criteria, there were no significant decreases, whereas 4 (12.5%) showed significant increases in the percentage of MRSA that were trimethoprim-sulfamethoxazole nonsusceptible in 2018 compared to 2012: New Jersey (2.4% in 2012 vs 19.3% in 2018; P <.001); Florida (9.1% in 2012 vs 22.4% in 2018; P < .001); Maryland (0.0% in 2012 vs 10.9% in 2018; P < .01); and Pennsylvania (1.7% in 2012 vs 6.5% in 2018; P < .001). Conclusions: Nationally, there was a modest but significant increase in the percentage of MRSA HAI isolates nonsusceptible to trimethoprim-sulfamethoxazole in 2018 compared to 2012; however, 3 of 4 states with significant increases in nonsusceptibility had substantial, potentially clinically relevant increases (>10%). Ongoing characterization of MRSA isolates from Florida and New Jersey may provide insight into the underlying cause of these shifting patterns in trimethoprim-sulfamethoxazole resistance among MRSA. Healthcare personnel should select appropriate antibiotic regimens based on local resistance patterns, should monitor patients for treatment failure, and should report changes in resistance to the appropriate public health department.Funding: NoneDisclosures: None

A large-scale investigation and identification of methicillin-resistant Staphylococcus aureus based on peaks binning of matrix-assisted laser desorption ionization-time of flight MS spectra.

Recent studies have demonstrated that the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) could be used to detect superbugs, such as methicillin-resistant Staphylococcus aureus (MRSA). Due to an increasingly clinical need to classify between MRSA and methicillin-sensitive Staphylococcus aureus (MSSA) efficiently and effectively, we were motivated to develop a systematic pipeline based on a large-scale dataset of MS spectra. However, the shifting problem of peaks in MS spectra induced a low effectiveness in the classification between MRSA and MSSA isolates. Unlike previous works emphasizing on specific peaks, this study employs a binning method to cluster MS shifting ions into several representative peaks. A variety of bin sizes were evaluated to coalesce drifted or shifted MS peaks to a well-defined structured data. Then, various machine learning methods were performed to carry out the classification between MRSA and MSSA samples. Totally 4858 MS spectra of unique S. aureus isolates, including 2500 MRSA and 2358 MSSA instances, were collected by Chang Gung Memorial Hospitals, at Linkou and Kaohsiung branches, Taiwan. Based on the evaluation of Pearson correlation coefficients and the strategy of forward feature selection, a total of 200 peaks (with the bin size of 10 Da) were identified as the marker attributes for the construction of predictive models. These selected peaks, such as bins 2410–2419, 2450–2459 and 6590–6599 Da, have indicated remarkable differences between MRSA and MSSA, which were effective in the prediction of MRSA. The independent testing has revealed that the random forest model can provide a promising prediction with the area under the receiver operating characteristic curve (AUC) at 0.8450. When comparing to previous works conducted with hundreds of MS spectra, the proposed scheme demonstrates that incorporating machine learning method with a large-scale dataset of clinical MS spectra may be a feasible means for clinical physicians on the administration of correct antibiotics in shorter turn-around-time, which could reduce mortality, avoid drug resistance and shorten length of stay in hospital in the future.

First report of mecC gene in clinical methicillin resistant S. aureus (MRSA) from tertiary care hospital Islamabad, Pakistan

BackgroundStaphylococcus aureus (S. aureus) is one of the leading causes of community and hospital acquired infections globally. The objective of the study was to assess the prevalence, study the carriage of antibiotic resistance genes and evaluate the molecular typing of S. aureus isolates from a tertiary care hospital in Islamabad. MethodsA total of 1528 staphylococci isolates were included in this study. Standard microbiological procedures were applied to identify S. aureus. Antimicrobial susceptability was evaluated using the disk diffusion method and Minimum Inhibitory Concentrations (MICs) were determined using microbroth dilution method following Clinical and Laboratory Standards Institute (CLSI) guidelines. Multiplex PCR was used to detect antibiotic resistance genes, and molecular typing was performed using agr, SCCmec, spa, and Multi-Locus Sequence Typing (MLST) and clonal relatedness by Pulse Field Gel Electrophoresis (PFGE) methods. ResultsOverall 65% were MRSA and 35% were methicillin sensitive Staphylococcus aureus (MSSA). Among MRSA isolates, 83% were multi-drug resistant and mecA was found in 54% isolates, mecC was in 3% while 1 MRSA carried both mecA and mecC genes. agrI (22%) was most prevalent group in MRSA, while agrIII (16%) was observed in MSSA. SCCmec types I, II, III, IV, and VI were detected, with high prevalence of type III while type V was absent. The prevelant spa type in MRSA was t657 with SCCmecIII elelments while in MSSA it was t021. One NEW spa type identified in MSSA isolates. In a subset of isolates, ST772 with SCCmecIV, ST1 carrying PVL marker, and ST1535 was reported first time from Pakistan. ConclusionsThe study presents a comprehensive analysis of prevalent S. aureus types and their antibiotic resistance profiles. It also reports for the first time SCCmec type VI and clinical MRSA isolates with mecC alone and in combination with mecA from Islamabad, Pakistan. This calls for further detailed investigations in other hospital settings in the region.

217. Combination Salvage Therapy with Cefazolin Plus Ertapenem for Refractory Methicillin-Susceptible Staphylococcus aureus Bacteremia

BackgroundSuboptimal therapy against methicillin-sensitive Staphylococcus aureus (MSSA) may have catastrophic consequences in severe infections such as endocarditis or epidural abscess. High MSSA inocula have been associated with clinical failure in patients receiving cefazolin (CZ), particularly when used at low doses, associated with a CZ inoculum effect. We previously described that adding ertapenem (ETP) to CZ led to synergism against MSSA and sensitized the pathogen to host innate immune factors. Here we expand our experience with CZ plus ETP as salvage therapy for 11 cases of refractory MSSA bacteremia (lacking source control problems) and explore CZ+ETP combination in vitro and in vivo.MethodsSix available MSSA strains from patients treated with CZ+ETP for refractory bacteremia were tested in Mueller–Hinton Broth or RPMI media at standard (105 CFU/mL) or high (107 CFU/mL) inocula by MIC, checkerboard, and time-kill assays using ETP, CZ or nafcillin (NAF) alone vs. ETP+NAF or ETP+CZ. Disk diffusion synergy assays between CZ and ETP were also performed. CZ, ETP and CZ+ETP were tested in a rat endocarditis model using well described MSSA, TX0117 and TX0117c.Results11 consecutive patients with MSSA bacteremia (6 confirmed endocarditis) refractory to standard CZ or NAF rapidly cleared with CZ+ETP. 9 patients had daily positive blood cultures, and 8 cleared in ≤24 hr, including those with ≥2 cm vegetations. All 11 survived hospitalization. In MHB, 3/6 MSSA exhibited a CZ inoculum effect (CZ MIC >3 log2 in 107 vs. 105 CFU/mL), but only 1 showed a significant CZ inoculum effect in RPMI. CZ+ETP was significantly more efficacious than CZ in a rat model of MSSA endocarditis utilizing a strain displaying a CZ inoculum effect, despite only modest benefit observed in vitro for 6 MSSA isolates.ConclusionCZ+ETP combination therapy yielded profound clinical success in severe MSSA infections with high bacterial densities, as demonstrated by rapid bacteremia clearance. Enhanced efficacy was also observed in a rat endocarditis model. The anti-staphylococcal activity of CZ+ETP in vivo exceeded that observed in vitro, consistent with our prior observations of host innate immune cooperativity with the regimen. CZ+ETP warrants further study for the treatment of refractory MSSA bacteremia and endocarditis.Disclosures All authors: No reported disclosures.

Nationwide Organism Susceptibility Patterns to Common Preoperative Prophylactic Antibiotics: What Are We Covering?

BackgroundMany periprosthetic joint infections (PJIs) are caused by organisms not susceptible to first-generation cephalosporins. We sought to evaluate the national susceptibility patterns of organisms to cefazolin and, or oxacillin, clindamycin, and vancomycin using antibiogram data. MethodsPublically available regional and state antibiograms were evaluated for antibiotic susceptibility patterns to commonly infecting gram-positive organisms. The number of isolates tested in each antibiogram and percent of strains susceptible to oxacillin, clindamycin, and vancomycin were recorded. Oxacillin is used as a surrogate to cefazolin in antibiograms. A comparison of antibiotic susceptibilities was performed. ResultsSeven state and 38 regional antibiograms were reviewed. Oxacillin was a sensitive antibiotic in 99.2 ± 4.8% of methicillin-sensitive Staphylococcus aureus (MSSA) isolates, 0 ± 0% of methicillin-resistant Staphylococcus aureus (MRSA) isolates, 44.5 ± 13.7% of coagulase-negative staphylococcus organism isolates (CNS), and 30.6 ± 10.5% of Staphylococcus epidermidis isolates. Clindamycin was a sensitive antibiotic in 75.8 ± 8.4% of MSSA isolates, 60.2 ± 13.2% of MRSA isolates, 60.3 ± 11.4% of CNS isolates, and 56.2 ± 6.5% of S epidermidis isolates. Vancomycin was a sensitive antibiotic in 99.9 ± 0.4% of MSSA isolates, 99.8 ± 0.4% of MRSA isolates, 99.8 ± 0.5% of CNS isolates, and 99.6 ± 0.7% of S epidermidis isolates. Clindamycin was significantly less sensitive in MSSA isolates as compared with oxacillin and vancomycin (P < .0001). Oxacillin was significantly less sensitive in CNS, S epidermidis, and MRSA isolates as compared with clindamycin and vancomycin (P < .0001). ConclusionThe national clindamycin susceptibility pattern is limited to MSSA and may not have an optimal susceptibility profile suitable for use as a prophylactic antibiotic. Cefazolin continues to have excellent coverage against MSSA.

Prevalence and antibiotic resistance patterns of methicillin-resistant &lt;i&gt;Staphylococcus aureus&lt;/i&gt; in raw milk and soft cheese (wara) sold in Abeokuta, Nigeria

The emergence of antibiotic-resistant bacteria in farm animals, their environment and food of animal origins is of significant potential public health importance. Methicillin resistant Staphylococcus aureus (MRSA) is an important opportunistic pathogen both in humans and in cattle. A total of 200 samples comprising of 100 each of raw milk and wara were collected from five different locations in Abeokuta, Ogun State. The samples were examined using standard bacteriological methods for the isolation and identification of Staphylococcus species including MRSA. Latex agglutination test of Penicillin-binding protein 2a (PBP2a) was used to further confirmed MRSA isolates. The susceptibility to antibiotics was determined by Kirby Bauer diffusion method. In all, S. aureus was detected in 52 (26%) of 200 samples of which 50 were confirmed as MRSA and two were Methicillin-sensitive Staphylococcus aureus (MSSA). Out of 50 MRSA isolates, 15 (15%) were from 100 raw milk and 35 (35%) were from 100 wara samples. The two MSSA isolates were from raw milk. The Staphylococcus aureus isolates from raw milk showed high resistance to ceftazidime 17 (100%), ampicillin 16 (94.1%), doxycycline 11 (64.7%), tetracycline 17 (100%), oxacillin 15 (88.2%), augmentin 17 (100%), gentamycin 15 (88.2%), colistin 15 (88.2%), and sulphamethoxazole 16 (94.1%). Isolates from wara were resistant to ceftazidime 35 (100.0%), ampicillin 35 (100%), doxycycline 15 (42.9%), tetracycline 23 (65.7%), oxacillin 35 (100.0%), streptomycin 20 (57.1%), augmentin 33 (94.3%), gentamycin 17 (48.6%), colistin 35 (100%), and sulphamethoxazole 27 (77.1%). The presence of MRSA in the raw cow milk and wara sold in Abeokuta may be due to overdependence on antibiotics in cattle production. Contamination along processing and marketing chain of wara due to unhygienic practices could also contribute to the presence of MRSA in the product. This constitutes a potential public health risk to consumers of milk and milk products in Abeokuta. Keywords: Antibiotics, Milk, MRSA, Resistance, Soft cheese, Unhygienic

Emerging discrepancies in conventional and molecular epidemiology of methicillin resistant Staphylococcus aureus isolated from bovine milk

Methicillin resistant Staphylococcus aureus (MRSA) is an emerging public health concern from dairy milk, and its diagnosis by phenotypic methodology is experiencing higher discrepancies. The present study was planned to estimate discrepancies in phenotypic identification of MRSA and MSSA (Methicillin sensitive Staphylococcus aureus) in relation to mecA, and prevalent risk factors from various localities. In-vitro oxacilline antibiotic disks were used for phenotypic identification of MRSA, whereas mecA gene was used as MRSA marker in Staph aureus by PCR. Total of 900 bovine milk samples from private and public farms located in district Faisalabad using convinent sampling technique were collected. Potential risk factors for MRSA prevalence identified by non-parametric statistical tests were compared among different subdistricts. Discrepancy in MRSA was calculated as percentage of mecA negative strains while that of MSSA was determined as percentage of mecA positive strains. Molecular identification presented 17.97% (55/306) of discrepancy in MRSA in terms of negative mecA strains from district Faisalabad while sub-district Faisalabad, sub-district Jaranwala, and sub-district Samundary presented 13.98% (13/93), 18.28% (17/93), and 20.83% (25/120) discrepant results, respectively. On the other hand, 29.1% (55/189) of discrepancy in MSSA in terms of mecA positive strains from MSSA isolates was noted. MSSA results were more discrepant than that of MRSA. Hence discrepancy ratio of MSSA over MRSA was noted to be 1.53, 1.50, and 1.21 from tehsil Faislabad, Samundary, and Jaranwala. Tick infestation, lactation stage, frequency of milking, dirty milker's hands, unhygienic milking procedures, and higher use of beta lactam of antibiotics were risk factors that were prevalent in increasing order from sub-district Faisalabad > Jaranwala > Samundary. The study concluded higher prevalence of MRSA in bovine milk samples, and found remarkable discrepancies in phenotypic and genotypic identification which demand immediate attention to tackle exacerbation in resistance patterns.