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• Predictive performance of antimicrobial resistance in Staphylococcus aureus varies by database and machine learning model. • LightGBM performs better in predicting resistance of ORSA compared with all Staphylococcus aureus and OSSA. • Specific and overlapping mass spectra features predict mecA and tier 1 antibiotic resistance. • Transfer learning enhances resistance prediction of some antibiotics using institutional data. • MALDI-TOF MS with machine learning rapidly predicts mecA and antimicrobial resistance in Staphylococcus aureus. The use of matrix-assisted laser desorption/ionisation-time-of-flight mass spectra (MALDI-TOF MS) with machine learning (ML) has been explored for predicting antimicrobial resistance. This study evaluates the effectiveness of MALDI-TOF MS paired with various ML classifiers and establishes optimal models for predicting antimicrobial resistance and the presence of mecA gene among Staphylococcus aureus. Antimicrobial resistance against tier 1 antibiotics and MALDI-TOF MS of S. aureus were analysed using data from the Database of Resistance against Antimicrobials with MALDI-TOF Mass Spectrometry (DRIAMS) and one medical centre (CS database). Five ML classifiers were used to analyse performance metrics. The Shapley value quantified the predictive contribution of individual features. The LightGBM demonstrated superior performance in predicting antimicrobial resistance for most tier 1 antibiotics among oxacillin-resistant S. aureus (ORSA) compared with all S. aureus and oxacillin-susceptible S. aureus (OSSA) in both databases. In DRIAMS, Multilayer Perceptron (MLP) was associated with excellent predictive performance, expressed as accuracy/AUROC/AUPR, for clindamycin (0.74/0.81/0.90), tetracycline (0.86/0.87/0.94), and trimethoprim-sulfamethoxazole (0.95/0.72/0.97). In the CS database, Ada and Light Gradient Boosting Machine (LightGBM) showed excellent performance for erythromycin (0.97/0.92/0.86) and tetracycline (0.68/0.79/0.86). Mass-to-charge ratio (m/z) features of 2411–2414 and 2429–2432 correlated with clindamycin resistance, whereas 5033–5036 was linked to erythromycin resistance in DRIAMS. In the CS database, overlapping features of 2423–2426, 4496–4499, and 3764–3767 simultaneously predicted the presence of mecA and oxacillin resistance. The predictive performance of antimicrobial resistance against S. aureus using MALDI-TOF MS depends on database characteristics and the ML algorithm selected. Specific and overlapping mass spectra features are excellent predictive markers for mecA and specific antimicrobial resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

The decrease in susceptibility to glycopeptides by oxacillin resistant Staphylococcus aureus (ORSA) has become a current problem. Objective: To evaluate susceptibility to glycopeptides in ORSA strains isolated in the University Hospital, Maracaibo, during the first quarter of 2010. Methods: Oxacillin resistance of the ORSA strains was verified by diffusion on agar (oxacillin 1 µg and cefoxitin 30 µg, OXOID®), a screening test in Müeller Hinton agar with 6 µg/mL of vancomycin (Sigma®), and E-test® for minimum inhibitory concentration (MIC) for oxacillin, detection of PBP2a (Latex, OXOID®) and the mecA gene by polymerase chain reaction (PCR). In addition, susceptibility to glycopeptides was determined by disk diffusion (teicoplanin, 30 µg OXOID®), MIC by E-test®, screening test in Müeller-Hinton agar with teicoplanin (5 µg/ml) or in brain heart infusion agar with vancomycin (6 µg/mL), glycopeptide hetero-resistance detection by GDR E-test® and detection of the vanA gene using PCR. Results: No ORSA strain was isolated with intermediate resistance (VISA or hVISA), nor with high-level resistance to glycopeptides. Conclusions: Locally, there is no incidence of ORSA strains resistant to glycopeptides; therefore, these antibiotics continue to be useful for treating infections produced by this important pathogen. [ABSTRACT FROM AUTHOR]

Background: Vancomycin is the treatment of choice for oxacillin-resistant Staphylococcus aureus (ORSA) infections in long bones. However, an inappropriate dosage of vancomycin may result in toxicity or treatment failure. Materials and methods: In this study, 21 patients infected with ORSA were treated with intravenous vancomycin. The concentration of serum vancomycin was measured by fluorescence polarization immunoassay. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were also measured at each blood sampling. Results: When vancomycin doses were given based on the manufacturer's recommendations, 46% (39/84) of the patients were found to have inappropriate blood levels. After the dose of vancomycin was then adjusted, at the third blood sampling, a higher percentage of adequate peak and trough serum vancomycin concentrations were found. There was no statistical difference in peak or trough levels produced by intravenous doses of vancomycin of 500 mg given every 6 h or 1,000 mg given every 12 h. However, initial dosing of 1,000 mg every 12 h may be a better choice than 500 mg every 6 h for younger patients. The CRP was significantly decreased ( P < 0.01) at the time of the second blood sampling during vancomycin treatment. Conclusions: The data from this study suggest that peak and trough vancomycin concentrations should be monitored for patients who have chronic osteomyelitis and prolonged vancomycin treatment. Further studies may help resolve whether such monitoring beneficially affects outcomes and health care costs. [ABSTRACT FROM AUTHOR]

Introduction: Methicillin resistant Staphylococcus aureus has emerged as an important pathogen in nosocomial and community acquired infections. Accurate and rapid identification of MRSA in clinical specimens is essential for timely decision of effective antimicrobial chemotherapy. Aim: The present study was conducted to compare efficacy of four conventional phenotypic methods, with mec- A based polymerase chain reaction (PCR) for MRSA identification. materials and methods: Methicillin resistance was determined in 200 S.aureus isolates by oxacillin disc diffusion, cefoxitin disc diffusion, Oxacillin Resistance Screening Agar and E-test. The results were compared with mec-A based PCR. Results: Among 200 S.aureus isolates 62 (31%) were positive for mec-A gene by PCR. Cefoxitin disc diffusion, Oxacillin Resistance Screening Agar and E-test showed 100% specificity. Oxacillin disc diffusion had lowest sensitivity (82.5%) and specificity (98.5%) among all. The conventional methods take more time than PCR for diagnosing MRSA. Linezolid, Vancomycin & Dalfopristin were the highly sensitive drugs against MRSA isolates. Conclusion: Cefoxitin disc diffusion, is rapid, simple and cheaper, hence can be used routinely as an alternative to PCR for detection of MRSA in resource constraint laboratories. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to characterize oxacillin-resistant Staphylococcus aureus (ORSA) isolates from livestock environments and meat market workers by molecular epidemiological analysis. Staphylococcal enterotoxin reversed passive latex agglutination (RPLA) and multiplex polymerase chain reactions (PCR) were used to detect enterotoxin-producing S. aureus. The molecular genetic similarity of ORSA was also compared by pulse-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). A total of 30 ORSA isolates were identified and 27 of these strains were from human sources—a higher contamination potential from human origin in the animal raising and handling field was suspected. The most common type of enterotoxin detected in this study was type B. Regarding the bacterial phylogenetic analysis of ORSA isolates, five major clusters of PFGE patterns were suggested with >80% similarity in cluster I. Seven MLST patterns were identified with the most prevalent types being ST338/ST338slv and ST59. Population genetic studies based on MLST have shown that major ORSA clones have emerged from six clonal complexes (CCs), with CC59 being the dominant one. In conclusion, a high prevalence of ORSA with enterotoxin type B as well as ST59 and ST338/ST338slv colonization was observed among livestock with human origins in this study. We suggest further tracking and comparing of the epidemiological evidence of community-acquired and hospital-acquired ORSA in human living environments and livestock-producing environments. [Copyright &y& Elsevier]