Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry facilitates rapid and accurate identification of pathogens, which is critical for sepsis patients. In this study, we assessed the accuracy in identification of both Gram-negative and Gram-positive bacteria, except for Streptococcus viridans, using four rapid blood culture methods with Vitek MALDI-TOF-MS. We compared our proposed lysis centrifugation followed by washing and 30% acetic acid treatment method (method 2) with two other lysis centrifugation methods (washing and 30% formic acid treatment (method 1); 100% ethanol treatment (method 3)), and picking colonies from 90 to 180min subculture plates (method 4). Methods 1 and 2 identified all organisms down to species level with 100% accuracy, except for Streptococcus viridans, Streptococcus pyogenes, Enterobacter cloacae and Proteus vulgaris. The latter two were identified to genus level with 100% accuracy. Each method exhibited excellent accuracy and precision in terms of identification to genus level with certain limitations.

Compared to routine isolated colony-based methods, direct testing of bacterial pellets from positive blood cultures reduces turnaround time for reporting of antibiotic susceptibility. The aim of this study was to compare the accuracy, and precision, of a rapid method for direct identification and susceptibility testing of blood cultures with the routine method used in our laboratory, using Vitek 2. A total of 60 isolates were evaluated using the candidate and the routine method. The candidate method had 100% accuracy for the identification of Gram negative bacteria, Staphylococcus and Enterococcus, 50% for Streptococcus and 33.3% for Corynebacterium species. Susceptibility testing of Gram negative isolates yielded 98-100% essential agreement. For Staphylococcus and Enterococcus isolates, essential agreement was 100% for 17 antibiotics except for moxifloxacin. Direct testing of blood culture samples with Vitek 2 produced reliable identification and susceptibility results 18-24h sooner for aerobic/anaerobic facultative Gram-negative bacteria and Gram-positive Staphylococcus and Enterococcus strains.

Panton-Valentine leukocidin (PVL) is a two-component toxin associated with the toxicity and virulence of Staphylococcus aureus. The presence of PVL is well documented in community-acquired methicillin-resistant S. aureus (CA-MRSA) and is observed in methicillin-susceptible S. aureus (MSSA) with variable prevalence. We assessed the prevalence of PVL in a sample of 93 MSSA patients in a healthcare facility in Eastern Saudi Arabia using real-time PCR for lukSF-PV genes. The presence or absence of PVL was correlated with age, gender, hospitalization status, infection site and antibiotic resistance. PVL was detected in 28 (30%) patient samples. PVL was associated with a greater likelihood of resistance to trimethoprim-sulfamethoxazole (a resistance of 39.2% of PVL-positive isolates compared to 6.1% of PVL-negative isolates) (p < 0.0007). These results suggest a significant prevalence of PVL expression in MSSA strains in the study population and call for monitoring of and surveillance programs for PVL status and the selection of appropriate antibiotic treatments.

Background:Methicillin-resistant Staphylococcus aureus (MRSA) infection is associated with increased morbidity, mortality, and financial burdens. Phenotyping methods are used to classify MRSA as either health care MRSA (HA-MRSA) or community-associated MRSA (CA-MRSA). Recent studies suggested the phenotyping methods are not always reliable, based on a lack of concordance with genotyping results.Objective:In this study, concordance of classification methods based on clinical characteristics or antibiotic susceptibility compared to the gold standard genotyping was assessed in the classification of MRSA.Methods:We compared the genotypes and phenotypes of MRSA in 133 samples taken from patients in Saudi Arabia. Statistical analyses included concordance, specificity and sensitivity, and logistic regression modeling.Results:There was fair a definite agreement between the health care risk and infection type methods (p < .001), but no statistically significant agreement between the susceptibility pattern and health care risk methods (p = 243), and between susceptibility pattern and infection type methods (p = .919). Reduced multiple regression modelling suggested the potential of a phenotyping-based method of antibiotic susceptibility pattern (OR = 15.47, p < .001) in conjunction with hospital admission profile(OR = 2.87, p = .008) to accurately identify MRSA as HA-MRSA and CA-MRSA.Conclusion:The use of a standardized phenotyping technique, using susceptibility pattern and hospital admission profiles to classify MRSA infections as either HA-MRSA or CA-MRSA, would facilitate diagnosis, infection control efforts, prevention, and assignment of appropriate therapies. The ability to use phenotyping in the classification of these strains would improve efforts to contend with this adept and evolving bacterial organism.