Comparison of Phenotypic and Genotypic Characterization Methods for the Detection of Methicillin-Resistant Staphylococcus Aureus.

Introduction Methicillin-resistant Staphylococcus aureus (MRSA) is associated with high morbidity and mortality due to the development of antimicrobial resistance secondary to irrational use of antibiotics, nonadherence to infection control practices, and increased use of intravascular devices in healthcare systems. Detection of MRSA is critical in clinical microbiology laboratories as it helps identify MRSA carriers and avoid treatment failure in patients. Hence, this study compared various phenotypic methods with the standard genotyping method to determine a method that permits rapid and accurate detection of MRSA. Materials & Methods Staphylococcus aureus (S. aureus) was initially identified based on colony morphology, Gram staining, standard biochemical tests, and antibiotic susceptibility using disk diffusion. MRSA was identified based on the detection of the mecA gene by polymerase chain reaction (PCR) and subsequent gel electrophoresis. Disk diffusion using cefoxitin or oxacillin and mannitol salt agar with 6-µg/ml oxacillin were used for phenotypic detection of MRSA. The D test was used to detect inducible clindamycin resistance in S. aureus isolates. Results Of the 100 S. aureus isolates analyzed, 37% were identified as MRSA by PCR and the cefoxitin disk diffusion method; however, only 31% were detected by the oxacillin disk diffusion method and 29% by the mannitol salt agar method. The sensitivity of the cefoxitin disk diffusion test, oxacillin disk diffusion, and mannitol salt agar methods was 86.05%, 83.78%, and 70.73%, respectively. Specificity was 100% for all the three phenotypic methods (p < 0.001). Notably, inducible clindamycin resistance was found in 37.2% of the MRSA isolates, indicating potential challenges in treatment. Conclusion Among the three phenotypic methods tested, the cefoxitin disk diffusion method had 100% sensitivity and specificity, which is similar to that of PCR-based MRSA detection. Hence, the cefoxitin disk diffusion method is recommended for use in clinical laboratories, where molecular methods are not available as it is both cost-effective and easy to perform.

Improved detection of Burkholderia pseudomallei from non-blood clinical specimens using enrichment culture and PCR: narrowing diagnostic gap in resource-constrained settings.

OBJECTIVES: To evaluate the diagnostic utility of enrichment culture and PCR for improved case detection rates of non-bacteraemic form of melioidosis in limited resource settings. METHODS: Clinical specimens (n = 525) obtained from patients presenting at a tertiary care hospital of South India with clinical symptoms suggestive of community-acquired pneumonia, lower respiratory tract infections, superficial or internal abscesses, chronic skin ulcers and bone or joint infections were tested for the presence of Burkholderia pseudomallei using conventional culture (CC), enrichment culture (EC) and PCR. Sensitivity, specificity, positive and negative predictive values of CC and PCR were initially deduced using EC as the gold standard method. Further, diagnostic accuracies of all the three methods were analysed using Bayesian latent class modelling (BLCM). RESULTS: Detection rates of B. pseudomallei using CC, EC and PCR were 3.8%, 5.3% and 6%, respectively. Diagnostic sensitivities and specificities of CC and PCR were 71.4, 98.4% and 100 and 99.4%, respectively in comparison with EC as the gold standard test. With Bayesian latent class modelling, EC and PCR demonstrated sensitivities of 98.7 and 99.3%, respectively, while CC showed a sensitivity of 70.3% for detection of B. pseudomallei. An increase of 1.6% (95% CI: 1.08-4.32%) in the case detection rate of melioidosis was observed in the study population when EC and/or PCR were used in adjunct to the conventional culture technique. CONCLUSIONS: Our study findings underscore the diagnostic superiority of enrichment culture and/or PCR over conventional microbiological culture for improved case detection of melioidosis from non-blood clinical specimens.

Clostridium difficile infection at a tertiary care hospital in south India.

OBJECTIVE: The objective of this study was to detect C. difficile in patients presenting with Antibiotic Associated Diarrhoea. METHODS: Stool samples from twenty-five patients collected over a period of four months were processed for C. difficile by culture and the isolates were identified following standard methods. C. difficile toxins A and B and C. perfringens enterotoxin were detected by ELISA performed directly on stool specimens. RESULTS: Four patients (16%) were found positive for C. difficile infection. All patients with C. difficile infection received prior treatment with third-generation cephalosporins or beta-lactam/beta-lactamase inhibitor antibiotics. C. perfringens enterotoxin was found in two (8%) patients. Severe colitis was seen in one (25%) of the four patients who had co-infection with C. difficile and C. perfringens. CONCLUSION: This study demonstrated a significant occurrence of C. difficile infection in this hospital population. There is a need to further evaluate the role of C. perfringens in causing antibiotic associated diarrhoea. Good clinical and laboratory studies to generate local epidemiological data are essential to increase awareness among the treating clinicians about C. difficile infection. Also limited and rational use of broad spectrum antibiotics is recommended.

Primary tubercular psoas abscess: a rare presentation.

Primary tubercular psoas abscess is a rare clinical entity and has seldom been reported in an otherwise healthy person. Here we report an interesting case of primary tubercular psoas abscess in an immunocompetent male with no other traceable source.

Isolated tuberculous epididymo-orchitis: an unusual presentation of tuberculosis.

Isolated epididymo-orchitis is an unusual presentation of tuberculosis. A case of bilateral epididymitis and right-sided orchitis with scrotal involvement in a 38-year-old male patient is presented. Strong clinical suspicion of tuberculous etiology was confirmed by appropriate investigations of epididymal biopsy. The patient improved clinically with antitubercular therapy.