Cross-country transport and isolation and identification of Streptococcus pneumoniae by use of alternate sources of blood supplemented media among laboratories in India

Background: The isolation of S. pneumoniae (Sp) depends on specimen integrity / transport, media and expertise. The non-availability of sheep blood agar poses a challenge in identification of colonial morphology and identification in India. Methods: Laboratories processed swabs containing either pure Sp or Sp in mixed cultures with a second (confounding) bacterium shipped across the country in cold conditions. Duplicate set of swabs was shipped back to the central laboratory to assess the impact of shipping on culture viability. The identical swab was cultured on sheep, human blood and one additional agar plate used in the laboratory. Results: 46/60(77%) of cultures containing only Sp were correctly identified. In specimens where Sp was present in mixed culture, the proportion of isolates in which Sp was correctly identified varied, with most variability attributed to the particular confounding organism rather than the media. There was no discernible impact of temperature-controlled (4-6°C) transport on the isolation of Sp from culture swabs. Conclusions: The study clearly elucidates the ability of laboratories for isolation of S. pneumoniae on human blood agar in resource limited settings. The results highlight the difficulties inherent in correctly identifying pathogens in mixed cultures in needs improvement using standardized tests across the study centers. The study also reaffirms the ability to transport biological specimens over long geographical distances without loss.

Modified PAP method to detect heteroresistance to vancomycin among methicillin resistant Staphylococcus aureus isolates at a tertiary care hospital.

This study was an attempt at developing, establishing, validating and comparing the modified PAP method for detection of hetero-vancomycin resistant Staphylococcus aureus (h-VRSA) with the routine antimicrobial susceptibility testing (using the BSAC standardized disc diffusion method), minimum inhibitory concentrations of vancomycin using standard E-test methodology and the Hiramatsu's screening method. A total of 50 methicillin resistant Staphylococcus aureus obtained from various clinical specimens, along with the Mu 3 and Mu 50 strains as controls, were studied. No VRSA isolates were obtained. However, four of the test strains were positive by the Hiramatsu's screening method, of which only one isolate could be confirmed by the modified PAP analysis method. This isolate was a coloniser from the drain fluid of a liver transplant recipient. The sensitivity, specificity, positive predictive value and the overall efficiency of the Hiramatsu's screening method with the modified PAP analysis as the gold standard were found to be 100, 93.8, 25 and 94%, respectively. It is very essential for clinical laboratories to screen for h-VRSA, given the increasing use of glycopeptide antibiotics in therapy and the potential for failed therapy in patients infected with these strains.