ABSTRACT
Background: Serpentine cord formation in BACTEC MGIT 960 medium was evaluated as a rapid method for the presumptive identification of M. tuberculosis complex (MTBC). Material & Methods: Total 2527 samples were processed for AFB culture using MGIT 960 TB system over a period of three months. AFB smears were prepared from 1000 MGIT tubes flagged positive by the MGIT instrument and stained by ZN method to examine presence or absence of serpentine cording. The cord formation was compared with PNBA [pnitro benzoic acid] test on MGIT system and all controversial cases were further evaluated by NAP [p-nitro-a-acetylaminophydroxypropiophenone] test on BACTEC 460 TB system. Results & Discussion: Of the 1000 culture positives, 904 (90.4%) were identified as mycobacteria, of which 869 (96%) showed cording by smear microscopy. One (0.1%) was identified as nocardia. In the remaining 95 (9.5%) cases, primary smear made from MGIT vial was negative. Of 869 cultures showing serpentine cord formation, 842 were confirmed as MTBC and 27 as NTM by PNBA assay on MGIT 960 TB system. The sensitivity, specificity, positive and negative predictive values are found to be 99.6%, 54%, 96% and 91% respectively. An average detection time for PNBA assay was found to be eight days whereas cording results were available on the same day of culture positivity. Conclusion: Though highly sensitive it is not very specific and hence cannot be the only test for presumptive diagnosis of MTBC.
ABSTRACT
BACKGROUND: Urine cultures are among the most numerous of culture types for microbiology studies. In this study, we evaluated the utility of CHROMagar Orientation (CO; Becton Dickinson, Cockeysville, MD, USA), a new chromogenic medium, for the detection, enumeration, and presumptive identification of urinary tract pathogens. METHODS: The 438 clinical urine samples sent for routine culture were plated onto CO and Bi-plate (blood/MacConkey agar). We compared the detection and enumeration of potential pathogens, and the agreement between presumptive identification directly from CO and the confirmative identification, which was performed using conventional biochemical tests and Vitek system. RESULTS: The detection rate of urinary tract pathogens on all two media, CO and Bi-plate were nearly identical. The enumeration of colony counts was consistent on the two media for 102 of the 108 (94%) microorganisms. Colony color and morphology on CO accurately differentiated Escherichia coli and Enterococcus spp. The overall agreement of presumptive identification on CO was 91 of the 108 (84%). CONCLUSION: The CO enabled accurate detection, count determination, and presumptive identification of common urinary pathogens, both in pure and mixed cultures.