Comparison of Phenotypic and Genotypic methods for Pyrazinamide susceptibility testing.

Objectives: To evaluate Pyrazinamide (PZA) susceptibility results obtained by phenotypic MGIT 960 TB system against enzymatic Pyrazinamidase assay and genotypic pncA gene sequencing. To find the prevalence of infections caused by M. bovis in PZA resistant M. tuberculosis complex isolates. Methods: 33 consecutive PZA resistant and 30 consecutive PZA susceptible isolates reported for PZA susceptibility testing by MGIT 960 TB system were included in this study. Presence of active pyrazinamidase enzyme was sought by using the Wayne assay. The pncA gene was amplified by PCR and then sequenced to screen mutations. All the PZA resistant isolates were further spoligotyped to identify M. bovis, if present. Results: Of 33 PZA resistant strains by MGIT 960, 31 were Wayne assay negative and two were positive. Of the 30 susceptible PZA strains six were Wayne assay negative reporting false resistance. PncA gene sequencing revealed that 32 of the 33 MGIT PZA resistant isolates had diverse nucleotide changes scattered throughout the pncA gene (one isolate did not show any mutation). Of the 30 phenotypically susceptible isolates, 21 were wild types whilst nine isolates showed the presence of a silent mutation C-T at codon 195. Fifteen mutations found in this study has not been described earlier. Not a single isolate of M. bovis was detected among PZA resistant M. tuberculosis complex isolates. Conclusion: MGIT 960 showed better concordance with sequencing results in comparison with Wayne assay. In present study, a high proportion (85%) of MDR-TB isolates from patients receiving anti-TB treatment were found to be resistant to PZA.

Comparing serology, antigenemia assay and polymerase chain reaction for the diagnosis of cytomegalovirus infection in renal transplant patients.

BACKGROUND: Cytomegalovirus (CMV) disease is responsible for significant morbidity and mortality following renal transplantation. Currently serology is the only method widely available in our country. Newer methods like early CMV pp65 antigenemia assay and CMV DNA amplification can diagnose CMV disease in its very early period. AIM: The aim of our study was to compare serologic method with antigenemia assay and CMV DNA amplification to diagnose CMV. METHODS: Seventy-three renal transplant recipients (from 7 centres) with clinical suspicion of CMV disease were studied prospectively. The diagnosis of CMV infection was suspected on the basis of fever and leucopenia. RESULT AND DISCUSSION: Three tests were done in all 73 patients and in 22 healthy subjects (control group). The sensitivity and specificity of serological test (CMV IgM) was 72.97 and 62.06%; of antigenemia assay was 89.18 and 100% and of PCR was 100 and 72.41%. CONCLUSION: Antigenemia assay is a sensitive and specific test for early and rapid diagnosis of CMV infection. Qualitative PCR is a sensitive marker but has low specificity.