Aims: Salmonella enterica serovar Typhi is the major causative agent for typhoidial fever around the globe among human population reported till date. Present research work was carried out for detection and molecular characterisation of Salmonella enterica serovar Typhi isolated from humans with Typhoidial fever by biochemical, phenotypical and virulence gene based polymerase chain reaction (PCR) techniques. The isolated strains were also investigated for antibiotic susceptibility patterns as a control measure. Methodology and Results: A total of 16 clinical samples were collected from the same numbers of patients (7 males and 9 females) from Coimbatore, Erode and Salem districts of Tamil Nadu and were processed via broth enrichment methods for isolation and identification of the causative agent S. enterica serovar Typhi. Microbiological and biochemical investigations revealed the presence of S. Typhi from 16 samples. The biotyping of the isolates showed that all the isolates belonged to biotype IV. The PCR analysis confirmed the presence of invA (Invasion gene, 244bp), tyv (Tyvelose epimerase gene, 615 bp), fliC-d (Phage-1 flagellin gene for d-antigen, 750 bp) and viaB (Vi antigen gene, 439bp) in all 16 clinical samples. The antibiotic susceptibility test that was carried out among the isolates against 12 antimicrobial agents, showed 100 % resistance to only ampicillin and 100 % sensitivity to carbenicillin, chloramphenicol, clindamycin, gentamycin, kanamycin and tetracycline. Conclusion, significance and impact of study: This study confirmed the association of virulent strains of S. enterica serovar Typhi from Typhoidial fever among human population and suggested that PCR based diagnostic could be very useful for the rapid detection of S. Typhi isolates. Present study emphasized the use of antibiotic like chloramphenicol or in combination with other antibiotics for the effective control of S. Typhi.

Aims: Present research is focused on the molecular level characterization of drug-resistant Listeria monocytogenes identified from food and water samples from Tamil Nadu, India. Methodology and results: A total of 39 food and water samples were collected from local markets and retail shops in Tamil Nadu, India and processed for the isolation and identification of bacteria. Morphology of the bacteria was analysed under a fluorescent microscope. Isolated bacteria were serotyped and screened for the presence of virulence-associated genes haemolysin (hlyA) and invasive associated protein (iapA) by Real-time polymerase chain reaction. The qPCR positive isolates were also typed by random amplified polymorphic DNA-PCR for epidemiological study. Antibiotic resistance test was done with 16 commercial antibiotics by disc diffusion method. A total of 8 (20.51%) L. monocytogenes were identified belonging to the serotype group 1/2a, 1/2b, 1/2c and 4b. PCR assays revealed the presence of hlyA (456 bp) and iapA (131 bp) genes. In RAPD, OPA-10 primer was found to generate the distinct polymorphic fragment among the isolates. All the isolates were 100% resistant to rifampicin, co-methoxazole, linezolid and oxacillin and 100% sensitive to tetracycline and chloramphenicol. Tetracycline and chloramphenicol are suggested to be a very effective antibiotic against the tested L. monocytogenes isolates. Conclusion, significance and impact of study The hlyA and iapA based quantitative PCR technique could be a rapid molecular technique for the detection of L. monocytogenes used in this study. Serotyping along with RAPD-PCR was able to discriminate between the isolates and therefore could serve as a robust and sensitive tool for typing antibiotic-resistant strains of L. monocytogenes.