A Study of Molecular Characterization of the Trimethoprim Resistant Salmonella typhi Strains Prevalent in Himachal Pradesh

Abstract

Typhoid is a major public health problem in tropical and subtropical countries including India. Salmonella typhi, the causative agent of typhoid fever, is a gram-negative, motile, rod shaped, facultative anaerobe. It is solely a human pathogen and there is no animal reservoir. Antibiotic therapy is the mainstay for the treatment of typhoid fever and the complications associated with it. Nowadays, emerging multidrug resistance among Salmonella typhi strains has become a major public health problem. Present research work was carried out for the identification and molecular characterization of Trimethoprim resistant Salmonella enterica serovar typhi strains from individuals suffering with typhoid fever by means of various techniques i.e.; biochemicals, phenotypical and drug resistant gene specific polymerase chain reaction (PCR). A total of 14 blood specimen of infected patients were collected from Solan district of Himachal Pradesh with varying age groups and were processed via broth enrichment methods for primary isolation and identification of typhoid bacilli. Microbiological and biochemical investigations revealed the presence of S. typhi in all 14 specimens. The antibiotic susceptibility assay was carried out for 11 antimicrobial to study the MDR pattern of the identified bacilli. It was observed that 14/14 S. typhi strains were 100% resistance to Trimethoprim, Co-trimoxazole, Sulfanilamide, Penicillin, Ampicillin, Oxacillin, Tetracycline and Erythromycin, and 70-100% susceptible to Levofloxacin, Amikacin and Amoxicillin. The PCR analysis of these MDR strains showed the presence of dhfr a7 (365 bp) gene in only 10/14 isolates. This study confirmed that Trimethoprim resistance in these strains were due to the presence of dhfr a7 gene and also that PCR based diagnosis could be very useful for the rapid detection of drug resistant S. typhi strains. Present study emphasize that Trimethoprim drug is no longer useful for the treatment of typhoid fever as its MIC optimization was very high (750μg/ml). This study may further help the researchers in selecting the appropriate therapeutic approaches targeting Trimethoprim resistant Salmonella typhi strains.