Detection of blaCTX-M Extended Spectrum Betalactamase Producing Salmonella enterica Serotype Typhi in a Tertiary Care Centre DC21-DC24
Dr. Uma Sekar,
No. 1, Ramachandra Nagar, Chennai-600116, Tamil Nadu, India.
Introduction: Infections caused by Salmonella are an important public health threat in tropical and subtropical countries. Due to the emergence of resistance to ampicillin, chloramphenicol and trimethoprim/sulfamethoxazole (multidrug resistant salmonellae) in the late 1980s, fluoroquinolones and extended spectrum cephalosporins became the drugs of choice. Resistance to cefotaxime and ceftriaxone due to the production of Extended Spectrum Beta-Lactamase (ESBL) and reduced susceptibility to ciprofloxacin have emerged resulting in treatment failure. The Cefotaximase (CTX-M) type ESBLs are the most widespread beta lactamase among Enterobacteriaceae including salmonellae.
Aim: To detect the presence of blaCTX-M in salmonellae causing human infections. Detection of qnr genes to identify the coexistence of blaCTX-M and qnr gene.
Materials and Methods: The study included 103 consecutive, non-repetitive salmonellae isolated from clinical specimens obtained from July 2015- June 2016 which were identified up to species level by conventional/automated methods. Susceptibility to various classes of antimicrobial agents was determined by disc diffusion method. Minimum Inhibitory Concentration (MIC) to cefotaxime and ceftriaxone was determined by agar dilution method. The results were interpreted in accordance with Clinical & Laboratory Standard Institute (CLSI) (guidelines 2015. Detection of the ESBL phenotype was performed by the combined disk method. Polymerase Chain Reaction (PCR) amplification of all isolates was performed using group specific primers to characterize the presence of blaCTX-M, qnrA, qnrB and qnrS.
Result: Of the 103 study isolates two isolates of Salmonella typhi were resistant to cefotaxime and ceftriaxone and had a MIC of 128µg/ml. PCR amplification and sequencing detected the presence of blaCTX-M-15 in these two isolates. These two isolates exhibited resistance to ciprofloxacin in vitro but qnr gene was not detected in these isolates.
Conclusion: Resistance to third generation cephalosporins among salmonellae is a cause for concern as it may lead to treatment failure. It is imperative to continuously monitor the susceptibility pattern as enteric fever is endemic in India.