Detection of multidrug resistance and associated genes among Salmonella species from enteric fever cases

Background: Salmonella spp. has rapidly gained resistance to ampicillin, chloramphenicol, cotrimoxazole, and tetracycline (ACCoT) which necessitated the use of fluoroquinolones and cephalosporins. However, there are reports on emergence of fluoroquinolone-resistant Salmonella isolates in various parts of Asia and low resistance to third-generation cephalosporins. The incidence of multi-drug resistant (MDR) Salmonella enterica serovar Typhi (S. Typhi) in India increased in the 1990s. After a decade, studies showed reduced MDR percentage. Hence this study was performed to detect antibiotic resistance patterns and associated genes among clinical isolates of Salmonella. Methods: A total of 171 clinical isolates of Salmonella isolates collected between 2011 to 2016 from a tertiary care hospital in Chennai, India were included. Antibiotic susceptibility testing and screening for extended-spectrum β-lactamase production was performed. Genes encoding resistance to β-lactam antibiotics (blaTEM, blaSHV, and blaCTX-M), chloramphenicol (cat, cmlA, and floR), co-trimoxazole (sul1, sul2, sul3, and dfr), and tetracycline (tet(A), tet(B), tet(C), tet(D), tet(E), and tet(G)) were detected using PCR and nucleotide sequencing analysis. Results: The majority of the isolates were susceptible to ACCoT antibiotics, cephalosporins, and carbapenems. Most of the isolates were resistant to nalidixic acid and 1.7% were sensitive to ciprofloxacin. All the isolates (n=171) were negative for ESBL. Multidrug resistance was seen in 4.1% isolates and all the MDR Salmonella isolates were found to contain blaTEM-1(TEM-1-type β-lactamase), cat, dfrA17, sul1, and tet(B) genes.