Detection of multidrug resistance and associated genes among <em>Salmonella</em> species from enteric fever cases

Abstract

Background: Salmonella spp. has rapidly gained resistance to ampicillin, chloramphenicol, co-trimoxazole, 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. Conclusion: We have observed a low MDR prevalence and reduced susceptibility to the fluoroquinolone, ciprofloxacin. This changing susceptibility pattern of Salmonella species over time warrants continuous monitoring and judicious use of antibiotics to prevent the emergence of resistant strains.

Keywords

• beta-lactamases, enteric fever, fluoroquinolones, multidrug resistance, salmonella species