title: Detection of TEM-, SHV- and CTX-M-type β-lactamase production among clinical isolates of Salmonella species.
abstract: Enteric fever is a major public health problem in developing countries. Due to the problem of resistance to first-line drugs and fluoroquinolone, cephalosporins are currently used for treatment of enteric fever. Cephalosporin resistance in Salmonella spp. is mainly due to production of extended-spectrum β-lactamases (ESBLs). The majority of ESBLs in Salmonella are derivatives of the TEM and SHV β-lactamase families. The objectives of this study were to detect antibiotic susceptibility patterns, ESBL production and TEM-, SHV- and CTX-M-encoding genes (blaTEM, blaSHV and blaCTX-M) among clinical isolates of Salmonella spp. A total of 134 Salmonella isolates [Salmonella Typhi (n = 101), Salmonella Paratyphi A (n = 31), Salmonella Paratyphi B (n = 1) and Salmonella Typhimurium (n = 1)] were included in this study. Multidrug resistance was seen in 5/134 (3.73%) isolates, all of which belonged to serotype S. Typhi. A better susceptibility profile was observed for first-line drugs (ampicillin, chloramphenicol, co-trimoxazole and tetracycline) and cephalosporins (cefotaxime, ceftazidime, ceftriaxone, cefixime and cefepime). However, 131 (97.76%) of the 134 isolates were resistant to nalidixic acid and one (0.75%) was resistant to ciprofloxacin. TEM-1-type β-lactamase (blaTEM-1) was detected in six (4.47%) of the 134 isolates, which belonged to the serotype S. Typhi. All six TEM-positive isolates were negative for the blaSHV gene and none of the isolates was positive for the blaCTX-M gene. The presence of the blaTEM gene encoding TEM-1 β-lactamase is believed to confer resistance only to penicillins and early cephalosporins; however, the resistance spectrum of TEM-1 descendants may extend to second-, third- and fourth-generation cephalosporins. The ESBLs derived from TEM-1 differ from their progenitors by as few as 1 aa, and have the ability to hydrolyse third-generation cephalosporins. Therefore, appropriate selection and rotation of antibiotics as well as continuous monitoring of antibiotic susceptibility profiles could help to control the emergence and spread of resistant strains.
authors.affiliation: Department of Microbiology, Dr ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai 600 113, Tamil Nadu, India.
authors.forename: Sathishkumar
authors.initials: S
authors.lastname: Elumalai
authors.affiliation: Central Research Laboratory, Sri Manakula Vinayagar Medical College and Hospital, Madagadipet, Pondicherry 605 107, India.
authors.forename: G
authors.initials: G
authors.lastname: Muthu
authors.affiliation: Department of Microbiology, ESIC Hospital, K. K. Nagar, Chennai 600078, Tamil Nadu, India.
authors.forename: R Esther Mary
authors.initials: REM
authors.lastname: Selvam
authors.affiliation: Department of Microbiology, Dr ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai 600 113, Tamil Nadu, India.
authors.forename: Srivani
authors.initials: S
authors.lastname: Ramesh
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D016133:Polymerase Chain Reaction; D012475:Salmonella / Q000145:classification* / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D012480:Salmonella Infections / Q000382:microbiology*; D001618:beta-Lactamases / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001618:beta-Lactamases