Molecular characterization of antimicrobial resistance in non-typhoidal salmonellae associated with systemic manifestations from India

Extended-spectrum cephalosporins and fluoroquinolones are essential antimicrobials for treating invasive salmonellosis, although emerging resistance to these antimicrobials is of growing concern, especially in India. Therefore, a study was conducted to characterize the antimicrobial susceptibility phenotypes, types of extended-spectrum β-lactamase (ESBL) gene plasmids and serological relationships of 21 non-typhoidal Salmonella isolates from patients who attended three different hospitals in India from 2006 to 2008. The isolates were cultured from stool, blood and cerebrospinal fluid samples obtained from patients presenting with diarrhoea and accompanying systemic manifestations such as fever, vomiting and meningism. Non-typhoidal Salmonella isolates were investigated using serotyping and antimicrobial susceptibility testing. PCR screening was also performed to detect the β-lactamase, qnr and aac(6′)-Ib-cr genes and class 1 integrons. Sequencing for quinolone resistance mutations and plasmid replicon typing were also performed. An antimicrobial resistance microarray was used for preliminary screening and identification of bla(TEM) and bla(SHV) genes, and phenotypic testing for the presence of efflux pumps was also performed. Ten out of 21 isolates (48%) possessed the extended-spectrum cephalosporin resistance phenotype, with PCR amplification and sequencing revealing that isolates possessed TEM-1, SHV-12, DHA-1, OXA-1-like and CTX-M-15 ESBL genes. FII(s) plasmid replicons were detected in seven isolates (33%). The involvement of efflux pumps was detected in four isolates (19%) resistant to ciprofloxacin. It was concluded that SHV-12-carrying Salmonella serotype Agona may play an important role in ESBL-mediated resistance in non-typhoidal salmonellae in India. The very high percentage (48%) of ESBL-producing non-typhoidal salmonellae isolated from these patients represents a real and immediate challenge to the effective antimicrobial therapy of Salmonella infections associated with systemic manifestations. Continued surveillance for the presence of ESBL-producing (non-typhoidal) salmonellae in India is essential.