Molecular Epidemiology, Antimicrobial Resistance and Characterization of Extended-Spectrum Beta-Lactamases of Salmonella enterica Serotype Paratyphi B Clinical Isolates

Abstract

Although Salmonella enterica serotype Paratyphi B is the less frequently isolated serotype worldwide and in Turkey, it is the most common serotype in our hospital, with a marked increase in 2007. The purpose of this study was to investigate the antibiotic susceptibility and the extended spectrum beta-lactamase (ESBL) profile, and molecular epidemiology of S. Paratyphi B isolates detected in our hospital microbiology laboratory. Seventy isolates identified as S. Paratyphi B from 109 Salmonella isolates obtained from clinical specimens from different patients between October 2005 and December 2012, were included in the study. In addition to conventional methods, isolates were identified using the Phoenix automated microbiology system (Becton Dickinson, USA). Serotyping of the isolates was performed on the basis of slide agglutination and the Kauffmann-White scheme. The antibiotic susceptibility of the isolates was determined using the BD Phoenix (TM) automated system and disk diffusion test. ESBL enzymes were investigated using the combined disk test, isoelectric focusing, polymerase chain reaction (PCR) and sequence analysis. The molecular epidemiology of the 51 isolates obtained between October 2005 and August 2008 was examined with pulsed-field gel electrophoresis (PFGE) using the Xbal enzyme. S. Paratyphi B isolates were obtained from 70 specimens (46 blood, 16 fecal, 4 bone marrow, 2 urine and 2 wound) each from different patients. Resistance to nalidixic acid was determined in 18.6%, resistance to ampicillin, cefotaxime and cefepime in 2.9% and to ceftazidime and co-trimoxazole in 1.4% of the isolates. ESBL production was detected only in two isolates; in one TEM-1 was accompanied by CTX-M-15 and in the other isolate CTX-M-3 was found. Forty-six of the 51 isolates (90%) were found to be genetically related by PFGE and were placed in cluster A. The distribution of the isolates in cluster A revealed six subtypes as A1 (n= 7), A2 (n= 11), A3 (n= 7), A4 (n= 18), AS (n= 2) and A6 (n= 1). Three different patterns not related to the cluster A were determined in the remaining five isolates (two were B, one of each was C, D and E). In conclusion, although the rate of antibiotic resistance was low in the S. Paratyphi B isolates in our hospital, rare types of ESBLs such as CTX-M-3 and CTX-M-15 were detected in Salmonellae. As far as the current literature is considered, this is the first report in Turkey of bla(CTX-M-15) in Salmonella spp. and bla(CTX-M-3) genes in S. Paratyphi B. The results may indicate a possible future threat to the treatment of Salmonella infections. Since most of the isolates were genetically related, this might suggest an epidemic in our region.