Molecular characterization of Salmonella enterica serovar Typhimurium strains isolated from humans in Turkey

Abstract

Multidrug resistant (MDR) Salmonella infections, especially infections due to Salmonella Typhimurium DT104 phage type strains are an important public health issue in many parts of the world. S.Typhimurium is the most common serotype isolated from clinical samples in Turkey but we have limited data about the phage types of these isolates. The aims of this study were to find out whether these MDR S.Typhimurium isolates are DT104 phage type isolates and have class 1 integrons and to investigate the relationships of these characteristics between plasmid and pulsed field gel electrophoresis (PFGE) profiles. A total of 66 S.Typhimurium stock strains selected from Enterobacteria Laboratory culture collections of Ankara University School of Medicine, Department of Medical Microbiology were investigated by plasmid profile analysis (PPA) and PFGE with the use of XbaI and SpeI enzymes. The presence of class 1 integrons and the phage type 104 were investigated by polymerase chain reaction (PCR). The strains used in the study were sporadically isolated cases from seven provinces after year 2000 with ACSSuT (63), ACGSSuTT/S (1), ACSSuTT/S (1) and ASSuTT/S (1) resistance types [ampicillin (A), chloramphenicol (C), gentamicin (G), streptomycin (S), sulphonamide (Su), tetracycline (T), trimethoprim/sulfamethoxazole (T/S)]. Of the isolates 65 were found as DT104 phage type. Forty-three S.Typhimurium DT104 isolates that carry class 1 integrons had five different bands between 350-1600 base pairs (bp); all of the isolates harbored 1-4 plasmids with sizes ranging from 1.0-180 kbp and 62 isolates had 90 kbp plasmid which was serotype specific and virulence related. S.Typhimurium DT104 isolates were grouped into five (X1-X5) and seven (S1-S7) profiles with XbaI and SpeI enzymes, respectively. When the profiles of the two enzymes were evaluated, 58 of the 65 (89.2%) isolates showed similar (X1.S1) profile. The molecular characteristics of the most S.Typhimurium isolates were clustered in similar groups when class 1 integron, plasmid and PFGE types were analyzed together. In this study we showed that nearly all S.Typhimurium isolates with five drug resistance pattern (ACSSuT) were DT104 isolates. PFGE profiles of these sporadic isolates suggested that they were epidemiologically related.