Phage types, antibiotic susceptibilities and plasmid profiles of Salmonella typhimurium and Salmonella enteritidis strains isolated in Istanbul, Turkey

Objective   To examine 13 Salmonella typhimurium and 22 S. enteritidis strains isolated from individual cases of gastroenteritis for their phage types, antibiotic susceptibilities and plasmid profiles.
Methods   The phage typing of S. typhimurium strains was done according to the method of Anderson et al, and the phage typing scheme of Ward et al was used for phage typing of S. enteritidis strains. Antibiotic susceptibility testing was performed by the Kirby–Bauer disk diffusion method. Extended-spectrum β-lactamase production of the strains was determined by the three-dimensional method. Plasmid profiles of the strains were examined using the method described by Kado and Liu with some modification by Graeber et al.
Results   Two S. typhimurium strains were DT 193 and one was DT 22, whereas 10 strains were untypable. PT 4 was the predominant phage type among S. enteritidis strains. Four S. enteritidis strains were DT 6a, three strains were PT 1 and one strain was PT 8, whereas only one strain was untypable. Eleven of 13 S. typhimurium and three of 22 S. enteritidis strains were found to be multiresistant. Ten different resistance patterns among S. typhimurium and four different resistance patterns among S. enteritidis strains were detected. Extended-spectrum β-lactamase production was detected in 10 of 13 S. typhimurium and in three of 22 S. enteritidis strains. All S. typhimurium strains but one were found to contain at least one plasmid, with molecular masses varying between 4 and 107 MDa, and 11 different plasmid patterns were determined. Plasmid pattern analysis permitted further differentiation of the S. enteritidis strains into nine groups. A serovar-specific virulence plasmid of 36 MDa was detected in 13 of 22 S. enteritidis strains.
Conclusions   The results suggest that the majority of S. typhimurium strains were closely related.