Molecular epidemiology of ampicillin-resistant clinical isolates of Salmonella enteritidis

Abstract

During the last 6 years in Greece, there has been a significant increase in the number of ampicillin-resistant Salmonella clinical isolates reported. In this study 23 ampicillin-resistant Salmonella strains, consecutively isolated from patients with epidemiologically unrelated cases of food poisoning, were investigated. By serotyping and phage typing, 21 of these strains were identified as Salmonella enteritidis phage type 6a, 1 was identified as Salmonella typhimurium, and 1 was identified as Salmonella saintpaul. By plasmid pattern analysis, the 21 S. enteritidis strains were further differentiated into five groups. Group I consisted of 5 strains (carrying two plasmids of ca. 38 and 34 MDa), group II consisted of 10 strains (three plasmids of ca. 38, 34, and 2.5 MDa), group III consisted of 3 strains (four plasmids of ca. 38, 34, 15, and 2.5 MDa), group IV consisted of 1 strain (five plasmids of ca. 100, 38, 34, 24, and 15 MDa), and group V consisted of 2 strains (three plasmids of ca. 100, 38, and 24 MDa). Ampicillin resistance was easily transferred to Escherichia coli and was associated with the transfer of the 34-MDa plasmid, classified in the N incompatibility group for all strains of groups I to IV, and with the transfer of the 100-MDa plasmid for the group V strains. EcoRI restriction endonuclease digestions showed an extensive homology among the 34-MDa conjugative R plasmids. Hybridizations of the EcoRI restriction fragments of the 34-MDa plasmids with a TEM-type probe revealed the locus of the P-lactamase gene to be situated on a ca. 6.6-MDa fragment, common in all plasmids. These results indicate that ampicillin resistance in Greece is due to the spread of a limited number of clones of S. enteritidis phage type 6a, carrying related 34-MDa R plasmids. Work is in progress to obtain a better understanding of ampicillin resistance in S. enteritidis. Nontyphoid salmonellas are recognized as important causes

Regional dissemination of Salmonella enterica serovar Enteritidis is season dependent

“…Ampicillin resistance in S . Enteritidis is usually owing to TEM‐type β‐lactamase encoded by genes on a 34 – 60 ‐ , or 100 Mda plasmid [22,23]. The resistance to trimethoprim‐sulfamethoxazole and ampicillin, ticarcillin was expressed in three isolates.…”

Salmonella enteritidis diarrhoea in Harare, Zimbabwe

“…(1997) found a high proportion of S. enteritidis to be resistant to ampicillin and doxycycline in Greece. The increase in resistance of S. enteritidis to ampicillin is due to a 34‐MDa conjugative plasmid ( Vatopoulos et al . 1994 ) which is easily transferred to recipient cells ( Tassios et al .…”

Antimicrobial resistance in Salmonella enterica var. Enteritidis human isolates in Bosnia and Herzegovina

“…Salmonella enterica var. Enteritidis is the most prevalent serotype in humans with salmonella infection in many countries [1,2]. In Bosnia and Herzegovina, twice as many S. Enteritidis isolates were obtained in 2000 as in 1998.…”