Conjugative Transfer of Plasmid Encoding Extended-Spectrum Beta-Lactamase to Recipient Salmonella Strains

Background. Salmonella enterica subsp. enterica is one of the most frequently occurring etiological factors of severe gastroenteritis in children. Young children are also commonly colonized by bacterial strains producing ESBL enzymes. These enzymes are encoded on plasmids and can be easy transferred by conjugation to other Gram-negative strains, especially from fecal flora. Objectives. This study examined the transferability of ESBL plasmid from Klebsiella pneumoniae strains to clinical Salmonella isolates and then between clinical Salmonella strains, which leads to Salmonella resistance to beta-lactam antibiotics, the most often used in treatment. Material and Methods. The transferability of beta-lactam resistance determinants was studied by the bacterial conjugation method. K. pneumoniae ATCC 700603 carrying SHV-18 ESBL genes and a clinical isolate of K. pneumoniae 20 (ESBL+) were used as the donors of ESBL plasmid. S. enterica serovar Enteritidis (n = 10), S. enterica serovar Typhimurium (n = 10), and S. enterica serovar Hadar (n = 10) isolates were used as the recipient strains. Before and after conjugation the MICs of amikacin (AK), ampicillin (AM), ceftriaxone (TX), ceftazidime (TZ), trimethoprim-sulfametoksazol (TS), and ciprofloxacin (CI) were measured by the E-test. All isolates were tested for ESBL activity by the disc diffusion test (the Jarlier Double-Disc test) and the E-test. The plasmid DNA patterns were analyzed by the alkaline method. Results. All S. Enteritidis (10/10), several S. Typhimurium (4/10), and one S. Hadar (1/10) isolate became transconjugants. All Salmonella transconjugants were identified as ESBL producers. After conjugation, increases in the MICs of AM, TX, and TZ were observed. Conclusion. The efficiency of ESBL plasmid transferability depended on the Salmonella serovar. The S. enterica serovar Enteritidis strains were the best ESBL plasmid recipients among the clinical Salmonella serovars (Adv Clin Exp Med 2009, 18, 1, 63-70).