In vitro conjugation kinetics of ESBL-producing Escherichia coli donors and various Enterobacteriaceae recipients

Abstract Background: Extended spectrum beta-lactamase (ESBL)-producing enterobacteria pose a major hazard to public health. Due to the possibility of genetic transfer, ESBL genes might spread to pathogenic enterobacterial strains. Thus, information on possible genetic transfer between enterobacteria is of high interest. It was therefore the aim of this in vitro study to screen the capacity of a wide range of Enterobacteriaceae for time dependent differences in conjugation with five ESBL-producing Escherichia (E.) coli strains. Results: Conjugation frequencies for five potential E. coli donor strains, producing the enzymes CTX-M-1, CTX-M-15, SHV-12, TEM-1, TEM-52 and CMY-2, and six potential recipient strains (E. coli, Serratia marcescens subsp. marcescens, Enterobacter cloacae, Salmonella Typhimurium and Proteus mirabilis) were obtained. Hence, different combinations of donor and recipient strains were co-incubated for between 0 and 22 hours and spread on selective agar. Conjugation frequencies were calculated as transconjugants per donor. Some of the donor and recipient strain combinations did not show plasmid transfer within 22 hours. Hence, the recipient Proteus mirabilis did not accept plasmids from any of the given donors and E. coli ESBL10716 was not able to transfer its plasmid to any recipient. Enterobacter cloacae only accepted the plasmids from the donors E. coli ESBL10708 and E. coli ESBL10716 while E. coli ESBL10708 did not transfer its plasmid to Serratia marcescens subsp. marcescens. E. coli IMT11716 on the other hand did not perform conjugation with the donor E. coli ESBL10689. The remaining mating pairs differed in conjugation frequency, ranging from log -5 to -8.5 transconjugants/donor. The earliest conjugation events were detected after 4 hours. However, some mating pairs turned positive only after 22 hours co-incubation.Conclusion: The results of this study suggest that conjugation is a frequent event in the spread of ESBL genes among commensal and pathogen bacteria. This should be considered when addressing antibiotic resistance issues.