Ciliates promote the transfer of the gene encoding the extended-spectrum β-lactamase CTX-M-27 between Escherichia coli strains

The mechanism by which Escherichia coli acquires multidrug resistance genes from other bacteria in the natural environment or livestock is still unclear. The ability of ciliates to promote the transfer of genes encoding extended-spectrum beta-lactamases (ESBLs) between the CTX-M-27 donor and clinically isolated recipient E. coli strains was investigated. Equal amounts (similar to 10(9) cfu) of donor cefotaxime-resistant E. coli and recipient ciprofloxacin-resistant E. coli strains were mixed together in the presence or absence of 10(5) ciliates in Page's amoeba saline for 24 h, in the presence or absence of certain drugs (cytochalasin D, cycloheximide and latrunculin B). Gene transfer frequency in the presence of ciliates was estimated at similar to 10(-6); in the absence of ciliates it was similar to 10(-10). Protein synthesis (cycloheximide) or phagocytosis (cytochalasin D or latrunculin B) inhibitors significantly reduced the frequency of gene transfer. Ciliates promote the transfer of genes encoding ESBLs between E. coli strains, implying that the presence of ciliates may provide a significant impact on emerging multidrug-resistant bacteria.