Caracterización molecular de mecanismos de resistencia a cloranfenicol en cepas de Shigella flexneri aisladas en niños chilenos con diarrea aguda

Background: Chloramphenicol is one of the therapeutic options for shigellosis, but resistance to this antimicrobial is increasing. Aim: To characterize molecular mechanisms conferring resistance to chloramphenicol (Cm^R) in Shigella flexneri strains isolated from Chilean children with acute diarrhea. Material and methods: Thirty one Shigella filexneri strains, including 22 with the Cm^R phenotype were analyzed. Strains were tested for antimicrobial susceptibility by plate dilution and for the presence of an internal fragment of the cat gene encoding for chloramphenicol o-acetyl-transferase, by polymerase chain reaction and Southern blot analysis. Results: All Cm^R strains had a minimal inhibitory concentration over 64 μg/ml and amplified the internal fragment of the cat gene. Southern blot analyses indicated that this gene was located in the bacterial chromosome. Conclusions: Resistance to chloramphenicol in this group of Shigella flexneri strains was mediated by a chromosomally located cat gene.