Long-term effects of antibiotic administration on clonal stability and emergence and persistence of resistance genes in the intestinal microflora

Abstract number: 1133_207

Löfmark S., Jernberg C., Edlund C.

Objectives:  

To study emergence and persistence of antibiotic resistance genes in the intestinal flora after antibiotic administration over a two-year period, and to monitor the stability of clonal selection and changes in the fingerprint patterns of the dominant members of the bacterial community. The commensal flora of the human intestine is a complex ecological system involved in host beneficial activities and disturbances of the microflora by antibiotic administration can lead to clinical implications. Exchange of resistance genes among the intestinal bacteria and bacteria passing through the colon might also be a serious threat to human health.

Methods:  

Four healthy subjects receiving clindamycin for seven days and four non-treated subjects were included in the study. Faecal samples collected at nine different time points prior to and during a two-year period following the antibiotic treatment were cultured for Bacteroides spp. strains. Twenty representative colonies were collected and phenotyped and tested for antimicrobial susceptibility to clindamycin, tetracycline and ampicillin according to NCCLS. Screening of specific resistance genes were performed by RealTime PCR. Resistance to the different antibiotics has shown to be connected and presence of tetQ, ermF, ermB, cepA and cfxA involved in these resistances were investigated. Specifically ermF and tetQ are common in the B. fragilis group and often reside on the same conjugative transposons. rep-PCR was used for clonal genotyping of the isolates and T-RFLP was used for fingerprinting of the total faecal bacterial community.

Results and Conclusion:  

Short-term administration of clindamycin resulted in major long-term ecological disturbances up to at least 24 months after administration. The trend showed a decline in species diversity, which did not return to pre-treatment levels for up to 18 months after administration. An increased frequency of resistance to clindamycin and tetracycline and a long-term enrichment of resistance genes (ermF and tetQ) among Bacteroides spp. were seen in exposed subjects. A broad baseline variation of clonal stability and antibiotic resistance between subjects were observed in both groups. This fingerprinting pattern of the total bacterial community challenges the common view of the intestinal microflora as a stable environment.