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Detection by PCR of the nim genes encoding 5-nitroimidazole resistance in Bacteroides spp.

ABSTRACT: A PCR method was developed for detection of the nim genes encoding 5-nitrolmidazole resistance in Bacteroides spp. Two PCR primers specific for nim genes were designed. They allowed amplification of a 458-bp fragment from all characterized plasmid- and chromosome-borne metronidazole resistance genes. The specificity of the method was tested with DNA from metronidazole-sensitive Bacteroides spp. strains and from other strains of unrelated species. Each DNA preparation was analyzed with and without an internal positive control to verify that the absence of PCR amplification product was not due to inhibition of the Taq polymerase inhibitors. By this technique, two newly discovered metronidazole-resistant clinical strains of Bacteroides fragilis were shown to harbor resistance genes undetectable by Southern blotting. In spite of the sequence divergence of the nim genes, the PCR method is thus suitable for epidemiological investigations. The amplification method also revealed that nim-related resistance genes were not present in either Streptomyces strain S6670, a natural producer of 2-nitroimidazole, or in Enterococcus faecalis strains, which have been suggested to possess metronidazole-inactivating enzyme.

SUBMITTER: Trinh S

PROVIDER: S-EPMC229193 | biostudies-other | 1996 Sep

REPOSITORIES: biostudies-other

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Detection by PCR of the nim genes encoding 5-nitroimidazole resistance in Bacteroides spp.

Trinh S S Reysset G G

Journal of clinical microbiology 19960901 9

A PCR method was developed for detection of the nim genes encoding 5-nitrolmidazole resistance in Bacteroides spp. Two PCR primers specific for nim genes were designed. They allowed amplification of a 458-bp fragment from all characterized plasmid- and chromosome-borne metronidazole resistance genes. The specificity of the method was tested with DNA from metronidazole-sensitive Bacteroides spp. strains and from other strains of unrelated species. Each DNA preparation was analyzed with and withou ...[more]

PMID: 8862561

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Project description:Transfer of antibiotic resistance genes by conjugation is thought to play an important role in the spread of resistance. Yet virtually no information is available about the extent to which such horizontal transfers occur in natural settings. In this paper, we show that conjugal gene transfer has made a major contribution to increased antibiotic resistance in Bacteroides species, a numerically predominant group of human colonic bacteria. Over the past 3 decades, carriage of the tetracycline resistance gene, tetQ, has increased from about 30% to more than 80% of strains. Alleles of tetQ in different Bacteroides species, with one exception, were 96 to 100% identical at the DNA sequence level, as expected if horizontal gene transfer was responsible for their spread. Southern blot analyses showed further that transfer of tetQ was mediated by a conjugative transposon (CTn) of the CTnDOT type. Carriage of two erythromycin resistance genes, ermF and ermG, rose from <2 to 23% and accounted for about 70% of the total erythromycin resistances observed. Carriage of tetQ and the erm genes was the same in isolates taken from healthy people with no recent history of antibiotic use as in isolates obtained from patients with Bacteroides infections. This finding indicates that resistance transfer is occurring in the community and not just in clinical environments. The high percentage of strains that are carrying these resistance genes in people who are not taking antibiotics is consistent with the hypothesis that once acquired, these resistance genes are stably maintained in the absence of antibiotic selection. Six recently isolated strains carried ermB genes. Two were identical to erm(B)-P from Clostridium perfringens, and the other four had only one to three mismatches. The nine strains with ermG genes had DNA sequences that were more than 99% identical to the ermG of Bacillus sphaericus. Evidently, there is a genetic conduit open between gram-positive bacteria, including bacteria that only pass through the human colon, and the gram-negative Bacteroides species. Our results support the hypothesis that extensive gene transfer occurs among bacteria in the human colon, both within the genus Bacteroides and among Bacteroides species and gram-positive bacteria.

Dataset Information

Detection by PCR of the nim genes encoding 5-nitroimidazole resistance in Bacteroides spp.

Publications

Detection by PCR of the nim genes encoding 5-nitroimidazole resistance in Bacteroides spp.

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