Non-plasmid associated transfer of antibiotic resistance in Bacteroides

We have examined 13 clinical isolates of the intestinal Bacteroides group using DNA probes representing Bacteroides macrolide-lincosamide-streptogramin B (MLS) (ermF) and tetracycline resistance (tetQ) determinants as well as an insertion sequence (1S4351) previously seen in association with erm genes. tetQ-hybridizing sequences were detected in 11 of 13 tetracycline-resistant clinical isolates. On the other hand, ermF-like sequences were detected in only three of eight clindamycin-resistant strains. One isolate displayed low-level, inducible resistance to clindamycin and was sensitive to erythromycin. This same isolate had IS4351-like sequences but was missing ermF-like sequences, in contrast to previous reports which demonstrated the common association of IS4351 and erm genes. Our results suggest the occurrence of unclassified MLS genes in the Bacteroides group and furthermore suggest that IS4351-like sequences are not always linked to Bacteroides ermF-like sequences. Finally, 4 of 13 isolates conjugally transferred tetracycline resistance or linked tetracycline-clindamycin (MLS) resistances, but this process did not involve plasmids.

“…Conjugation and selection of tranconjugants were performed as previously described (8). Plasmid DNA extraction followed the method of Birnboim and Doly (1).…”

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confidence: 99%

“…DNA was digested with restriction enzymes as specified by the manufacturer (GIBCO/BRL, Gaithersburg, Md. (6,8,19,25).…”

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confidence: 99%

Molecular survey of clindamycin and tetracycline resistance determinants in Bacteroides species

Fletcher

Macrina

1991

“…(7,11,13); clindamycin resistance genes homologous to the plasmid resistance genes appeared to be located in the chromosome of many different Bacteroides * isolates (7,11,13). The same location is suggested for transferable tetracycline resistance (11,13). Until (Fig.…”

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confidence: 74%

“…Matings between Bacteroides spp. were carried out for 16 h on membrane filters (type HA; pore size, 0.45 ,m; Millipore Corp.) as described by Macrina et al (11). Transconjugant selection was made on agar plates containing Cm (16 pug/ml), clindamycin (16 ,ug/ml), ampicillin (16 ,ug/ml), or tetracycline (2 pg/ml), plus the counterselective drug (rifampin at 32 ,ug/ml or fusidic acid at 16 ,ug/ml).…”

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confidence: 99%

Transferable plasmid-linked chloramphenicol acetyltransferase conferring high-level resistance in Bacteroides uniformis

Martı́nez-Suárez¹,

Baquero²,

Reig³

et al. 1985

Bacteroides uniformis RYC3373 resistant to 64 ,ug of chloramphenicol per ml was isolated from a peritoneal pelvic abscess of a patient not previously treated with this drug. Chloramphenicol resistance was transferable at low frequency to a suitable Bacteroides fragiis recipient. The acquisition of resistance was linked to the presence of a 39.5-kilobase plasmid (pRYC3373), which was subsequently transferred to a secondary recipient.The transfer of Cm resistance occurred by a conjugation-like process. Donor and transconjugant strains produced chloramphenicol acetyltransferase constitttively. The Km for chloramphenicol was 40 ,uM, and its inactivation by 5-5'-dithiobis(2-nitrobenzoic acid) suggested its similarity to the type II enterobacterial enzymes encoded by different conjugative plasmids and also toa previously described enzyme of B. fragilis F47 and F48. The specific activity and the resistance level in pRYC3373-bearing strains were more than 10-fold higher than in the case of the enzyme from B. fragilis strains F47 and F48. The genetic basis of chloramphenicol acetyltransferase synthesis in Bacteroides spp. had not been previously established.At present, one of the limited uses of chloramphenicol (Cm) is the treatment of some serious infections caused by organisms of the Bacteroides fragilis group (6, 18). In susceptibility studies, Cm resistance proved to be very rare in this group of organisms (6), although clinical failures have been described (21).Cm resistance in most pathogenic bacteria is plasmid borne and due to the presence of an enzyme, chloramphenicol acetyltransferase (CAT), which catalyzes the acetyl coenzyme A-dependent acetylation of the antibiotic (23). Britz and Wilkinson have characterized a CAT determining intermediate resistance in fecal isolates of B. fragilis (4). The enzyme was apparently similar to the CAT type II from enterobacteria, encoded by several conjugative plasmids (23). However, the genetic basis of CAT synthesis in Bacteroides spp. has not been established.To date, all plasmids studied in Bacteroides spp. confer clindamycin resistance (7,12,24,26,27). All are selftransmissible, and their conjugative host range seems to be limited to the B. fragilis group. Nevertheless, intra-and intergeneric transfers of Cm resistance among strains of the B. fragilis group and from Bacteroides spp. to E. coli, respectively, have been described, but neither the plasmids nor the resistance mechanisms were investigated (14,20).In this study, we report isolation of a transferable plasmid associated with resistance to Cm in a clinical isolate of B. uniformis as well as comparison of the CAT involved in the resistance with previously described enzymes from E. coli and B. fragilis.(Part of this work was presented in the 4th Mediterranean Congress of Chemotherapy, Rhodos, Greece, 1984 Media and culture conditions. The solid media used were brain heart infusion agar for the growth of E. coli, and brucella blood-supplemented agar for Bacteroides spp. The liquid medium was brain heart infusion broth...

“…No clindamycin-resistant strains of B. uniformis were detected, yet this was the least common isolate and was not statistically significant. Filter matings have demonstrated successful transfer of clindamycin resistance from B. fragilis to B. uniformis in vitro (12,14), but unfortunately, no survey has stated the incidence of clindamycin resistance in the latter species.…”

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confidence: 99%

Modified broth-disk surveillance of clindamycin-resistant Bacteroides fragilis group

Zar¹

1983

The modified broth-disk susceptibility test was used to assess the incidence of clindamycin resistance in the Bacteroidesfragilis group. Over a 34-month period, 544 isolates were tested, 21 (4%) of which were found to be resistant. There was no significant difference in resistance among the six species, and resistance did not increase with time. In a 12-disk assay, the concentrations of clindamycin achieved approximated the concentrations expected (expected breakpoint, 4.8