Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation

Cuchural, George J.; Tally, Francis P.; Jacobus, Nilda V.; Aldridge, Kenneth E.; Cleary, Timothy J.; Finegold, Sydney M.; Hill, Gale B.; Iannini, Paul B.; O'Keefe, J. Paul; Pierson, Carl L.

doi:10.1128/aac.32.5.717

Cited by 142 publications

(61 citation statements)

References 11 publications

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“…The Anaerobe Working Group for the National Committee for Clinical Laboratory Standards (NCCLS) recommends that susceptibility testing of the B. fragilis group be done with a distribution of test isolates to approximate the species distribution normally isolated from infections (7). Several multicenter susceptibility studies have shown that the B. fragilis species comprises 58 to 63% of isolates (1,5,6,17). Such distribution rates have been relatively evident in studies reported during the 1980s and early 1990s.…”

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In Vitro Susceptibilities of the Bacteroides fragilis Group Species: Change in Isolation Rates Significantly Affects Overall Susceptibility Data

Aldridge

O’Brien

2002

J Clin Microbiol

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A comparison of antimicrobial susceptibility data of species of the Bacteroides fragilis group for 1989-1990 and 1998-1999 studies showed statistically significant increases or decreases in in vitro activity. Overall significant increases in resistance were noted for ampicillin-sulbactam and clindamycin, while significant decreases in resistance were noted for ertapenem and cefoxitin. Susceptibilities to piperacillin-tazobactam, imipenem, meropenem, and trovafloxacin remained virtually the same for the two studies. Importantly, a change in the rates of isolation of the various species showed the B. fragilis species comprised 58% of the isolates in 1989 to 1990 and 45% of the isolates in 1998 to 1999. This change in rates of isolation of B. fragilis versus non-B. fragilis species had an overall effect on susceptibility data.

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confidence: 93%

In Vitro Susceptibilities of the Bacteroides fragilis Group Species: Change in Isolation Rates Significantly Affects Overall Susceptibility Data

Aldridge

O’Brien

2002

J Clin Microbiol

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“…fragilis is the anaerobe most frequently isolated from human infections (8,33) and may constitute up to 60% of pathogenic anaerobic isolates from hospitalized patients (20). Apart from its resistance traits to various antibiotics (25), the species B. fragilis appears phenotypically homogeneous; however, DNA-DNA hybridization experiments have shown that it separates into two DNA homology groups, I and II, which have ca.…”

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confidence: 99%

Genotypic identification of two groups within the species Bacteroides fragilis by ribotyping and by analysis of PCR-generated fragment patterns and insertion sequence content

et al. 1995

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Molecular typing allowed the separation of the species Bacteroides fragilis into two genotypically distinct groups. A unique set of 50 strains of B. fragilis carrying the chromosomal metallo-␤-lactamase gene cfiA was subjected to a comparative analysis with respect to sets of up to 250 randomly collected strains devoid of this gene. The two groups were found to be distinct on the basis of the following results: (i) ribotyping, after DNA digestion with AvaI, revealed a practically homogeneous DNA fragment pattern for the cfiA-positive strains and distinct multiple patterns for the cfiA-negative strains; (ii) PCR, arbitrarily primed with an experimentally selected decamer, generated fragment patterns typical for the strains of each group; (iii) the three insertion sequences described to date in the species B. fragilis, i.e., IS4351, IS942, and IS1186, were all but confined to the cfiA-positive group, in which they were capable of providing promoter sequences for the transcription of cfiA; and (iv) the cepA gene, encoding the so-called endogenous cephalosporinase of B. fragilis, was found exclusively in the cfiA-negative group, in which it was present in ca. 70% of the strains. The cfiA-, cepA-negative fraction was not characterized further. In a natural population of 500 randomly selected strains of B. fragilis, the cfiA-positive and cfiA-negative groups represented ca. 3 and 97% of the strains, respectively. Analysis of 82 metabolic traits revealed no difference between the two groups.The genus Bacteroides sensu stricto, which is part of the Cytophaga-Flavobacter-Bacteroides phylum (10), is distant, in evolutionary terms, from most other bacteria of medical interest and appears to be one that evolves rather rapidly (41). According to a proposal by Shah and Collins (34), it has been restricted to 10 closely related species, with Bacteroides fragilis as the type species.B. fragilis is the anaerobe most frequently isolated from human infections (8, 33) and may constitute up to 60% of pathogenic anaerobic isolates from hospitalized patients (20). Apart from its resistance traits to various antibiotics (25), the species B. fragilis appears phenotypically homogeneous; however, DNA-DNA hybridization experiments have shown that it separates into two DNA homology groups, I and II, which have ca. 65 to 70% intergroup and 80 to 90% intragroup homology (15,16). Strains belonging to group II have been reported to be less susceptible than those of group I to the synergistic inhibitory effect of clavulanic acid and ␤-lactam antibiotics (3, 43).Two chromosomal cephalosporinase genes, considered to be species specific, have been described in B. fragilis; these are cepA (32), coding for an enzyme related to the ␤-lactamases of class A (2), and cfiA (38), also called ccrA (26), coding for a metallo-␤-lactamase of class B (1). Neither gene is consistently expressed in naturally occurring strains of B. fragilis. High-level expression of the so-called endogenous cephalosporinase gene cepA has been studied recently by Rogers et al. (32...

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“…Tetracycline transfer elements (TET elements [21]) located on the chromosomes of several Bacteroides species of clinical importance may be responsible for the spread of the tetracycline resistance determinant. There have been reports of outbreaks of clindamycin-resistant (ClnR) B. fragilis strains in hospital settings (2). Several plasmids carrying a determinant for clindamycin-erythromycin resistance (ermF [21]) have been isolated from these B. fragilis strains; indeed, >90% of all clindamycin-resistant B. fragilis strains show homology in either their chromosomal DNA or within their autonomous plasmids when tested with the ermF probe (12).…”

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Conjugal transfer of antibiotic resistance factors in Bacteroides fragilis: the btgA and btgB genes of plasmid pBFTM10 are required for its transfer from Bacteroides fragilis and for its mobilization by IncP beta plasmid R751 in Escherichia coli

1991

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Transferable plasmids play an important role in the dissemination of clindamycin-erythromycin resistance in Bacteroides fragilis. We previously described the isolation and propetties of pBFTM10, a 14.9-kb ClnR transfer factor from B. fragilis TMP10. We also reported the isolation of a transfer-deficient deletion derivative of pBFTM10 contained in the B. fragilis-Escherichia coli shuttle vector pGAT400. In the present study we used pGAT400 and a similar shuttle vector, pGAT550, to characterize and sequence a region of pBFTM10 required for its transfer from B. fragilis to B. fragiis or E. coli recipients and for its mobilization by the broadhost-range plasmid R751 from E. coli donors to E. coli recipients. Deletion of certain BglIl restriction fragments from pBFTM1O resulted in partial or complete loss of transfer ability. TnlOOO insertions into this same region also resulted in altered transfer properties. We used the sites of TnlO00 insertions to determine the DNA sequence of the transfer region. Two potential open reading frames encoding proteins of 23.2 and 33.8 kDa, corresponding to two genes, btgA or btgB, were identified in the sequence. TnlOOO insertions within btgA or btgB or deletion of all or portions of btgA or btgB resulted in either a transfer deficiency or greatly reduced transfer from B. fragilis donors and alterations in mobilization by R751 in E. coli. A potential oriT sequence showing similarity in organization to the oriT regions of the IncP plasmids was also detected. Thus, pBFTMIO encodes and requires at least two proteins necessary for efficient transfer from B. fragilis. These same functions are expressed in E. coli and are required for mobilization by R751.There is increasing awareness that the occurrence and dissemination of drug resistance determinants in bacteria of medical importance play a significant role in the virulence of these organisms. Indeed, for Bacteroidesfragilis, one of the major obligately anaerobic bacteria involved in infections of humans, resistance to tetracycline, once rare, is now seen in more than 60% of all clinical isolates (25 addition, a region of approximately 4 kb that is essential for autonomous replication in B. fragilis has been localized (6). This leaves less than 5 kb for all remaining plasmid functions, including transfer, although it is possible that sites or functions involved in transposition and/or replication may also play a role in transfer. For this reason others have hypothesized that pBFTM10 cannot truly be self-transferable but instead must be mobilized by as yet uncharacterized products from the bacterial chromosome (21). pBFTM10 has been fused to the Escherichia coli plasmid pDG5, a pBR322 derivative containing the oriT region from the broad-host-range plasmid RP4 (6)

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Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation

Cited by 142 publications

References 11 publications

In Vitro Susceptibilities of the Bacteroides fragilis Group Species: Change in Isolation Rates Significantly Affects Overall Susceptibility Data

In Vitro Susceptibilities of the Bacteroides fragilis Group Species: Change in Isolation Rates Significantly Affects Overall Susceptibility Data

Genotypic identification of two groups within the species Bacteroides fragilis by ribotyping and by analysis of PCR-generated fragment patterns and insertion sequence content

Conjugal transfer of antibiotic resistance factors in Bacteroides fragilis: the btgA and btgB genes of plasmid pBFTM10 are required for its transfer from Bacteroides fragilis and for its mobilization by IncP beta plasmid R751 in Escherichia coli

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