The role of neuraminidase in haemagglutination and adherence to colon WiDr cells by Bacteroides fragilis

The role of neuraminidase in haemagglutination and adherence to colon WiDr cells by eight strains of Bacteroides fragilis and four strains of oral black-pigmented gram-negative anaerobes was studied. Neuraminidase treatment resulted in a very small increase of haemagglutination by some of the strains but had no effect on adherence to WiDr cells by all bacterial strains tested except one strain of Prevotella intermedia (HG 110). Inhibition of neuraminidase had no effect on haemagglutination or adherence, nor was any correlation found between haemagglutinating ability and neuraminidase activity in the B. fragilis strain. The results indicated that haemagglutination and adherence of B. fragilis to WiDr cells were not mediated by neuraminidase.

Two sialidases which preferentially hydrolyze sialyl alpha 2-8 linkage from Bacteroides fragilis SBT3182

Bacteroides fragilis SBT3182 produced two sialidases which differ in molecular weight on SDS-PAGE. These sialidases, a 50 kDa and a 55 kDa enzymes, were purified separately and their properties were compared. Both enzymes preferentially hydrolyze sialyl alpha 2-8 linkage rather than alpha 2-3 and alpha 2-6 bonds. The Km values for Neu5Ac alpha 2-3lactose, Neu5Ac alpha 2-6lactose, and colominic acid, which is a homopolymer of N-acetylneuraminic acid linked by alpha 2-8 bonds, were identical between the two enzymes. These enzymes had Km value of 1.0-1.2 mM for Neu5Ac alpha 2-3lactose and 1.3-1.5 mM for Neu5Ac alpha 2-6lactose, which are in the ranges reported for other sialidases. However, the Km values for colominic acid (0.03-0.04 mM) were lower than those of other sialidases, indicating that sialidases from B. fragilis SBT3182 show high affinity for the sialyl alpha 2-8 linkage. The two sialidases also had identical N-terminal amino acid sequences and did not reveal any homology to known sialidases. PAS-staining suggested that these two sialidases were glycoproteins. In the lectin analysis, the 50 kDa enzyme was stained with Con A, DBA, and UEA-I while the 55 kDa sialidase was stained only with Con A. This suggested that the difference in molecular weight may be due to the carbohydrate composition. When the 50 kDa enzyme was incubated with UEA-I, which is a lectin specific for alpha-fucose residue, the activity decreased by 20%.

Cloning and characterization of the endogenous cephalosporinase gene, cepA, from Bacteroides fragilis reveals a new subgroup of Ambler class A beta-lactamases

Bacteroides fragilis CS30 is a clinical isolate resistant to high concentrations of benzylpenicillin and cephaloridine but not to cephamycin or penem antibiotics. beta-Lactam resistance is mediated by a chromosomally encoded cephalosporinase produced at a high level. The gene encoding this beta-lactamase was cloned from genomic libraries constructed in Escherichia coli and then mated with B. fragilis 638 for identification of ampicillin-resistant (Apr) strains. Apr transconjugants contained a nitrocefin-reactive protein with the physical and enzymatic properties of the original CS30 isolate. The beta-lactamase gene (cepA) was localized by deletion analysis and subcloned, and its nucleotide sequence was determined. The 903-bp cepA open reading frame encoded a 300-amino-acid precursor protein (predicted molecular mass, 34,070 Da). A beta-lactamase-deficient mutant strain of B. fragilis 638 was constructed by insertional inactivation with the cepA gene of CS30, demonstrating strict functional homology between these chromosomal beta-lactamase genes. An extensive comparison of the CepA protein sequence by alignment with other beta-lactamases revealed the strict conservation of at least four elements common to Ambler class A. A further comparison of the CepA protein sequence with protein sequences of beta-lactamases from two other Bacteroides species indicated that they constitute their own distinct subgroup of class A beta-lactamases.

A role for Bacteroides fragilis neuraminidase in bacterial growth in two model systems

Two Bacteroides fragilis neuraminidase-deficient mutants were used to study the role of neuraminidase activity in growth of B. fragilis in tissue culture monolayers (CHO cells) and in the in vivo rat granuloma pouch. The nanH structural gene for neuraminidase was cloned from B. fragilis TM4000 and was used to create two isogenic strains with chromosomal disruptions at the nanH gene. B. fragilis VRC404 contains an insertion flanked by disrupted copies of the nanH gene, and B. fragilis VRC426 contains a deletion of a significant portion of nanH coding sequences. The insertion mutant VRC404 is capable of reverting to nanH+. It grew as well as the wild type in CHO monolayers. However, between 48 and 72 h after infection, the bacterial population was enriched with nanH+ bacterial cells (10 to 20%). In the rat pouch 48 h after infection, more than 90% of the population sampled had become nanH+. The deletion mutant VRC426 showed a severe growth defect in the rat pouch model. In addition, VRC426 was efficiently outgrown by the wild type in competition experiments, even when the mutant was present at 10 times the number of wild-type cells at the time of infection. A common characteristic of both model systems is a drastic decrease in the free glucose concentration 16 to 24 h postinfection. We suggest that neuraminidase activity may be required for B. fragilis to grow to maximal levels in the tissue culture and rat pouch systems by making other carbon sources available after glucose levels are reduced.

Susceptibility patterns and resistance to imipenem in the Bacteroides fragilis group species in Japan: a 4-year study

A study was undertaken in Japan to evaluate the susceptibility patterns of Bacteroides fragilis group species (849 strains) isolated from December 1986 through May 1991. All of the strains, which included B. fragilis (610 strains), Bacteroides thetaiotaomicron (201 strains), and Bacteroides distasonis (38 strains), were studied for susceptibility to imipenem and 16 other antimicrobial agents by an agar dilution method. Metronidazole was the most active agent; the minimal concentration for 90% inhibition (MIC90) was 0.78 micrograms/mL, and no isolate was noted to be resistant to it during the entire study period. Amongst the beta-lactam agents tested, imipenem was the most effective antimicrobial drug; the rate of resistance to this agent was only 3.3%. Cefoperazone/sulbactam (MIC90, 6.25 micrograms/mL) and cephamycins (MIC90, 25-50 micrograms/mL) were found to be more active against B. fragilis strains, whereas minocycline (MIC90, 6.25 micrograms/mL) showed better activity against B. thetaiotaomicron and B. distasonis strains. Increasing resistance to imipenem was observed in B. fragilis (2.0%-5.9%) and B. thetaiotaomicron (2.5%-6.1%) during the 4-year study period. Detailed investigation of beta-lactamases from imipenem-resistant strains demonstrated that, amongst them, six of the B. fragilis strains for which the MICs of imipenem were > or = 25 micrograms/mL were producing imipenem-hydrolyzing metallo-beta-lactamase.

Susceptibility of anaerobic bacteria to beta-lactam antibiotics in the United States

beta-Lactam antibiotics are critical agents in the treatment of anaerobic infections. Susceptibility to these agents, however, varies widely, depending on the specific drug and organism; has not been constant over time; and differs in various geographic locations within the United States for many species. For the organisms in the Bacteroides fragilis group, the beta-lactam antibiotics with the most consistent activity are imipenem and combinations of a beta-lactam drug plus a beta-lactamase inhibitor, such as ticarcillin/clavulanate and ampicillin/sulbactam. Antibiotics with less activity include cefoxitin, piperacillin, cefotetan, and ceftizoxime. In other species of anaerobic gram-negative bacilli, beta-lactamase production is seen with increasing frequency. In vitro susceptibility of these strains is now similar to that of the B. fragilis group, with imipenem, ticarcillin/clavulanate, ampicillin/sulbactam, and cefoxitin being the most active drugs. The anaerobic gram-positive cocci and bacilli remain, for the most part, highly susceptible to penicillins and imipenem.

Molecular characterization of a fructanase produced by Bacteroides fragilis BF-1

The Bacteroides fragilis BF-1 fructanase-encoding gene (fruA) was cloned and expressed in Escherichia coli from the recombinant plasmid pBS100. The fruA gene consisted of 1,866 bp encoding a protein of 622 amino acids with a calculated M(r) of 70,286. The apparent M(r) of the fructanase, determined by in vitro cell-free transcription-translation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, was approximately 71,500. An alignment of the amino acid sequences of the B. fragilis BF-1 fructanase and the Bacillus subtilis levanase revealed that 45.5% of the amino acids were identical. The fruA gene was expressed in E. coli from its own promoter; however, no E. coli promoter-like sequence was evident upstream from the gene. A major E. coli transcription start point and a single B. fragilis BF-1 transcription start point were located. Expression of the fruA gene was constitutive in E. coli(pBS100) and B. fragilis BF-1. The ratio of sucrase activity to inulinase activity (S/I ratio) was constant for enzyme preparations from E. coli (pBS100), indicating that both activities were associated with the fructanase. For B. fragilis BF-1, the S/I ratio varied considerably depending on the carbon source used for growth, suggesting that a separate sucrase is produced in addition to the fructanase in B. fragilis BF-1. Localization experiments and TnphoA mutagenesis indicated that the fructanase was exported to the periplasm. Sequence analysis of the N-terminal region of the fructanase revealed a putative 30-amino-acid signal peptide. The enzymatic properties of the purified fructanase were investigated. The enzyme was able to hydrolyze sucrose, raffinose, inulin, and levan but not melezitose, indicating that it was a beta-D-fructofuranosidase which was able to hydrolyze beta(2-->6)-linked fructans.

A reporter gene vector to investigate the regulation of glutamine synthetase in Bacteroides fragilis Bf1

The Clostridium acetobutylicum eglA gene, encoding a beta-1,4-endoglucanase (EG), was shown to be a useful reporter gene for the study of gene expression in Bacteroides fragilis. The eglA reporter gene has the advantages that it can be easily identified in both Escherichia coli and B. fragilis on agar media containing carboxymethylcellulose, and EG production can be rapidly quantified in liquid medium. Since the B. fragilis glutamine synthetase (GS) is inactivated in permeabilized cells and cell extracts, the eglA reporter gene was used to study the regulation of GS production in B. fragilis. Gene fusions containing the GS glnA promoter region fused to the promoterless eglA gene showed that glnA expression was regulated by nitrogen in B. fragilis at the transcriptional level. A glnA upstream region containing a near-perfect direct repeat sequence was essential for efficient GS expression and for regulation by nitrogen.

Purification and characterization of a sialidase from Bacteroides fragilis SBT3182

A sialidase from Bacteroides fragilis SBT3182 was purified 2,240-fold to apparent homogeneity by ammonium sulfate precipitation and sequential chromatographies on DEAE-Toyopearl 650M, Hydroxyapatite, MonoS and Superose6 columns. The N-terminal amino acid sequence of this sialidase, Ala-Asp-X-Ile-Phe-Val-Arg-Glu-Thr-Arg-Ile-Pro-, was determined. Substrate specificity of this enzyme using a variety of sialoglycoconjugates showed a 1.5- and 2.2-fold preference for sialyl alpha 2-8 linkages when compared with alpha 2-3 and alpha 2-6 bound sialic acids, respectively. The native sialidase had a molecular weight of 165kDa, as determined by Superose6 gel filtration chromatography and consisted of three subunits each of 55kDa by SDS-polyacrylamide gel electrophoresis. This enzyme had optimal activity at pH6.1 with colominic acid as substrate.

Epidemiological aspects of infections caused by Bacteroides fragilis and Clostridium difficile

Bacteroides fragilis and Clostridium difficile are two of the most common anaerobes associated with human disease. Studies on the epidemiology of Bacteroides fragilis are limited and are based predominantly on serogrouping, which suggests intraspecies differences. Further studies using newer techniques for typing are required to elucidate the epidemiological characteristics of this important pathogen. By contrast, numerous phenotypic, immunological and molecular methods have been developed for typing and fingerprinting of Clostridium difficile and applied in epidemiological studies to show conclusively that Clostridium difficile is nosocomially acquired and that there is transmission and cross-infection between hospital patients.

Characterization of restriction endonuclease BfrBI from Bacteroides fragilis strains BE3 and AIP 10006

A new type II restriction endonuclease, named BfrBI, was detected in two strains of Bacteroides fragilis, BE3 and AIP 10006 (NCTC 9343T). The enzyme BfrBI, an isoschizomer of NsiI and AvaIII, recognized the hexanucleotide sequence [5'-ATG decreases CAT-3'], with a cleavage site generating blunt ends.

Biochemical characterization of the metallo-beta-lactamase CcrA from Bacteroides fragilis TAL3636

The CcrA beta-lactamase from Bacteroides fragilis TAL3636 was cloned into Escherichia coli and purified from inclusion bodies. This group 3 metalloenzyme hydrolyzed most beta-lactam antibiotics, including cephamycins and carbapenems. Following inhibition by chelators, enzyme activity was recovered with the cations Zn2+ and Co2+. Clavulanate and sulbactam were activators; tazobactam at 10 microM inactivated the enzyme.

Conjugal transfer of imipenem resistance in Bacteroides fragilis

Transfer of imipenem resistance in Bacteroides fragilis was studied. Clinical isolate B. fragilis 10-73 was highly resistant to imipenem. Imipenem resistance was transferred from 10-73 to B. fragilis strain TM4000 at a frequency of 10(-6)/input recipient by a filter mating technique. The resistance could also be retransferred. B. fragilis 10-73 and both primary and secondary transcipients produced an imipenem-hydrolyzing metallo-beta-lactamase. Acquisition of imipenem resistance correlated with the appearance of plasmid DNA with a size (ca. 13.6 kb) similar to that of the donor strain. TM4000 transformed by electroporation with purified DNA of the 13.6-kb plasmid pBFUK1 produced the metallo-beta-lactamase and was resistant to imipenem. Transfer was resistant to DNase treatment and no transfer was seen with a sterile filtrate of the donor culture. It is suggested that gene transfer in B. fragilis has the properties of a conjugation system rather than those of transformation or transduction.

Purification and characterization of an imipenem hydrolysing metallo-beta-lactamase from Bacteroides fragilis

An imipenem resistant beta-lactamase producing strain of Bacteroides fragilis was isolated from a clinical specimen. The specific activity of the unpurified beta-lactamase was 5.5 U/mg protein. The beta-lactamase was purified 60-fold by Q Sepharose, Sephacryl S-300 and Mono Q column passages. The strain was able to inactivate imipenem and cefoxitin in broth cultures. The enzyme hydrolysed imipenem more rapidly than ampicillin, benzylpenicillin, cephalothin and cefoxitin. The activity of the enzyme was Zn2+ dependent and was completely inhibited by EDTA. The inhibition was reversed by ZnSO4. Preincubation with the common beta-lactamase inhibitors clavulanic acid, sulbactam and tazobactam did not reduce the enzyme activity. The molecular weight was determined by sodium dodecyl sulfate gradient gel electrophoresis to be 31,000 Daltons and the isoelectric point was 4.5.

A silent carbapenemase gene in strains of Bacteroides fragilis can be expressed after a one-step mutation

High-level carbapenem-resistant (CpmR) mutants, with MICs for imipenem and carbapenem of greater than 128 micrograms/ml, were selected in vitro from four carbapenem-susceptible (CpmS) clinical isolates of Bacteroides fragilis. The CpmS strains produced very low levels of beta-lactamase activity, which was increased approx. 50- to 100-fold in the CpmR mutants. Isoelectric focussing and enzyme kinetic analysis (Km and Vrel) of the 'carbapenemases' from the CpmR mutants and similarly resistant clinical isolates suggested a close relatedness of the enzymes. A probe covering most of the cfiA gene encoding such an enzyme (Thompson, J.S. and Malamy, M.H. (1990) J. Bacteriol. 172, 2584-2593) hybridized with DNA from the CpmR mutants, their CpmS parental strains as well as clinical CpmR isolates, but not from randomly chosen carbapenem-susceptible strains. The possibility is considered that mutations leading to expression of the silent carbapenemase gene, and thereby to clinically relevant carbapenem resistance, may also occur in the clinical setting.

Survey of Bacteroides fragilis group susceptibility patterns in Canada

The in vitro activities of penicillin, clindamycin, chloramphenicol, metronidazole, piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin-sulbactam, cefoxitin, ceftizoxime, cefotetan, moxalactam, and imipenem against 348 Bacteroides fragilis group isolates collected from six Canadian cities during 1990 were determined by the National Committee for Clinical Laboratory Standards (NCCLS) agar dilution technique. All isolates were susceptible to chloramphenicol, metronidazole, piperacillin-tazobactam, and imipenem. For the other antibiotics tested, the following resistance rates were observed: penicillin, 97%; clindamycin, 9%; piperacillin, 19%; ticarcillin, 31%; ticarcillin-clavulanate, 0.28%; ampicillin-sulbactam, 0.85%; cefoxitin, 26%; ceftizoxime, 15%; cefotetan, 53%; and moxalactam, 17%. Susceptibility profiles to beta-lactam antibiotics varied among the different species tested: B. fragilis and Bacteroides vulgatus demonstrated lower resistance rates than Bacteroides distasonis and indole-positive Bacteroides thetaiotaomicron and Bacteroides ovatus. Ceftizoxime results should be interpreted cautiously, because the MICs obtained with the recommended NCCLS control strain were lower than expected.

In vitro susceptibility vs. in vivo efficacy of various antimicrobial agents against the Bacteroides fragilis group

In vitro susceptibility testing is only one step in the evaluation of the potential efficacy of antimicrobial agents against the Bacteroides fragilis group. An assessment of in vivo efficacy, with a consideration of the factors that can best be studied in an infected host, is also an integral part of this process. Abscess models in rodents have been used to correlate in vitro activity with in vivo efficacy against this group of microorganisms. For metronidazole, clindamycin, moxalactam, and cefoxitin, the correlation was strong; for chloramphenicol and carbenicillin, it was not. In vivo studies of mixed infection with the B. fragilis group and Escherichia coli showed that cefoxitin and imipenem were effective; in contrast, cefotetan was not effective against resistant strains. Only strains susceptible to ceftizoxime in the agar dilution test were also affected by this drug in vivo. The so-called inoculum effect noted with ceftizoxime may explain this finding. In vivo elimination of encapsulated organisms of the B. fragilis group was found to be more difficult than elimination of unencapsulated isolates. The beta-lactamase produced by Bacteroides species can protect the enzyme-producing organism as well as its partners in mixed infections from the effects of beta-lactam antibiotics. These data illustrate the complexity and difficulties encountered when in vitro activity is correlated with in vivo efficacy.

beta-Lactamase produced by a highly beta-lactam-resistant strain of Bacteroides fragilis: an obstacle to the chemotherapy of experimental mixed infections

A strain of Bacteroides fragilis, which produces a metallo-beta-lactamase, was inoculated into pouches on the backs of rats together with a beta-lactamase-negative Escherichia coli highly sensitive to beta-lactam antibiotics. The mixed infection rat pouch model was treated with either flomoxef (susceptible to hydrolysis by the beta-lactamase produced by B. fragilis), or cefmetazole (relatively resistant to hydrolysis). In this model of mixed infection flomoxef showed weak in-vivo activity against E. coli, although showing the same strong activity in a model of single infection with E. coli. On the other hand, cefmetazole showed strong activity against E. coli, even in the model of mixed infection. The concentrations of both drugs in the pouches were decreased in infections with the strain of B. fragilis. There was a greater decrease in the concentration of flomoxef than of cefmetazole. Flomoxef was unstable whereas cefmetazole was relatively stable in the pouch exudates that had been infected with B. fragilis. These experimental data suggest that bacteria that produce a metallo-beta-lactamase decrease the in-vivo efficacy of beta-lactam antibiotics against other co-infecting bacteria. Thus, it is suggested that it is important in the chemotherapy of mixed bacterial infections that include these highly resistant beta-lactamase-producing bacteria to use antibiotics that are stable to hydrolysis by these enzymes.

Single mid-chain GlcNAc beta 1-6Gal beta 1-4R sequences of linear oligosaccharides are resistant to endo-beta-galactosidase of Bacteroides fragilis

Endo-beta-galactosidase (EC 3.2.1.103) of Bacteroides fragilis, at 250 mU ml-1, did not cleave the internal galactosidic linkage of the linear radiolabelled trisaccharide GlcNAc beta 1-6Gal beta 1-4GlcNAc, or those of tetrasaccharides Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4GlcNAc and Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4Glc. The isomeric glycans which contained the GlcNAc beta 1-3Gal beta 1-4GlcNAc/Glc sequence were readily cleaved.

Comparative susceptibility of cefminox and cefoxitin to beta-lactamases of Bacteroides spp

The susceptibility of the new cephamycin antibiotic, cefminox, to hydrolysis by various types of beta-lactamase produced by organisms of the Bacteroides fragilis group was compared with that of cefoxitin. Several enzymes were able to achieve complete hydrolysis of both drugs during overnight incubation, but no marked difference between the rates of inactivation of cefminox and cefoxitin was observed. Susceptibility of the cephamycins to crude extracts of beta-lactamases from the test strains of Bacteroides spp. did not correlate with the results of conventional minimum inhibitory concentration titrations. Possible reasons for these discrepancies are discussed.

Lactate dehydrogenase activity as a cause of metronidazole resistance in Bacteroides fragilis NCTC 11295

Enzymes acting on pyruvate as a parameter of the ATP regeneration system were studied as a cause of metronidazole resistance in Bacteroides fragilis NCTC 11295. The resistant strain had higher lactate dehydrogenase activity and produced more lactate than susceptible strains, suggesting that the enzyme is more active in lactic acid fermentation. Furthermore, the reaction catalysed by lactate dehydrogenase occurred up to 48 mg/L metronidazole, whereas the reaction catalysed by pyruvate: ferredoxin oxidoreductase reaction stopped at 2 mg/L. The mechanism of metronidazole resistance in B. fragilis NCTC 11295 may be due to the high activity of lactate dehydrogenase which compensates for the decreased activity of pyruvate: ferredoxin oxidoreductase in the presence of metronidazole.

[Determination and comparison of beta-glucuronidase activity among strains of B. fragilis and E. coli]

We determined and compared the beta-glucuronidase (beta-G) activity among strains of B. fragilis and E. coli under the optimum condition. Results showed that the mean beta-G activity of strain B. fragilis ATCC25285 was 94.7u. B. fragilis ATCC25285 strain was selected as the model strain to establish the animal model of bilirubin gallstones because its beta-G activity was obviously higher than that of B. fragilis CDC14462 and E. coli 3362 (O157K88) strain.

Susceptibilities of 394 Bacteroides fragilis, non-B. fragilis group Bacteroides species, and Fusobacterium species to newer antimicrobial agents

The susceptibilities of 374 selected beta-lactamase-producing gram-negative anaerobes (including 22 cefoxitin-resistant strains and 36 strains refractory to the enhancing effect of beta-lactamase inhibitors) and 20 beta-lactamase-negative strains were tested by agar dilution against selected new agents. The organisms included 217 Bacteroides fragilis group strains, 137 non-B. fragilis group Bacteroides spp., and 40 fusobacteria. All strains were susceptible to piperacillin-tazobactam, imipenem, and meropenem. For the B. fragilis group, 96% were susceptible to ampicillin-sulbactam, 95% were susceptible to amoxicillin-clavulanate and cefoperazone-sulbactam, 94% were susceptible to tosufloxacin, 91% were susceptible to cefoxitin, 88% were susceptible to trospectomycin, and 73% were susceptible to cefotetan. For the beta-lactamase-positive non-B. fragilis group Bacteroides spp., greater than or equal to 94% were susceptible to cefoxitin, amoxicillin-clavulanate, ampicillin-sulbactam, cefoperazone-sulbactam, and trospectomycin, 90% were susceptible to cefotetan, and 85% were susceptible to tosufloxacin (the most resistant strains were B. bivius and B. disiens). For the beta-lactamase-positive fusobacteria, greater than or equal to 97% were susceptible to amoxicillin-clavulanate, ampicillin-sulbactam, cefoperazone-sulbactam, trospectomycin, and cefoxitin, 90% were susceptible to cefotetan, and 89% were susceptible to tosufloxacin. All agents showed excellent activity against beta-lactamase-negative strains (for trospectomycin, 95% were susceptible; for all other drugs, 100% were susceptible). Overall, both carbapenems and piperacillin-tazobactam were most active. Amoxicillin-clavulanate, ampicillin-sulbactam, and cefoperazone-sulbactam lacked activity against some cefoxitin-resistant B. fragilis group strains but had excellent activity against other organisms. Tosufloxacin, a new quinolone, had very good activity against B. fragilis group strains (94% susceptible), good activity against other beta-lactamase-positive strains (less than or equal 85% susceptible), and excellent activity against beta-lactamase-negative strains (100% susceptible; MIC for 90% of strains, 0.5 microgram/ml). Trospectomycin was active against >90% of all strains except for B. fragilis group strains (88% susceptible; MIC for 90% of strains, 32 microgram/ml). Clinical studies are required to delineate the role of newer agents in the therapy of anaerobic infections.