Differences in susceptibilities of species of the Bacteroides fragilis group to several beta-lactam antibiotics: indole production as an indicator of resistance

Effects of blackcurrant extract on indole and ammonia productions in an in vitro human fecal culture model

Blackcurrant is available as a traditional medicine in Europe. However, the detailed effects of blackcurrant on the human gut microbiota remain unknown. In this study, we investigated the prebiotic effects of a blackcurrant extract using a human fecal culture model in six healthy subjects. Feces were individually inoculated into a medium with or without the blackcurrant extract and then fermented for 48 hr under anaerobic conditions. The results obtained from analysis of samples from the fermented medium demonstrated that after 48 hr of fermentation, the pH of the medium with the blackcurrant extract was significantly decreased (control, 6.62 ± 0.20; blackcurrant extract, 6.41 ± 0.33; p=0.0312). A 16S rRNA gene sequencing analysis of the microbiota of the fermented medium showed a significant increase in the relative abundance of Bifidobacteriaceae. In measuring the concentrations of putrefactive components in the fermented medium, we found that the blackcurrant extract significantly reduced ammonia levels and displayed a tendency toward reduced indole levels. Our results suggest that blackcurrant extract could be a potential ingredient for relief of putrefactive components in the gut.

Diversity of the Tryptophanase Gene and Its Evolutionary Implications in Living Organisms

Tryptophanase encoded by the gene tnaA is a pyridoxal phosphate-dependent enzyme that catalyses the conversion of tryptophan to indole, which is commonly used as an intra- and interspecies signalling molecule, particularly by microbes. However, the production of indole is rare in eukaryotic organisms. A nucleotide and protein database search revealed tnaA is commonly reported in various Gram-negative bacteria, but that only a few Gram-positive bacteria and archaea possess the gene. The presence of tnaA in eukaryotes, particularly protozoans and marine organisms, demonstrates the importance of this gene in the animal kingdom. Here, we document the distribution of tnaA and its acquisition and expansion among different taxonomic groups, many of which are usually categorized as non-indole producers. This study provides an opportunity to understand the intriguing role played by tnaA, and its distribution among various types of organisms.

A multicentre study to evaluate the effect of sulbactam/ampicillin combination on anaerobic micro-organisms

Ampicillin combined with the beta-lactamase inhibitor sulbactam was compared with ampicillin alone, cefoxitin and metronidazole against 569 clinical strains of anaerobic organisms. The strains included 289 species of Bacteroides, 160 strains of Clostridium and 120 strains of various species of Streptococcus/Peptostreptococus, Fusobacterium, Veillonella, Eubacterium, Bifidobacterium, Actinomyces and Propionibacterium. Sulbactam/ampicillin was as effective as cefoxitin and metronidazole against all anaerobic species tested, inhibiting more than 90% of strains at the breakpoints (16, 32 and 32 mg/l, respectively). Sulbactam/ampicillin was also significantly more active than ampicillin against strains of Bacteroides, the minimal inhibitory concentration being at least four-fold lower. In contrast, the activity of the combination did not differ from that of ampicillin alone against Fusobacterium species and Gram-positive rods and cocci.

Susceptibilities of species of the Bacteroides fragilis group to 10 antimicrobial agents

A total of 94 clinical isolates of the Bacteroides fragilis group was tested for susceptibility to metronidazole, chloramphenicol, clindamycin, cefoxitin, cefotetan, cefmetazole, moxalactam, mezlocillin, amoxicillin-clavulanic acid, and imipenem. All the strains tested were susceptible to imipenem, metronidazole, amoxicillin-clavulanic acid, and chloramphenicol. The rate of resistance to clindamycin was 21%. The results of this study demonstrate a difference in resistance rates from one species of the B. fragilis group to another.

In vitro activity of cefoperazone/sulbactam and other antimicrobials against anaerobic bacteria

Sulbactam inhibits the hydrolytic activity of several, clinically important beta-lactamases including those produced by anaerobic bacteria. This study was undertaken to determine the effect of sulbactam on the activity of cefoperazone against 250 anaerobic bacteria including 174 isolates belonging to the Bacteroides fragilis group and to compare the activity of cefoperazone/sulbactam with other antimicrobial agents. beta-lactamase activity was detected in 98% of the isolates of the Bacteroides fragilis group but not in the other species evaluated. Antagonistic activity between cefoperazone and sulbactam was not observed with any of the species. Forty-two percent of the isolates belonging to the B. fragilis group were resistant to cefoperazone. Ninety-four percent of these were converted to either the susceptible or moderately susceptible range upon the addition of sulbactam. Sixty-seven percent were susceptible to the combination cefoperazone/sulbactam and 27% were moderately susceptible. Overall, metronidazole and chloramphenicol were the most active antimicrobials. Significant differences in the antimicrobial susceptibility patterns of members of the B. fragilis group were observed. Sulbactam demonstrated some intrinsic activity against all of the species tested.

Comparative in vitro activity of cefoxitin, cefotaxime alone, and in combination with desacetylcefotaxime against the Bacteroides species

The agar dilution method was used to determine the inhibitory activity of cefotaxime (CTX) alone, desacetylcefotaxime (dCTX) alone, CTX plus dCTX, and cefoxitin against 74 clinical isolates of the Bacteroides species recovered from diabetic patients with foot ulcers. The study concluded that the addition of dCTX to CTX increased the inhibitory activity from 45% to 73% for all strains tested and from 50% to 81% among the 32 strains of Bacteroides fragilis. This synergistic interaction against B. fragilis resulted in a four- to nine-fold reduction in the MIC of seven strains (64-128 micrograms/ml, resistant category MICs). While the lowest CTX MIC for B. fragilis was 2 micrograms/ml (four strains), the addition of dCTX also produced a remarkable reduction in susceptible range CTX MICs to 0.05-2 micrograms/ml in 16 strains (50%). The overall susceptibility to cefoxitin and CTX plus dCTX was as follows: 100% and 100% for Bacteroides vulgatus, 50% and 66% for Bacteroides thetaiotaomicron, 100% and 33% for Bacteroides ovatus, and 83% and 82% for Bacteroides species other than the B. fragilis group.

A multicenter study of the in vitro antianaerobic activity of cefotetan compared with other antimicrobial agents

The in vitro antianaerobic activity of cefotetan was compared with that of chloramphenicol, clindamycin, cefoxitin, and penicillin in a multicenter study. Both agar dilution and broth microdilution testing procedures, as described by the National Committee for Clinical Laboratory Standards (NCCLS), were employed; a total of 1,377 strains were examined. Results were interpreted using the U.S. Food and Drug Administration- and NCCLS-recommended criteria. This study indicates that Bacteroides fragilis, Clostridium difficile, and most other clinically significant anaerobic bacteria are susceptible to cefotetan.

Inactivation of cefoxitin and moxalactam by Bacteroides bivius beta-lactamase

Moxalactam and cefoxitin are known for their high stability against Bacteroides beta-lactamases. We investigated the beta-lactamase activity of crude extracts obtained from three strains of Bacteroides bivius and two strains of Bacteroides fragilis against cefoxitin and moxalactam. In a spectrophotometric antibiotic assay with a 24-h incubation period, B. bivius extracts decreased the initial concentration (10 micrograms/ml) of moxalactam and cefoxitin by 60%, whereas B. fragilis extracts had no effect. In a microbiological assay, when B. bivius or B. fragilis extracts were added to cephalothin (10 micrograms/ml) or cefamandole (4 micrograms/ml), we observed complete disappearance of the inhibitory zones against the indicator strain (Clostridium perfringens ATCC 13124). Only the B. bivius extracts were able to decrease the inhibitory activity (from 10 to 100%) of cefoxitin and moxalactam (each at 10 micrograms/ml). Prior addition of clavulanic acid to crude extracts prevented the losses of antibacterial activity. Furthermore, the inhibition of the beta-lactamase hydrolysis of nitrocefin by cefoxitin or moxalactam was prevented by a 12-h preincubation of the beta-lactam with the B. bivius extracts but not with the B. fragilis extracts. Finally, with the B. bivius strain producing the most beta-lactamase, we showed an effect of inoculum size on the MICs of cefoperazone, cefoxitin, and moxalactam with a broth dilution technique. Increasing the inoculum size with the B. fragilis strains had no effect on the MISs of cefoxitin and moxalactam. These results indicate a slow and clavulanate-sensitive beta-lactamase activity of B. bivius extracts against cefoxitin and moxalactam.

Survey of anaerobic susceptibility patterns in Canada

The in vitro activity of penicillin, cefoxitin, moxalactam, ticarcillin, clindamycin, chloramphenicol, and metronidazole against 590 anaerobic isolates collected from five Canadian hospitals during 1984 was determined by an agar dilution technique. Cefoxitin, clindamycin, chloramphenicol, and metronidazole were very active against most of the isolates. No major regional differences in the susceptibility patterns were observed.

Predicting the susceptibility of anaerobes to cefoperazone, cefotaxime, and cefoxitin with the thioglycolate broth disk procedure

A variety of clinical anaerobic isolates were tested against cefoperazone (216 strains), cefoxitin (120 strains), and cefotaxime (120 strains) by the thioglycolate anaerobic broth disk method, and the results were compared with the National Committee for Clinical Laboratory Standards reference agar dilution method. The broth disk and reference breakpoint concentrations were as follows: cefoperazone, 60 and 64 or 30 and 32 micrograms/ml; cefotaxime, 30 and 32 micrograms/ml; cefoxitin, 18 and 16 micrograms/ml, respectively. Discrepant results were retested to obtain a mode. There was 99% agreement between the broth disk and reference methods for cefotaxime, 98% for cefoperazone with 60- and 64-micrograms/ml breakpoints and 91% with 30- and 32-micrograms/ml breakpoints, and 75% for cefoxitin. All but one of the strains that produced false susceptibility results by broth disk were members of the Bacteroides fragilis group, 1 with cefoperazone using the 60-micrograms/ml concentration, 14 with cefoperazone at the 30-micrograms/ml concentration, and 27 with cefoxitin. One strain of Clostridium difficile produced false susceptibility results to cefoperazone at the 30-micrograms/ml concentration. The lack of agreement between the broth disk and reference methods with cefoxitin may be a reflection of the number of isolates at the 16-micrograms/ml level and that the broth disk breakpoint was slightly higher than this concentration. Increased incubation time did not improve the results significantly.

Sensitive reagents for detection of indole production by bacteria

A number of substituted 4-aminobenzaldehydes were compared with more commonly employed reagents for the detection of indole-producing organisms among the Enterobacteriaceae. Factors such as rate of colour intensity and stability were compared in tests with reference organisms and clinical isolates, and with appropriate concentrations of pure indolic standards. 2-Methoxy 4-dimethylaminobenzaldehyde and 4-N pyrrolidylbenzaldehyde produced immediate and intense red to purple colourations when used in the indole test both in liquid media and on multipoint inoculated plates. Both reagents were considered to be superior to the traditional Ehrlich's reagent and also to 4-dimethylaminocinnamaldehyde which is often used as an alternative.

Six-year retrospective survey of the resistance of Bacteroides fragilis group species to clindamycin and cefoxitin

Two hundred and forty-six strains of the Bacteroides fragilis group, all clinical isolates, collected at the Wadsworth Veterans Administration Medical Center from 1977 to 1982, were tested for susceptibility to clindamycin and cefoxitin. There was no significant change in resistance to either clindamycin or cefoxitin over the time period tested for any individual species, nor for the B. fragilis group in toto. Striking differences in susceptibility to the two drugs were seen among species of the B. fragilis group. B. fragilis displayed resistance to cefoxitin (32 micrograms/ml) and clindamycin (8 micrograms/ml) of 0.0% and 0.8%, respectively, whereas B. thetaiotaomicron showed resistances of 12.7% to cefoxitin (32 micrograms/ml) and 9% to clindamycin (8 micrograms/ml). B. thetaiotaomicron, B. distasonis, and B. ovatus are distinctly more resistant to cefoxitin than B. fragilis and B. vulgatus. Similarly B. thetaiotaomicron and B. distasonis are much more resistant to clindamycin than are the other B. fragilis group species. It is apparent that determination of species within the B. fragilis group is important in evaluating a potential therapeutic regimen.

In vitro activity of cefbuperazone against Bacteroides spp

The activity of cefbuperazone was tested in vitro against 287 clinical isolates of Bacteroides spp. Cefbuperazone showed good activity against B. fragilis, B. vulgatus, and other Bacteroides species, comparable to that of cefoxitin. It was relatively ineffective against B. distasonis and the B. thetaiotaomicron-ovatus group and was not active against cefoxitin-resistant Bacteroides spp.

In vitro activity of Sch 34343 and cefbuperazone against anaerobic bacteria

The in vitro activities of Sch 34343, a new penem antibiotic, and cefbuperazone, a new cephamycin antibiotic, were determined against 459 clinical anaerobic bacterial isolates and compared with the activities of imipenem and cefoxitin, respectively, by an agar dilution method. Both penems showed potent and similar activity against all anaerobic bacteria tested, particularly Peptococcus spp., Bacteroides fragilis, and Clostridium perfringens. All organisms except a single strain of Fusobacterium necrogenes were inhibited by an 8 micrograms/ml concentration of either Sch 34343 or imipenem. Overall, gram-positive bacilli, particularly Lactobacillus species, Clostridium difficile, and Bifidobacterium and Actinomyces species, were relatively more resistant to either penem than other genera of anaerobic bacteria tested. Cefbuperazone demonstrated only modest activity against a wide spectrum of anaerobic bacteria. It had excellent and selective activity against B. fragilis and Bacteroides vulgatus but was highly inactive against Bacteroides distasonis and Bacteroides thetaiotaomicron within the B. fragilis group. Both cephamycins showed virtually no activity against C. difficile and Lactobacillus spp. Although cefbuperazone was more active against Bifidobacterium spp., it had less activity against Fusobacterium spp., Eubacterium spp., and all Bacteroides spp. other than B. fragilis and B. vulgatus.

In vitro efficacy of sulbactam combined with ampicillin against anaerobic bacteria

An ampicillin-sulbactam combination was compared with ampicillin alone, chloramphenicol, clindamycin, and metronidazole against 272 strains of anaerobic bacteria. Chloramphenicol and ampicillin-sulbactam were the most effective, inhibiting 98 to 99% of strains tested at breakpoint (16 micrograms/ml). The combination of sulbactam and ampicillin was much more effective than ampicillin alone against Bacteroides fragilis strains but did not differ substantially from ampicillin alone against Fusobacterium spp., gram-positive rods, and gram-positive cocci.

Establishment of MICs of moxalactam for control and reference anaerobic organisms in agar dilution and microdilution techniques

The MICs of moxalactam were determined for eight National Committee for Clinical Laboratory Standards control and reference strains and for Fusobacterium nucleatum ATCC 10953 by agar and microdilution techniques. The recommended MIC for the control strain Bacteroides fragilis in both agar and microdilution tests is 0.5 micrograms/ml. Recommended MICs for Bacteroides thetaiotaomicron ATCC 29741 and Clostridium perfringens ATCC 13124 by agar dilution are 8 and 0.063 micrograms/ml, respectively. These two strains gave inconsistent results in microdilution tests. Variation in results with microdilution procedures was seen, which illustrates problems in reading endpoints and with modifications of media. Recommended MICs for the reference strains are presented.

Disc diffusion method to screen for high-level resistance to clindamycin and erythromycin in the Bacteroides fragilis group

High-level clindamycin resistance in Bacteroides species was investigated by measuring zone sizes surrounding 2 micrograms clindamycin and 60 micrograms erythromycin discs, using a nonstandardized disc diffusion method, and by determining minimal inhibitory concentrations (MIC). The absence of a zone of inhibition surrounding either disc was predictive for all isolates having high-level resistance to both antibiotics (MIC greater than 256 micrograms/ml), characteristic of macrolide-lincosamide-streptogramin (MLS) cross-resistance. Although zone size could not be used as an absolute predictor of MIC, a clindamycin zone diameter of less than 17 mm was suggestive of strains with a moderate level of clindamycin resistance (MIC greater than or equal to 8 micrograms/ml), regardless of erythromycin zone size. Disc diffusion testing using a combination of clindamycin and erythromycin discs can be a useful screening method for detection of clindamycin-resistant Bacteroides species, occurring either alone or as part of the MLS resistance phenotype.

Effect of clavulanic acid on the activities of ten beta-lactam agents against members of the Bacteroides fragilis group

Clavulanic acid reduced the MICs of amoxicillin, carbencillin , cefamandole, cefotaxime, ceftazidime, ceftizoxime, cephalothin, and penicillin G, but not of cefoxitin or moxalactam, against 77 isolates of the Bacteroides fragilis group, all rapidly beta-lactamase positive by the nitrocefin slide test. It had no effect on the susceptibilities of eight Bacteroides distasonis strains that were slowly beta-lactamase positive (18 h of incubation).

Moxalactam (latamoxef). A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Moxalactam (latamoxef) is a new synthetic oxa-beta-lactam antibiotic administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, is particularly active against Enterobacteriaceae and is resistant to hydrolysis by beta-lactamases. Moxalactam has moderate activity against Pseudomonas aeruginosa, but on the basis of present evidence can not be recommended as sole antibiotic treatment of known or suspected pseudomonal infections. Like the related compounds, the cephalosporins, moxalactam is effective in the treatment of complicated urinary tract infections and lower respiratory tract infections caused by Gram-negative bacilli. As moxalactam is also active against Bacteroides fragilis it has considerable potential in the treatment of intra-abdominal infections in patients with normal immunological mechanisms, as well as in immunocompromised patients, when used alone or in combination with other antibiotics. Likewise, its ready penetration into the diseased central nervous system, its high level of activity against Gram-negative bacilli, and the lack of necessity to monitor drug plasma concentrations, indicate its potential value in the treatment of neonatal Gram-negative bacillary meningitis. Further clinical experience is needed before it can be determined whether moxalactam alone can be used in the treatment of conditions for which the aminoglycosides are drugs of choice, but if established as equally effective, moxalactam has the advantage of being devoid of nephrotoxicity. Bleeding is a potentially serious problem, however, particularly in the elderly, malnourished and in the presence of renal impairment.

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

The modified broth-disk susceptibility test was used to assess the incidence of clindamycin resistance in the Bacteroides fragilis 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 micrograms/ml).

Establishment of minimum inhibitory concentrations of cefoperazone for control and reference anaerobic organisms

The minimum inhibitory concentrations of cefoperazone were determined in a collaborative study for eight National Committee for Clinical Laboratory Standards control and reference strains of anaerobic bacteria by agar and microdilution techniques with several types and sources of media. Recommended minimum inhibitory concentrations for the control strains, Bacteroides fragilis ATCC 25285 and Bacteroides thetaiotaomicron ATCC 29741, are 32 to 64 micrograms/ml and 64 micrograms/ml, respectively. Clostridium perfringens ATCC 13124 gave inconsistent results, and no value is recommended. Recommended values for reference strains are presented. Modification of media did not significantly change the minimum inhibitory concentrations.

Cefotaxime. A review of its antibacterial activity, pharmacological properties and therapeutic use

SYNOPSIS

Cefotaxime is a new 'third generation' semisynthetic cephalosporin administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, and is generally more active against Gram-negative bacteria than the 'first' and 'second generation' cephalosporins. Although cefotaxime has some activity against Pseudomonas aeruginosa, on the basis of present evidence it cannot be recommended as sole antibiotic therapy for pseudomonal infections. However, cefotaxime has been effective in treating infections due to other 'difficult' organisms, such as multidrug-resistant Enterobacteriaceae. Like other cephalosporins, cefotaxime is effective in treating patients with complicated urinary tract and lower respiratory tract infections, particularly pneumonia caused by Gram-negative bacilli. High response rates have also been achieved in patients with Gram-negative bacteraemia. Although favourable clinical results have been obtained in patients with infections caused by mixed aerobic/anaerobic organisms (such as peritonitis or soft tissue infections), the relatively low in vitro activity of cefotaxime against Bacteroides fragilis may restrict its usage in situations where this organism is the suspected or proven pathogen. In preliminary studies, males and females treated with a single intramuscular dose of cefotaxime for uncomplicated gonorrhoea caused by penicillinase-producing strains of Neisseria gonorrhoeae responded very favourably. Encouraging results have also been reported in open studies in children including neonates, treated with cefotaxime for meningitis and various other serious infections. In some situations, cefotaxime has been given in combination with another antibiotic such as an aminoglycoside, but the merits of such a combination have not been clearly established. Whether cefotaxime alone is appropriate therapy for conditions previously treated with aminoglycosides (other than pseudomonal infections) also needs additional clarification, but if established as equally effective in such conditions cefotaxime offers potentially important clinical and practical advantages in its apparent lack of serious adverse effects and freedom from the need to undertake drug plasma concentration monitoring.