Nationwide study of the susceptibility of the Bacteroides fragilis group in the United States

A nationwide susceptibility survey of the Bacteroides fragilis group was continued at New England Medical Center in 1983. A total of 555 strains were obtained from eight centers in the United States. In addition to the nine antimicrobial agents studied in the two previous years, three other agents were added to the evaluation: cefamandole, cefuroxime, and cefonicid. The results for the strains tested with the original nine drugs in 1983 were compared with those for 1,292 isolates tested in 1981 and 1982. The most active beta-lactam drug was piperacillin, which had an 8% resistance rate. Cefoxitin resistance increased from 10% in 1982 to 16% in 1983. High rates of resistance to cefotaxime, cefoperazone, cefamandole, cefonicid, and cefuroxime were encountered. No metronidazole- or chloramphenicol-resistant isolates were found during the 3 years of the study. Susceptibility patterns varied at the eight hospitals: the outbreak of cefoxitin resistance reported in 1982 at New England Medical Center remitted, while a high clindamycin resistance rate was documented at one hospital in 1983. These data indicate the need for determining the susceptibility patterns for the B. fragilis group of organisms at each hospital.

A prospective double-blind comparison of piperacillin, cephalothin and cefoxitin in the prevention of postoperative infections in patients undergoing intra-abdominal operations

Piperacillin has been shown to be as safe and effective an agent as cephalothin and cefoxitin when used in patients undergoing elective intra-abdominal surgical procedures. Enterococcus species have been shown in other studies to be susceptible to piperacillin, perhaps making it the preferred antibiotic for prophylaxis in clinical settings when enteric flora will be encountered.

Bacteroides gracilis, an important anaerobic bacterial pathogen

Clinical isolates of agar-pitting, formate-fumarate-requiring, anaerobic gram-negative bacilli were recharacterized in consideration of the species descriptions of Bacteroides ureolyticus and the newly described B. gracilis, Campylobacter concisus, and Wolinella sp. During an 11-year period, 7.5% (101 of 1,341) of all specimens yielding anaerobes were found to contain an organism in this group. Of the 71 isolates that were available for study, 43 were B. ureolyticus, 23 were B. gracilis, and 5 were in the Wolinella-C. concisus group. The role in infection and patterns of antimicrobial susceptibility for B. ureolyticus and B. gracilis were studied. Review of the clinical data indicated that 83% of B. gracilis strains were recovered from patients with serious visceral or head and neck infection, whereas 73% of B. ureolyticus isolates were recovered from superficial soft-tissue or bone infections. The strains of B. ureolyticus were uniformly susceptible to the tested antimicrobial agents. B. gracilis, however, showed some striking resistance, with penicillin active against only 67% and the cephalosporins active against 67 to 84% of the isolates tested. The association of B. gracilis with serious deep-tissue infection, coupled with the relatively high frequency of antibiotic resistance, indicates that it is an important, previously unrecognized, pathogen.

Rapid methods in clinical microbiology. Rapid methods. Overview and prospects for the future

The field of infectious diseases covers many entities that can be considered true medical emergencies. Included are meningitis, brain abscess, spinal epidural abscess, epiglottitis, pneumonia, bacteremia, endocarditis, certain intraabdominal infections, gas gangrene, and necrotizing fasciitis. Because emergencies related to infectious agents are potentially the most readily reversible of all medical emergencies, it behooves us to diagnose them as rapidly and specifically as possible so that appropriate life-saving therapy may be begun expeditiously. This article reviews and summarizes the presentations of others in this issue and presents views on future prospects in the rapid diagnosis of infectious diseases.

In vitro activity of imipenem against anaerobic bacteria

The in vitro activity of imipenem, metronidazole, clindamycin, moxalactam, and cefoxitin against 203 strains of anaerobic bacteria isolated from patients at the Veterans Administration Wadsworth Medical Center in Los Angeles was studied. Imipenem and metronidazole were the most active agents overall, inhibiting 98% and 99%, respectively, of all anaerobes tested. At breakpoint levels all of the agents tested were very active against anaerobic cocci. Clostridium perfringens, and Bacteroides species other than those of the Bacteroides fragilis group. Imipenem, metronidazole, and clindamycin were the most active agents against the B. fragilis group in this study, although more recent experience with clindamycin indicates less potency. Marked variation among the susceptibility results obtained at various centers may be due to differences in technique, including inoculum size, media, and incubation time. In all instances, however, imipenem has clearly been the most active of the beta-lactam agents.

Impact of imipenem/cilastatin therapy on normal fecal flora

The impact of parenteral imipenem/cilastatin therapy on the bowel flora of six patients was evaluated. Stool samples were collected before and during therapy and qualitative and quantitative bacteriologic studies were performed. Imipenem had no effect on total microorganism counts. Two patients acquired Candida albicans during therapy, and three patients acquired Proteus species. Pseudomonas species in one patient acquired resistance. Imipenem appears to have a relatively modest effect on the bowel flora and apparently does not readily induce resistance in the resident flora as compared with other agents.

In-vitro activity of Sch 34343 against anaerobic bacteria

The in-vitro activity of Sch 34343, was compared with that of imipenem against 226 strains of anaerobic bacteria. Sch 34343 was identical in activity to imipenem, inhibiting 99.5% of the organisms tested at 16 mg/l (the breakpoint for both drugs). Imipenem was slightly more active than Sch 34343 against Bacteroides, Fusobacterium and Veillonella, although both drugs inhibited all organisms in these groups below breakpoint levels.

Antigenic distinctiveness of Mobiluncus curtisii and Mobiluncus mulieris

A total of 26 Mobiluncus strains (17 M. curtisii and 9 M. mulieris strains) were compared serologically by double immunodiffusion and immunoblotting against antisera prepared against representative isolates of each species. All strains from the same species were strongly reactive with homologous antisera but generally weakly reactive with antisera to the heterologous Mobiluncus spp. The antisera did not react with strains of the unrelated genera Campylobacter, Succinivibrio, Wolinella, Actinomyces, Anaerobiospirillum, and Anaerovibrio.

In vitro activity of cefbuperazone against anaerobic bacteria

The in vitro activity of cefbuperazone was compared with that of cefoxitin, moxalactam, and piperacillin against 305 strains of anaerobic bacteria. Piperacillin was the most active overall, inhibiting 97% of all anaerobes tested at 128 micrograms/ml. Cefbuperazone had poor activity against the Bacteroides fragilis group and Clostridium difficile (43 and 0% susceptible, respectively) but good activity (90.5%) against all other anaerobic bacterial species tested.

Susceptibility of anaerobic bacteria to thiamphenicol

The activity of thiamphenicol, an analogue of chloramphenicol without a nitro group, was compared with that of chloramphenicol against anaerobic bacteria. A plate dilution technique on brucella agar supplemented with laked sheep blood and vitamin K1 was used. Chloramphenicol exhibited slightly greater activity than thiamphenicol in vitro, but the difference was too small to be of potential clinical significance.

Alterations in human fecal flora, including ingrowth of Clostridium difficile, related to cefoxitin therapy

To evaluate the effects of parenteral cefoxitin therapy on human fecal flora, we cultured fecal specimens obtained from six patients before, during, and after therapy and used standard methods to identify and quantify all microorganisms. The major changes (observed in at least three patients) included the acquisition or proliferation of group D Streptococcus species, coagulase-negative Staphylococcus species, cefoxitin-resistant members of the family Enterobacteriaceae, Pseudomonas species, and various species of the Bacteroides fragilis group. The most striking finding was ingrowth of Clostridium difficile, noted in five of the six patients. There was concomitant eradication or decrease of cefoxitin-susceptible Enterobacteriaceae family members, Bacteroides species other than the B. fragilis group, Clostridium species other than C. difficile, and Lactobacillus species. These marked alterations of fecal flora may have important clinical consequences.

Antimicrobial susceptibilities of 1,292 isolates of the Bacteroides fragilis group in the United States: comparison of 1981 with 1982

A susceptibility survey of 537 strains of the Bacteroides fragilis group from eight centers in the United States was continued at the Tufts New England Medical Center in 1982. The results were compared with those of 755 organisms analyzed in 1981. Nine antimicrobial agents were tested by an agar dilution method. The respective percentages of resistance for 1981 and 1982 were as follows (%): cefoxitin, 8 and 10; moxalactam, 22 and 12; cefotaxime, 54 and 48; cefoperazone, 57 and 54; piperacillin, 12 and 7; clindamycin, 6 and 3; metronidazole, 0 and 0; chloramphenicol, 0 and 0; and tetracycline, 63 and 59. Regional differences in resistance rates were found. Declines in resistance to moxalactam, piperacillin, and clindamycin were noted at the participating hospitals. An outbreak of cefoxitin resistance was noted at the Tufts New England Medical Center, where the rate increased from 14 to 30%. The various species of the B. fragilis group had differing patterns of resistance; B. fragilis was the most susceptible species. Significant cross resistance among the beta-lactam agents was found. These data indicate the need to determine the susceptibility patterns of the B. fragilis group organisms within each hospital.

Brain abscess and cerebritis

Eighteen consecutive cases of brain abscess or cerebritis seen at the Veterans Administration Wadsworth Medical Center (Los Angeles, Calif.) during 1970-1982 were analyzed. Fifteen occurred after the computerized axial tomographic (CT) scanner for diagnosis and follow-up became available in 1976. The patient population included 14 individuals with significant underlying medical problems and with a clearly identifiable contiguous or distant source. Four patients had multiple brain abscesses; the most common site of involvement in the remaining 14 patients was the parietal lobe. Microorganisms were isolated from 14 patients and included a variety of aerobic and anaerobic bacteria. Of the 27 isolates, 12 were microaerophilic species or strictly anaerobic bacteria. Therapy was most often a combination of surgical drainage and antimicrobial agents. Usually the drug regimen included penicillin and chloramphenicol and, more recently, the combination of penicillin and metronidazole. One of the two patients with brain abscess treated with antimicrobial agents alone died. Two patients with presumed bacterial cerebritis improved with chemotherapy alone. This study reaffirms the important role of anaerobes in brain abscess. The advent of the CT scanner appears to have been a valuable development in both diagnosis and monitoring of therapy, but mortality (22%) still remains relatively high. Although metronidazole will likely prove to represent a significant advance in antimicrobial therapy, surgical drainage still appears to be the mainstay of therapy for treatment of established abscesses.

Role of anaerobic bacteria in bite-wound infections

The etiologic agents usually involved in wound infections due to human or animal bites are the aerobic skin flora of the victim, e.g., Staphylococcus aureus, and/or the aerobic oral flora of the biter, e.g., Pasteurella multocida. While anaerobic bacteria are predominant in the normal oral flora of humans and animals, their importance in the pathogenesis of bite-wound infections has not been stressed. Most investigators in this field have either not cultured these wounds for anaerobic bacteria or not utilized optimal culture techniques. In a series of studies on human and animal bite wounds, methods that are optimal for recovery of anaerobic bacteria were used. Anaerobes were found in significant quantities in 39% of animal bite wounds, 50% of human bite wounds, and 56% of clenched-fist injuries. Several species of anaerobes usually were present in the wounds and always were present in mixed culture with aerobic oral flora. The anaerobes most commonly isolated included Bacteroides asaccharolyticus, Bacteroides bivius, Bacteroides disiens, Bacteroides melaninogenicus, Bacteroides oralis, Bacteroides ruminicola, Bacteroides pneumosintes, Bacteroides ureolyticus, Fusobacterium nucleatum, Fusobacterium russii, Peptococcus species, Peptostreptococcus species, and Veillonella species. Initial, empiric antimicrobial therapy for bite wounds should be directed against potential anaerobic as well as aerobic pathogens.

Anaerobic mediastinitis

Anaerobic bacteria often are neglected in discussions of the bacteriology of mediastinitis. Two cases of anaerobic mediastinitis are reported and the literature in this field is reviewed. Anaerobes are important pathogens in the etiology of mediastinitis secondary to perforation of the esophagus, extension of a retropharyngeal abscess, or extension of cellulitis or abscess of dental origin from the neck. Although anaerobes indigenous to the oral cavity predominate in these cases, there are also a few cases reported involving Bacteroides fragilis. The source of the mediastinitis should be considered when antimicrobial therapy is initiated so that appropriate anaerobic coverage can be included when indicated.

Anaerobes in burn-wound infections

Anaerobic bacteria are not routinely considered in discussions of the etiology of burn-wound infection. However, this review of the literature reveals that there are numerous case reports that document clinically significant anaerobic burn-wound infection and some prospective data that suggest a possible role of anaerobes in the clinical setting of burn-wound sepsis. Further studies are needed to answer the questions of how often anaerobes colonize burn wounds and how often anaerobes invade the wounds to cause clinically significant burn-wound sepsis.

Problems encountered in clinical anaerobic bacteriology

Despite the rapid progress made in the technology of anaerobic bacteriology during the last 15 years, substantial variation in the practices and resources of different laboratories still exists. All steps, from the collection of the specimen to final identification, may involve pitfalls. Aspirated pus and tissue samples that are anaerobically transported are always preferable to swabs. Failure to examine gram-stained preparations and wet mounts and to inoculate the specimen promptly onto fresh supplemented media, including selective media, is still common. Generating and maintaining anaerobiosis requires careful monitoring. Plates often are discarded prematurely. The results of final identification with PRAS (prereduced, anaerobically sterilized) biochemicals and gas-liquid chromatography usually arrive too late to guide the clinician to proper therapy. Preliminary tests, along with growth on selective and differential media, are essential for prompt identification of clinically significant anaerobes. Future efforts should be directed toward diminishing the heavy work load of anaerobe laboratories by developing simpler and more rapid procedures.

A rat model of unilateral utero-tubo-ovarian abscess

Unilateral (utero-tubo-ovarian) abscesses were produced in rats with Bacteroides fragilis in pure culture. One horn of the rat's bicornuate uterus was ligated, and the inoculum of B. fragilis was placed in the uterine horn above the point of ligation. The 50% infecting dose (ID50) of B. fragilis was approximately 10(5) colony forming units (cfu). When harvested the abscesses contained up to 10(8) cfu of B. fragilis in pure culture as well as many white blood cells. Abscesses were 2-3 cm in length and contained 0.5-1.5 ml of purulent material. The oxidation-reduction potential (Eh) of the abscesses ranged from -230 to -323 millivolts. Abscess formation was comparable in all four phases of the estrous cycle. In rats treated with depoestradiol (to create a high-estrogen state), the rate of growth and size of the abscesses (3-5 cm in length and 2-3 ml of purulent material) were greater than in untreated rats.

Polyacrylamide gel electrophoresis patterns produced by Clostridium difficile

Clostridium difficile is a major cause of pseudomembranous colitis following antimicrobial therapy. There is evidence to suggest that this organism may be hospital acquired. Polyacrylamide gel electrophoretic (PAGE) analysis of protein profiles of C. difficile cell extracts was examined for possible usefulness in epidemiologic studies. At least 50 bands could be distinguished in soluble cell extracts of C. difficile. Freeze-thawing of extracts and/or length of storage time did not affect the protein profiles. While all strains tested were nearly identical, several strains were unique in their lack of a 34,000-dalton polypeptide. Protein patterns of C. difficile could easily be distinguished from those of Clostridium sordellii. Additionally, surface antigens extracted from several strains of C. difficile and from a few strains of C. sordellii revealed marked differences. Ethylenediaminetetraacetate (EDTA) extracts from C. difficile showed two or three major bands in PAGE analysis; strains could be divided into two major subgroups on the basis of band distribution. EDTA extracts from C. sordellii bore no similarity to those of C. difficile.

Comparative in vitro activities of cefpiramide and apalcillin against anaerobic bacteria

The in vitro activities of two new antimicrobial agents, apalcillin and cefpiramide (SM-1652), were evaluated against 324 strains of anaerobic bacteria. Apalcillin (a penicillin derivative) and cefpiramide (a semisynthetic cephalosporin) were compared with piperacillin, moxalactam, and cefoxitin. Organisms studied included the Bacteroides fragilis group, other Bacteroides species, fusobacteria, clostridia, nonsporeforming gram-positive rods, and anaerobic cocci. Piperacillin was found to be the most active overall, inhibiting 96% of the strains tested at its achievable level in serum (128 micrograms/ml). Apalcillin was comparable in activity to piperacillin, inhibiting 93% of anaerobes tested at this concentration. The other antibiotics inhibited ca. 80% of the strains at 32 micrograms/ml. In terms of activities against particular species, apalcillin was active against 75% of B. fragilis group strains and 97 to 100% of all other anaerobes. Cefpiramide inhibited 37% of B. fragilis group strains at 32 micrograms/ml and 68% at 64 micrograms/ml (a level that may be achievable with this drug). Cefpiramide inhibited 92% of all other anaerobes at 32 micrograms/ml and 95% at 64 micrograms/ml. The clostridia other than Clostridium perfringens were the most resistant (84% inhibited at 32 micrograms/ml and 95% inhibited at 64 micrograms/ml).