“Bacteroides” bacteremia

Clinical and bacteriologic data relating to 250 patients with bacteremia due to anaerobic, nonsporulating, gram-negative bacilli, “bacteroides,” were analyzed. A total of 433 human blood culture specimens submitted included nine Bacteroides species and four species of Fusobacterium; twenty-nine were mixed with other microorganisms. The characteristic clinical syndrome consisted of hectic fever, rigors and diaphoresis. The gastrointestinal tract was the probable portal of entry for the majority of Bacteroides, the lung and oropharynx for Fusobacterium species. Prior surgery, malignant neoplasms, diabetes mellitus, and steroid, immunosuppressive or cytotoxic therapy were common associated factors. Emboli, thrombophlebitis, endocarditis and metastatic abscesses were common complications. The over-all mortality of the patients was 32 per cent. The mortality of patients with B. fragilis bacteremia, the most common organism involved, was 34 per cent. The death rate of patients with B. oralis and B. variabilis was approximately 70 per cent, but none of the patients with B. melaninogenicus bacteremia died. Patients treated with tetracyclines, sulfonamides, incision and drainage, or a combination of these, showed the highest survival rate.     

The clinical importance of anaerobic bacteria in wound infections after gastrointestinal surgery.

Wound cultures from 54 patients with infections after gastrointestinal surgery were examined. Cultures from wounds after surgery on the upper gastrointestinal tract grew few organisms, mainly aerobic gram-positive cocci. Culture from wounds on the lower gastrointestinal tract grew strains of bacteria, aerobic and anaerobic gram-negative rods dominating. Indirect immunofluorescence studies on acute and convalescent phase sera showed significant immune response against Bacteroides fragilis in a majority of cases. Immune response against anaerobic cocci was seldom found. Very high antibody titres against Clostridium perfringens were often found, both in patients' and control sera.     

Endocarditis due to anaerobic bacteria

This review describes the microbiology, diagnosis and management of endocarditis due to anaerobic bacteria. Anaerobic bacteria are an uncommon but important cause of endocarditis. Most cases of anaerobic endocarditis are caused by anaerobic cocci, Propionibacterium acnes and Bacteroides fragilis group. Predisposing factors and signs and symptoms of endocarditis caused by anaerobic bacteria are similar to those seen in endocarditis with facultative anaerobic bacteria with the following exceptions: the gastrointestinal tract was the most common source for B. fragilis group endocarditis, the head and neck were the most common origin for Fusobacterium and Bacteroides spp., and the head and neck and genitourinary tract were the most common source for peptostreptococci. Complications with anaerobic endocarditis include valvular destruction, multiple mycotic aneurysms, aortic-ring abscess, aortitis, cardiogenic shock, dysrhythmias and septic shock. The mortality rate for patients with anaerobes endocarditis is 21-43%. Treatment of endocarditis involving anaerobic bacteria includes the use of antibiotic therapy effective against these organisms.     

Metronidazole therapy of anaerobic bacteremia, meningitis, and brain abscess.

Four patients with Bacteroides fragilis bacteremia, one patient with a brain abscess due to Bacteroides species, Fusobacterium naviforme, and Peptostreptococcus species, and an infant with Bacteroides species ventriculitis and meningitis were treated with metronidazole. In all cases the anaerobic pathogens were eradicated. Five of the six patients recovered. One patient with leukemia in whom B fragilis bacteremia was eradicated by metronidazole treatment subsequently died of Pseudomonas aeruginosa bacteremia. Ventricular fluid and serum concentrations of metronidazole were determined in the case of meningitis and are reported.     

Susceptibility of anaerobic bacteria to metronidazole: relative resistance of non-spore-forming gram-positive baccilli.

Susceptibility of 358 clinical isolates of obligate anaerobes to metronidazole was determined by an agar-dilution technique. Only 66% of all isolates were inhibited by 6.25 mug/ml, whereas 30% required larger than or equal to 50 mug/ml. Considerable variation in susceptibility was observed among different genera and species of bacteria. Fusobacterium was most senstitive, followed by Clostridium, Bacteroides and Peptococcus, Peptostreptococcus, Veillonella and Acidaminococcus, and non-spore-forming gram-positive bacilli. Bacteroides fragilis was more sensitive than other species of Bacteroides. Similarly, Clostridium perfringens was more susceptible than other species of Clostriduim. While metronidazole appears to be a promising antimicrobial agent for infections caused by Fusobacterium, Clostrididium, and B.fragilis, therapy for infections with other anaerobic bacteria should be guided by in vitro tests of sensitiivity.     

Bacteremia caused by non-sporulating anaerobes in cancer patients. A 12-year experience

The clinical, epidemiological and laboratory characteristics of bacteremia caused by anaerobic organisms other than Clostridium spp. in cancer patients are described and compared to other previously reported series. Of the 315 episodes, 246 (78%) were caused by a single organism and 69 (22%) were polymicrobial. The most common underlying malignancies were genitourinary and gynecological tumors, acute leukemia, and gastrointestinal malignancies. Most patients (94%) were febrile, and septic shock was documented in 24% of monomicrobial episodes and in 58% of those with polymicrobial infection. Soft-tissue infection was present in 44% of the cases, and it presented as tissue necrosis in 11%. The most common sites identified as the portal of entry were intra-abdominal abscesses, soft tissue, and the oropharynx. The most common organisms were Bacteroides fragilis (57%) and other Bacteroides spp. (22%). Most polymicrobial infections were caused by 2 organisms, the second most commonly another anaerobe or an aerobic gram-negative bacillus. The most active antibiotic in vitro was chloramphenicol. High rates of resistance to penicillin were observed not only among B. fragilis, but also among Bacteroides spp. The frequency of penicillin resistance increased throughout the study years. The overall survival was 70%. The cure rate for monomicrobial bacteremias was 76% vs. 51% for polymicrobial episodes. Infection was the cause of death in 20 and 16 episodes, respectively. The response rate for patients in septic shock was 47% in contrast to an 85% recovery rate for those without it. Ninety-five patients had documented abscesses accompanying the bacteremic episode. The most effective antibiotics were clindamycin and chloramphenicol. Overall response to penicillin was only 13%. Suboptimal responses were also observed for the antipseudomonal penicillins. High response rates (82%) were also obtained with cefoxitin, metronidazole, and moxalactam.     

Epidemiology, antimicrobial susceptibility, pathogenicity, and significance of Bacteroides fragilis group organisms isolated at Los Angeles County-University of Southern California Medical Center

The epidemiology of species of the Bacteroides fragilis groups isolated at Los Angeles County-University of Southern California Medical Center was examined. In addition, frequency of resistance to six beta-lactam antibiotics (cefmetazole, cefotetan, ceftizoxime, imipenem, penicillin, and cefoxitin) and to clindamycin, chloramphenicol, and metronidazole was determined for each species. While B. fragilis was most commonly isolated, the other species of the B. fragilis group accounted for half of the isolates. Seven percent of 1,128 patients with infections due to species of the B. fragilis group were bacteremic. A review of bacteremic cases indicated that non-fragilis species were highly pathogenic. Resistance to clindamycin ranged from 8% to 22% among species and was most common among isolates of Bacteroides distasonis and Bacteroides thetaiotaomicron. Significant differences in antimicrobial activity were noted among the agents tested. Only imipenem, chloramphenicol, and metronidazole were predictably effective against non-fragilis species of the B. fragilis group. Prompt identification of species and susceptibility testing of clinical isolates of this group are needed if a newer beta-lactam agent or clindamycin is to be used for initial therapy.     

Septic arthritis caused by Bacteroides fragilis

As improvements in bacteriologic techniques have enhanced the recovery of anaerobic bacteria from clinical specimens, there has been an increasing awareness of the role of anaerobes in disease. Bacteroides fragilis is the most common anaerobic organism found in clinical specimens. Although it is the anaerobe most frequently associated with bacteremia and a common isolate in intraabdominal infections, infections of the female genital tract, wounds, and abscesses, B. fragilis is a rare cause of septic arthritis. The isolation of this organism from four patients with septic arthritis in three Cleveland hospitals between 1978 and 1982 suggests that septic arthritis due to B. fragilis may be a more common clinical entity than previously appreciated. In this report we describe these cases and review the pertinent literature.     

Aerobic and anaerobic microbiology of paronychia

Pus specimens from 28 patients with paronychia of the finger yielded bacterial growth by techniques for cultivation of aerobic and anaerobic bacteria. Anaerobic and aerobic organisms only were isolated in pure culture in five (18%) and eight patients (29%), respectively; mixed aerobic and anaerobic flora were present in 15 patients (54%). Seventy-two isolates were recovered, or 2.6 isolates per specimen. The predominant anaerobic organisms were Gram-positive anaerobic cocci, Bacteroides species, and Fusobacterium species. The predominant aerobic organisms were Staphylococcus aureus, gamma-hemolytic streptococci, Eikenella corrodens, group A beta-hemolytic streptococci, alpha-hemolytic streptococci, and Klebsiella pneumoniae. Candida albicans was recovered in four cases. This study demonstrates the mixed aerobic and anaerobic bacteriology of paronychia.     

Protective efficacy of immunization with capsular antigen against experimental infection with Bacteroides fragilis

The protective efficacy afforded by immunization with the capsular antigen of Bacteroides fragilis against abscess formation and bacteremia due to this organism was studied in an experimental rat model of intraabdominal sepsis. Of unimmunized animals, animals immunized with methylated bovine serum albumin and complete Freund's adjuvant, and animals immunized with lipopolysaccharide of Bacteroides thetaiotaomicron, greater than 90% developed abscesses when challenged intraperitoneally with strains of B. fragilis or Bacteroides distasonis (given with an enterococcus) or with the cecal contents of meat-fed rats. In contrast, animals immunized with B. fragilis capsular polysaccharide, given with or without methylated bovine serum albumin and complete Freund's adjuvant, and animals immunized with the outer membrane of B. fragilis strain 23745 were protected to a significant degree from abscesses caused by challenge with B. fragilis or B. distasonis. Such immunization had no overall effect on the development of abscesses in animals challenged with the entire cecal contents of meat-fed rats; however, B. fragilis was eliminated from the abscesses of these animals. Animals immunized with the capsular polysaccharide were protected from early B. fragilis bacteremia.     

Retrospective analysis of Fusobacterium associated infections; experience at Aomori Prefectural Hospital with 108 cases from 1995 to 1999

We experienced 108 cases of Fusobacterium associated infections, including otolaryngeal, oral, pleuropulmonary, intraabdominal, skin and soft tissue infections, at Aomori Prefectural Hospital during The 5 year-period from 1995 to 1999. A total of 433 organisms, included 113 Fusobacterium spp. (80 Fusobacterium nucleatum, 18 Fusobaterium necrophorum, 5 Fusobacterium varium, 4 Fusobacterium mortiferum, 6 Fusobacterium spp.), were recovered with an average of 4.0 organisms per case of the 108 cases, 68% were mixed aerobic and anaerobic and yielded 185 anaerobic bacteria (2.5 per case) and 137 aerobic bacteria (1.9 per case) with an average of 4.4 per case. The remaining 32% were purely anaerobic and yielded 111 organisms with an average of 3.2 per case, Prevotella spp., Bacteroides fragilis group, Streptococcus milleri group, Enterobacteriaceae, Peptostreptococcus spp. Staphylococcus spp. were most frequently coisolated with Fusobacterium spp.     

Anaerobic bacteremia in a general hospital: retrospective five-year analysis

Anaerobic bacteremia (116 cases) represented 5.4% of the total cases of bacteremia in the Hospital Nuestra Se?ora de Covadonga of Oviedo, Spain, during a five-year period (1981-1985). Microbiologic data for all 116 cases and clinical data for 63 patients were analyzed. A total of 129 isolates were identified as gram-negative bacilli (45.7%), gram-positive bacilli (38.0%), gram-positive cocci (14.0%), and gram-negative cocci (2.3%). Bacteroides fragilis and Clostridium perfringens were the most frequently occurring species. Anaerobic polymicrobial infection was detected in 21 patients. The most relevant clinical features were fever (79%), metastatic abscesses (33%), anemia (27%), septic shock (25%), and disseminated intravascular coagulation (6%). The overall mortality rate was 25.4%, and the factors associated with a poor prognosis were age over 60 years, lack of adequate surgical treatment, severe underlying disease, metastatic foci, and polymicrobial and/or nosocomial infection.     

Surface antigens as virulence factors in infection with Bacteroides fragilis

Organisms of the genus Bacteroides represent the major group of obligate anaerobes involved in human infections. Bacteroides usually cause either bacteremia or localized abscesses. Of the numerous species of Bacteroides, Bacteroides fragilis is the single most frequent clinical isolate. B. fragilis and Bacteroides melaninogenicus have chemically incomplete lipopolysaccharides as compared with the lipopolysaccharides (endotoxins) of aerobic bacteria, and the lipopolysaccharides of Bacteroides lack the biologic potency characteristic of endotoxin. This inactivity may account for the very infrequent occurrence of disseminated intravascular coagulation or purpura that can accompany sepsis due to these organisms. Furthermore, strains of B. fragilis have an immunologically common capsular polysaccharide. In an animal model of intraabdominal sepsis, the encapsulated strains caused abscesses when given without other organisms, but abscess formation from unencapsulated strains of Bacteroides generally required the administration of a synergistic aerobe. The abscesses caused by encapsulated strains were shown to be directly attributable to the capsular polysaccharide, which is an important virulence factor of this organism. Patients or experimental animals infected with B. fragilis develop antibodies to the capsular polysaccharide, and these antibodies can be detected in a radioactive antigen-binding assay.     

Anaerobic wound infection: Bacteroides mediastinitis after cardiovascular surgery

A case of postoperative anaerobic mediastinitis after coronary artery bypass grafting is reviewed. One of the causative organisms, Bacteroides oralis, has never previously been described as a pathogen causing mediastinitis after median sternotomy incision. There was associated Bacteroides fragilis bacteremia. Only three cases of Bacteroides species mediastinitis after open heart surgery have been reported. This anaerobic bacterium remains a rare pathogen in median sternotomy infections despite the increasing number of cases of mediastinitis seen in association with the burgeoning number of patients undergoing cardiac surgery. Multiple risk factors may contribute to mediastinal infections, which occur in about 2% of patients undergoing coronary artery surgery. When infection occurs, aerobic and anaerobic wound cultures should be made and appropriate antimicrobial and surgical therapy instituted.     

Acute appendicitis and Bacteroides fragilis.

Bacteria belonging to the Bacteroides fragilis group (B. fragilis, B. ovatus, B. vulgatus, B. distasonis, B. thetaiotaomicron and B. uniformis) were cultured in quantities of less than or equal to 10(5) c.f.u./ml from the excised appendix from 30 patients. Twenty-two patients (group I) had an acute purulent appendicitis (three with perforation), four were classified as slightly inflamed cases (group 2) and four had a normal appendix (group 3). The B. fragilis group of bacteria dominated among the anaerobic isolates, but Bifidobacteria, Fusobacteri, Clostridium perfringens, Lactobacilli, Leptotrichia and Veillonella, in decreasing order, were isolated as well. Among isolates of aerobic bacteria, E. coli was most frequently isolated (26/30 patients). No other genus was isolated from more than four of the appendices. Serological investigations of the humoral antibody response to polysaccharide antigens from four of the Bacteroides species showed that a doubling of the titer, or more, in paired serum samples could be observed as follows: against B. fragilis 6/22 patients (group 1), 3/8 patients (groups 2 and 3). The corresponding figures for B. ovatus were 11/22 and 2/8, B. vulgatus 3/22 and 0/8 and B. distasonis 4/22 and 0/8. Sera from two patients with ruptured appendix, and B. fragilis cultivated, showed the highest titer increases against the B. fragilis antigen. The data from the bacteriological and immunological investigations make us conclude that (i) the B. fragilis group of bacteria is the most common anaerobic group of bacteria isolated from normal and diseased appendices, (ii) the mere isolation of B. fragilis, encapsulated or not, does not imply an etiological role in appendicitis since there was no obvious difference in titer increases against B. fragilis in sera from patients with or without an inflamed appendix, and (iii) high, and significant, titer increases against B. fragilis are seen in sera from patients with ruptured appendix.     

Anaerobic bacteremia in the elderly

Anaerobic bacteremia occurred in 68 patients over the age of 60 in a university hospital. These elderly patients were more likely than younger patients to have an underlying malignancy. Anaerobes involved included Bacteroides fragilis group (64 isolates), Bacteroides melaninogenicus group (11) and Clostridium species (11). Polymicrobial bacteremia was common, occurring in 32.3% of patients. Mortality in patients who had surgery to remove the source of anaerobes was 43.3%, compared to 81.7% in patients with no surgical treatment. Overall mortality was 66.1%, much higher than noted in younger populations.     

Plasmid-mediated, transferable resistance to clindamycin and erythromycin in Bacteroides fragilis.

A clindamycin- and erythromycin-resistant strain of Bacteroides fragilis, TMP10, that had been isolated from a blood culture transferred its drug resistance in a Millipore mating procedure to another strain of B. fragilis, TM2000, and to a strain of Bacteroides thetaiotaomicron. Donor strain TMP10 contained numerous species of extrachromosomal DNA ranging from approximately 2 x 10(6) to 20 x 10(6) daltons in molecular weight, as revealed by agarose gel electrophoresis. Clindamycin- and erythromycin-resistant transcipient cells of B. fragilis strain TM2000 always contained at least two plasmid species with molecular weights of 2 x 10(6) and 20 x 10(6) daltons, respectively, although other plasmid species were also transferred.     

Detection of specific IgG antibody in sera from patients infected with Bacteroides fragilis by enzyme-linked immunosorbent assay.

During a period of 13 months, 28 serious infections caused by Bacteroides were seen in 27 patients. Sixteen patients yielded Bacteroides fragilis; sera from 13 (81%) of these 16 had increased levels of IgG specific for B. fragilis lipopolysaccharide (LPS) antigens by enzyme-linked immunosorbent assay (ELISA). Sera from 20 normal controls did not have increased specific IgG. Sera from 22 of 23 patients with bacteremia caused by other gram-negative rods also failed to yield increased levels of specific antibody (P less than 0.0012). Analysis of sera from patients with B. fragilis infections disclosed a significant correlation between the levels of specific IgG to B. fragilis LPS measured by ELISA and the IgG antibody to the infecting B. fragilis by indirect immunofluorescence (r = 0.84, P less than 0.012). Two of the remaining 12 infections caused by Bacteroides not apparently due to B. fragilis organisms were also associated with increased levels of specific IgG to B. fragilis LPS antigens. Specific IgG antibody response may be an important adjunct in diagnosis of common B. fragilis infections and may allow better management of antimicrobial agents.     

Anaerobic bacteria in biliary disease in elderly patients.

Gallbladder bile from 52 elderly subjects who had undergone biliary tract surgery was examined for the presence of bacteria. Twelve patients had sterile bile, 18 specimens of bile yielded anaerobes as well as aerobes, and 22 yielded aerobic bacteria only. Escherichia coli was the most commonly isolated organism (30 strains). Bacteroides fragilis was the most frequently encountered anaerobic bacterium and was found in 15 patients. The Klebsiella-Enterobacter group was the second most commonly isolated group and B. fragilis was third. Clostridium perfringens was recovered in 10 specimens of bile. Anaerobic bacteria were recovered more frequently in patients with ductal obstruction. The relatively frequent isolation of anaerobes, especially of B. fragilis, in this study may be related to the anaerobic techniques used, to the age of the patients, and to the high incidence of pigment stones among the subjects.     

Bacterial colonization, tracheobronchitis, and pneumonia following tracheostomy and long-term intubation in pediatric patients.

Serial tracheal cultures for aerobic and anaerobic bacteria were obtained from 27 pediatric patients during one year of follow-up. The patients had required tracheostomy and prolonged intubation for periods ranging from 3 to 12 months (average, 7 1/2 months). Cultures of tracheal aspirates yielded 1,508 isolates of pathogenic aerobic (969 isolates) and anaerobic (539 isolates) bacteria. The most frequent aerobic isolates were Streptococcus pneumoniae and Staphylococcus aureus. The predominant anaerobes were anaerobic gram-positive cocci, Fusobacterium nucleatum, and Bacteroides fragilis. Replacement of one pathogen by another occurred frequently. Tracheobronchitis occurred in 24 patients, all of whom had episodes of pneumonia. The data suggest that anaerobic bacteria are a part of the bacterial flora in colonization, tracheobronchitis, and pneumonia in patients with tracheostomy and prolonged intubation.