Management of anaerobic infections.

Anaerobic infections are reviewed with emphasis on management. Most anaerobic pulmonary infections respond to penicillin G, even when Bacteroides fragilis (penicillin-resistant) is present. Clindamycin is suitable in penicillin-sensitive patients. Intraabdominal infections have a complex flora usually involving anaerobes, especially B. fragilis. It is desirable to use antimicrobial therapy to cover potential pathogens of all types. Surgical drainage and debridement are extremely important considerations. Anaerobic bacteria were found in 72% of 200 patients with female genital tract infections and were the exclusive isolates in 30%. Surgical therapy is primary, but antimicrobial and anticoagulant therapy are also important. A variety of soft-tissue infections involve anaerobes. Surgery is the major therapeutic approach. Anaerobic endocarditis is uncommon but may be difficult to manage. Chloramphenicol is ordinarily the drug of choice for brain abscess. New antimicrobial agents, which are under investigation and are promising, include new penicillins, new cephalosporins, new tetracyclines, and metronidazole.     

Pericarditis due to anaerobic bacteria

This review describes the microbiology, diagnosis and management of pericarditis due to anaerobic bacteria. The predominant anaerobes recovered from patients with pericarditis were: gram-negative bacilli (mostly of the Bacteroides fragilis group), anaerobic streptococci, Clostridium spp., Fusobacterium spp., and Bifidobacterium spp. Anaerobic bacteria can be isolated in pericarditis resulting from the following mechanisms: (1) spread from a contiguous focus of infection, either de novo or after surgery or trauma (pleuropulmonary, esophageal fistula or perforation, and odontogenic); (2) spread from a focus of infection within the heart, most commonly from endocarditis; (3) hematogenous infection, and (4) direct inoculation as a result of a penetrating injury or cardiothoracic surgery. No differences were found in the clinical diagnostic features between cases of pericarditis due to anaerobic bacteria and those due to aerobic and facultative bacteria. Anaerobic gram-negative bacilli have increased their resistance to penicillins and other antimicrobials in the last decade. Complete identification and testing for antimicrobial susceptibility and lactamase production are therefore essential for the management of infections caused by these bacteria. Treatment of pericarditis involving anaerobic bacteria includes the use of antibiotic therapy effective against these organisms.     

Bacterial interference by oropharynegeal and clinical isolates of anaerobic bacteria.

Anaerobic isolates were tested for bacterial inhibitory activity. Of 144 isolates, 102 were from oropharynegeal washings, and 42 were from clinical specimens. Thirteen facultative bacterial species (seven members of the Enterobacteriaceae and six species of gram-positive cocci) were used as indicators of inhibition. Eleven anaerobic species were isolated from oral secretions. All isolates of Bacteroides melaninogenicus, the most commonly recovered species, consistently inhibited several species of indicator bacteria. Bacteroides fragilis, Bacteroides oralis, and Peptostreptococcus anaerobius had unprecictable inhibitory activity, whereas most of the other oral anaerobes were noninhibitory. The 42 clinical species were generally noninhibitory.     

The bacteriology of aspiration pneumonia

A prospective study of 54 cases of pulmonary infection following aspiration was performed. Specimens utilized for bacteriologic study were either transtracheal aspirates, empyema fluid or blood. Appropriate anaerobic bacteriologie methods were employed. Anaerobic bacteria were recovered in 50 patients (93 per cent) and were the only pathogens in 25 (46 per cent). The predominant species were Bacteroides melanino-genicus, Fusobacterium nucleatum and anaerobic or microaerophilic gram-positive cocci. Bacteroides fragilis, which is resistant to many commonly used antibiotics, was recovered in nine patients (17 per cent). Aerobic and facultative bacteria were present in 29 patients (54 per cent), but anaerobes were present concurrently in all but 4. Enteric gram-negative bacilli and pseudomonads were particularly common in patients whose disease developed in the hospital. Eleven patients with mixed aerobic and anaerobic infections were treated successfully with antibiotics which were active only against the anaerobic isolates, thereby further implicating the pathogenic role of these microorganisms. The results indicate that anaerobes play a key role in most cases of infection following aspiration.     

Clinical characteristics of anaerobic bactibilia.

During a two-year period, 1,892 patients underwent biliary tract surgery at the Mayo Clinic. Both aerobic and anaerobic bile cultures were performed in 371 patients and 253 of these were positive. Anaerobes were isolated from 100 patients, although only twice in pure culture. Only aerobes grew from cultures from 153 patients. One hundred cases of biliary tract infections involving anaerobes and an equal number involving aerobes only were reviewed in order to determine their clinical characteristics. Prominent features of anaerobic bactibilia included (1) a history of complex, multiple, biliary tract surgeries often involving biliary-intestinal anastomoses and common bile duct manipulation, (2) severe symptoms, (3) high incidence of postoperative infectious complications, especially wound infections. Further analysis of anaerobic biliary infections suggested that Bacteroides fragilis was more often associated with serious pathologic conditions of the biliary tract than was Clostridium.     

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.     

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.     

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.     

Recovery of anaerobic bacteria from 3 patients with infection at a pierced body site.

We describe 3 adolescents who developed infections due to anaerobes at pierced body sites: the nipple, the umbilicus, and the nasal septum. Anaerobes (Prevotella intermedia and Peptostreptococcus anaerobius) were recovered from pure culture of specimens obtained from 1 patient with nipple infection and were mixed with aerobic bacteria in cultures of specimens obtained from 2 patients (Streptococcus aureus, Peptostreptococcus micros, and Prevotella melaninogenica were recovered from a patient with nasal septum infection, and Bacteroides fragilis and Enterococcus faecalis were recovered from a patient with umbilical infection). The infection resolved in all patients after removal of the ornaments and use of antimicrobial drug treatment.     

Anaerobic bacterial bacteremia: 12-year experience in two military hospitals

Clinical and microbiologic data of 296 patients with anaerobic bacteremia were reviewed. Anaerobes were isolated with aerobic or facultative bacteremia in 23 instances. The Bacteroides fragilis group accounted for 148 (70%) of 212 isolates of Bacteroides species. B. fragilis accounted for 78% and B. thetaiotaomicron for 14%. Among other species, there were 20 (6%) Fusobacterium organisms, 63 (18%) Clostridium isolates, and 53 (15%) anaerobic cocci. Seventy-five patients died: 40 had B. fragilis group isolates - B. fragilis, 28, and B. thetaiotaomicron, 8 - and 21 had Clostridium organisms isolated. The primary portals of entry were the gastrointestinal tract (42%), decubiti and gangrene (10%), the female genital tract (8%), and the oropharynx (7%). The gastrointestinal tract, decubiti, and gangrene were the predominant sources for B. fragilis and Clostridium organisms, the female genital tract and oropharynx for anaerobic cocci and Fusobacterium species, and the oropharynx for pigmented Bacteroides. Foreign body was associated with Propionibacterium acnes and Clostridium species. Factors predisposing to bacteremia were abscesses, 53; malignancy, 51; surgery, 30; and intestinal obstruction or perforation, 27.     

Antimicrobial activity of antituberculosis agents against anaerobic bacteria.

Anaerobic infections may coexist with tuberculosis, and can be mistaken for one another. The effect of therapy with antituberculosis chemotherapeutic agents against anaerobic bacteria (with the exception of rifampin) is unknown. We therefore examined the in vitro efficacy of certain commonly used antituberculosis agents (rifampin, isoniazid, and ethambutol) against 370 strains of anaerobic bacteria, including 86 isolates of Bacteroides fragilis. Rifampin at a concentration of 2 microgram/ml inhibited 91 percent of all anaerobic isolates. Both ethambutol and isoniazid were totally ineffective against any of the anaerobes tested, even at 64 microgram/ml. Therapy with rifampin in an unsuspected anaerobic infection can be misdiagnosed for tuberculosis. Therefore, when tuberculosis is suspected, isoniazid and ethambutol can be used and rifampin withheld until the acid-fast bacilli are demonstrated by additional diagnostic procedures, such as transtracheal aspiration.     

Clindamycin and gentamicin for aerobic and anaerobic sepsis.

Thirty-eight adult patients with serious pleuropulmonary, soft-tissue, bone, and intra-abdominal infections caused by combinations of aerobic, facultative, and anaerobic bacteria were treated with parenterally given clindamycin phosphate and gentamicin sulfate and surgery when appropriate. Nine had associated bacteremia. In 29, infections failed to respond to other therapeutic regimens, which included penicillins, cephalosporins, aminoglycosides, and chloramphenicol. Results with clindamycin and gentamicin were excellent and were attributed primarily to the activity of clindamycin against anaerobes, particularly Bacteroides fragilis. Serum concentrations of clindamycin surpassed by manyfold the minimal inhibitory concentrations (MICs) for anaerobes. Serum concentrations of gentamicin did not consistently surpass the MICs for Enterobacteriaceae and Pseudomonas aeruginosa, although those organisms were consistently gentamicinsusceptible by disk diffusion susceptibility tests. Persistent colonization with Enterobacteriaceae, P aeruginosa, enterococci, or Candida were common, and occasionally they were significant in prolonging the clinical courses of patients with extensive infections.     

Antibiotic resistance of oral anaerobic bacteria and their effect on the management of upper respiratory tract and head and neck infections

Anaerobes of oral origin are common in chronic upper respiratory tract and other head and neck infections. Anaerobes are the predominant components of the normal human oropharyngeal flora, and are therefore a common cause of bacterial infections of the upper respiratory tract that are of endogenous origin. These bacteria can be isolated in chronic otitis media, sinusitis, and tonsillitis, and their complications. Anaerobes also predominate in deep oral and neck infections and abscesses. Their isolation requires appropriate methods of collection, transportation, and cultivation of specimens. In addition to their active pathogenic role in these infections, many anaerobes express an indirect effect through their ability to produce the enzyme beta-lactamase. This enables these organisms to shield non-beta-lactamase-producing bacteria (BLPB) from penicillins. Inadequate therapy against BLPB may lead to clinical failures. Treatment of anaerobic infection is complicated by their slow growth, their polymicrobial nature, and the growing resistance of anaerobic bacteria to antimicrobials. Antimicrobial therapy is often the only form of therapy needed, whereas in other instances it is an important adjunct to a surgical approach. Because anaerobes generally are isolated mixed with aerobic organisms, therapy should provide for adequate coverage of both types of pathogens.     

Carbenicillin for treatment of Bacteroides fragilis infections: why not penicillin G?

Carbenicillin has been advocated for treatment of infections caused by Bacteroides fragilis and other anaerobic bacteria. Wide-scale use of the drug in this setting could result in a substantial increase in carbenicillin-resistant Pseudomonas aeruginosa, an effect that would have serious implications. Thirty-four strains of B. fragilis, one-half from bacteremic infections, were tested in vitro, and penicillin G was found to be twice as active as carbenicillin on an equal weight basis; 94% of the strains were inhibited by 32 microgram of penicillin/ml, a level easily achieved therapeutically. Penicillin killed B. fragilis organisms as rapidly as carbenicillin. In two subjects given equivalent doses (100 mg/kg intravenously) of carbenicillin and aqueous penicillin G, the bactericidal activity of serum against B. fragilis after administration of each drug was the same. Controlled clinical trials of treatment of anaerobic bacterial infections with penicillin G in high dosage, carbenicillin (or closely related ticarcillin), clindamycin, and chloramphenicol should be undertaken. Carbenicillin (and ticarcillin) for the present would seem better reserved for P. aeruginosa infections.     

'Punch' actinomycosis causing osteomyelitis of the hand

Osseous actinomycosis usually results from direct invasion of bone from adjacent soft-tissue infection. Involvement of the jaw and vertebral column has been frequently reported, but involvement of the bones of the wrist or hand is rare. A patient with osteomyelitis of the distal right first metacarpal bone due to Actinomyces israelii following a punch injury during fisticuffs is described. Review of similar cases revealed a striking association of this type of infection with punch injuries; hence the term, punch actinomycosis. Analysis of the pus in these infections typically reveals sulfur granules; strict anaerobic conditions must be employed to culture the etiologic agent, A israelii. Management of individual cases should include surgical débridement combined with high-dose parenteral penicillin, followed by long-term penicillin therapy, orally.     

Clindamycin vs penicillin for anaerobic lung infections. High rate of penicillin failures associated with penicillin-resistant Bacteroides melaninogenicus

Thirty-seven adult patients with anaerobic lung infections (27 lung abscesses and 10 necrotizing pneumonias) were submitted to transthoracic needle-aspiration and/or bronchoscopic specimen brush cultures before therapy and thereafter in all cases considered to be failures. Patients were randomly assigned to receive either clindamycin, 600 mg intravenously every 6 hours, or penicillin G, 2 million U every 4 hours for no less than 8 days, until clinical and radiological improvement became apparent. Treatment was continued orally with clindamycin, 300 mg every 6 hours, or penicillin V, 750 mg every 6 hours, until completing a minimum of 4 weeks. Ten of the 47 anaerobes initially isolated from the lung (nine Bacteroides melaninogenicus and one Bacteroides capillosus) were resistant to penicillin, but none were resistant to clindamycin. Five of the nine patients harboring these penicillin-resistant Bacteroides received penicillin, and all failed to respond to therapy. Overall, eight of the 18 patients in the penicillin group and one of 19 in the clindamycin group failed to respond to therapy. These drugs were equally well tolerated in both groups. The presence of penicillin-resistant Bacteroides is a frequent cause of penicillin failure in patients with anaerobic lung infections. In this setting, clindamycin appears to be the current therapy of choice for initial treatment.     

Microbiologic profile of intra-abdominal infections at Belo Horizonte,Brazil

Intra-abdominal infections (IAIs) represent one of the most common clinical problems in hospital practice, especially in surgical areas and centers of intensive care. The treatment of IAIs generally involves the draining of abscesses and empirical antimicrobial therapy. In this study, among 150 patients suffering from IAI, 106 (70.7%) yielded samples that presented microbial growth. Polyinfection was detected in 51.9% of the cases and varied from 2 to 9 distinct microbes per specimen. The overall mean number of micro-organisms isolated per patient was 2.17. Aerobic bacteria (as strict aerobes and facultative anaerobes), strict anaerobic bacteria, and fungi of the genus Candida represented 93.4%, 30.2%, and 13.2% of the cases positive for micro-organisms, respectively. The most common aerobic bacteria were those of the genera Staphylococcus, Escherichia, Proteus, and Streptococcus. Despite the frequent prior use (52%) with antimicrobials of recognized action against strict anaerobes, these micro-organisms constituted 30.9% of the total isolates, and the most frequently found were of the Bacteroides fragilis group and Prevotella species. The high prevalence of anaerobes in the specimens obtained from IAI demonstrates the need to give greater importance to these micro-organisms by making available material and human resources to carry out culture of the anaerobes as part of routine hospital procedures.     

Bacteroides fragilis bacteremia and infected aortic aneurysm presenting as fever of unknown origin: diagnostic delay without routine anaerobic blood cultures.

We report the case of a 71-year-old male with Bacteroides fragilis bactermia and infected aortic aneurysm that went undiagnosed, in part, because routine anaerobic blood cultures were not obtained. Bacteremia caused by anaerobes has been reported to be declining, and recommendations to discontinue routine anaerobic blood cultures have been implemented in some hospitals. To our knowledge, this is the first report of an anaerobic bacteremia and infection that had a delay in diagnosis due to this change in blood-culturing protocol. The potential impact of deleting anaerobic blood cultures from routine protocols is discussed.     

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.     

Anaerobic myocardial abscess following myocardial infarction

An anaerobic myocardial abscess due to Bacteroides fragilis developed in a 60-year-old man when he had an acute myocardial infarction while recuperating from surgery for a paracolonic abscess. Anaerobic bacteremia is a common event and may lead to infection in areas of low oxygen tension far removed from the original portal of entry.