Journal of Postgraduate Medicine
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Year : 1998  |  Volume : 44  |  Issue : 3  |  Page : 63-6  

Anaerobic bacteraemia: a review of 17 cases.

DE Anuradha, K Saraswathi, A Gogate 
 Department of Microbiology, L.T.M. Medical College, Sion, Mumbai.

Correspondence Address:
D E Anuradha
Department of Microbiology, L.T.M. Medical College, Sion, Mumbai.


Of 93 blood cultures received with a suspicion of anaerobic bacteraemia over a period of two years, only 17 (18.3%) showed anaerobic growth. Twelve grew anaerobes alone while five had a polymicrobial flora. Seven of these patients (4.3%) had pre-existing heart disease while others had history of prior surgery, diabetes mellitus or urinary tract infection. Oropharynx was the commonest portal of entry, followed by gastrointestinal tract. The anaerobes isolated were anaerobic streptococci, Bacteroides fragilis group and Bilophila and Eubacterium species. Fifteen patients developed major complications such as congestive cardiac failure, systemic embolisation, and perforative peritonitis. The mortality rate among the cases with anaerobic bacteraemia was 23.5% in this study.

How to cite this article:
Anuradha D E, Saraswathi K, Gogate A. Anaerobic bacteraemia: a review of 17 cases. J Postgrad Med 1998;44:63-6

How to cite this URL:
Anuradha D E, Saraswathi K, Gogate A. Anaerobic bacteraemia: a review of 17 cases. J Postgrad Med [serial online] 1998 [cited 2020 Mar 28 ];44:63-6
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  ::   IntroductionTop

One of the major causes of anaerobic bacteraemia is subacute bacterial endocarditis, which is usually due to preexisting heart disease or major embolic phenomenal[1],[2]. Other factors predisposing to bacteraemia are surgical procedures, prior antibiotic therapy, steroids, diabetes mellitus, malignancies, neutropenic patients, chronic obstructive pulmonary disease (COLD), chronic debilitation, etc[1]. Complications may be due to cardiac sequelae, e.g. congestive heart failure, or following bacteraemia. The latter includes deep abscesses, endotoxic shock, empyema, peritonitis, pelvic inflammatory disease, thrombophlebitis, etc. The diagnosis of subacute bacterial endocarditis is usually done by collecting three sets of blood cultures at an interval of one hour apart. Though anaerobic bacteraemia is on the decline, and there is an increase in fungaemia and enteric gram negative rods (except E. coli, Bacteroides species, anaerobic streptococci and Clostridium species continue to be isolated from cases of subacute bacterial endocarditis[1],[2],[3],[4]. We report 17 cases of anaerobic bacteraemia encountered in our hospital over a period of two years. The possible routes of entry, predisposing factors and complications are also discussed along with mortality rate.

  ::   Material and methodTop

A total of 93 blood cultures were received in the microbiology laboratory over a period of two years from 73 adults and 20 children with suspicion of anaerobic bacteraemia. Simultaneous aerobic as well as anaerobic blood cultures were put up. For children two to five ml of blood was collected in 2050 ml of medium and for adults ten ml of blood in 100 ml of medium. For aerobic culture, three sets of blood were collected one hour apart in trypticase soy broth and incubated aerobically at 37C. It was subcultured onto blood agar and MacConkey agar plates on second, fourth and tenth day. For anaerobic culture, three sets of blood were collected one hour apart in modified thioglycollate broth supplemented with haemin, vitamin K and sodium bicarbonate, without indicator. They were incubated anaerobically in McIntosh Filde's jar at 37?C. Bottles were inspected twice daily for 72 hours and once daily thereafter for seven days. One blind subculture was done within 1218 hours, regardless of whether macroscopic evidence of growth was seen. Thereafter subcultures were done on third, seventh and tenth day onto neomycin blood agar and Bacteroides bile esculin agar plates and incubated anaerobically for three to five days. Colonies growing in both aerobic and anaerobic plates were identified by standard procedures[5],[6]. History of all patients were also taken to find out the possible routes of entry, any predisposing factors and complications if any.

  ::   ResultsTop

Out of 93 blood cultures, 13 showed aerobic growth (13.9%) and 17(18.3%) showed anaerobic growth. Of 13 aerobic growth, seven grew only aerobic bacteria, one Candida albicans and five mixture of aerobes and anaerobes. Of 17 anaerobic growth, five grew mixture of aerobes and anaerobes and 12 only anaerobic bacteria. Amongst 17 patients showing anaerobic growth, 11 were adults (eight males and three females) and six were children (five males and one female). Amongst aerobes, six Staphylococcus, four Klebsiella, one Acinetobacter and one Enterobacter were isolated. Amongst anaerobes, six Bacteroides fragilis, five Peptostreptococcus asaccharolyticus, two P. anaerobius, one Bilophila wadsworthiae, one Eubacterium and in two cases Bacteroides and Eubacterium were isolated together. The [table] shows the various bacteria isolated form 17 patients, possible portal of entry, predisposing factors, complications, and outcome.

Four patients died out of 93. Overall, mortality rate 4.3%, but mortality amongst cases of anaerobic bacteraemia is 23.5%.

  ::   DiscussionTop

Anaerobic bacteraemia is gradually decreasing over the past few years because of empirical treatment with antibiotics, surgical prophylaxis with antibiotics against anaerobes and decreased utilization of blood cultures by surgeons[7]. History of dental extraction, cleaning of teeth or presence of very poor dental repair is the commonest predisposing factor for subacute bacterial endocarditis caused by viridans and microaerophilic streptococci[8]. The commonest predisposing factor for anaerobic endocarditis is any underlying cardiac lesion which ultimately might lead to congestive heart failure (CHF)[8]. Our study shows that 7 out of 17 patients (43%) had cardiac lesions. Three developed CHF and one arrhythmia. In congenital heart disease, commonest cardiac malformation is ventricular septal defect, Tetralogy of Fallot and patent ductus arteriosus (PDA)[9]. We encountered two cases of Tetralogy of Fallot and one case of PDA.

Ten patients (57%) did not have any cardiac lesion. Previous surgery, diabetes mellitus and renal infections were other important predisposing factors in our study, as has been reported by other workers also[1],[2]. Other factors in our study were cholecystitis, appendicitis, COLD and chronic debilitation. Isolation of Bacteroides fragilis and anaerobic streptococci from blood cultures is well documented and some of them are only a part of mixed infections[1],[2],[3],[10],[11]. In five out of 17 cases (29.4%), we isolated mixture of aerobes and anaerobes. An interesting finding in our study is that anaerobic streptococci were isolated from blood culture of six patients who had an underlying cardiac lesion, whereas Bacteroides were isolated from patients with other predisposing factors. SBE due to Eubacterium is also reported[12]. We isolated three Eubacterium, one along with Staphylococcus and two along with Bacteroides.

From a case of appendicitis, we isolated Bilophila wadsworthiae in pure culture, as identified by Summanan et al[13]. Isolation of this anaerobe in association with appendicitis and peritonitis has already been reported[13].

Thirty percent anaerobes are detected during first 18 hours of incubation of blood culture. We isolated five anaerobes  four Bacteroides sp. and one Eubacterium sp. on third subculture (i.e. on seventh day). The remaining 12 (70.6%) were isolated on first subculture (i.e. within 1824 hours). 6 Bacteroides thetaiotaomicron was isolated in pure culture from a male patient suffering from renal infection, who later developed a perinephric abscess. The other seven Bacteroides were B. fragilis.

Reasons for negative blood cultures of patients with infective endocarditis are use of antibiotics in aetiologically undefined febrile illness, right sided endocarditis, prolonged duration of SBE ("bacteriafree" state), presence of renal disease and errors in techniques of obtaining and culturing blood[8].

Anaerobes are normal inhabitants of oropharynx. So in six out of 17 cases (35.3%) the portal of entry was oropharynx, followed by gastrointestinal tract in four, genitourinary tract in three, skin in two and lungs in two cases. Felner and Dowell[1] has reported oropharynx as the portal of entry for anaerobes in onethird cases.

Amoxycillinclavulanic acid combination and amikacin for 2842 days form the mainstay of treatment, metronidazole added to it if anaerobes are suspected. Clindamycin plus an aminoglycoside well be very effective in the treatment of endocarditis and intraabdominal sepsis, as clindamycin is very effective against Bacteroides sp., anaerobic streptococci, Staphylococci and facultative Streptococci (except S. fecalis). The success rate of clindamycin in intraabdominal sepsis ranges from 75100%, with average of 86.2%[14]. Prophylaxis for genitourinary or gastrointestinal manipulations or surgery remain empiric to prevent blood stream invasion by enterococci. Antibiotics are started an hour before operation and continued for two to three days. Prophylaxis is only indicated at time of delivery in pregnant women with cardiac disorders, initiated at onset of labour and continued through second post partum day[15].

Mortality due to anaerobic endocarditis has been reported to be 2141%[1],[2]. Mortality due to anaerobic bacteraemia in our study is 23.5%, whereas overall mortality rate is 4.3%. Four patients died due to cerebral embolism, pulmonary embolism, perforative peritonitis and pelvic inflammatory disease along with peritonitis. In all the four cases B. fragilis were isolated.

Frequency of bacteriologically proved cases of infective endocarditis has been decreased since the advent of effective antibiotic treatment[8]. But anaerobic endocarditis still persists, as shown in our study. If only aerobic culture is done, it might apparently be negative, as in 12 of our cases, only anaerobic bacteria were isolated. Thus, from our study it is suggested that both aerobic and anaerobic blood cultures are advisable for all cases of SBE.

  ::   AcknowledgmentsTop

The technical assistance of Ms. Madhuri Kuwalekar is acknowledged.


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