|Year : 2002 | Volume
| Issue : 3 | Page : 150-152
Anaerobes in pleuropulmonary infections
A De, A Varaiya, M Mathur
Department of Microbiology, LTM Medical College and Hospital, Sion, Mumbai - 400 022, India
Department of Microbiology, LTM Medical College and Hospital, Sion, Mumbai - 400 022, India
A total of 76 anaerobes and 122 aerobes were isolated from 100 patients with pleuropulmonary infections, e.g. empyema (64), pleural effusion (19) and lung abscess (13). In 14% of the patients, only anaerobes were recovered, while a mixture of aerobes and anaerobes was encountered in 58%. From all cases of lung abscess, anaerobic bacteria were isolated, alone (04) or along with aerobic bacteria (13). From empyema and pleural effusion cases, 65.6% and 68.4% anaerobes were recovered respectively. Amongst anaerobes, gram negative anaerobic bacilli predominated (Prevotella melaninogenicus 16, Fusobacterium spp. 10, Bacteroides spp. 9), followed by gram positive anaerobic cocci (Peptostreptococcus spp. 31). Coliform bacteria (45) and Pseudomonas aeruginosa (42) were the predominant aerobic isolates.
|How to cite this article:|
De A, Varaiya A, Mathur M. Anaerobes in pleuropulmonary infections. Indian J Med Microbiol 2002;20:150-2
A lot of emphasis has been laid since past two decades on the role of anaerobic bacteria in pleuroplumonary infections., Anaerobes are being increasingly reported in cases of empyema, lung abscess, etc. in the recent years.,, Thus, the present study was undertaken to study the bacteriological findings with special reference to anaerobic bacteria in patients presenting with empyema, lung abscess and pleural effusion.
| ~ Materials and Methods|| |
A total of 100 patients radiologically diagnosed as having pleuropulmonary infection and admitted in our hospital were included in the study, which consisted of 64 patients with empyema, 19 with pleural effusion and 17 cases of lung abscess.
The specimens (one specimen per patient) were collected by ultrasonography guided percutaneous transtracheal aspiration in sterile syringe and needle, tip of needle sealed with sterile rubber cork, transported to the laboratory and processed immediately within 1-2 hours of collection. A Gram stained smear was prepared from each specimen which were directly inoculated onto blood agar and MacConkey agar plates and incubated aerobically at 37°C for 24 hours. For anaerobes, specimens were directly inoculated on neomycin blood agar (NBA) and bacteroides bile esculin (BBE) agar plates and incubated anaerobically in McIntosh Fildes jar at 37°C for 48 hours. Each specimen was also inocluated into thioglycollate broth, incubated anaerobically for 48 hours and subcultured onto NBA and BBE plates if direct anaerobic culture showed no growth. The plates were observed upto 7 days for any growth. The colonies were further identified as aerobic and anaerobic bacteria by standard laboratory techniques.
| ~ Results|| |
Anaerobic bacteria were isolated from 72% patients with pleuropulmonary infections and were the only isolates in 14% patients. [Table - 1] shows the pattern of pleuroplumonary infections in 100 patients. Out of 100, males comprised 63 and females 37. There were only seven children, remaining 93 being adults. The presence of anaerobes ranged from 65.6% in cases of empyema to as high as high as 100% in cases of lung abscess. Mixture of aerobic and anaerobic bacteria were encountered in 58% cases, only anaerobes in 14% cases and only aerobes in 28% cases.
A total of 76 anaerobes were recovered from these specimens. Gram negative anaerobic bacilli (GNANB) predominated (38) followed by Gram positive anaerobic cocci (GPANC-35). Amongst GNANB, 16 Prevotella melaninogenicus, 10 Fusobacterium species and 8 B.fragilis were isolated. Amongst GPANC, 17 were Peptostreptococcus asaccharolyticus. [Table - 2] shows the anaerobes isolated from these 100 patients. In four specimens, more than one anaerobic organisms were isolated - from one case of empyema, P.melaninogenicus and P.asaccharolyticus and in another case of empyema P.asaccharolyticus and Eubacterium lentum were isolated; in one case of lung abscess P.anaerobius and Veilonella parvula; and in one case of pleural effusion, P.melaninogenicus and P.asaccharolyticus were recovered.
A total of 122 aerobes were isolated from 86 specimens, the remaining 14 specimens grew only anaerobes [Table - 1]. Out of 86 samples, 54 grew single aerobe, 28 grew two aerobes and four grew three aerobes. Coliform bacteria (45), Pseudomonas aeruginosa (42), Acinetobacter species (17), Staphylococcus aureus (11), Streptococcus pyogenes (03), Streptococcus faecalis (02) and Branhamella catarrhalis (02) were the aerobic bacteria isolated.
| ~ Discussion|| |
Anaerobic bacteria are the most overlooked bacterial pathogens of the lower respiratory tract. They are often infrequently recovered from this site probably because of improper specimen collection and lack of appropriate anaerobic identification techniques. Isolation of anaerobic bacteria in the present study in 65.6% cases of empyema correlated well with the study of Ayyagiri et al. However, in various other studies, isolation of anaerobes in cases of empyema is as high as 76-100%, to as low as 31-39%. The predominant anaerobes were P.melaninogenicus (9), F.nucleatum (5) and Peptostreptococcus species (19) in our study, which were also recovered in previous studies., However, we could not recover any Clostridium species as reported by other workers., Primary Gram stained smears also did not reveal any spore bearing organism in this study. S.aureus and S.pneumoniae , the predominant aerobes in the past, have been replaced by coliforms and Pseudomonas species as seen in our study. A total of 42 P.aeruginosa , 31 coliform bacilli and 10 Acinetabacter species were isolated from cases of empyema in this study.
In the 19 cases of pleural effusion, 13 yielded anaerobes, majority being GPANC. Mainly coliform bacteria were isolated among the aerobes (9) followed by S.fecalis. In the past, we have recovered P.melaninogenicus and Fusobacterium species from pleural fluids.
From all the 17 cases of lung abscesses, anaerobes were isolated - 76.5% along with aerobic bacteria and 23.5% only anaerobes. Ayyagiri et al had isolated anaerobes from 77% cases of lung abscesses. Again, P.melaningogenicus (5) and Fusobacterium spp. (5) formed the predominant isolates. In a recent study, in 40 cases of lung abscess, anaerobes were found in 58% cases.
Microorganisms which predominate the oropharyngeal flora, usually gain access to deeper lung tissues, as a result of aspiration of the oropharyngeal secretions with high concentration of both aerobic and anaerobic bacteria. Therefore, in the already diseased lung, these organisms might overcome the defence mechanism and establish infection. Specimens in this study were collected by transtracheal aspiration which totally by passed the upper respiratory tract. This highlights the fact that the anaerobic organisms are not just casual but have a causal aetiology.
B.fragilis is not found in normal oropharyngeal flora in the upper respiratory tract. However, transdiaphragmatic spread can occur by haematogenous dissemination from distant sites of suppuration.,,,, We encountered eight B.fragilis, five of them being from cases of empyema. Other studies have also reported B.fragilis from such cases.,, Thus in all cases of pleuropulmonary infections apart from surgical drainage, antibiotic coverage should be given for both aerobic and anaerobic organisms and all such samples should be processed for both aerobic and anaerobic bacteria.
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