Bacteriological assessment of healthcare-associated pneumonia using a clone library analysis

The causative pathogens of healthcare-associated pneumonia (HCAP) remain controversial, and the use of conventional cultivation of sputum samples is occasionally inappropriate due to the potential for oral bacterial contamination. It is also sometimes difficult to determine whether methicillin-resistant Staphylococcus aureus (MRSA) is a true causative pathogen of HCAP.

We evaluated the bacterial diversity in bronchoalveolar lavage fluid (BALF) using molecular and cultivation methods in 82 HCAP patients. BALF specimens were obtained from the lesions of pneumonia using bronchoscopy. The bacterial flora was analyzed according to the clone library method using amplified fragments of the 16S ribosomal RNA gene with universal primers. In addition, sputum cultures and the above specimens were assessed.

Eighty (97.6%) of the 82 BALF samples obtained from the patients with HCAP showed positive polymerase chain reaction results. The predominant phylotypes detected in the BALF in this study included bacteria common in cases of community- and hospital-acquired pneumonia. In addition, the phylotypes of streptococci and anaerobes were detected in 19 (23.2%) and 8 (9.8%) cases, respectively. In particular, phylotypes of streptococci were highly detected among the patients 75 of age or older. Staphylococcus aureus was cultured in 23 (28.0%) cases using conventional cultivation methods and detected in only 6 (7.3%) cases as predominant phylotypes according to the clone library method.

The clone library analysis of BALF in the HCAP patients detected heterogeneous bacteria and a high incidence of streptococci compared with that observed using cultivation methods. In addition, the results of our study may indicate a lower incidence of MRSA than previously expected in HCAP patients.