Etiology and susceptibility of bacterial pathogens isolated from severe/complicated bronchitis

Purpose: This community based study of severe/complicated bronchitis (AECB), describes the causative bacterial pathogens, and their susceptibility, to antibiotics frequently prescribed for lower respiratory tract infections (LRTI). Methods: Significant bacterial isolates of >10⁵ cfu/mL from the homogenized sputa of patients (> 40 years old) participating in a large study were evaluated. Patients presented with complicated/severe AECB with the following inclusion criteria: failed previous antibiotic treatment within prior 2-4 wks; regional susceptibility data showing high number of previous resistant pathogens; >3 AECB episodes within the past year; and/or >3 co-morbid conditions. Isolates were identified and their susceptibility to the range of antimicrobials listed was determined by the micro-broth dilution technique. Results: Of eight hundred and eighty-nine primary isolates positively identified and cultured, the incidence of the bacterial pathogens isolated was: [Italic]Haemophilus spp , 28%; M catarrhalis, 18%; S. aureus, 17%; S. pneumoniae, 7%; Enterobacteriaceae, 17.5% and P aeruginosa, 4%. Beta-lactamase production using the nitrocefin method showed 38% of H influenzae, 10% of H parainfluenzae and 85% of M catarrhalis to be positive. Oxacillin disc screening as a marker of penicillin insensitivity for S pneumoniae (DRSP) showed 35% of isolates to be intermediate or fully resistant to penicillin. Antibiotics tested against these 889 isolates included; amoxycillin, cefuroxime, TMX-SMX, tetracycline, cefaclor, coamoxyclav, clarithromycin, azithromycin and ciprofloxacin. NCCLS or FDA criteria for susceptibility testing will be applied. Conclusions: The preliminary in-vitro data suggests that previous antibiotics may have a limited role in the treatment of severe/complicated AECB. Also, the causative pathogens of AECB seem to be changing over time, with a predominance of Gram negative organisms prevailing. DRSP accounted for <2% of all isolates. Clinical Implications: Empiric antibiotic therapy for patients with AECB should include agents with excellent activity against Gram negative pathogens, as the role of S pneumoniae appears to be minimal.