Objective To analyze the species distribution and in vitro susceptibility of pathogenic bacteria isolated from the lower respiratory tract of the patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD), and to provide guidance for the treatment of pulmonary infections in this kind of patients.

Methods The AECOPD patients with suspected lower respiratory tract sample infection from January 2015 to December 2024 were included. The data of species identification and in vitro drug susceptibility testing results of pathogenic bacteria isolated from the lower respiratory tract were retrospectively collected. The detection rate, species distribution, in vitro susceptibility of predominant species, and ratios of multidrug-resistant (MDR) bacteria were compared among different sample types. Data were analyzed using WHONET 5.6 and SPSS 26.0 software.

Results A total of 25253 lower respiratory tract samples from 3861 patients were included. The pathogen detection rates in sputum, aspirates and bronchoalveolar lavage fluids were 27.2% (6463/23722), 33.5% (135/403), and 48.9% (551/1128), respectively, with a statistically significant difference of detection rate (P < 0.001). Among the 3,824 non-repetitive strains, the ratio of the isolates recovered from outpatients and emergency patients to those from inpatients is 1∶6, and the ratio of the isolates from intensive care unit patients to those from other units is 1∶7. Gram-negative bacteria accounted for 93.1%, with the predominant species including Acinetobacter baumannii complex (23.7%), Pseudomonas aeruginosa (21.4%), Klebsiella pneumoniae (12.6%), Stenotrophomonas maltophilia (11.7%), and Escherichia coli (4.6%). Gram-positive bacteria accounted for 6.9%, with Staphylococcus aureus was the most common species (3.2%). Fastidious bacteria accounted for 6.4%, including Haemophilus influenzae (3.9%), Moraxella catarrhalis (1.6%), and Streptococcus pneumoniae (0.9%). The detection rate of methicillin-resistant S. aureus (MRSA) was 41.8%. The detection rates of carbapenem-resistant E. coli, K. pneumoniae, A. baumannii complex, and P. aeruginosa were 12.0% (21/175), 18.1% (87/480), 69.9% (635/908), and 29.3% (240/819), respectively. Compared with sputum, non-sputum specimens showed a higher detection rate of MDR bacteria (P < 0.01).

Conclusion Gram-negative bacteria were the predominant pathogenic bacteria detected from the low respiratory tract of AECOPD patients, with a low isolation rate of fastidious bacteria. Non-sputum samples exhibited a higher detection rate of MDR bacteria.