Distribution and drug resistance of gram-negative bacteria causing lower respiratory tract infections in patients with acute exacerbation of chronic obstructive pulmonary disease

Abstract

Objective To investigate the pathogen distribution and drug resistance of gram-negative bacteria causing lower respiratory tract infections in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). Methods A total of 742 sputum samples were collected from AECOPD patients with lower respiratory tract infections in Taizhou Hospital of Zhejiang Province during January 2013 and December 2014. Vitek 2 Compact system combined with disk diffusion was used for strains identification and drug susceptibility test. Modified Hodge test and ethylenediamine tetraacetic acid (EDTA) synergic test were used to screen carbapenem-resistant strains. Statistical analysis was performed using WHONET 5.6 and SPSS 20.0 software. Results A total of 593 strains of gram-negative bacteria were isolated, in which 367 strains were nonfermentative bacteria (61.89%), 220 strains were enterobacteriaceae (37.10%), and the rest 6 strains (1.01%) were other gram-negative bacteria. Acinetobacter baumannii (186 strains), Pseudomonas aeruginosa (99 strains), Stenotrophomonas maltophilia (33 strains) and Burkholderia cepacia (22 strains) were top 4 nonfermentative bacteria, and they all showed high resistance to ampicillin, ampicillin/sulbactam, cefazolin, ceftriaxone, cefotetan and nitrofurantoin with resistant rates of 67.20%-100.00%. Drug resistance rates to other β-lactams, fluoroquinolones, aminoglycoside, compound sulfamethoxazole and minocycline were significantly higher in carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa strains than those in non-carbapenem-resistant strains, and the differences were statistically significant (P<0.05 or <0.01). Stenotrophomonas maltophilia and Burkholderia cepacia strains were only sensitive to levofloxacin, compound sulfamethoxazole and minocycline. Klebsiella pneumonia (89 strains), Escherichia coli (80 strains) and Enterobacter cloacae (25 strains) were top 3 enterobacteriaceae, which were almost completely resistant to ampicillin, but were sensitive to piperacillin/tazobactam, cefoperazone/sulbactam, amikacin and carbapenems (with resistant rates <15%). More than 50% strains of extended spectrum β-lactamases (ESBLs)-producing Klebsiella pneumonia and Escherichia coli were moderately or highly resistant to ampicillin/sulbactam, most cephalosporins (except cefotetan and cefoperazone/sulbactam), gentamycin, tobramycin, fluoroquinolones, aztreonam, compound sulfamethoxazole and minocycline, and the resistant rates were higher than those in non-ESBLs-producing strains (P <0.05 or <0.01). Conclusions Nonfermentative bacteria and enterobacteriaceae are the most prevalent gram-negative bacterial pathogens in lower respiratory tract infections in patients with AECOPD. Carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa strains, as well as ESBLs-producing Klebsiella pneumonia and Escherichia coli strains are highly resistant to most antibacterial agents. Key words: Pulmonary disease, chronic obstructive; Gram-negative bacteria; Carbapenems; Extended-spectrum beta lactamases; Drug resistance, multiple