In vitro activity of minocycline against respiratory pathogens from patients with cystic fibrosis

Our objective was to determine the in vitro activity of minocycline against isolates of Burkholderia cepacia (BC), Stenotrophomonas maltophilia (SM), and Pseudomonas aeruginosa (PA) cultured from the respiratory tract of patients with cystic fibrosis (CF). Cultures of BC, SM, and PA were isolated in a hospital bacteriology laboratory from the sputum or oropharyngeal cultures obtained from patients attending a Cystic Fibrosis Center, and were prospectively tested for in vitro sensitivity to minocycline by Kirby-Bauer disk diffusion. From January 1994 to July 1995, 116 cultures from 61 patients had at least one of the three pathogens; 9/61 (15%) patients had an isolate of BC, and 7/9 (78%) had an initial isolate sensitive to minocycline, of which 3 were sensitive only to minocycline; 2 cultures were resistant to all antibiotics. Four of 7 patients with BC were treated with minocycline; 3 patients developed resistant isolates 3-13 months after therapy. Five of 61 patients (8%) had an isolate of SM: 4/5 (80%) of these isolates were sensitive to minocycline, of which 1 was sensitive only to minocycline. Fifty-five of 61 patients (90%) had at least one PA isolate, with 112 morphotypes recovered from 90 cultures: 40/112 morphotypes (36%) were sensitive to minocycline, 65 (58%) were resistant, and 7 (6%) were intermediate in sensitivity. We conclude that the marked in vitro activity of minocycline against BC and SM isolated from patients with CF suggests that minocycline may have an adjunct role in the antimicrobial therapy of multidrug resistant, respiratory pathogens in CF.