Multidrug-resistant Pseudomonas aeruginosa in Brooklyn, New York: molecular epidemiology and in vitro activity of polymyxin B.
Multidrug-resistant strains of Pseudomonas aeruginosa have become increasingly problematic in certain hospitals. For a 3-month period in 2001, all unique patient isolates were collected from 15 hospitals in Brooklyn, New York, USA. Of 691 isolates, only 70% were susceptible to imipenem and 56% to ciprofloxacin. These susceptibility rates were lower than those found in a prior surveillance study in 1999 (76% and 71% susceptible to imipenem and ciprofloxacin, respectively; p<0.001). The rate of imipenem resistance was associated with fluoroquinolone usage at each hospital (p=0.04). All isolates were susceptible to polymyxin B and 95% to amikacin. Among 195 imipenem-resistant isolates, 47 unique ribotypes were found. However, four ribotypes accounted for >50% of isolates and were shared by most hospitals. Time-kill studies with 13 unique multiresistant strains revealed that polymyxin B was bactericidal against all strains at 4 mg/l, but only against 3 of 13 (23%) strains at 2 mg/l. Using 2 mg/l, significant bacterial regrowth was evident for 5 of 13 (38%) strains. The addition of azithromycin to polymyxin B (2 mg/l) produced a mean decrease of 1 log cfu/ml greater than polymyxin alone and allowed bacterial regrowth in only 2 of 13 (15%) strains. Multiresistant P. aeruginosa is highly endemic to this city, with a few strains having spread among most hospitals. Polymyxin B remains active against all isolates and produces concentration-dependent killing in vitro. Azithromycin appears to enhance the in vitro activity of polymyxin B. The clinical utility of this combination remains to be established.
Bratu
S
S
Department of Medicine, Infectious Diseases Division, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Box 77, Brooklyn, NY 11203, USA.
Quale
J
J
Cebular
S
S
Heddurshetti
R
R
Landman
D
D
D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D009518:New York; D011112:Polymyxin B / Q000494:pharmacology*; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
D000900:Anti-Bacterial Agents; D011112:Polymyxin B