NATIONAL SURVEY OF SUSCEPTIBILITY TO ANTIMICROBIALS AMONGST CLINICAL ISOLATES OF PSEUDOMONAS-AERUGINOSA

Between September and December 1993, each of 24 hospitals in the UK co llected up to 100 consecutive clinical isolates of Pseudomonas aerugin osa and sent these to the London Hospital Medical College (LHMC). Of 2 184 cultures received, 1991 contained viable P. aeluginosa. Minimum in hibitory concentrations (MICs) of antimicrobials were determined by ag ar dilution. The frequencies of resistance to low breakpoints were as follows: gentamicin, MIC > 2 mg/L, 11.7%; amikacin, MIC > 4mg/L, 10.5% , carbenicillin, MIC > 128mg/L, 11.7%; azlocillin, MIC > 16 mg/L, 10.9 %; ceftazidime, MIC > 4 mg/L, 9.6%; ciprofloxacin, MIC > 1mg/L, 8.1%; imipenem, MIC > 4mg/L, 2.5% and meropenem, MIC > 4mg/L, 1.1%. Resistan ce to each antimicrobial except amikacin was commoner among the 134 is olates from patients in intensive care units (ICUs) than amongst the 1 042 isolates from other in-patients (P < 0.01). Resistance to penicill ins and ceftazidime, though not to other agents, was rarer among the 7 97 isolates from out-patients than amongst those from non-ICU in-patie nts (P < 0.01). Compared to a similar study in 1982, during which 1866 isolates had been examined, the frequency of resistance to the aminog lycosides increased (P < 0.05) as had those to the penicillins and cef tazidime (P < 0.01). Ciprofloxacin and the carbapenems were not tested in 1982. Cross-resistance patterns suggested that the increases in re sistance to aminoglycosides and beta-lactams were largely a reflection of greater numbers of isolates with barrier or efflux mechanisms and were not due to an increase in isolates with antibiotic-degrading enzy mes. The participating hospitals mostly employed Stokes' disc diffusio n method and, when the results were compared to the MICs determined at the LHMC, fewer than 9% of the isolates reported as susceptible were found to be resistant. However, up to 72% of those reported by the hos pitals as resistant were found to be susceptible.