Serotype, antimicrobial susceptibility and clone distribution of Pseudomonas aeruginosa in a university hospital

To study the epidemiology of Pseudomonas (P.) aeruginosa, serotyping and an tibiotic susceptibility testing were performed on 208 clinical isolates. Si xteen of these isolates were additionally examined by pulsed-field gel elec trophoresis (PFGE) of chromosomal DNA. All 208 isolates belonged to 13 of t he 16 described serotypes. Thirty isolates (14.4 %) belonged to serotype O6 , 75 (36%) to serotype O11 and 53 (25.6 %) to other serotypes, 42 (20.2 %) were polyagglutinating and eight (3.8 %), autoagglutinating. Twenty-six per cent of isolates were resistant to piperacillin, 9.1 % to ceftazidime, 9.6 % to imipenem, 45.7 % to ciprofloxacin, 39.9 % to amikacin, 51 % to gentam icin, 48.6 % to netilmicin and 45.2 % to tobramycin. Antibiotic resistance varied according to serotype and was highest in serotype O11. Sixteen isola tes were analysed by PFGE; nine were multiresistant serotype O11 isolates r ecovered in four hospital units, while seven were susceptible serotype O6 o f O11 isolates from a single unit. The multiresistant serotype O11 isolates had Mo PFGE patterns indicating that they were capable of spreading: one P FGE pattern was shared! by the isolates recovered in spring and the other b y those recovered in autumn 1997; The seven susceptible O6 and O11 isolates from a single unit had seven different PFGE patterns. Our results have sho wn that serotype O11 was the most prevalent P. aeruginosa serotype in our h ospital and that its antibiotic resistance was high. The discriminatory pow er of serotyping is inadequate to permit the tracing of different strains. Macrorestriction analysis of chromosomal DNA was found to provide the best means of strain discrimination.