Serotype, Antimicrobial Susceptibility and Clone Distribution of Pseudomonas Aeruginosa in a University Hospital

To study the epidemiology of Pseudomonas (P.) aeruginosa, serotyping and antibiotic susceptibility testing were performed on 208 clinical isolates. Sixteen of these isolates were additionally examined by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA. All 208 isolates belonged to 13 of the 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 gentamicin, 48.6% to netilmicin and 45.2% to tobramycin. Antibiotic resistance varied according to serotype and was highest in serotype O11. Sixteen isolates were analysed by PFGE; nine were multiresistant serotype O11 isolates recovered in four hospital units, while seven were susceptible serotype O6 or O11 isolates from a single unit. The multiresistant serotype O11 isolates had two PFGE patterns indicating that they were capable of spreading: one PFGE pattern was shared by the isolates recovered in spring and the other by those recovered in autumn 1997. The seven susceptible O6 and O11 isolates from a single unit had seven different PFGE patterns. Our results have shown that serotype O11 was the most prevalent P. aeruginosa serotype in our hospital and that its antibiotic resistance was high. The discriminatory power 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.