EMERGENCE OF MULTIDRUG-RESISTANCE IN UBIQUITOUS AND DOMINANT PSEUDOMONAS-AERUGINOSA SEROGROUP O 11/

The serotypes of 88 nonreplicate nosocomial Pseudomonas aeruginosa iso lates from 11 Greek hospitals were studied in relation to their antibi otic susceptibilities. Rates of resistance to beta-lactams, aminoglyco sides, and quinolones ranged from 31 to 65%, except for those to cefta zidime (15%) and imipenem (21%). Four serotypes were dominant: O:12 (2 5% of isolates), O:1 (17%), O:11 (16%), and O:6 (10%), Multidrug resis tance rates in the major serogroups O:12 (91%) and O:11 (79%) were hig her than those in serogroups O:1 (40%) and O:6 (43%). Further typing w ith respect to pulsed-field gel electrophoresis patterns following Xba I digestion of genomic DNA discriminated the isolates into 74 types, P ulsed-field gel electrophoresis revealed that the ubiquitous O:12 grou p was genetically homogeneous, since 95% of strains belonged to two cl usters of genotypic similarity, while the O:11 strains, present in 8 o f the 11 hospitals, were distributed among five such clusters. Therefo re, apart from the already reported O:12 multidrug-resistant European clone, an O:11 population, characterized by a serotype known to be dom inant in the environment and the hospital in several parts of the worl d, but previously not associated,vith multidrug resistance to antibiot ics, has progressed to a multidrug-resistant state.