STUDY OF PSEUDOMONAS-AERUGINOSA SEROTYPE O12 ISOLATES WITH A COMMON ANTIBIOTIC SUSCEPTIBILITY PATTERN

A multicentre European study of Pseudomonas aeruginosa serotype O12 is olates with a common antibiotic resistance pattern was conducted. Resi stance to beta-lactams and aminoglycosides was observed in 24 of the 2 5 isolates, as often reported in Europe, and all 25 isolates were sign ificantly more susceptible to fosfomycin than 189 isolates of other se rotypes (72% vs. 13.2%). The mutational frequency of serotype O12 was similar to that of other serotypes and thus could not explain the susc eptibility to fosfomycin. As a number of epidemiological studies using various methods, especially ribotyping with EcoRI, have shown that mo st strains are similar, it has been suggested that a single strain of this serotype is widespread. However, in this study ribotyping with Ec oRI and Pvull distinguished seven clones among 24 ticarcillin resistan t serotype O12 isolates, although one ribotype predominated (67%). Thu s the hypothesis of spread of one clone across Europe cannot explain t he common resistance phenotype observed in different clones of serotyp e O12, Resistance of beta-lactams and aminoglycosides might be explain ed by greater receptiveness for transposable resistance mechanisms, an d susceptibility to fosfomycin by increased permeability of the outer membrane.