LOSS OF SENSITIVITY TO ANTIBIOTICS OF PSE UDOMONAS-AERUGINOSA STRAINSDURING THE TREATMENT

BACKGROUND: Loss of sensitivity to betalactamic, quinolones and aminog lucoside antibiotics has been described during treatment of infections produced by strains of Pseudomonas aeruginosa. Sixteen nosocomial str ains isolated over a year during which sensitivity to one or several a ntibiotics of the above mentioned groups had been lost during the cour se of treatment were studied. METHODS: The strains were identified by conventional techniques. Sensitivity to antibiotics was studied by det ermination of the minimum inhibitory concentration in solid medium, ac cording to the guidelines of the National Committee for Clinical Labor atory Standards Plasmidic beta-lactamases were identified by analytic isoelectric focusing. Hyperproduction of chromosomic lactamase was stu died by a qualitative technique. The 0 antigens were studied against r abbit antisera. The pyocinetype was determined according to the Fyfe m ethod. Plasmids were detected by alkaline lysis extraction and electro phoresis in agarose gel. RESULTS: The 16 strains in which changes in s ensitivity were observed during the course of treatment represent 4.47 % of all P. aeruginosa isolates during one year. Loss of sensitivity t o betalactamic antibiotics was observed in 10 strains, in one to amino glucosides, in two to ciprofloxacin, simultaneously to aminoglucosides and ciprofloxacin in one and to betalactamic and ciprofloxacin in ano ther two. Six of the 13 patients (46%) required a change in antibiotic treatment CONCLUSIONS: The convenience of following the sensitivity o f the strains of Pseudomonas aeruginosa isolated in a patients is sugg ested to thereby avoid therapeutic failure and the potential danger of clonal dissemination of the strains which have lost sensitivity.