Relationship of antibiotic resistance phenotype to the R-pyocin susceptibility pattern in clinical isolates of Pseudomonas aeruginosa.

One hundred sixteen clinical isolates of Pseudomonas aeruginosa were collected from 7 hospitals in Athens. All strains were studied for their susceptibility to cefotaxime, ceftazidime, carbenicillin, aztreonam, imipenem, nalidixic acid, ciprofloxacin, gentamicin, and chloramphenicol. In addition, the R-pyocin susceptibility pattern was determined and the strains were O-serotyped and tested for their agglutination in acriflavine. The isolates included 53 strains resistant to both gentamicin and carbenicillin, 13 to carbenicillin only, 20 to gentamicin only, and 30 sensitive to gentamicin and carbenicillin. The multiresistant isolates displayed relatively higher resistance to all other antibiotics except aztreonam and cefotaxime. Remarkably 30 out of 53 multiresistant isolates reacted with one pyocin only, namely pyocin R2. This R-pyocin response was not encountered in any other strains of the other antibiotic resistance phenotypes. These isolates belonged to the 0-12 serogroup. The 0-12 serogroup was represented only in a minority of strains giving other R-pyocin reactions. It is interesting that strains reacting with pyocin R5 only were mostly susceptible to antibiotics. The results clearly indicate lipopolysaccharide-core mutations in multiresistant clinical isolates of P. aeruginosa. Despite the fact that the R-pyocin resistance pattern can not define the precise possible defect, the multiple and high level resistance associated with R2-pyocin reaction seems to be an interesting trait.

Importance of carbenicillin and gentamicin cross-resistant serotype 0:12 Pseudomonas aeruginosa in six Athens hospitals.

One hundred and six clinical isolates of Pseudomonas aeruginosa, collected from various hospitals were typed with O-antisera and studied for their susceptibility to antibiotics and phages. Forty-four of 49 multiresistant isolates belonged to the O12 serogroup, a serogroup rarely found among strains of other resistance phenotypes. Eleven of the 45, O12 isolates were resistant to all phages, and 31 were sensitive only to phage 68. The latter pattern was encountered in nine of the 61 strains comprising the other O-serogroups.