Specific and rapid identification of multiple-antibiotic resistant Pseudomonas aeruginosa clones isolated in an intensive care unit.

Seventeen multiple-antibiotic-resistant Pseudomonas aeruginosa isolates were collected from two patients hospitalized in the same intensive care unit. They showed a parallel acquisition of resistance to antibiotics and they were, therefore, thought to have a common clonal origin. These strains were typed by biotyping, serotyping, plasmid profile, three different PCR-based techniques, and macrorestriction analysis to determine their relationship. Only the use of PCR techniques and macrorestriction analysis allowed an accurate identification of the clones and revealed that each patient was infected by A unique multidrug-resistant strain. Therefore, there was no cross-infection or reinfection with a new strain.

Resistance to antibiotics in clinical isolates of Pseudomonas aeruginosa.

OBJECTIVES: To analyse the global resistance to some antibiotics used to treat nosocomial infections by Pseudomonas aeruginosa, specially to carbapenems, and its relationship with the presence of carbapenemases, OXA, VIM and IMP. METHODS: The study included 229 P. aeruginosa isolates from a Hospital in Northern Spain (year 2002). Susceptibility to antimicrobial agents was determined by the analysis of the MIC. Genetic typing was carried out by RAPD-PCR fingerprinting with primer ERIC-2. Genetic experiments to detect class-1 integrons were performed by PCR with primers 5'CS and 3'CS. Detection of carbapenemases was done by phenotypic (Hodge test and DDST) and genotypic methods (PCR with primers for imp, vim1, vim2 and oxa40 genes). RESULTS: 23.9% of isolates were resistant to ceftazidime, 35.9% to cefotaxime, 5.3% to amikacin, 54.9% to gentamicin, 14.6% to imipenem and 6.6% to meropenem. Isolates resistant to imipenem (33) were furtherly tested. Genetic typing didn't show clonal relatedness among the most of the isolates. Class-1 integrons were present in most isolates (sizes 600-1700 bp). Phenotypic methods for carbapenemases showed 5 positive isolates. Genotypic methods showed the presence of two isolates with the oxa40 gene. CONCLUSIONS: Meropenem, amikacin and imipenem were the most active agents to treat infections caused by Pseudomonas aeruginosa. In our study, the presence of carbapenemase enzymes wasn't high. Phenotypic tests cannot be considered as accurate screening tool to detect carbapenemases. This is the fist report of the oxa40 gene in Pseudomonas aeruginosa isolates.