title: [Spread in hospital units of a Pseudomonas aeruginosa phenotype producing a beta-lactamase highly inducible by clavulanic acid in vitro].
abstract: Pseudomonas aeruginosa strains belonging to the serogroup O:11 exhibiting susceptibility to ticarcillin (TIC) and resistance to the ticarcillin-clavulanic acid (CA) combination were found in 19 inpatients over a 14 month period. Mean inhibition diameters obtained using the agar diffusion method were 21.75 mm around the TIC disks (75 micrograms) and 15.96 mm around the TIC+CA disks (75 + 10 micrograms). With control PaO:11 strains, these diameters were 25.27 and 25 mm, respectively. MIC for ticarcillin determined using the checkerboard method rose to 64 mg with CA levels of 16 mg/l or more. CA exhibited dose-dependent antagonism on TIC killing curves when TIC levels approximated the MIC; this effect was no longer present with higher TIC levels. In the crude bacterial extract, a betalactamase of the cephalosporinase type was detected in the absence of induction and increased threefold after exposure to cefoxitin (100 mg/l) and fourfold after exposure to CA (5 mg/l). All these PaO:11 strains exhibited the same antimicrobial resistance phenotype with decreased susceptibility to ureidopenicillins and resistance to aminoglycosides and fluoroquinolones. The induction of a chromosome-encoded cephalosporinase by CA proved useful as an epidemiologic marker. Nosocomial spread of this phenotype was likely the result of selection due to use of antimicrobials.
authors.affiliation: Hôpital d'Instruction des Armées du Val-de-Grâce, Paris.
authors.forename: Y
authors.initials: Y
authors.lastname: Buisson
authors.forename: J Y
authors.initials: JY
authors.lastname: Nizou
authors.forename: A
authors.initials: A
authors.lastname: Talarmin
authors.forename: M
authors.initials: M
authors.lastname: Meyran
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D019818:Clavulanic Acid; D002969:Clavulanic Acids / Q000494:pharmacology*; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology*; D004352:Drug Resistance, Microbial; D004359:Drug Therapy, Combination / Q000494:pharmacology; D005602:France; D006801:Humans; D066298:In Vitro Techniques; D015994:Incidence; D007362:Intensive Care Units; D011552:Pseudomonas Infections / Q000453:epidemiology / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification; D013982:Ticarcillin / Q000494:pharmacology; D001618:beta-Lactamases / Q000032:analysis* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002969:Clavulanic Acids; D019818:Clavulanic Acid; D001618:beta-Lactamases; D013982:Ticarcillin
vernacular_title: Diffusion à l'hôpital d'un phénotype de Pseudomonas aeruginosa produisant une bêtalactamase fortement inductible in vitro par l'acide clavulanique.