Laboratory mutants of OXA-10 beta-lactamase giving ceftazidime resistance in Pseudomonas aeruginosa.
Several extended-spectrum beta-lactamases (ESBLs) belonging to molecular Class D have been described from Pseudomonas aeruginosa isolates collected in Turkey. Four of these, OXA-11, -14, -16 and -17, are derivatives of OXA-10 beta-lactamase. We tried to select similar mutants in vitro from OXA-10-producing transconjugants of P. aeruginosa, using a multistep method on ceftazidime-containing agars. Forty-four such mutants were obtained; all had increased resistance to ceftriaxone, cefsulodin, cefepime, cefpirome, latamoxef, aztreonam and, especially, ceftazidime whereas MICs of piperacillin, carbenicillin, cefotaxime, cefoperazone and carbapenems were little altered. Genes related to blaOXA-10 were sequenced from five mutants. One mutant enzyme had aspartate instead of glycine at position 157, and corresponded exactly to natural OXA-14 beta-lactamase. Another mutant strain appeared to have both OXA-14 and a new pI 6.2 enzyme, designated OXA-M102, with serine instead of alanine at position 124 and aspartate instead of glycine at position 157. This latter variant resembled natural OXA-16 enzyme, which has threonine at position 124 and aspartate at position 157. The remaining three mutant enzymes differed from any so far found in wild-type isolates. Two had leucine replacing tryptophan at position 154 (this enzyme was named OXA-M101) while the third (OXA-M103) had a pI of 7.6, and had lysine instead of asparagine at position 143. A different mutation at this position was previously found in OXA-11, a wild-type OXA-10 mutant. Thus, some of the ESBL mutants selected (OXA-14 and OXA-M102) correspond exactly or almost exactly to ESBLs found in wild-types, whereas others (OXA-M101 and OXA-M103) were totally new.
Danel
F
F
Department of Medical Microbiology, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK. franck.danel@roche.com
Hall
L M
LM
Livermore
D M
DM
D002442:Ceftazidime / Q000378:metabolism / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006868:Hydrolysis; D007525:Isoelectric Focusing; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D001618:beta-Lactamases / Q000235:genetics*
D002511:Cephalosporins; D002442:Ceftazidime; D001618:beta-Lactamases