Overproduction of a metallo-beta-lactamase by a strong promoter causes high-level imipenem resistance in a clinical isolate of Pseudomonas aeruginosa.
BACKGROUND
Metallo-beta-lactamase is one of the feared resistance mechanisms in Pseudomonas aeruginosa.


METHODS
beta-Lactamase activity was determined using crude enzymes. Cloned plasmids were transformed in P. aeruginosa KG2505, PAO1 derivative without an AmpC beta-lactamase and a MexAB-OprM efflux pump.


RESULTS
P. aeruginosa No. 20232 was highly resistant to imipenem (minimum inhibitory concentration >512 microg/ml). It possessed IMP-10 and the activity was 1.89 +/- 0.42 micromol/min/mg of protein, which was 5-8 times higher than other tested isolates. The bla(IMP-10) promoter was strong (-35 region, TTGACA; -10 region, TAAACT); on the other hand, bla(IMP) of other isolates had a hybrid promoter. Transformants with plasmid encoding bla(IMP-10) with a strong promoter had higher enzymatic activity and were less susceptible to imipenem than those encoding bla(IMP-10) with a hybrid promoter.


CONCLUSIONS
The high metallo-beta-lactamase activity caused by a strong promoter was a major determinant for high-level imipenem resistance of P. aeruginosa No. 20232.
Pharmacology Research Laboratories, Astellas Pharma Inc., Osaka, Japan. shinobu.takeda@jp.astellas.com
Shinobu
S
Takeda
Toru
T
Nakai
Fumiaki
F
Ikeda
Kazuo
K
Hatano
D003001:Cloning, Molecular; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D015378:Imipenem; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011550:Pseudomonas aeruginosa / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
D015378:Imipenem; D001618:beta-Lactamases