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J Antimicrob Chemother. 2003 Jul;52(1):29-35. Epub 2003 May 29.

Effect of D240G substitution in a novel ESBL CTX-M-27.

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Laboratoire de Bactériologie, Faculté de Médecine, Service de Bactériologie-Virologie, 28 Place Henri-Dunant, 63001 Clermont-Ferrand Cedex, France.


Escherichia coli clinical strain Gre-1 collected in 2000 from a French hospital harboured a novel CTX-M-encoding gene, designated blaCTX-M-27. CTX-M-27 differed from CTX-M-14 only by the substitution D240G and was the third CTX-M enzyme harbouring this mutation after CTX-M-15 and CTX-M-16. The Gly-240-harbouring enzyme CTX-M-27 conferred to E. coli higher MICs of ceftazidime (MIC, 8 versus 1 mg/L) than did the Asp-240-harbouring CTX-M-14 enzyme. Comparison of CTX-M-14 and CTX-M-27 showed that residue Gly-240 decreased Km for ceftazidime (205 versus 940 microM), but decreased hydrolytic activity against good substrates, such as cefotaxime (kcat, 113 versus 415 s-1), probably owing to the alteration of beta3 strand positioning during the catalytic process.

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