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We report on a novel CTX-M extended-spectrum β-lactamase (ESBL), designated CTX-M-42, with enhanced activity toward ceftazidime. CTX-M-42 was identified in a hypermutable Escherichia coli nosocomial isolate (isolate Irk2320) and is a Pro167Thr amino acid substitution variant of CTX-M-3. By molecular typing of ESBL-producing E. coli strains previously isolated in the same hospital ward, we were able to identify a putative progenitor (strain Irk1224) of Irk2320, which had a mutator phenotype and harbored the CTX-M-3 β-lactamase. To reproduce the natural evolution of CTX-M-3, we selected for ceftazidime resistance mutations in bla CTX-M-3 gene in vitro both in clinical isolate Irk1224 and in laboratory-derived hypermutable ( mutD5 ) strain GM2995. These experiments yielded CTX-M-3 Pro167Ser and CTX-M-3 Asn136Lys mutants which conferred higher levels of resistance to ceftazidime than to cefotaxime. CTX-M-3 Asn136Lys had a level of low activity toward ampicillin, which may explain its absence from clinical isolates. We conclude that the selection of CTX-M-42 could have occurred in vivo following treatment with ceftazidime and was likely facilitated by the hypermutable background.

A new model is proposed for methane monooxygenase activation of O 2 on binuclear catecholate iron complexes as catalytic centres in the presence of hydrazobenzene as a reducing agent, to oxidize alkanes (including methane).

A model is proposed for the activation of O 2 by methane monooxygenase using a supported binuclear iron complex as a catalytic centre in the presence of Zn as a reducing agent, methylviologen as a mediator, and acetic acid as an effector.

A new model is proposed for methane monooxygenase activation of O 2 on binuclear catecholate iron complexes as catalytic centres in the presence of hydrazobenzene as a reducing agent, to oxidize alkanes (including methane).