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Antimicrobial Agents and Chemotherapy, July 2000, p. 1936-1942, Vol. 44, No. 7
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Novel CTX-M beta -Lactamase (CTX-M-8) in Cefotaxime-Resistant Enterobacteriaceae Isolated in Brazil

R. Bonnet,1,* J. L. M. Sampaio,2 R. Labia,3 C. De Champs,1 D. Sirot,1 C. Chanal,1 and J. Sirot1

Laboratoire de Bactériologie, Faculté de Médecine, 63001 Clermont-Ferrand Cedex,1 and UMR 175, CNRS-MNHN, 29000 Quimper,3 France, and Setor de Bacteriologia, Laboratório Lâmina LTDA, 71 Botafogo, Rio de Janeiro, Brazil 22280-0302

Received 18 October 1999/Returned for modification 25 March 2000/Accepted 12 April 2000

To estimate the diversity of extended-spectrum beta -lactamases in Brazil, 18 strains from different species of the family Enterobacteriaceae exhibiting a positive double-disk synergy test were collected by a clinical laboratory from several hospitals in Rio de Janeiro, Brazil, in 1996 and 1997. Four strains (Proteus mirabilis, Enterobacter cloacae, Enterobacter aerogenes, and Citrobacter amalonaticus) hybridized with a 550-bp CTX-M probe. The P. mirabilis strain produced a CTX-M-2 enzyme. The E. cloacae, E. aerogenes, and C. amalonaticus isolates harbored a bla gene which was identified by cloning and sequencing as a blaCTX-M gene. E. coli HB101 transconjugants and the E. coli DH5alpha transformant harboring a recombinant plasmid produced a CTX-M beta -lactamase with an isoelectric point of 7.6 conferring a resistance phenotype characterized by a higher level of resistance to cefotaxime than to ceftazidime, as observed with the other CTX-M enzymes. The deduced protein sequence showed a novel Ambler class A CTX-M enzyme, named CTX-M-8, which had 83 to 88% identity with the previously described CTX-M enzymes. The phylogenic study of the CTX-M family including CTX-M-8 revealed four CTX-M types, CTX-M-8 being the first member of a new phylum of CTX-M enzymes. The evolutionary distances between the four types of CTX-M were large, suggesting that the four clusters branched off early from a distant unknown enzyme and that intermediate enzymes probably existed.

* Corresponding author. Mailing address: Faculté de Médicine, Service de Bactériologie-Virologie, 28, Place Henri Dunant, 63001 Clermont-Ferrand Cedex, France. Phone: 33 (0) 4 73 60 80 18. Fax: 33 (0) 4 73 27 74 94. E-mail: Richard.Bonnet{at}u-clermont1.fr.

Antimicrobial Agents and Chemotherapy, July 2000, p. 1936-1942, Vol. 44, No. 7
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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