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JAC Advance Access published online on September 4, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn347
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© The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

Genetic determinants for cfxA expression in Bacteroides strains isolated from human infections

Nuria García1, Gloria Gutiérrez2, María Lorenzo1, José E. García3, Segundo Píriz1 and Alberto Quesada2,*

1 Departamento de Medicina y Sanidad Animal, Facultad de Veterinaria, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain 2 Departamento de Bioquímica, Facultad de Veterinaria, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain 3 Departamento de Microbiología, Hospital Universitario, Universidad de Salamanca, Paseo San Vicente 58-182, 37007 Salamanca, Spain

Received 29 April 2008; returned 18 July 2008; revised 31 July 2008; accepted 1 August 2008

* Corresponding author. Tel: +34-927257000, 1334; Fax: +34-927257110; E-mail: aquesada{at}unex.es

Objectives: To identify genetic determinants that determine β-lactamase expression in Bacteroides strains isolated from human infections.

Methods: β-Lactam susceptibility and β-lactamase enzyme expression were characterized in selected strains. β-Lactamase genes and surrounding regions were analysed by PCR, inverse PCR and Southern hybridization.

Results: High resistance to penicillins and cephalosporins was found among most isolated strains, in which all known β-lactamase genes from Bacteroides are represented, but differences were found in their expression of enzyme activity. In contrast to the cepA gene, ubiquitously found but frequently inactive, or cfiA, which only confers carbapenem resistance in two strains, the detection of high β-lactamase expression correlates closely with the presence of cfxA genes. This genetic determinant shares variability of upstream regulatory elements, including sequence tags from Tn4555, Tn4351 and IS614B, and polymorphisms of encoded amino acid sequences at positions G57C and Y259C, which might determine enzyme expression characteristics.

Conclusions: The main determinant for β-lactamase expression in Bacteroides strains is the cfxA gene, in which IS614B integration upstream of the coding sequence represents a molecular marker for higher levels of enzyme activity.

Key Words: β-lactamases , enzyme expression , antibiotic resistance , mobile elements , up-regulation


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