Cefuroxime non-susceptibility in multidrug-resistant Klebsiella pneumoniae overexpressing ramA and acrA and expressing ompK35 at reduced levels

Abstract

Objectives: The aims were to study if efflux and down-regulation of porins contribute to cefuroxime resistance in Klebsiella pneumoniae and to co-resistance to unrelated antibiotics. Methods: Ten cefuroxime-non-susceptible but cefotaxime-susceptible blood culture isolates of K. pneumoniae and one multiply antibiotic-resistant (MAR) laboratory strain (selected by chloramphenicol) were examined. Transcription of the genes acrA, ompK35, ramA, marA and soxS was determined with quantitative RT-PCR. Results: All clinical isolates andthe MAR laboratory strain had similar antibiograms with non-susceptibility to cefuroxime, tigecycline, chloramphenicol and nalidixic acid. Phenylalanine arginine β-naphthylamide (PAβN) increased susceptibility to tigecycline, chloramphenicol and nalidixic acid, but not to cefuroxime. Increased acrA transcription and decreased ompK35 transcription was seen in all strains. Increased ramA transcription was seen in all strains except one clinical isolate. Conclusions: This multidrug-resistant phenotype of K. pneumoniae is associated with increased acrA and ramA transcription and decreased ompK35 transcription. Since the cefuroxime resistance was not reversed by PAβN, it was probably attributable to decreased levels of OmpK35, rather than to efflux. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.