A-033. Mechanism of How a Bacterial Pathogen Develops Resistance/Tolerance to Host Cationic Antimicrobial Pepetides

J. Cummins1, C. Baysse2, F. Reen1, F. O' Gara1;
1Univ. Coll., Cork, IRELAND, 2Rennes Univ., Rennes, FRANCE.

Pseudomonas aeruginosa, a Gram-negative opportunistic pathogen, is one of the main causes of nosocomial infections, infecting individuals with severe burns, AIDS, and cancer. P. aeruginosa is known to cause increased morbidity in individuals suffering from cystic fibrosis (CF) and more recently has also received attention due to its resistance to a wide variety of conventional antibiotics resulting from an intrinsically impermeable outer membrane and multi drug resistance efflux pumps (Nikaido, 1998). This has lead to an increased interest in cationic antimicrobial peptides (CAMPs) as potential therapeutic molecules. CAMPs are ubiquitous in nature, and are key components of the innate immune response. They are the first lines of defence against infecting microbes (Zhang et al., 2004) and are known to interact with the outer membrane through binding to lipid A acyl chains of the LPS, increasing membrane permeability. LPS modification is known to be a primary mechanism by which cells become resistant to colistin challenge. Some P. aeruginosa and Staphylococcus aureus CF isolates produce a variant LPS that renders the bacterial cells less susceptible to CAMPs (Guo et al., 1998; Ernst, 1999). The existence of alternative CAMP resistance mechanisms is likely, although many of these remain to be identified, placing constraints on current therapies. To further understand the interaction between CAMPs and bacteria, and identify factors involved in emergence of resistance, we utilized DNA microarray technology to investigate the influence of sub-inhibitory colistin on the transcriptome of P. aeruginosa. Analysis of this ‘colistin signature’ reveals transcriptional changes in several functional classes of genes in response to sub-inhibitory colistin; these global changes implicate biofilm formation, transport, virulence and defence in the bacterial response to colistin. The array data was validated and confirmed both by semi-quantitative RT-PCR and phenotypic assay. Nikaido, H., 1998. Current Opinions in Microbiology 5: 516-23 Zhang et al, 2004. Expert Opin. Investig. Drugs, 13(2): 97-106 Guo L, et al 1998 Cell, 95(2): 189-98 Ernst et al, 1999. Science, 286(5444): 1561-5