Submitted to: Antimicrobial Chemotherapy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2008
Publication Date: 1/15/2009
Citation: Jeon, B., Muraoka, W., Scupham, A.J., Zhang, Q. 2009. Roles of Lipooligosaccharide and Capsular Polysaccharide in Antimicrobial Resistance and Natural Transformation of Campylobacter jejuni. Antimicrobial Chemotherapy. 63(3):462-468. Interpretive Summary: Campylobacter is the leading bacterial food-borne pathogen in the United States causing greater than 2 million cases annually. Treatment of campylobacteriosis is compromised by an increasing level of antibiotic resistance in this agent. It has been discovered that Campylobacter is adept at importing naked DNA from the environment and incorporating it into the chromosome (transformation), and it is believed that the observed increase in antibiotic resistance is due in part to this ability. Capsular polysaccharide (CPS) and lipooligosaccharide (LOS) on the bacterial surface are a key virulence determinant for this bacterium, allowing ever-changing camouflage from the host immune system. It is even possible for the bacteria to truncate or stop the production of these moieties. The current work examines the roles of CPS and LOS in DNA uptake by this pathogen. Experimental destruction of the genes responsible for CPS and LOS production, individually and in concert, resulted in 4.4-fold to 97-fold increases in transformation frequency. These results indicate that Campylobacter can indirectly increase its resistance to certain antibiotics by changing its cell surface.
Technical Abstract: Objectives: To investigate the roles of surface polysaccharides, such as capsular polysaccharide (CPS) and lipooligosaccharide (LOS), in modulating natural transformation and antimicrobial resistance in Campylobacter jejuni. Methods: A series of C. jejuni mutants, which are defective in either CPS or LOS or both, were constructed. The natural transformation frequency, DNA binding and uptake rate, antimicrobial susceptibility, and hydrophobicity were measured and compared between the surface polysaccharide mutants and the wild type. Results: Loss of CPS and truncation of LOS increased the transformation frequency by 4.4-fold and 25-fold, respectively, and mutation of both CPS and LOS resulted in a 97-fold increase in the transformation frequency. Consistently with the increased transformation frequencies, the CPS and LOS mutants showed an enhanced rate of DNA uptake, suggesting that the surface polysaccharide constitute a limiting factor for natural transformation. Loss of CPS did not result in significant changes in the susceptibility to antimicrobial resistance, but truncation of LOS greatly reduced (8-fold) the intrinsic resistance of C. jejuni to erythromycin, a key antibiotic used for treating human campylobacteriosis. Notably, loss of LOS also significantly decreased (16-32 fold) the acquired resistance to macrolide, which is conferred by a point mutation (A2074G) in the 23S rRNA gene. The increased susceptibility to erythromycin in the LOS mutant was probably due to the enhanced permeability to this antibiotic, because the LOS mutation rendered the surface of C. jejuni more hydrophobic. Conclusions: These results demonstrate that the surface polysaccharides in C. jejuni restrict natural transformation, but enhance the resistance to certain antibiotics such as erythromycin.