P-053. Fitness Cost of Macrolide Resistance in Campylobacter jejuni

F. Han, S. Pu, B. Ge;
Louisiana State Univ., Baton Rouge, LA.

The occurrence and persistence of macrolide-resistant Campylobacter jejuni in food animals and corresponding food products are dependent upon the fitness cost associated with resistance. In this study, C. jejuni strains with common genetic backgrounds were used to estimate this potential cost. Genomic DNAs prepared from naturally occurring macrolide-resistant Campylobacter coli strains with defined mutations in the 23S rRNA genes were used to transform the parent strain - C. jejuni 81-176. Additionally, natural inductants of the parent strain were obtained by plating C. jejuni 81-176 on erythromycin-containing agar plates. The fitness of the transformants and inductants was compared with the parent strain by assessing noncompetitive growth rate, pairwise competitive growth, and tolerance to chilling. On average, the acquisition of macrolide resistance imposed a fitness burden of approximately 20% estimated by the competitive growth experiment. Additionally, both transformants and inductants demonstrated slower growth rates (doubling time approximately 110 minutes versus 67 min of the parent strain). Surprisingly, the mutants were equally competent in their ability to tolerant the chilling process. Our findings indicated that macrolide resistance was associated with a significant competitive fitness cost in C. jejuni. Conversely, the ability of macrolide-resistant C. jejuni strains to tolerate the chilling treatment commonly used in the poultry processing plants may render them persistent in the processing plants and the food products.