Colonisation of a phage susceptible Campylobacter jejuni population in two phage positive broiler flocks

Abstract

The pathogens Campylobacter jejuni and Campylobacter coli are commensals in the poultry intestine and campylobacteriosis is one of the most frequent foodborne diseases in developed and developing countries. Phages were identified to be effective in reducing intestinal Campylobacter load and this was evaluated, in the first field trials which were recently carried out. The aim of this study was to further investigate Campylobacter population dynamics during phage application on a commercial broiler farm. This study determines the superiority in colonisation of a Campylobacter type found in a field trial that was susceptible to phages in in vitro tests. The colonisation factors, i.e. motility and gamma glutamyl transferase activity, were increased in this type. The clustering in phylogenetic comparisons of MALDI-TOF spectra did not match the ST, biochemical phenotype and phage susceptibility. Occurrence of Campylobacter jejuni strains and phage susceptibility types with different colonisation potential seem to play a very important role in the success of phage therapy in commercial broiler houses. Thus, mechanisms of both, phage susceptibility and Campylobacter colonisation should be further investigated and considered when composing phage cocktails.

Figure 1. Minimum spanning tree of MLST allelic profiles depicting the clustering of the sequence types.

Red dots: Isolates presented in this paper (field trial farm 1*) Isolates for comparison: Isolates of farm 2* from 2011 (yellow dots) and 2012 (orange dots), isolates published by Gripp et al. 2011 (green dots) Clonal complexes (maximum two allele difference between neighbouring STs) are indicated by coloured shading around circles. Most important STs and CCs are indicated by numbers. *including isolates from Kittler et al. 2013 (18 farm 1 isolates, 7 farm 2 isolates).

Figure 2. Phage susceptible Campylobacter jejuni isolates colonised both flocks of the investigated field trial (farm 1).

White bars: Samples containing non- susceptible isolates only Grey bars: Samples containing susceptible and non- susceptible isolates Black bars: Samples containing susceptible isolates only For each sampling time n = 9 samples and >65 isolates (n = 15 for flock 1 at day 31).

Figure 3. Mean motility of C. jejuni differed significantly between isolates with diverging GGT activity and susceptibility.

Motility was tested on semisolid agar inoculating drops of 1 µl McFarland 3 (approx. log₁₀ 8 cfu/ml) suspension. Differences of p<0.05 were considered as significant. Stars on vertical lines represent level of significance (***:P<0.0001; **:P<0.001; *:P<0.05). Error bars represent standard error of the mean. (A) Comparison of mean motility in isolates with and without GGT activity (B) Comparison of mean motility of isolates exibiting different phage susceptibility classes.