Enumeration and diversity of campylobacters and bacteriophages isolated during the rearing cycles of free-range and organic chickens

Abstract

Campylobacters and Campylobacter-specific bacteriophages were isolated and enumerated during the rearing cycle of free-range (56 days) and organic chickens (73 days) at 3-day intervals from hatching until slaughter. In both flocks Campylobacter jejuni was the initial colonizer but Campylobacter coli was detected more frequently from 5 weeks of age. The diversity of the Campylobacter isolates was examined by pulsed-field gel electrophoresis of SmaI-digested genomic DNA and antimicrobial resistance typing. Bacteriophages were isolated from 51% (19 of 37 birds) of Campylobacter-positive organic birds (log10 2.5 to log10 5.7 PFU/g of cecal contents). The bacteriophages were all typical group III Campylobacter bacteriophages in terms of genomic size but could be characterized in terms of their host range and placed into five different groups. In contrast to the organic birds, anti-Campylobacter activity (bacteriocin-like) was observed in 26% (10 of 38 birds) of Campylobacter-positive free-range birds, and only one bacteriophage was isolated. Appearance of either bacteriophages or anti-Campylobacter activity was associated with changes in the levels of colonization and the predominant genotypes and species isolated. The frequency and potential influence of naturally occurring bacteriophages and/or inhibitory substances on the diversity and fluctuations of populations of campylobacters have not previously been reported in either free-range or organic chickens.

FIG. 1.

Enumeration of campylobacters and phages in the cecal contents of extensively reared chickens. The flocks were sampled every 3 or 4 days until the end of the rearing cycle. Three birds were sacrificed at each time point starting at day 14. Before this date fresh excreta samples were collected from chicks for detection without enumeration. (A) Mean number of campylobacters enumerated from the organic flock (± standard deviation [SD]). No campylobacters were isolated before day 31, and here only one of the three birds sampled was Campylobacter positive; hence, the SD could not be calculated. (B) Mean number of campylobacters enumerated from the free-range flock (± SD). The day 31 datum point is the mean of two birds as the third bird was Campylobacter negative; hence, there is no SD. (C) Phages enumerated from the organic flock. The data points record the phage titers from individual birds sampled at each time point. The limit of detection was log₁₀ 2 PFU/g of cecal contents.