Abstract
Phages infecting Campylobacter jejuni are considered a promising intervention strategy at broiler farms, yet phage sensitivity of naturally occurring poultry isolates is not well studied. Here, we investigated phage sensitivity and identified resistance mechanisms of C. jejuni strains originating from Danish broilers belonging to the most prevalent MLST (ST) types. Determining plaque formation of 51 phages belonging to Fletchervirus or Firehammervirus showed that 21 out of 31 C. jejuni strains were susceptible to at least one phage. While C. jejuni ST-21 strains encoded the common phase variable O-methyl phosphoramidate (MeOPN) receptor of the Fletchervirus and were only infected by these phages, ST-45 strains did not encode this receptor and were exclusively infected by Firehammervirus phages. To identify internal phage resistance mechanism in ST-21 strains, we performed comparative genomics of two strains, CAMSA2002 sensitive to almost all Fletchervirus phages and CAMSA2038, resistant to all 51 phages. The strains encoded diverse clustered regularly interspaced short palindromic repeats (CRISPR) spacers but none matched the tested phages. Sequence divergence was also observed in a predicted SspE homolog and putative restriction modification systems including a methyl-specific McrBC endonuclease. Furthermore, when mcrB was deleted, CAMSA2038 became sensitive to 17 out of 43 phages, three being Firehammervirus phages that otherwise did not infect any ST-21 strains. Yet, 16 phages demonstrated significantly lower efficiencies of plating on the mcrB mutant suggesting additional resistance mechanism still restricting phage propagation in CAMSA2038. Thus, our work demonstrates that C. jejuni isolates originating from broilers may have acquired several resistance mechanisms to successfully prevent phage infection in their natural habitat.
Highlights
Campylobacter jejuni is a zoonotic pathogen and the major cause of food borne associated gastroenteritis in the European Union (EU) (European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2019)
To identify putative novel phage resistance mechanisms in C. jejuni, we obtained a collection of 31 strains from Statens Serum Institute, which were isolated from broilers in Denmark between 2007 and 2009 and had previously been characterized by MLST typing
Despite implementation of numerous intervention strategies during the last decades, C. jejuni remains the major cause of foodborne gastroenteritis in EU as well as in developing countries (Platts-Mills and Kosek, 2014; European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2019)
Summary
Campylobacter jejuni is a zoonotic pathogen and the major cause of food borne associated gastroenteritis in the European Union (EU) (European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2019). C. jejuni resides as a commensal in poultry and the main transmission route leading to human infection is the consumption of improperly handled or undercooked contaminated poultry meat (Young et al, 2007; Cody et al, 2019; European Food Safety Authority [EFSA] and European Centre for Disease Prevention and Control [ECDC], 2019) Novel interventions such as applying phages for biocontrol in poultry farms have been proposed and are currently being explored The effect of adding phages directly on chicken meat to reduce the number of C. jejuni has been investigated (Goode et al, 2003; Zampara et al, 2017) Successful implementation of such strategies requires a better understanding of phage sensitivity of the highly diverse C. jejuni originating from the poultry habitat
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