Prevalence and Antimicrobial Resistance of Salmonella Dublin and Thermotolerant Campylobacter in Liver from Veal Calves in Québec, Canada.

Salmonella Dublin and Campylobacter spp. are two foodborne pathogens of importance. A small number of studies reported that consumption of veal liver was associated with an increased risk of human illness from these two pathogens. To better characterize the risk of exposure from liver, a cross-sectional study was conducted to estimate the prevalence of white veal calf liver contamination with these two pathogens and to characterize the antimicrobial non-susceptibility patterns of isolates. Veal liver samples were collected at two slaughterhouses in Quebec, Canada, in 2016 and 2017. Samples were submitted for polymerase chain reaction (PCR) screening followed by culture of Salmonella and thermotolerant Campylobacter. Isolates were tested for antimicrobial susceptibility using broth microdilution. Salmonella Dublin was the only serotype cultured from 3.6% (95% confidence interval [CI]: 0.0-7.9) of 560 liver samples. Among them and for technical reasons, 498 were tested by PCR for Campylobacter. The prevalence of PCR-positive livers was estimated to be 65.8% (95% CI: 58.7-72.9) for Campylobacter jejuni and 7.0% (95% CI: 3.9-10.1%) for Campylobacter coli. Fourteen Salmonella Dublin isolates were submitted for antimicrobial resistance (AMR) testing; all were non-susceptible to at least eight antimicrobials from six different classes. Most (81.4%) of the 188 C. jejuni isolates submitted for AMR testing were non-susceptible to tetracycline, and 23.0% of isolates were non-susceptible to nalidixic acid and ciprofloxacin. Of the seven C. coli isolates, four were multidrug resistant. This study highlights the importance of veal liver as a potential source of exposure to multidrug-resistant Salmonella Dublin and thermotolerant Campylobacter spp.

Mutational Analysis of the Antitoxin in the Lactococcal Type III Toxin-Antitoxin System AbiQ.

The lactococcal abortive phage infection mechanism AbiQ recently was classified as a type III toxin-antitoxin system in which the toxic protein (ABIQ) is regulated following cleavage of its repeated noncoding RNA antitoxin (antiQ). In this study, we investigated the role of the antitoxin in antiphage activity. The cleavage of antiQ by ABIQ was characterized using 5' rapid amplification of cDNA ends PCR and was located in an adenine-rich region of antiQ. We next generated a series of derivatives with point mutations within antiQ or with various numbers of antiQ repetitions. These modifications were analyzed for their effect on the antiphage activity (efficiency of plaquing) and on the endoribonuclease activity (Northern hybridization). We observed that increasing or reducing the number of antiQ repeats significantly decreased the antiphage activity of the system. Several point mutations had a similar effect on the antiphage activity and were associated with changes in the digestion profile of antiQ. Interestingly, a point mutation in the putative pseudoknot structure of antiQ mutants led to an increased AbiQ antiphage activity, thereby offering a novel way to increase the activity of an abortive infection mechanism.

Effect of the abortive infection mechanism and type III toxin/antitoxin system AbiQ on the lytic cycle of Lactococcus lactis phages.

To survive in phage-containing environments, bacteria have evolved an array of antiphage systems. Similarly, phages have overcome these hurdles through various means. Here, we investigated how phages are able to circumvent the Lactococcus lactis AbiQ system, a type III toxin-antitoxin with antiviral activities. Lactococcal phage escape mutants were obtained in the laboratory, and their genomes were sequenced. Three unrelated genes of unknown function were mutated in derivatives of three distinct lactococcal siphophages: orf38 of phage P008, m1 of phage bIL170, and e19 of phage c2. One-step growth curve experiments revealed that the phage mutations had a fitness cost while transcriptional analyses showed that AbiQ modified the early-expressed phage mRNA profiles. The L. lactis AbiQ system was also transferred into Escherichia coli MG1655 and tested against several coliphages. While AbiQ was efficient against phages T4 (Myoviridae) and T5 (Siphoviridae), escape mutants of only phage 2 (Myoviridae) could be isolated. Genome sequencing revealed a mutation in gene orf210, a putative DNA polymerase. Taking these observations together, different phage genes or gene products are targeted or involved in the AbiQ phenotype. Moreover, this antiviral system is active against various phage families infecting Gram-positive and Gram-negative bacteria. A model for the mode of action of AbiQ is proposed.