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bioRxiv2021

Detection of Campylobacter in air samples from poultry houses using shot-gun metagenomics - a pilot study

BackgroundFoodborne pathogens such as Campylobacter jejuni are responsible for a large fraction of the gastrointestinal infections worldwide associated with poultry meat. Campylobacter spp. can be found in the chicken fecal microbiome and can contaminate poultry meat during the slaughter process. The current standard methods to detect these pathogens at poultry farms use fecal dropping or boot swaps in combination with cultivation / PCR. In this study, we have used air filters in combination with shotgun metagenomics for the detection of Campylobacter in poultry houses and MOCK communities to test the applicability of this approach for the detection of foodborne pathogens. ResultsThe spiked MOCK communities showed that we could detect as little as 200 CFU Campylobacter per sample using our protocols. Since we were interested in detecting Campylobacter, a DNA extraction protocol for Gram negative bacteria was chosen, and as expected, we found that the DNA extraction protocol created a substantial bias affecting the community composition of the MOCK communities. It can be expected that the same bias is present for poultry house samples analyzed. We observed significant amounts of Campylobacter on the air filters using both real-time PCR as well as shotgun metagenomics, irrespective of the amount of spiked in Campylobacter cells, suggesting that the flocks in both houses harboured Campylobacter spp.. Interestingly, in both houses we find diverse microbial communities present in the indoor air. In addition, have we tested the Campylobacter detection rate using shotgun metagenomics by spiking with different levels of C. jejuni cells in both the mock and the house samples. This showed that even with limited sequencing Campylobacter is detectable in samples with low abundance. ConclusionsThese results show that air sampling of poultry houses in combination with shotgun metagenomics can detect and identify Campylobacter spp. present at low levels. This is important since early detection of Campylobacter in food production can help to decrease the number of food-borne infections.

microbiology↗

bioRxiv2020

The prevalence and genomic context of Shiga toxin 2a genes in E. coli found in cattle

Shiga toxin-producing Escherichia coli (STEC) that cause severe disease predominantly carry the toxin gene variant stx2a. However, the role of Shiga toxin in the ruminant reservoirs of this zoonotic pathogen is poorly understood and strains that cause severe disease in humans (HUSEC) likely constitute a small and atypical subset of the overall STEC flora. The aim of this study was to investigate the presence of stx2a in samples from cattle and to isolate and characterize stx2a-positive E. coli. In nationwide surveys in Sweden and Norway samples were collected from individual cattle or from cattle herds, respectively. Samples were tested for Shiga toxin genes by real-time PCR and amplicon sequencing and stx2a-positive isolates were whole genome sequenced. Among faecal samples from Sweden, stx1 was detected in 37%, stx2 in 53% and stx2a in 5% and in skin samples in 64%, 79% and 2% respectively. In Norway, 79% of the herds were positive for stx1, 93% for stx2 and 17% for stx2a. Based on amplicon sequencing the most common stx2 types in samples from Swedish cattle were stx2a and stx2d. Multilocus sequence typing (MLST) of 39 stx2a-positive isolates collected from both countries revealed substantial diversity with 19 different sequence types. Only a few classical LEE-positive HUSEC were found among the stx2a-positive isolates, notably a single O121:H19 and an O26:H11. Known LEE-negative HUSEC lineages were also recovered including O113:H21 (ST-223), O130:H11 (ST-297), and O101:H33 (ST-330). We conclude that E. coli encoding stx2a in cattle are ranging from well-known HUSEC to unknown STEC variants. Comparison of isolates from human HUS cases to related STEC from the ruminant reservoirs can help identify combinations of virulence attributes necessary to cause HUS, as well as provide a better understanding of the routes of infection for rare and emerging pathogenic STEC.

microbiology↗