Genetic characteristics and potential pathogenic agents in Campylobacter upsaliensis based on genomic analysis

Campylobacter upsaliensis was the most common Campylobacter species in pets' gastrointestinal tracts and has been isolated from patients with bacteremia, hemolytic-uremic syndrome, spontaneous abortion, and Guillain-Barré syndrome. However, the genetic characteristics and the full extent of its significance as a human pathogen remain to be fully understood. This study involved an investigation for genomic analysis of 154 strains from different sources and additional antimicrobial resistance profiles of 26 strains for this species. The genomes contained 1,558-1,971 CDS and the genome sizes were estimated to vary from 1.53 Mb to 1.86 Mb, with an average GC content of  34.71%. The entire analyzed genomes could be divided into three clades (A, B, and C) based on ANI and phylogenomic analysis. Significantly, nearly all strains in Clade B were isolated from patient samples, and the virulence-related sequences FlgD, GmhA, and CdtC might serve as determining factors for the classification of Clade B. Half of the tested isolates had MIC values over 64 μg mL-1 for nalidixic acid, gentamicin, and streptomycin. Isolates from pets in China carried more resistant elements in the genomes. This study both provided a comprehensive profile of C. upsaliensis for its genomic features and suggested some pathogenic agents for human infection with this species.

Population Genetics and Antimicrobial Susceptibility of Canine Campylobacter Isolates Collected before and after a Raw Feeding Experiment

In recent years, increasing numbers of consumers have become interested in feeding raw food for their pet dogs as opposed to commercial dry food, in the belief of health advantages. However, raw meat and internal organs, possibly contaminated by pathogens such as Campylobacter spp., may pose a risk of transmission of zoonoses to the pet owners. Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans but C. upsaliensis has also been associated with human disease. In this study we investigated the effect of different feeding strategies on the prevalence of Campylobacter spp. in Finnish dogs. We further characterized the isolates using multilocus sequence typing (MLST), whole-genome (wg) MLST and antimicrobial susceptibility testing. Dogs were sampled before and after a feeding period consisting of commercial raw feed or dry pellet feed. Altogether 56% (20/36) of the dogs yielded at least one Campylobacter-positive fecal sample. C. upsaliensis was the major species detected from 39% of the dogs before and 30% after the feeding period. Two C. jejuni isolates were recovered, both from raw-fed dogs after the dietary regimen. The isolates represented the same genotype (ST-1326), suggesting a common infection source. However, no statistically significant correlation was found between the feeding strategies and Campylobacter spp. carriage. The global genealogy of MLST types of dog and human C. upsaliensis isolates revealed weakly clonal population structure as most STs were widely dispersed. Major antimicrobial resistance among C. upsaliensis isolates was against streptomycin (STR MIC > 4 mg/l). Apart from that, all isolates were highly susceptible against the antimicrobials tested. Mutations were found in the genes rpsL or rpsL and rsmG in streptomycin resistant isolates. In conclusion, increasing trend to feed dogs with raw meat warrants more studies to evaluate the risk associated with raw feeding of pets in transmission of zoonoses to humans.

Development of real-time PCR and hybridization methods for detection and identification of thermophilic Campylobacter spp. in pig faecal samples

AIMS

To develop a real-time (rt) PCR for species differentiation of thermophilic Campylobacter and to develop a method for assessing co-colonization of pigs by Campylobacter spp.

METHODS AND RESULTS

The specificity of a developed 5' nuclease rt-PCR for species-specific identification of Campylobacter jejuni, Campylobacter coli, Campylobacter lari, Campylobacter upsaliensis and of a hipO gene nucleotide probe for detection of C. jejuni by colony-blot hybridization were determined by testing a total of 75 reference strains of Campylobacter spp. and related organisms. The rt-PCR method allowed species-specific detection of Campylobacter spp. in naturally infected pig faecal samples after an enrichment step, whereas the hybridization approach enhanced the specific isolation of C. jejuni (present in minority to C. coli) from pigs.

CONCLUSIONS

The rt-PCR was specific for Campylobacter jejuni, C. coli, C. lari, and C. upsaliensis and the colony-blot hybridization approach provided an effective tool for isolation of C. jejuni from pig faecal samples typically dominated by C. coli.

SIGNIFICANCE AND IMPACT OF THE STUDY

Species differentiation between thermophilic Campylobacter is difficult by phenotypic methods and the developed rt-PCR provides an easy and fast method for such differentiation. Detection of C. jejuni by colony hybridization may increase the isolation rate of this species from pig faeces.

High-resolution genotyping of Campylobacter upsaliensis strains originating from three continents

Ninety-six Campylobacter upsaliensis strains that originated from Australia, Canada, and Europe (Germany) and that were isolated from humans, dogs, and cats were serotyped for their heat-stable surface antigens. All of them were genotyped by enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) profiling, and 83 strains were genotyped by macrorestriction analysis with the endonuclease XhoI. Eighty-four percent of the strains belonged to five different serotypes (serotypes OI, OII, OIII, OIV, and OVI), with the proportions of strains in each serotype being comparable among the groups of strains from all three continents. Two serotypes, OIII and OIV, were prevalent at rates of 35 to 40%. Serotypes OI, OII, and OVI were detected at rates of 1.5 to 15%. Between 10 and 17.7% of the strains did not react with the available antisera. Analysis of the ERIC-PCR profiles revealed two distinct genotypic clusters, which represented the German and the non-European strains, respectively. XhoI macrorestriction yielded two genotypic clusters; one of them contained 80.2% of the German strains and 34.6% of the non-European strains, and the second cluster consisted of 65.4% of the non-European strains and 19.8% of the German strains. Fourteen strains from all three continents were analyzed for their 16S rRNA gene sequences. Only two minor variations were detected in four of the strains. In conclusion, C. upsaliensis has undergone diverging processes of genome arrangement on different continents during evolution without segregating into different subspecies.