Multilocus sequence typing of human and canine C. upsaliensis isolates.

Risk of Campylobacter infection in humans has been associated with many sources, including dogs. C. upsaliensis is the most common species found in canines, and has been occasionally isolated from symptomatic humans. This study aimed to investigate the genetic diversity of 41 C. upsaliensis isolates carried by dogs and from nine isolates carried by humans using Multilocus sequence typing (MLST). We identified considerable genetic diversity amongst the C. upsaliensis isolates from both dogs and humans, identifying 45 different sequence types (STs). All STs were new, apart from that of the reference strain. Only three STs were found in more than one isolate: ST-72 (2 isolates), ST-98 (2 isolates) and ST-104 (3 isolates). ST-104 was the only ST to be encountered in both dogs and humans. Thirty-one of the 45 STs were assigned to one of 13 clonal complexes (CCs). Four of these CCs contained STs originating from both humans and dogs. None of the CCs contained exclusively human isolates, and two isolates from dogs within the same kennel belonged to the same CC. The large amount of diversity found in both dog and human isolates of C. upsaliensis, combined with the relatively small database, made it difficult to assign strains to sources of infection. This emphasizes the need to increase the size of the database. Dog and human isolates occasionally grouped together, however there were insufficient human-derived isolates to determine whether or not dogs are a common source of infection. Although C. upsaliensis infection is rare in humans, dogs still remain a potential source, and are therefore a possible zoonotic risk. Further work is needed to investigate the epidemiology of C. upsaliensis infection in humans.