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Pathogenicity investigation of Campylobacter jejuni, C. upsaliensis and C. helveticus isolated from dogs and cats using Galleria mellonella larvae

Campylobacter jejuni (CJ), C. upsaliensis (CU) and C. helveticus (CH) are commonly isolated from dog and cat faeces, but association with clinical signs is discordant or lacking. CJ is a recognized human pathogen, CU is considered an 'emerging' pathogen and CH is not considered pathogenic despite a high level of genetic similarity. Recently, the Greater Wax Moth, Galleria mellonella, was described as an animal model of disease ; these invertebrates have a high degree of functional and structural homology with the mammalian innate immune system. This study aimed to evaluate the pathogenic potential of CJ, CU and CH using the Galleria mellonella larvae model. Twelve isolates of CJ, 14 of CU and 11 of CH from dogs and cats were used for the inoculation of 2, 490 larvae. Inocula were prepared by suspending isolates in phosphate- buffered saline (PBS) from which three 100-fold dilutions were made. Each dilution was tested in duplicate sets of 10 larvae. Each larva was injected with 10–15 µl into the haemocoel via the last left pro-leg using 31G insulin syringes. Controls consisted of 246 PBS inoculated larvae and 267 un-inoculated larvae. Survival of larvae at 37°C in an H2-enriched microaerobic atmosphere was monitored for 8 days postinjection. One subset of isolates was grown in Mueller-Hinton broth and used for the preparation of secretory products, and another grown on blood-agar and suspended in PBS for heat inactivation of 10 minutes at 100°C for testing of whole-cell lysates and heat-stable insoluble and soluble components. The overall median survival of larvae was 80% with CJ [IQR 10–100], 100% with CU [IQR 80–100], 100% with CH [IQR 60–100], 100% with PBS [IQR 92–100] and 100% for un- inoculated larvae [IQR 100–100]. A dose-dependent association was evident for each species with larval survival being similar between a low bacterial dose and PBS. Larval survival presented a consistent pattern between species for medium and high bacterial loads ; CJ had a higher and faster larval death rate than CU and CH (p < 0.001), but no difference was observed between CU and CH (p = 0.06). There were no significant differences between species in any of the assays with secretory products, inactivated cells and soluble/insoluble cellular components. The observations within this invertebrate disease model support a varying pathogenic potential between the species studied that appears related to the (patho)biology of the species rather than their cellular components or metabolic products. The invertebrate animal model is promising in comparative pathogenicity studies.

Galleria mellonella ; pathogenicity ; virulence ; Campylobacter ; dose response ; emerging pathogens ; zoonosis ; survival ;

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