Diagnostic and pathophysiological aspects of Capnocytophaga canimorsus infections

Abstract

Dog- and cat-related wound-infections in humans are common. Capnocytophaga canimorsus and Capnocytophaga cynodegmi can be transmitted from dogs and cats to humans via bites or scratches. C. canimorsus is considered to be invasive and may cause sepsis, meningitis or endocarditis, whereas C. cynodegmi appears to be less virulent and is mainly associated with wound-infections. During 2007-2010, I collected clinical isolates of animal bite associated Capnocytophaga species, which was used in all projects included in this thesis.

In study I, we used our collection of n=22 isolates to evaluate the performance of the recently introduced MALDI-TOF instrument and compared the results with the conventional typing method VITEK2. A species-specific PCR was established and used as the reference method. MALDI-TOF analysis identified all blood isolates as C. canimorsus and 13/14 wound isolates were identified as C. cynodegmi. Taken together, we found that MALDI-TOF was more accurate, faster and more cost-effective than conventional typing methods.

In study II we analysed the interaction of human serum with C. canimorsus and C. cynodegmi. Whole blood and serum bactericidal assays unequivocally showed that both C. canimorsus and C. cynodegmi were sensitive to the bactericidal properties of whole blood and serum.

In study III we continued to work with one of the strains in our collection, which could not be typed by the species specific PCR in study I. Whole-genome sequencing of the 22 Capnocytophaga species isolates in our collection revealed that the non-typable isolate in fact constituted a novel species, which we named “Capnocytophaga stomatis”.

Finally, in study IV we determined the antibiotic profiles against Capnocytophaga spp. Currently, there is a lack of comprehensive knowledge on the antibiotic susceptibility patterns for Capnocytophaga spp. Therefore, in study IV, we set out to study the antibiotic susceptibility profiles against Capnocytophaga spp. We found that two strains of C. cynodegmi and 2 strains of C. stomatis were resistant to amoxicillinclavulanate, the first-line antibiotic therapy for animal bite related infections. Detailed analysis of whole genome data revealed that these strains carried a previously undescribed class D beta-lactamase gene with carbapenemase activity.

Thus, our findings suggest that animal associated bacteria could serve as a potential reservoir for antibiotic resistance genes, which could have clinical implications when treating animal bite associated infections. Taken together, the data presented in this thesis may improve diagnosis, increase the understanding of the pathogenesis and facilitate correct antibiotic treatment of animal bite associated Capnocytophaga infections.