Both clinical and environmental Caulobacter species act as opportunistic pathogens [article]

Gabriel M Moore, Zemer Gitai
2019 bioRxiv   pre-print
The Caulobacter genus, including the widely-studied model organism Caulobacter crescentus, has been thought to be non-pathogenic and thus proposed as a bioengineering vector for various environmental remediation and medical purposes. However, Caulobacter species have been implicated as the causative agents of several hospital-acquired infections, raising the question of whether these clinical isolates represent an emerging pathogen or whether Caulobacters on whole possess
more » ... d virulence capability. Given the proposed environmental and medical applications for C. crescentus, understanding the potential pathogenicity and human health implications of this bacterium is crucial. Consequently, we sequenced a clinical Caulobacter isolate to determine if it has acquired novel virulence determinants. We found that the clinical isolate represents a new species, Caulobacter mirare, that phylogenetically resembles both C. crescentus and the related C. segnis, which was also thought to be non-pathogenic. The similarity to other Caulobacters and lack of obvious pathogenesis markers suggested that C. mirare is not unique amongst Caulobacters and that consequently other Caulobacters may also have the potential to be virulent. We tested this hypothesis by characterizing the ability of Caulobacters to infect the model animal host Galleria mellonella. In this context, two different lab strains of C. crescentus prove as pathogenic as C. mirare, while lab strains of E. coli were non-pathogenic. Further characterization showed that Caulobacter pathogenesis is mediated by a dose-dependent, cell-associated toxic factor that does not require active bacterial cells or host cellular innate immunity to elicit its toxic effects. Finally, we show that C. crescentus does not grow well in standard clinical culture conditions, suggesting that Caulobacter infections may be more common than generally appreciated but rarely cultured. Taken together, our findings redefine Caulobacters as opportunistic pathogens and highlight the importance of broadening our methods for identifying and characterizing pathogens.
doi:10.1101/645515 fatcat:j5yjzjixxjdwlfwntsqwlahnlq