Bacteria with Public Health Relevance in the Head Section of Common Cat Fleas

Background: The present study investigated the microbiome of dissected cat flea heads for bacteria with clinical relevance for human infections. Methods: A total of 112 cat fleas (Ctenocephalides felis) were collected from 30 cats in Attica, Greece. The heads of the insects were aseptically dissected, pooled in groups by host ani-mals and analyzed with Ion Torrent 16S rRNA metagenomic sequencing. Results: Of the 1578 bacterial species detected, 119 (7.5 %) are known human pathogens. These include the classic flea-borne agents Bartonella henselae, B. clarridgeiae, and B. gra-hamii. Most pathogens (89 species, 74.8 %) can cause both bloodstream and skin or soft-tissue infections. Ten species are linked to bacteremia of unknown origin; among these, Haemophilus influenzae, Salmonella enterica, and Streptococcus pyogenes are typically associated with community-onset infections, whereas Enterococcus faecalis, Escherichia coli, Proteus mirabilis, and Staphylococcus aureus display varied epidemiological profiles related to both community-acquired and hospital-acquired bacteremias. Conclusions: The head microbiome of C. felis is exceptionally diverse and includes nu-merous bacteria of clinical importance. While the presence of DNA alone does not prove vector competence, the combination of biofilm capacity and the flea’s haematophagous behaviour supports a plausible—yet unproven—role of fleas in the transmission of un-conventional bacterial infections.