The natural antimicrobial carvacrol inhibits Campylobacter jejuni motility and infection of epithelial cells.
BACKGROUND
Natural compounds with anti-microbial properties are attractive reagents to reduce the use of conventional antibiotics. Carvacrol, the main constituent of oregano oil, inhibits the growth of a variety of bacterial foodborne pathogens. As concentrations of carvacrol may vary in vivo or when used in animal feed, we here investigated the effect of subinhibitory concentrations of the compound on major virulence traits of the principal bacterial foodborne pathogen Campylobacter jejuni.


RESULTS
Motility assays revealed that subinhibitory concentrations of carvacrol inhibited the motility of C. jejuni without affecting bacterial growth. Immunoblotting and electron microscopy showed that carvacrol-treated C. jejuni still expressed flagella. The loss of motility was not caused by reduced intracellular ATP levels. In vitro infection assays demonstrated that subinhibitory concentrations of carvacrol also abolished C. jejuni invasion of human epithelial cells. Bacterial uptake of invasive Escherichia coli was not blocked by carvacrol. Exposure of C. jejuni to carvacrol prior to infection also inhibited cellular infection, indicating that the inhibition of invasion was likely caused by an effect on the bacteria rather than inhibition of epithelial cell function.


CONCLUSIONS
Bacterial motility and invasion of eukaryotic cells are considered key steps in C. jejuni infection. Our results indicate that subinhibitory concentrations of carvacrol effectively block these virulence traits by interfering with flagella function without disturbing intracellular ATP levels. These results broaden the spectrum of anti-microbial activity of carvacrol and support the potential of the compound for use in novel infection prevention strategies.
Department of Infectious Diseases and Immunology, Utrecht University, Utrecht, The Netherlands.
Lieke B
LB
van Alphen
Sara A
SA
Burt
Andreas K J
AK
Veenendaal
Nancy M C
NM
Bleumink-Pluym
Jos P M
JP
van Putten
D000255:Adenosine Triphosphate / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001688:Biological Products / Q000494:pharmacology*; D016123:Campylobacter jejuni / Q000187:drug effects* / Q000502:physiology; D002460:Cell Line; D000081007:Cymenes; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000382:microbiology*; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology; D005407:Flagella / Q000187:drug effects*; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects / Q000382:microbiology*; D008854:Microscopy, Electron; D039821:Monoterpenes / Q000494:pharmacology*; D009068:Movement / Q000187:drug effects; D009154:Mutation; D059008:Time-Lapse Imaging
D000900:Anti-Bacterial Agents; D001688:Biological Products; D000081007:Cymenes; D039821:Monoterpenes; D000255:Adenosine Triphosphate; C073316:carvacrol