The most clinically relevant species are Campylobacter jejuni (C. jejuni) and C. coli, which are responsible for almost 95% of Campylobacter-associated diarrheal diseases. Other emerging species have been recently identified as human or animal pathogens. The involvement of some of these species in human disease is still unclear.
Campylobacter are a group of small, curved, gram-negative, non-spore-forming, motile bacteria with a single polar flagellum or bipolar flagella.
Thermotolerant Campylobacter species (e.g. C. jejuni, C. coli) are able to grow at temperatures between 37° and 42˚C but not below 30˚C, while strains of non-thermotolerant Campylobacter species (e.g. C. fetus subsp. venerealis, C. fetus subsp. fetus) may not grow at 42˚C. Generally, they are highly sensitive to oxygen, desiccation, osmotic stress, and low pH , and they cannot grow in foods during handling or storage at room temperature in moderate climates. Freezing reduces the number of viable Campylobacter, but it must nevertheless be stressed that the bacteria can survive extended periods of refrigeration and freezing.