The effects of UVB and temperature on the survival of natural populations and pure cultures of Campylobacter jejuni, Camp. coli, Camp. lari and urease‐positive thermophilic campylobacters (UPTC) in surface waters

K. OBIRI‐DANSO, N. PAUL AND K. JONES. 2001. Aims: To determine whether diurnal and seasonal variations in campylobacters in surface waters result from the effects of temperature and u.v. radiation, and whether natural populations of Campylobacter lari and urease‐positive thermophilic campylobacters (UPTC) from birds survive better in surface waters than Camp. jejuni from sewage. Methods and Results: Natural populations of Camp. lari and UPTC in sea water, and Camp. jejuni in river water, were exposed to artificial sunlight (equivalent to a sunny day in June). Both populations became non‐culturable within 30 min, with T90s of 15 min and 25 min, respectively. Cultures of Camp. jejuni became non‐culturable within 40 min and those of Camp. coli, Camp. lari and UPTC, within 60 min. In darkness, survival was temperature‐dependent. Natural populations took 12 h at 37°C and 5 days at 4°C to become non‐culturable in sea water, and slightly less in river water. Cultures of Camp. lari and UPTCs survived for significantly longer than Camp. jejuni and Camp. coli. Loss of culturability for all isolates was most rapid at 37°C and slowest at 4°C. Newly isolated strains from sea water and river water behaved in an almost identical manner to NCTC strains. Conclusions: Campylobacter lari and UPTCs survive for longer in surface waters than Camp. jejuni and Camp. coli, particularly in the dark. Low Campylobacter numbers in coastal waters in the summer, especially in the afternoon, are due to the combined effects of higher temperatures and higher levels of u.v. radiation. Significance and Impact of the Study: Campylobacter lari and UPTCs from birds predominate in bathing waters in Morecambe Bay because they are better able to survive; they also originate from closer to the shore than Camp. jejuni and Camp. coli in sewage effluent, which survive poorly and die before the incoming tide reaches the shore. The predominance of Camp. jejuni in river water results from its dominance of the inputs and not from its ability to survive.