Biofilms reduce solar disinfection of Cryptosporidium parvum oocysts

Abstract

Solar radiation reduces Cryptosporidium infectivity. Biofilms grown from stream microbial assemblages inoculated with oocysts were exposed to solar radiation. The infectivity of oocysts attached at the biofilm surface and oocysts suspended in water was about half that of oocysts attached at the base of a 32-μm biofilm.

Fig 1

Summary of oocyst infectivity results for solar exposure experiments on July 9, July 15, and August 25. White columns are light-exposed treatments. Gray bars are dark control treatments. Lab stock infectivity for each experiment was 5.8% (July 9), 5.3% (July 15), and 10.4% (August 25). The July 9 and July 15 experiments were performed with the same oocyst lot. n, number of individual flow chambers.

Fig 2

Biofilm transmittance in Monocacy Creek water and deionized water (100% relative transmittance by calibration for clean flow chamber with deionized water). UV-C, 100 to 280 nm; UV-B, 280 to 315 nm; UV-A, 315 to 400 nm.