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DO AUTOCHTHONOUS BACTERIA AFFECT GIARDIA CYST SURVIVAL IN NATURAL WATERS?
Citation:
Revetta*, R P., M R. Rodgers, AND B. K. Kinkle. DO AUTOCHTHONOUS BACTERIA AFFECT GIARDIA CYST SURVIVAL IN NATURAL WATERS? Presented at American Society for Microbiology General Meeting, Orlando, FL, 5/20-24/2001.
Description:
Giardia lamblia survives in and is transmitted to susceptible human and animal populations via water, where it is present in an environmentally resistant cyst form. Previous research has highlighted the importance of water temperature in cyst survival, and has also suggested the potential role for autochthonous bacteria in cyst degradation. An understanding of the ecology of this human pathogen in environmental waters is of obvious importance for maintenance of safe drinking water sources. With this in mind, we initiated studies on bacteria isolated from environmental waters to determine if they are capable of killing G. lamblia cysts. Cyst viability was determined by cost morphology, as viewed with phase contrast microscopy, and incorporation of the fluorogenic dye, propidium iodide, which is only capable of passing through damaged cell membranes. A total of 22 bacterial strains isolated from a KY stream were cultivated on R2A medium and screened for virulence against G. lamblia (strain CH-3) cysts. Eleven bacterial isolates exhibited a strong degradative effect on cysts. To date, 6 of the 11 bacterial isolates have been identified by 16S ribosomal RNA sequence comparisons, with three isolates belonging to the Cytophaga/Flavobacterium group and three isolates belonging to the Proteobacteria group. One bacterium, designated strain SR1, is most closely related to Cytophaga sp. strain Type 0092. Strain SR1 is a Gram negative rod which produces a yellow pigment and exhibits a spreading colony morphology when grown on low nutrient agar. Strain SR1 kills 96% of Giardia cysts in 48 hrs. The remaining five unidentified isolates are Gram negative and exhibit diverse colocy morphologies and growth rates. We propose that bacteria, such as SR1, may be an important factor influencing the survival of cysts in environmental waters.