EFFECT OF AGGREGATION ON VIBRIO-CHOLERAE INACTIVATION

Extensive research has shown that microorganisms exhibit increased res istance due to clumping, aggregation, particle association, or modific ation of antecedent growth conditions. During the course of investigat ing a major waterborne Vibrio cholerae outbreak in Peru, U.S. EPA inve stigators discovered an extremely rough form of Vibrio cholerae that w as highly resistance to disinfection by chlorine. This form of Vibrio cholerae also tends to form large aggregates, which contribute to the resistance. Particle counting was used to characterize each of the cul tures examined. Statistical analysis revealed that the rugose, or roug h, strain of Vibrio cholerae was much more resistant to disinfection t han the common, or smooth, strain. Resistance was attributed to both a ggregation and a mucoid coating. The larger aggregates associated with the rugose organism are of a size as to be easily removed by filtrati on, but if the variant were to contaminate a distribution system throu gh a line break or cross connection it would be difficult to control b y chlorine disinfection.