A rapid turbidimetric assay for the study of serum sensitivity of Escherichia coli

A rapid turbidimetric assay was developed to test bacteria for serum sensitivity. The lysis of bacterial suspensions in a microtitration plate was measured by a conventional vertical photometer. The comparison with the classical viable count test showed that the method was simple and fast, and gave comparable results. Escherichia coli mutants selected for resistance to a K1-specific bacteriophage were screened with the assay. Mutants from a rough K1-encapsulated serum-resistant strain were serum-sensitive irrespective of their capsular sialic acid content or reactivity with anti-K1, whereas similar mutants derived from an 018:K1 strain were resistant.