sentence: We therefore examined the cap operons of all isolates in the collection to identify whether any mutations within the cap operons could be linked to an in vitro CP-negative phenotype.Both Cocchiaro et al. and Boyle-Vavra et al. [ 51 , 55 ] identified specific genetic mutations in the capsular polysaccharide biosynthetic operon , which they showed by complementation experiments may contribute to the lack of observed capsule expression in vitro .