Prophage induction in lysogenic Aggregatibacter actinomycetemcomitans cells co-cultured with human gingival fibroblasts, and its effect on leukotoxin release

► Co-cultures of Actinobacillus actinomycetemcomitans (Aa) lysogens were prepared. ► Pure cultures of Aa spontaneously released low levels of phage. ► Co-cultures of Aa with human fibroblasts greatly enhanced phage induction. ► Phage induction was not stimulated by co-culture with epithelial cells. ► Leukotoxin release accompanied fibroblast-mediated phage induction of Aa lysogens.