in vitro biofilm formation is associated with isolation source. in vitro biofilm formation on polystyrene surface of 71 commensal and 28 medical device (nosocomial) S. epidermidis isolates. Commensal isolates are subdivided by the skin type (dry, sebaceous and moist) as defined in Grice et al. . Each point represents the average of four replicates. Statistical significance was calculated using Mann-Whitney, two-tailed.