Coagulase-negative staphylococci in low birth weight infants: environmental factors affecting biofilm production in Staphylococcus epidermidis.

Coagulase-negative staphylococci (CoNS) are the most common cause of biofilm-associated sepsis in very low birth weight infants (VLBW). Standard biofilm assays may not predict the pathogenic potential of CoNS since biofilm production is regulated by diverse environmental stimuli. Staphylococcus epidermidis isolated from blood cultures from VLBW infants were evaluated for biofilm production in response to various environmental stimuli, including intravenous solutions and skin preparations. While responses to environmental stimuli were variable for individual isolates and products, some trends were observed. Biofilm production by hospital S. epidermidis isolates (predominantly ica and biofilm-positive) was most commonly increased at 30°C and decreased in the presence of intravenous solutions and moisturisers. Commensals (mainly biofilm-negative and lacking the ica gene) were more often induced to produce biofilm than hospital isolates. These results indicate that biofilm production in S. epidermidis can vary in response to environmental stimuli encountered in the clinical setting, that standard biofilm assays are unlikely to predict clinical outcome, and that harmless skin commensals may be induced to produce biofilm by some of the products used in neonatal units.