Effect of different environmental conditions on biofilm formation in staphylococci isolated as the causative agent of bacteriemia

INTRODUCTION AND AIM: Staphylococcus aureus and coagulase-negative staphylococci are common cause of bacteriemia and catheter-related infections and they frequently produce biofilm. Biofilm production is a serious virulence factor and it causes treatment failure especially in patients who have indwelling catheters. The aim of this study is to determine the biofilm production in staphylococci that are isolated from clinical blood samples of the bacteriemic patients and to evaluate the effect of different aerial conditions (normal, CO2, anaerobic) on biofilm production. MATERIALS AND METHOD: 63 clinical isolates of different types of staphylococci were enrolled in the study. The isolates were firstly identified by MaldiTOF-MS, then antimicrobial susceptibility testing was carried out by using VITEK System. The biofilm production was evaluated in the 96-well flat-bottom microplates. E. coli ATCC 25922 was used as positive control and uninoculated broth was used as a negative-control. The CO2 condition was achieved in a candle jar while anaerobic gas pack was used in a closed jar to create anaerobic condition. All tests were done three times and the mean values were determined. Biofilm production were divided into four categories which were None (0), Weak (+), Moderate (++), and Strong (+++). The results were evaluated with scientific statistics software with appropriate statistics methods and the data with a p value ≤0.05 was accepted as significant. RESULTS: The number of types of staphylococci is 63 samples divided as follows: Staphylococcus aureus 17 samples, Staphylococcus haemolyticus 3 samples, Staphylococcus epidermidis 22 samples, Staphylococcus hominis 16 samples, and Staphylococcus capitis 5 samples. The distribution of biofilm production was as follows: under normal condition and CO2 condition 61 of the isolates (97%) produced biofilm, while under anaerobic condition, 48 of the isolates out of 63 (76%) were positive for biofilm production. Under anaerobic condition, the ability of biofilm production of the isolates was decreased (p≤0.05). There was no significant difference between normal and CO2 conditions in terms of capacity to produce biofilm (p>0.05). Under different conditions, the capacity of biofilm formation among S. aureus was not affected. But there was a significant difference among coagulase negative staphylococci (p≤0.05). DISCUSSION AND CONCLUSION: Staphylococci are highly pathogenic opportunistic pathogens and they are significant cause of hospital and community-acquired infections. They have an extraordinary ability to encase themselves in a protective environment called a biofilm, where they can survive and cause serious and hard-to-treat infections. In this study, production of biofilm in Staphylococci was determined as a serious virulence factor evaluated under different environmental conditions. Although these data are derived from relatively small number of samples, with the evaluation of the larger sample groups and other environmental and nutritional conditions, understanding of biofilm production in Staphylococci can be clarified and new alternative treatment modalities can be developed. KEY WORDS: Staphylococci, Staphylococcus aureus, Biofilm formation, Bacteriemia, Methicillin resistance.