Journal of the Indian Fisheries Association 19 30, 2003, 19-22 EFFECTS OF PROBIOTICS AND ANTIBIOTICS ON BIOFILMS B. Pradeep, P. K. Pandey* and S. Ayyappan Central Institute of Fisheries Education, Fisheries University Road, Versova, Mumbai — 400 061 ABSTRACT Experiments were conducted to study the effects of probiotics and antibiotics on 3-months old biofilms formed on three different substrates, namely glass, granite and fibreglass reinforced plastic. The variations in heterotrophic bacterial populations associated with biofilms were monitored for a period of one month after one-time application of the probiotic Biogreen (Gee Key Marine Pvt. Ltd, Chennai) at 0.2 mg P and the antibiotic tetracycline at 1.0 mg P. The variations in heterotrophic bacterial populations associated with biofilms were compared with that of control to analyse the effects of probiotics and antibiotics on biofilms. The observations showed that the biofilm formation and succession in aquatic environment is substrate dependent and that the resistance to antibiotics also depends on the substrate. The probiotics did not show significant effect on biofilms. Keywords: Bacterial biofilms, substrates, probiotics, antibiotics INTRODUCTION Microorganisms colonise on all substrates in natural environments, but the rate of adsorption depends on the prop6rties of substrate (Characklis, 1990; Balareddy, 2001). The intensity of microbial colonization on substratum appears to increase with the increasing roughness of the substratum (Geesey and Costerton, 1979; Bakke et al., 1984; Characldis, 1984). This is because of the greater surface area available for microbial adsorption and reduced desorption due to the lower shear force experienced by cells shielded from the main flow (Characklis, 1984). Weise and Rheinheimer (1978), Geesey and Costerton (1979), and Beeftink and Staugaard (1986) suggested that attached microorganisms are mostly concentrated on crevices rather than on smooth surfaces. Bakke et al. (1984) reported that bacteria did not selectively colonise cavities and grooves despite the fact that roughening the substratum surface greatly increased the rate of bacterial colonisation. Although initial colonisation may be in the crevices and grooves, subsequent spreading of the colonies due to growth may occur over the entire surface. Another important characteristic feature of the substrate surface is the wettability, i.e., hydrophilic or hydrophobic nature of the subStratum (Wardell, 1988). According to Fletcher and Loeb (1979) many bacteria tend to attach in large numbers to hydrophobic (Teflon, polyethylene) than hydrophilic (glass, mica,. oxidised plastics) surfaces. 4' Corresponding author