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Objective(s): This study was designed to investigate the effect of AgNPs (10 nm and 30 nm) on different phenotypes of Staphylococcus aureus biofilm consortia. Materials and Methods: A total of eighteen biofilm-producing isolates of Methicillin-Resistant S. aureus (MRSA) were used in the present study. Tube methods, Congo-red agar method, and scanning electron microscopy (SEM) were used to study biofilm phenotypes. Population analysis assay on a tryptone soya agar (TSA) plate was applied to study the different phenotypes of biofilm consortia. The effect of AgNPs was evaluated by broth dilution assay. Results: Results showed that biofilm consortia harbour different phenotypes, i.e., planktonic, metabolically inactive cells, and small colony variants (SCVs) or persister cells. The focus of the present study is the effect of AgNPs on biofilm consortia of MRSA, particularly on the SCVs population. Large size AgNPs (30 nm) were unable to diffuse through extracellular matrix material coverings of the biofilm consortia; they were only active against the planktonic population that occupies the outer surface of consortia. The smaller AgNPs (10 nm), on the other hand, were found to diffuse through the matrix material and hence were effective against planktonic as well as metabolically inactive population of consortia. Moreover, 30 nm AgNPs take 6 hr to disperse off and kill planktonic and upper surface indwellers. The 10 nm AgNPs disperse and kill the majority of biofilm indwellers within 20 min. Conclusion: The present study showed that 10 nm AgNPs can easily penetrate inside the biofilm and are active against all of the indwellers of consortia. [ABSTRACT FROM AUTHOR]

Objectives: Objective: This study was designed to explore the role of different phenotypes of P. aeruginosa in the development, stability and persistence of biofilm. Methods: A total of seventeen (17) waterborne biofilm producing strains of P. aeruginosa were studied. These isolates were identified on the basis of typical phenotypic characters and the tube method was used for the study of biofilms. Population and phenotypic variance were studied by the drop plate method. The hydrophobicity of strains was evaluated by the bacterial adhesion to apolar solvent test. Results: Study showed that the subject isolates of P. aeruginosa adopted a biofilm life style after 36 h of incubation at 35 °C. After 24 h the adhesion started, but it was reversible and easily dispersed by simple washing. However, after 36 h the irreversible adhesion was noticed. The biofilm consortia harbor three different phenotypes: i. wild types, showed typical P. aeruginosa characters on Cetrimide agar; ii. Slow growers, showed poor pigmentation and take >36 h for colony development, and iii. Small colony variants (SCVs) are metabolically inactive and producing pinpointed non pigmented colonies. Comparative analysis showed that these phenotypes i.e. SCVs were highly hydrophobic and persistent in biofilm consortia due to the production of excessive amounts of exopolysaccharides. Conclusions: This study showed that phenotypic heterogeneity is a characteristic feature of P. aeruginosa biofilms and all of these phenotypes have a major role in stability and persistence of biofilm consortia. [ABSTRACT FROM AUTHOR]