Biofilm formation of Pasteurella multocida on bentonite clay

Background and Objectives: Biofilms are structural communities of bacterial cells enshrined in a self produced polymeric matrix. The studies on biofilm formation of Pasteurella multocida have become imperative since it is a respiratory pathogen and its biofilm mode could possibly be one of its virulence factors for survival inside a host. The present study describes a biofilm assay for P. multocida on inert hydrophilic material called bentonite clay. Materials and Methods: The potential of the organism to form in vitro biofilm was assessed by growing the organism under nutrient restriction along with the inert substrate bentonite clay, which will provide a surface for attachment. For quantification of biofilm, plate count by the spread plate method was employed. Capsule production of the attached bacteria was demonstrated by light microscopic examination following Maneval staining and capsular polysaccharide estimation was done using standard procedures. Results and Conclusion: The biofilm formation peaked on the third day of incubation (1.54 ×106 cfu/g of bentonite clay) while the planktonic cells were found to be at a maximum on day one post inoculation (8.10 ×108 cfu/ml of the broth). Maneval staining of late logarithmic phase biofilm cultures revealed large aggregates of bacterial cells, bacteria appearing as chains or as a meshwork. The capsular polysaccharide estimation of biofilm cells revealed a 3.25 times increase over the planktonic bacteria. The biofilm cells cultured on solid media also produced some exclusive colony morphotypes.