Fig 3. Resistance of biofilm-associated Vibrio cholerae to lytic phages JSF3 and JSF4.

Phage susceptibility of biofilm-associated cells were compared to that of respective freshly grown planktonic cells or cells physically dispersed from biofilms by shaking with glass beads and suspended in LB. Different cell suspensions and intact biofilms were exposed to 1 x 10³ pfu/ml of JSF3 or JSF4 phage in LB supplemented with 5 mM CaCl₂ and 5 mM MgCl₂ and incubated at 37^°C with shaking. At different time intervals, the residual bacterial cells were estimated. The survival rate of planktonic and biofilm-associated cells of V. cholerae O1 El Tor strain C6706 and O139 strain MO1220 after exposure to specific phages JSF4 and JSF3 respectively for different time periods are shown. Data points represent mean values and standard deviations of three different observations. The p values for the difference between survival of biofilm associated cells and planktonic cells when exposed to JSF3 (*) and JSF4 (**), and those for V. cholerae cells dissociated from biofilms by physical agitation vs fresh cultures of the bacteria exposed to JSF3 (†) and JSF4 (††), are shown.