Different responses of planktonic and attached Bacillus subtilis and Pseudomonas fluorescens to sanitizer treatment

Three commercial sanitizers containing iodophor (I), peracetic acid/hydroge n peroxide (PAH), or chlorhexidine gluconate (CG) were evaluated in vitro a gainst planktonic and sessile Bacillus subtilis or Pseudomonas fluorescens cells grown in Standard One Nutrient froth. Sessile cells were attached to stainless steel or polyurethane test surfaces. Planktonic and attached cell s of both bacteria were enumerated by plate counts after sanitizer treatmen t for 1, 3, or 5 min. Sessile cells were dislodged from test surfaces by sh aking them with beads. Cell morphologies were monitored by scanning electro n microscopy (SEM). Attached B. subtilis and P. fluorescens cells on both s urface types were less susceptible to all three sanitizers than their plank tonic counterparts. PAH, I, and CG were equally effective against planktoni c P. fluorescens cells, which were reduced by 99.999% after 1, 3, and 5 min exposure. PAH was the only sanitizer effective against attached P. fluores cens cells on both surface types; it reduced counts by less than or equal t o 99.9% after 1, 3, and 5 min exposure. PAH was also the most effective san itizer against planktonic B. subtilis cells, reducing counts by 99.9% after 1, 3, and 5 min. Sessile B. subtilis cells on both surface types were the least susceptible to all sanitizers; counts were reduced by only 99.5%, or less after exposure to PAH for 5 min. SEM revealed that planktonic and atta ched cells of both bacteria exhibited symptoms of surface roughness, indent ations, and shape distortions after treatment with any of the sanitizers.