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Appl. Environ. Microbiol., 06 1995, 2252-2256, Vol 61, No. 6
CT Huang, FP Yu, GA McFeters and PS Stewart
Fluorescent stains in conjunction with cryoembedding and image analysis
were applied to demonstrate spatial gradients in respiratory activity
within bacterial biofilms during disinfection with monochloramine. Biofilms
of Klebsiella pneumoniae and Pseudomonas aeruginosa grown together on
stainless steel surfaces in continuous-flow annular reactors were treated
with 2 mg of monochloramine per liter (influent concentration) for 2 h.
Relatively little biofilm removal occurred as evidenced by total cell
direct counts. Plate counts (of both species summed) indicated an average
1.3-log decrease after exposure to 2 mg of monochloramine per liter. The
fluorogenic redox indicator 5-cyano-2,3- ditolyl tetrazolium chloride (CTC)
and the DNA stain 4',6-diamidino-2- phenylindole (DAPI) were used to
differentiate respiring and nonrespiring cells in biofilms. Epifluorescence
micrographs of frozen biofilm cross sections clearly revealed gradients of
respiratory activity within biofilms in response to monochloramine
treatment. These gradients in specific respiratory activity were quantified
by calculating the ratio of CTC and DAPI intensities measured by image
analysis. Cells near the biofilm-bulk fluid interface lost respiratory
activity first. After 2 h of biocide treatment, greater respiratory
activity persisted deep in the biofilm than near the biofilm-bulk fluid
interface.
Copyright © 1995, American Society for Microbiology
Nonuniform spatial patterns of respiratory activity within biofilms during disinfection
Department of Microbiology, Montana State University, Bozeman 59717, USA.
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