casses. Because ALF has greater affinity for
the anchor sites than do the bacterial cells,
this substance can displace attached bacteria
cells, detaching the cells, and facilitating
removal. The electrostatic ALF blocks bac-
terial cells from attachment and/or displaces
cells from attachment sites. Rinsing can
remove bacteria more completely. The bind-
ing of ALF to outer membrane proteins of
bacterial cells disrupts the cell membrane of
Gram-negative cells and kills bacteria
(Naidu, 2002). Thus, ALF exhibits a bacteri-
cidal affect on bacterial cells that may
remain on a product surface. The detrimen-
tal effect of this compound on bacterial
attachment to surfaces qualifies it as a viable
candidate for improved equipment sanita-
tion as well as carcass treatments. Attach-
ment of bacteria such as L. monocytogenes
to stainless steel may be counteracted by the
ability of ALF to displace attached cells.
Although limited research has been con-
ducted in this area, there appears to be
potential benefits for equipment cleaning.
The binding affinity of ALF for cell sur-
faces may also explain the antiviral activity
that has been observed for this compound.
Attachment of ALF to eukaryotic cells
appears to prevent the adhesion of viruses to
the cell surface, which is a necessary step for
the virus to infect the cell. The binding of
iron is the probable explanation of why ALF
can inhibit the growth of bacterial cells.
Since iron is an essential growth element for
many bacteria, limiting its availability retards
growth. The effectiveness of ALF as a
growth inhibitor also exists in iron-rich envi-
ronments such as meat. Thus, ALF is a
potential microbial inhibitor when applied
to retail fresh or processed meats.
Potential Microbial Resistance
The ability of microorganisms to adapt to
adverse environmental conditions presents a
challenge to sanitarians. It is probable that
bacteria develop resistance to sanitizing
compounds, especially the quaternaryammo-
nium compounds, similar to how they develop
antibiotic resistance. Those sanitizers that
kill and then rapidly disappear (oxidizers)
seem to create less opportunity for resistance
to develop (Clark, 2003). It has not been
fully resolved if resistance to sanitizers is the
reason why bacteria survive and proliferate.
Bacterial resistance to antibiotics and
environmental stresses results from changes
in the bacterial genome and is driven by two
genetic processes and bacteria: mutation and
selection known as vertical evolution. It is
uncertain if mutations occur in response to
environmental stresses and if antibiotic
resistance is involved. Many of the biocides
incorporated in food processing facilities
provide such a powerful attack on the
microorganisms that the development of
resistance to the attack is difficult.
Microbial populations may not develop
resistance to chlorine or quaternary ammo-
nia because of their powerful lethal effects.
Bacteria are more likely to develop resistance
to organic acids than halogens. Milder
organic acid treatments are safer to use and
effective in some applications, but they may
generate resistant strains of bacteria because
they can adapt and become acid tolerant.
However, a broad-spectrum biocide such as
chlorine is powerful enough to prevent such
change.
Sanitizer rotation is a commonly employed
strategy to reduce microbial resistance. The
various mechanisms of biocidal attack pro-
vide logic for sanitizer rotation. If microor-
ganisms develop resistance to one form of
attack, logic would suggest a switch to a dif-
ferent sanitizer. Although various sanitizers
may be incorporated, the most common
rotation involves some form of chlorine dur-
ing the week and a quaternary ammonium
sanitizer to provide a residual effect over the
weekend.Sanitizers 187