The Effect of Plasmids and Other Biomolecules on the Effectiveness of Antibiofilm Agents - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 160

German Veterinary Society guidelines as references for testing disinfectants used in
the dairy and food industries. In order to simulate the conditions found in real life,
they used low fat milk as an organic load and reported the significance of choosing
an appropriate disinfectant because the inclusion of a challenging substance
(organic material) is important to access the proper bactericidal activity. Bessems
( 1998 ) demonstrated that a QAC tested on three microorganisms (a Gram-positive,
a Gram-negative bacterium and a yeast) had a similar killing rate in the absence of
interfering substances. After the inclusion of 17dH water hardness, a strong reduc-
tion of the killing activity was found for the Gram-negative bacteria; however, the
same behaviour was not observed for the other two microorganisms. Jono
et al. ( 1986 ) assessed the effect of dried yeast extract and human serum on the
activity of BAC, concluding that the bactericidal activity of the QAC was inhibited
by solutions of 2.5 % dried yeast extract and 10 % human serum. The inhibition by
yeast extract was more pronounced than human serum at the given concentrations.
They also concluded that the presence of dried yeast increased the concentration of
biocide necessary to kill bacteria.
In the treatment of oral infections, one potential factor reducing the activity of
the disinfecting agents is also the chemical environment of the root canal. The root
canal system contains a complex mixture of organic and inorganic compounds.
Portenier et al. ( 2001 ) showed that a number of organic compounds, including BSA,
reduced the antimicrobial effectiveness of root canal medicaments (calcium
hydroxide, chlorhexidine and iodine potassium iodide). Later, Pappen
et al. ( 2010 ) revealed that high concentrations of BSA significantly decreased the
antimicrobial activity of sodium hypochlorite against oral microorganisms.
2 Case Studies
2.1 Case Study 1: The Influence of Plasmids pET28
and pUC8 on Biofilm Formation and Resistance
The influence of the presence of a non-conjugative plasmid on the biofilm-forming
and resistance capacity of E. coli cells was studied in a flow cell system (Fig. 3 ), as
described by Teod´sio et al. ( 2012 ). The planktonic cell concentration was similar
for transformed and non-transformed strains, but the number of sessile cells was
higher for the plasmid-bearing strains when compared to the non-transformed strain
(Teod´sio et al. 2012 ). This observation has also been reported by other authors
(Huang et al. 1993 , 1994 ). Diaz Ricci and Hern´ndez ( 2000 ) showed that, in certain
conditions, plasmids can positively affect cell growth of E. coli JM109, as it did
here in regard to biofilm. The percentage of viable biofilm-associated cells was
about 2-fold lower for the transformed strains (Teod´sio et al. 2012 ). Previous
studies suggest that cells bearing a plasmid may suffer from a metabolic burden
resulting from plasmid maintenance, replication and/or protein expression (Glick