The Effect of Plasmids and Other Biomolecules on the Effectiveness of Antibiofilm Agents - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 155

1 Introduction

Biofilms cause serious problems in environmental, industrial and biomedical fields.
Nevertheless, the biofilms with the worst reputation are those found in the health
sector (Bryers 2008 ), since more than 50 % of all microbial infections in humans
are believed to be linked to the formation of biofilms (Costerton et al. 1999 ). This
chapter focuses on biofilms made by Bacillus cereus , Escherichia coli and Pseu-
domonas fluorescens , which can be hugely problematic in both medical and indus-
trial environments.
With over 250 serotypes, the Gram-negative bacterium E. coli is a highly
versatile organism ranging from harmless gut commensal to a dangerous pathogen
(Beloin et al. 2008 ). Its frequent community lifestyle and the availability of a wide
array of genetic tools have contributed to establish E. coli as an excellent model
organism for biofilm studies (Beloin et al. 2008 ; Wood 2009 ). In the health sector,
pathogenic strains of E. coli are responsible for 70-95 % of urinary tract infections,
one of the most common bacterial diseases (Dorel et al. 2005 ; Jacobsen et al. 2008 ).
These infections are especially frequent in cases of catheterisation (due to biofilm
development on the indwelling catheters) where the incidence of infection increases
5-10 % per day (Dorel et al. 2005 ). B. cereus also exists in hospital environments
and can attach to the surface of catheters and cause persistent and chronic infec-
tions, especially among immunosuppressed patients (Kuroki et al. 2009 ; Bottone
2010 ). P. fluorescens is an unusual agent for disease in humans. Nonetheless, this
bacterium demonstrates haemolytic activity and it has been known to infect donated
blood (Gibb et al. 1995 ). Other strains from the Pseudomonas genus are notorious
for their impact in medical settings. For example, Pseudomonas aeruginosa has
been shown to form biofilms on the tissues of the cystic fibrosis lung (Govan and
Deretic 1996 ) and on abiotic surfaces such as contact lenses and catheter lines
(Miller and Ahearn 1987 ; Nickel et al. 1985 ).
The biofilm mode of growth leads to a large increase in resistance to antimicro-
bial agents, including antibiotics, biocides, and preservatives, compared with cul-
tures grown in suspension (Stewart and Costerton 2001 ; Brown and Smith 2003 ). In
fact, when cells exist in a biofilm, they become 10 to 1,000 times less susceptible to
the effects of antimicrobial agents. Some factors that contribute to biofilm resis-
tance to antibiotics and biocides include physical or chemical diffusion barriers to
agent penetration within the biofilm matrix, slow growth rate of biofilm cells due to
nutrient limitation, activation of the general stress response, and the presence of
“persister” cells or antibiotic-resistant small-colony variants (Mah and O'Toole
2001 ). This high level resistance makes most device-related infections difficult or
impossible to eradicate by conventional antimicrobial chemotherapy. Therefore,
there is now a perceived need to elucidate resistance mechanisms and develop
effective antibiofilm strategies.
In the first case study presented in this chapter, the effects of a QAC—
benzyldimethyldodecylammonium chloride (BDMDAC)—on transformed and
non-transformed E. coli cells were assessed regarding their biofilm removal