Biomedical Engineering Reference
In-Depth Information
Fig. 1
Scanning electron
micrograph of a mixed-
species biofilm of
Candida
albicans
and
Staphylococcus
epidermidis
. Smaller
bacterial cells can be seen
adherent to both yeasts and
hyphae (Shirtliff et al.
2009
)
3 Biofilms: A Challenge for Antibiotic Therapy
The pathogenicity of biofilms is amplified by two of their major characteristics:
(1) their increased tolerance to antimicrobials; (2) their protection of cells against
the host's defense mechanisms. Overall, the combined action of different mecha-
nisms is believed to contribute to increased resistance and tolerance in biofilms:
slow growth; phenotypic variation and differential regulation of the cell metabolic
activity caused by nutrient limitation, stress, and cell density; over-expression of
resistance genes and amplified expression of efflux pumps; a changing sterol
composition in the membrane; limited diffusion of antibiotics and immunological
molecules through the extracellular matrix; and presence of persisters in the
biofilm, which are able to tolerate high concentrations of antibiotics.
Microbes within biofilms are significantly more resistant to standard antibiotic
therapy and may require up to 1,000 times the antibiotic dose to achieve efficacy
(Davies
2003
; Lewis
2005
). Therefore, the doses of antibiotics used effectively
against planktonic cells are usually not enough to tackle biofilms, leading to
resistant subpopulations remaining in the biofilm and causing recurring infections.
This has led to a more judicious approach for antibiotic use in order to limit further
development of resistant strains. The emergence of biofilm-associated infections
and rise in resistant strains has threatened the efficacy of current antimicrobial
agents, and therefore newer antimicrobial tools and strategies are needed to combat
such infections. Here, we have reviewed some of the novel and successful strategies
and approaches being used to prevent and control the biofilm infections.
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