Biomedical Implications of the Porosity of Microbial Biofilms - Porous Media: Applications in Biological Systems and Biotechnology - page 134

conditions for cell to cell interactions, as well as aggregate to aggregate interac-
tion, including aggregates formed from different microbial species. Several bac-
terial pathogens were shown to be associated with this phenomenon, including
Legionella pneumophila (Murga et al. 2001), S. aureus (Raad et al. 1992),
Listeria monocytogenes (Wirtanen et al. 1996), Campylobacter spp. (Buswell
et al. 1998), E. coli O157:H7 (Camper et al. 1998), Salmonella typhimurium
(Hood and Zottola 1997), V. cholera (Watnick and Kolter 1999), and Heli-
cobacter pylori (Stark et al. 1999). Although all these organisms are capable
of attaching themselves to surfaces to form biofilms, most, if not all, appear
incapable of forming single-species biofilms of their own. This may be due to
their fastidious growth requirements or due to their inability to compete with
indigenous organisms. The mechanism of interaction and growth apparently
varies with the pathogens involved, and at least for L. pneumophila , which
appears to require the presence of free-living protozoa to grow in biofilm form
(Murga et al. 2001). Survival and growth of pathogenic organisms within
biofilms might also be enhanced by the association and metabolic interac-
tions with indigenous organisms. Camper and colleagues (1998) showed that
Salmonella typhimurium persisted in a model distribution system containing
undefined heterotrophic bacteria from an unfiltered reverse osmosis water sys-
tem for more than 50 days, which suggests that the normal biofilm flora of
this water system provided niche conditions supporting the growth of this
microorganism.
The isolation of multiple discrete species from biofilm-colonized implants
derived from patients provides the most compelling evidence of the medical
importance of polymicrobial (or heterotypic) biofilms (Costerton et al. 1999).
Studies of polymicrobial biofilms formed by C. albicans and S. epidermidis
indicate that the exopolymeric matrix produced by the fungal species may
protect the bacteria against antibiotics, while the bacterial matrix protects
the fungi from antifungal agents. Other studies of polymicrobial biofilms have
provided evidence of enhanced interspecies transfer of antimicrobial resistance
traits, symbiotic interactions, and sequential colonization patterns. These
observations raise the intriguing possibility that virulence traits associated
with biofilm commensalism may be coselected through enhanced persistence
and antimicrobial tolerance of such polymicrobial biofilms (Wargo and Hogan
2006; Hansen et al. 2007).
4.3.4 Antimicrobial Resistance in Infectious
Bacterial Biofilms
Biofilms of pathogenic bacteria and fungi have substantial impact on public
health, as they are dicult to eradicate and affect chronic or recurrent infec-
tions. Biofilm infections constitute a number of clinical challenges, including
diseases involving uncultivable species, chronic inflammation, impaired wound
healing, and rapidly acquired antibiotic resistance.