Control of Polymicrobial Biofilms: Recent Trends - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 338

Indeed, the use of growth media is extremely important and bacteria respond very
differently to challenges when grown in different growth media. As a case in point,
Umland et al. ( 2012 ) demonstrated that genes identified as being possible antimi-
crobial targets in Acinetobacter baumannii , using nutrient media, overlapped
poorly with those identified by growing the bacterium in human ascites, an
ex vivo medium that reflects the infection environment. The authors underscored
the importance of using “clinically relevant media and in vivo validation while
screening for essential genes for the purpose of developing new antimicrobials”
(Umland et al. 2012 ). Another example demonstrating the importance of environ-
mentally germane conditions was presented by Du and Kolenbrander ( 2000 ) who
demonstrated that various genes, including those that produce coaggregation
adhesins, are upregulated in human saliva compared with brain heart infusion
medium. Such issues are likely compounded if (as in polymicrobial biofilms)
multiple species are present in the community that is being studied because
interactions between component species may be masked (Kolenbrander 2011 ). In
addition, it is becoming clear that not only is growth of species in laboratory media
likely to elicit different responses by bacteria as compared to growth in real-world
environmental conditions, but repetitive growth in such un-representative labora-
tory media can lead to the clonal selection of strains with characteristics unlike the
originally isolated wild-type progenitor (Sato et al. 2002 ; Davidson et al. 2008 ;
McLoon et al. 2011 ). Thus, approaches to directly assess the effectiveness of new
technologies to control polymicrobial biofilms need to be performed under condi-
tions representative of the natural environment and with multispecies communities
that have not been grown in artificial conditions. Such a notion has begun to make
its way into polymicrobial biofilm research studies and model systems that are
located in the environment being studied, such as retrievable enamel chip models in
dental plaque biofilm studies (Palmer et al. 2001 ) or using in vivo bioluminescence-
based technologies (Chauhan et al. 2012 ; Vande Velde et al. 2013 ), are being
developed. Alternatively, models are being refined to closely replicate the original
environment by using harvested real-world milieu and polymicrobial biofilm
material. Examples range from dental plaque biofilm microfluidic devices (Nance
et al. 2013 ) to constant depth film fermenter domestic drain microcosms (McBain
et al. 2003 ). With the use of representative model systems and real-world
polymicrobial communities, the evaluation of the effectiveness of new technologies
to inhibit or control polymicrobial biofilms will likely be more sensitive and
revealing.
In conclusion, a thankfully unbridled understanding of the nature as well as
approaches to control polymicrobial communities has developed over the last few
decades. Instead of being reductionist in our approaches, we have begun to be
holistic and consider polymicrobial communities at individual and multispecies
levels. This has allowed us to unravel the reasons why bacteria within
polymicrobial biofilms possess enhanced abilities, compared to free-floating com-
munities, and why effective biological or technological strategies to control these
communities need to take into account the properties of individuals within these
communities and the properties of biofilm as a whole. The recent developments in