7/28/2019 Centrifugal Compaction Causes Changes in the Surface Properties of Bacterial Cells

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FACTORS INFLUENCING ON THE INVITRO STUDY OF ORAL BIO FILM:

Centrifugal compaction causes changes in the surface properties of bacterial cells. It has been

shown previously that the surface properties of plank tonic cells change with increasing

centrifugal compaction. This study aimed to analyze the influences of centrifugal compaction

and environmental conditions on the visco-elastic properties of oral biofilms. Biofilms weregrown out of a layer of initially adhering streptococci, actinomyces or a combination of these.

Different uni-axial deformations were induced on the biofilms and the load relaxations were

measured over time. Linear-Regression-Analysis demonstrated that both the centrifugation

coefficient for streptococci and induced deformation influenced the percentage relaxation.

Centrifugal compaction significantly influenced relaxation only upon compression of the

outermost 20% of the bio film (p < 0.05), whereas bio film composition became influential when

50% deformation was induced, invoking re-arrangement of the bacteria in deeper bio film

structures. In summary, the effects of centrifugal compaction of initially adhering, centrifuged

bacteria extend to the visco-elastic properties of biofilms, indicating that the initial bacterial layer

influences the structure of the entire bio film.

Evaluation of basic parameters of biofilm formation

Investigation of biofilm structures and bacterial interaction required establishment of reliable

biofilm setup protocols. For this purpose, different culture media were tested in a static biofilm

setup to evaluate the best conditions forin vitro simulation of biofilm generation. It is assumedthat not much liquid exchange occurs during periodontitis in vivo, thus static conditions best

mimic this situation and also allow the action of potential signalling molecules in mixed species

cultures. Six different media were examined for their effect on mono-species biofilm formation

for a time period up to five days. Safranin staining was employed as an easy read-out approach.

This method is used for the determination of biofilm mass, comprising bacterial cells and

extrapolymeric substances. Typically, an OD492 nm with a value of more than 0.05 is required to

indicate biofilm formation. Lower values are mostly caused by scattered bacteria in monolayers

(data not shown). For comparison, also the growth curves of planktonic cells were recorded for

each culture medium. Thetable S1summarizes the results for all bacteria analyzed. However,

the present study will only focus on the detailed results ofS. mitis, S. mutans andA.actinomycetemcomitans as representatives of the physiological, cariogenic and periodontitis-

associated oral microflora, respectively.

Monitoring the S. mitis, S. mutans andA. actinomycetemcomitans mono-species cultures for

biofilm mass over a period of five days showed that biofilm formation ofS. mutans occurred

within the first 24 hours of incubation time in CDM without glucose (chemically defined medium;

http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013135#pone.0013135.s005http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013135#pone.0013135.s005http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013135#pone.0013135.s005http://www.plosone.org/article/info:doi/10.1371/journal.pone.0013135#pone.0013135.s005

7/28/2019 Centrifugal Compaction Causes Changes in the Surface Properties of Bacterial Cells

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