(190al) Not Always Resistant: Antibiotic Susceptibility of Bacterial Cells Changes during Early Stage Biofilm Formation

Huan Gu^1,2, Zhaowei
Jiang^1,2,and Dacheng Ren^1,2,3,4*

¹Department
of Biomedical and Chemical Engineering, ²Syracuse Biomaterials
Institute, ³Department of Civil and Environmental Engineering, ⁴Department
of Biology, Syracuse University, Syracuse, NY 13244, USA

Bacteria
can attach to essentially any surface and form multicellular structures known
as biofilms. A hallmark characteristic of biofilms is the high-level antibiotic tolerance (up to 1000
times) compared to planktonic cells. 
However, how antibiotic susceptibility changes in these sessile cells
during biofilm formation is still not clear. Here, we report our new findings
of how antibiotic susceptibility changes during early stage biofilm formation
and demonstrate that biofilm cells are not always more tolerant to antibiotics
than planktonic cells. Specifically, the
antibiotic susceptibility of Escherichia
coli cells attached on glass surfaces in lysogeny broth increased in the
first 2.5 hours due to cell-surface interactions, consistent with the increase
in transcriptional activities. After this stage, biofilm antibiotic
susceptibility decreased as cells start to produce biofilm matrix. However, the
embedded biofilm cells remained active and thus sensitive to antibiotics if dispersed from the surface. Using patterned
biofilm formation, we discovered that E.
coli biofilm cells are more
susceptible to antibiotics due to the active interactions at this stage because cells in interactions are more
sensitive to antibiotics than cells embedded in clusters.
Collectively, these results shade new lights on bacterial antibiotic resistance
during biofilm formation and may help the design of better antifouling surfaces.