## 3 Results
### Protective Effect of \(\gamma\)-PGA-Based Hydrogels on Probiotic Cells in Low pH  
The results of the protective effect of the selected \(\gamma\)-PGA-based hydrogels on probiotic bacteria in pH 3.0 and 1.5, expressed as Log\({}_{10}\) CFU/mL, are presented in Figures 5 and 6. For the test carried out in pH 3.0, 25 mg hydrogel samples were used, while the test carried out in pH 1.5 was performed for 25 and 50 mg of the hydrogel samples. For free cells and cells entrapped in the PEG400 and PEG1000 hydrogels, similar loss in cell viability was observed (2.62, 2.58, and 2.66 Log CFU/mL, respectively) after incubation for 2 h at pH 3.0 (Figure 5). At the same time, loss in cell viability for bacteria entrapped in the PEG1000-3 arm hydrogel was significantly lower (0.89 Log CFU/mL). After 4 h of the experiment, the viable cell count of the free cells and cells entrapped in the PEG400 and PEG1000 hydrogels further decreased (reaching values of 2.80, 3.84, and 2.86 Log CFU/mL, respectively), although for cells entrapped in the PEG400 hydrogel, the decrease was smaller than that after the first experiment period. Cells entrapped in the PEG1000-3 arm hydrogel maintained the highest viability (5.54 Log CFU/mL). Importantly, the survival rate of probiotic bacteria in the PEG400 and PEG1000-3 arm hydrogels after exposure to acid conditions for 4 h was higher than that for free cells.  
Total loss in viability of free cells was observed after incubation at pH = 1.5 for 2 h, while bacteria entrapped in the hydrogels survived for 4 h under these conditions (Figure 6). After 2 and 4 h, loss in cell viability for bacteria entrapped in 25 mg of the PEG1000-3 arm hydrogel was lower than that for bacteria entrapped in 25 mg of the PEG400 hydrogel. Similar results were observed for the test performed at pH = 3.0. Increasing the hydrogel amount to 50 mg per sam  
Figure 5: Viability of probiotic bacteria (free cells = control and cells entrapped in \(\gamma\)-PGA-based hydrogels) exposed to pH = 3.0 (\(n\) = 3; error bars, standard deviation).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Diameter of Zone of Inhibition (mm)**} \\ \cline{2-5}
**Total Time (h)** & \multicolumn{2}{c}{_S. aureus_} & \multicolumn{2}{c}{_E. coli_} \\ \cline{2-5}  & **Antibiotics** & **Hydrogel + Antibiotics** & **Antibiotics** & **Hydrogel + Antibiotics** \\ \hline
24 & 23.6 \(\pm\) 1.2 & 19.0 \(\pm\) 1.0 & 18.6 \(\pm\) 0.6 & 14.7 \(\pm\) 1.5 \\
48 \({}^{\text{a}}\) & 5.0 \(\pm\) 0.1 & 13.0 \(\pm\) 1.0 & 5.0 \(\pm\) 0.1 & - \\
120 \({}^{\text{b}}\) & 5.0 \(\pm\) 0.1 & 18 \(\pm\) 1.7 & 5.0 \(\pm\) 0.1 & 13.7 \(\pm\) 0.6 \\ \hline \hline \end{tabular}  
After first 24 h, samples were transferred onto freshly seeded tryptic soy agar (TSA) plates, and zones of inhibition were measured again after another 24 h\({}^{\text{a}}\) and 96 h\({}^{\text{b}}\).  
\end{table}
Table 3: Inhibitory effect of PEG1000-3 arm hydrogel discs loaded with antibiotics toward _S. aureus_ and _E. coli_ (\(n\) = 3).  
cell survival rate, e.g., bacteria entrapped in 50 mg of the PEG1000-3 arm hydrogel maintained a cell population of 6.53 Log CFU/mL after incubation for 2 h in pH = 1.5. The viable cell count of cells entrapped in 50 mg of both hydrogels after 4 h of incubation in a solution with pH = 1.5 was higher than 4.0 Log CFU/mL.