# Methicillin Resistance of Food-Borne Biofilm-Forming Staphylococcus-Crocei
## 3 Results
### Evaluation of Biofilm-Forming Ability on Tree Types of Surfaces
Likewise, variations in the opposite direction indicate a decrease in the biofilm forming-ability of the isolates. This can be illustrated by isolates 15 (_S. aureus_) and isolate 30 (_S. xylosus_) as good biofilm producers and by isolates 49 (_S. aureus_) and isolate 40 (_S. pasteuri_) as poor biofilm producers (Figure 3). Data from the assessment of the biofilm-forming ability of the 18 isolates on glass and stainless steel are positively correlated with each other (r = 0.54, Table 4) and with Dim1 (Figure 3), indicating that higher Dim1 values correspond, in general, to an increase in the capacity of biofilm formation of the isolates. Likewise, variations in the opposite direction indicate a decrease in the biofilm formation capacity of the isolates. This can be illustrated by isolates 18 (_S. warneri_) and 43 (_S. pasteuri_) as good biofilm producers and by isolates 28 (_S. xylosus_) and 47 (_S. aureus_) as poor biofilm producers (Figure 3). On the other hand, the enumeration method based on cell counts on stainless steel surfaces is positively correlated with the two components, Dim1 and Dim2, which indicates that higher values of Dim1 added to the contribution of Dim2 correspond to an increase in the ability to form biofilm (isolate 43--_S. pasteuri_) (Figure 3). Figure 2: Biofilm-forming ability of CPS and CNS isolates assessed on the three tested surfaces. Means followed by the same letter do not differ statistically from each other, according to the Tukey test at a 5% probability level. Evaluation of Methicillinin Resistance of Biofilms Produced on Polystyrene Surface (P24 Microplates)  
Regarding the evaluation of the susceptibility of biofilms to methicillin, high resistance was observed with all methicillin concentrations tested (up to 32 \(\mathrm{\SIUnitSymbolMicro/mL}\)). Figure 4 shows the logarithmic reduction of biofilm after exposure to the different concentrations of methicillin used. In general, reductions ranging from 1.5 to 2.3 Log CFU/cm\({}^{2}\) were observed. The species _S. saprophyticus_ showed reductions of less than 1.6 Log CFU/cm\({}^{2}\) with all concentrations tested. _S. warneri_ isolates showed no difference in reduction with the different methicillin concentrations tested. _S. aureus_ showed reductions of less than 1.7 log CFU/cm\({}^{2}\), with high concentrations of the antibiotic (16 and 32 \(\mathrm{\SIUnitSymbolMicro/mL}\)). For _S. xylosus_, log reductions varied as a function of antibiotic concentration, from 2 \(\mathrm{\SIUnitSymbolMicro/mL}\) to 8 \(\mathrm{\SIUnitSymbolMicro/mL}\). With the highest concentrations (16 and 32 \(\mathrm{\SIUnitSymbolMicro/mL}\)) of methicillin there was no difference in the logarithmic reductions of the isolates. The greatest reduction in viable cells observed were obtained in _S. warneri_ and _S. xylosus_ species with 8 \(\mathrm{\SIUnitSymbolMicro/mL}\). On the other hand, the smallest reductions (greater difficulty in eradicating biofilms) were observed in the species _S. saprophticus_ (close to 1.5 Log CFU/cm\({}^{2}\) with all methicillin concentrations tested). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Glass** & **Polystyrene** \\ \hline Stainless steel & r = 0.54 & r = 0.04 \\  & _p_-value = 0.02 & _p_-value = 0.86 \\ \hline Polystyrene & r = \(-\)0.09 & \\  & _p_-value = 0.72 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Pairwise Spearman rank order correlation coefficient (r) for biofilm analysis on three different surfaces. Figure 3: Principal component analysis of data from enumeration of cells from biofilms of the 18 _Staphylococcus_ isolates on the three surfaces used: stainless steel (cupons); glass (test tubes), and polystyrene (24\(-\)well polystyrene microplates\(-\)24 microplates). The antibiotic would be considered effective if a 3-log reduction in viable bacterial counts had been achieved. For each methicillin concentration tested, different letters in the columns indicate significant differences (\(p<0.05\)). At least two biological replicates were performed, with two technical replicates each.