## 3 Results
In a month-to-month comparison, SCC of group B are significantly higher than the ones of group A in April and May while in June the situation reverses, and group A's SCC are higher than those of group B (Figure 1). Likewise, when compared on a month-to-month basis the CNS counts of the two groups, group B shows statistically significant higher counts every month except from July where no significant difference is noted (Figure 2). Figure 1: Comparison of somatic cell counts (SCC) between the samples of group A and B during the six months of observation (* denotes statistically significant differences between Group A & B for the specific month according to ANOVA \(p\) < 0.05). In our study, once per month and for the whole milking period (March-August) a milk sample was tested from every bulk tank (20 tanks for group A and 20 tanks for group B). Every sample was first tested by 10 (ten) different methods (all of them based on the inhibition of growth principle) to escape the particularities of each method and then it was boiled and tested again. The samples which were found positive by at least one method after heating, were characterized as true positive (Table 2). Table 2 presents an interesting comparison. Group A shows 54 positives out of 120 samples before heating while Group B shows 42 out of 120 samples (45.00% and 35.00%, respectively) before heating. After heating the percentage is 18.34% true positive samples for group A (22/120) and 5.84% (7/120) true positive samples for group B. _S. aureus_ was isolated from two samples in group A in the beginning of the milking period and from four samples in group B, three of which in the first half of the milking \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & \multicolumn{6}{c}{**Group A**} \\ \hline  & **March** & **April** & **May** & **June** & **July** & **August** & **Total** \\ \hline BH (+) & 9 & 7 & 15 & 11 & 4 & 8 & 54 \\ \hline AH (+) & 6 & 2 & 7 & 6 & 0 & 1 & 22 \\ \hline FP & 3 & 5 & 8 & 5 & 4 & 7 & 32 \\ \hline  & \multicolumn{6}{c}{**Group B**} \\ \hline  & **March** & **April** & **May** & **June** & **July** & **August** & **Total** \\ \hline BH (+) & 5 & 5 & 5 & 5 & 9 & 13 & 42 \\ \hline AH (+) & 1 & 0 & 3 & 0 & 3 & 0 & 7 \\ \hline FP & 4 & 5 & 2 & 5 & 6 & 13 & 35 \\ \hline \end{tabular} BH (+): positive samples before heating/20 samples, AH (+): positive samples after heating (true positive)/20 samples, FP: false positive samples/20 samples.  
\end{table} 
Table 2: Positive, true positive and false positive samples for antibiotics residues. Figure 2: Comparison of Coagulase negative Staphylococcus (CNS) counts between the samples of group A and B during the six months of observation (* denotes statistically significant differences between Group A & B for the specific month according to ANOVA \(p<0.05\)). period and one more in the middle of the second half. _E. coli_ was isolated from 1 sample in group B and from four samples in group A, one every other month and one in August (Table 1). According to the results of the susceptibility study, most of the _S. aureus_ strains either from the group A or the group B were sensitive to the majority of antibiotics with few exceptions (Table 3). From the eight _S. aureus_ isolates, two belonged in group A and six in group B. Both isolates from group A proved multi resistant in 7 out of 21 drugs while those from group B were sensitive (one strain), resistant in one or two antibiotics (four strains) and in one case in three. Seven _E. coli_ strains from group A and one strain from group B were also screened for their susceptibility in 16 antibiotics. Almost all strains (except one) were multi resistant to at least three and up to seven antibiotics.