Study Of Formation Factors On Biofilms Of Staphylococcus Aureus From Raw Cow Milk Samples

Staphylococcus aureus isolated from fresh cow milk were compared with the type strain, according to 16S rDNA sequence analysis showed that their homology can get to 98% .Established and validated the method which including cultivation and qualitative analysis and quantitative analysis of strains of Staphylococcus aureus biofilm . Staphylococcus aureus biofilm were observed according to the scanning electron microscopy and silver staining methods, the results showed that mature biofilm can be formed after 12h .And the shape of biofilm is blank lamellar or floccules according to the silver staining methods ,and scanning electron microscopy observed that there is much mucus wire between the bacterias .The viable count of Staphylococcus aureus biofilm were tested by the method of ultrasonic plate and the result showed that viable count of biofilm can get to 105cfu/mL and viable count of biofilm has no significant change during the 7 days which is the gowth cycle.Single factor tests and orthogonal tests showed that the best condition is that:power is 100w, temperature is 35℃and the time is 12min by the Ultrasonic plate method which method can be used to remove and dissection the biofilm of Staphylococcus aureus on thesurface of stainless steel. The model of Response surface analysis were established and the analysisi of variance results show that the model is the significant (p<0.05) and coefficient of determination is 0.9107(R2) and the correction factor is 0.7172(adj R2).The model is fit well with the actual situation.And three factors which impact on the effection of ultrasonic plate method as follows:power> time> temperature.Formation conditions of Staphylococcus biofilm were studiedand results showed that cultured temperature, exogenous sugars, sodium chloride, mixed culturation with lactobacillus, planktonic bacteria, metal cations and chelating agents ( EDTA) and other factors can affect the growth of biofilm.The optimum temperature of Staphylococcus aureus is benefit to the formation of biofilm. Formation of biofilm can be induced accoreding to adding to the different desity exogenous sugar and the result showed that fructose and glucose affected the formation of biofilm significantly (P<0.001). The growth of biofilm could be promoted by adding to little sodium chloride.lactobacillu (Streptococcus thermophilus, Lactobacillus bulgaricus) were mixed with Staphylococcus aureus when they were cultured and the result showed that lactobacillu can control the formation of biofilm.And planktonic bacteria can directly affect the the formation of biofilm , planktonic bacteria was inversely correlated with the formation of biofilm.The study that divalent cations and the Chelation of EDTA effect the growth of on S.aureus biofilm show that Ba²⁺ and Ca²⁺ have no significant effection on the formation of biofilm,and Mg²⁺ can enhance the formation of biofilm .And the biofilm can be induced by Fe²⁺,but if the Fe²⁺ is lack of or too high in the culture media could control the growth of S.aureus biofilms. The biofilm could against or dispersed by the EDTA,but divalent cations can block EDTA-induced detachment and the effection order is Fe²⁺ï¹¥Ca²⁺ï¹¥Mg²⁺ï¹¥Ba²..