Study on relationships between the expressions of cidA and lrgA and biofilm formation of Staphylococcus epidermidis clinical isolates
Objective To investigate the relationships between the expressions of cidA and lrgA and the biofilm formation of Staphylococcus epidermidis clinical isolates. Methods Thirty-nine S. epidermidis clinical isolates were divided into biofilm formation group and non-biofilm formation group according to adhesion assays and icaA amplification, 20 strains for biofilm formation group and 19 strains for another group respectively. Amplify cidA and lrgA fragment with PCR, detect mRNA levels of cidA and lrgA with RT-PCR and then calculate the ratios of cid/lrg mRNA. Results All of the 39 isolates of S. epidermidis existed cidA and lrgA gene.Select 2 strains of S. epidermidis, Y36 and Y26, at random for detecting the cidA and lrgA mRNA levels of different phases, the highest level of cidA mRNA shows on 4 h's culture while lrgA shows on6 h. The relative expression levels of cidA of 39 isolates of S. epidermidis were 0.340 + 0.250 in biofilm formation group and 0. 406 +0. 408( P =0. 541 ) in non-biofilm formation group for 4 h culture, while the relative expression levels of lrgA were 0.325 ± 0.218 and 0.253 ± 0.211 respectively ( P = 0. 299). There were no significant differences between these two groups. The ratios of cid/lrg mRNA were 1.067 ±0.529 and 1.958 ±1.877 respectively, the difference of population distribution was significant( P = 0.001 ). Conclusion The expressions of cidA and lrgA of S. epidermidis clinical isolates may be time-limited. There were no significant differeces of expressions of cidA and lrgA between biofilm formation group and non-biofilm formation group. The ratios of cid/lrg mRNA maybe have some biological significance. 
 
Key words: 
Staphylococcus epidermidis; Bacterial biofilm; cidA; lrgA