| Staphylococcus epidermidis is a common symbiotic bacterium on the surface of human skin and is considered as a contaminated bacterium for a long time. However, investigators hardly study the molecular epidemiology of S. epidermidis due to the lack of systematic research data. In recent years, it was found that the majority of blood stream infections in infants and catheter related blood stream infections (CRBSI) were caused by S. epidermidis. The main characteristics of clinical isolates were methicillin resistance and biofilm formation. Different molecular characteristics of S. epidermidis have different epidemiologic features and pathogenecity. The most important pathogenic mechanism of S. epidermidis is biofilm formation. It is important to study the molecular characteristics and the mechanism of biofilm formation of clinical isolates in the prevention and treatment of related infections. S. epidermidis, which has the ability of biofilm formation, can cause chronic and recurrent infections, so treatment of related infections brings a huge trouble to the clinicians. Thus, it is urgent to find a new drug, which is used against S. epidermidis infections, especially for the drug that can effectively kill the bacteria enveloped in biofilm. Studies showed that gallium nitrate that is used to treat malignant hypercalcemia, can inhibit biofilm formation in Pseudomonas aeruginosa. Thus, we speculate gallium nitrate also have an ability of biofilm inhibition in S. epidermidis. Meanwhile, this paper will explore the molecular biological characteristics of S. epidermidis by SCCmec and agr genotyping, and further explore the ability of biofilm forming, carrier situation of biofilm’s related genes and the pathway of biofilm production. In addition, this study will analyze the anti-biofilm function of gallium nitrate, and lay a foundation for the research of treating related infections.We adopted confocal laser scanning microscope (CLSM) and semiquantitative biofilm adhesive test to determine biofilm formation of 86 S. epidermidis strains isolated from the clinical blood specimens. Here 58 strains of S. epidermidis were positive for biofilm formation (67.44%). This indicates that the majority of the isolated S. epidermidis stains have biofilm forming ability. By analyzing the drug-resistant genes and phenotypes,75 strains carried mecA genes (87.21%). Moreover, for 8 antibiotics (gentamycin, ciproflaxin, levofloxacin, SMZ, erythromycin, clindamycin, penicillins and oxacillin), the drug resistance rates of Methicillin-Resistant S. Epidermidis (MRSE) were higher than that of Methicillin-Sensitive S. epidermidis (MSSE), indicating the other drug-resistant genes may be integrated into the SCCmec gene cassette with mecA genes, and then showed the relevance between drug resistance and mecA genes.Results of SCCmec and agr genotyping using multiplex PCR indicated that there was a regional difference and were mainly SCCmec Ⅰ, Ⅳ, Ⅴ types and agr I type. S. epidermidis SCCmec gene cassette polymorphism is beneficial to understand the epidemiologic features of MRSE. By analyzing the relationship between molecular biological characteristics and drug-resistant phenotypes, it showed that SCCmec III type had a higher drug resistance rate to 7 antibiotics simultaneously, including SMZ, ciproflaxin, gentamycin, levofloxacin, ripampicin, erythromycin and clindamycin. It may be attribute to longer SCCmec III fragments and multiple drug resistance genes, and indicate drug resistance performance and molecular biological characteristics have relevance. By virtue of PCR technology, biofilm related genes in clinical strains were detected and these genes displayed different carrier situations. Since the process of biofilm formation is complicate and the biofilm can be developed by multiple approaches, only carriers of a single gene were studied and displayed no relevance with biofilm formation. Generation situation of the strain polysaccharide intercellular adhesin (PIA) detected by Congo red-broth agar indicated the biofilm formation may has both PIA-dependent and PIA-independent approaches. Morphological differences of biofilm formed in the two approaches were analyzed by virtue of confocal laser scanning microscope. With PIA, biofilm will be multilayered, because in PIA independent biofilm compound, though proteins can replace PIA to mediate biofilm formation since it is not easy to form three-dimensional stereochemical structure.Analysis of antibacterial action and anti-biofilm function of gallium nitrate towards PIA-dependent biofilm formation strains and S. epidermidis standard strains showed that the same MIC value with 312.50μmol/L in both clinical strains and laboratory standard strains. By selecting 300μmol/L and 1000μmol/L of gallium nitrate to act on biofilm in initial stage and biofilm in mature period, respectively, it was found that gallium nitrate played an inhibitory effect on S. epidermidis PIA dependent biofilm formation, especially in the initial stage. This study also found that the inhibitory effect of gallium nitrate on biofilm have concentration dependency.In conclusion, the majority of S. epidermidis derived from the blood specimens were SCCmec type I, IV, V and agr type I MRSE with the ability of biofilm formation. The mechanisms of biofilm formation included PIA-dependent and PIA-independent pathways. Gallium nitrate is able to inhibit PIA-dependent biofilm formation of S. epidermidis, and it can be considered as a novel agent for treatment of S. epidermidis. |
PDF Full Text Request