| ObjectiveMethicillin resistant Staphylococcus aureus (MRSA) is a kind of opportunistic pathogen, which can be found easily in hospital and community. Because of its multi-drug resistance and high mortality rate, the infection caused by MRSA has become a widespread problem in the global medical community, also brings a heavy burden to each country. Therefore, we explored and established a bacteraemia model of mice and kinds of skin infection models infected by MRSA with different methods. Theses animal models can be used to simulate the development mechanism of different diseases caused by MRSA in clinic. We study these models from different perspectives and treat models with antibiotics, which sets the foundation for basic research and development of effective drugs for MRSA infection diseases.MethodsSixty-two specific pathogen free SKH-1hairless mice were randomly divided into4groups:the PBS control, low-dose infection, high-dose infection and drug-treated infected groups. Sterile PBS buffer was given to mice from control group by intravenous tail injection. Meanwhile, mice from the low-dose group were challenged with MRSA (ST-239) suspension containing108CFU/ml organisms by intravenous tail injection, and the same with mice from the high-dose and the drug-treated group with a concentration of109CFU/ml. The bacteraemia models were evaluated from body weight, mortality, blood tests, blood bacterial concentrations, organs infection measuring, pathological examination and molecular biology, and the models were also verified with antibiotic teicoplanin.Eighty specific pathogen free SKH-1hairless mice and thirty-six nude mice of BALB/c strain were randomly divided into4groups:the PBS control, infection model, nude mice and drug-treated groups. Sterile PBS buffer was given to mice from control group by subcutaneous injection. Mice from other groups were challenged with MRSA (ST-239) suspension by subcutaneous injection. Teicoplanin was given locally to infected skin of mice from drug-treated group for3days. After the infection developed, the animal models were evaluated from abscesses appearance, changes of the volumes of abscesses, CFU extracted from skin, pathological morphology and molecular biology.Forty-eight specific pathogen free SKH-1hairless mice were randomly divided into4groups:the subcutaneous injection PBS control, the needle-injury PBS control, the subcutaneous injection group and the needle injury group. Mice from the PBS control groups were treated with sterilized PBS, by subcutaneous injection and being placed on the needle-injury respectively; mice from subcutaneous injection group were challenged with MRS A (ST-239) by subcutaneous injection; mice from needle injury group were applied MRS A on skin after needle injury. Models were evaluated by appearance and volume of abscesses or ulcers, CFU extracted from skin and morphology.ResultsIn the bacteraemia model, the infected mice from different groups all had evident weight loss, the difference was significance (p<0.01), compared with mice from control group. The mortality varied greatly among different groups.4days after infection, the mortality of low-dose group was14%,70%with the high-dose group and10%with the drug-treated group. Sharp changes were found in blood tests, the total WBC increased a lot, with significance difference (p<0.01), compared with normal value. High bacterial concentration was tested in the blood, and the concentration reached105CFU/mL in blood from the high-dose group. Teicoplanin can reduce the bacterial content of the blood, which was supported by the result that the concentration of drug-treated group was lower than those from the low-dose and high-dose groups by one grade. Compared with heart, spleen and lung, liver and kidney are susceptible organs, with a concentration of10CFU/organ from kidney. Teicoplanin also had a significant effect in the reduction of the internal organs infection, sharply reducing the heart, lung and kidney infection. Pathological alterations like varying degrees of inflammation and necrosis were found in many internal organs. In addition, many abscesses were found at the skin. Multi-PCR test results show that the bacterial strain causing bloodstream infection in mice was the experimental strain MRSA.In skin abscess model, the volumes of abscesses were different among groups at the early-mid infection, especially between the nude mice group and drug-treated group (p<0.05). Apparent changes in CFU exacted from skin were observed during the experimental period. The difference of CFU exacted from skin from the nude mice group and the infected model group was significant. There was no dissemination in internal organs of mice from infected model and drug-treated groups. However, varying degrees of dissemination was found in different organs of nude mice, of which the most serious liver and lung, reaching104to105CFU/organ. Pathological alterations were obvious in skin from every infected mouse. The structure of dermis and subcutaneous tissue was destroyed, and abscesses were observed at the early stage of infection, which was instead by fibrous connective tissue at late stage of infection. The result of immunohistochemical in neutrophil was positive, and so was the Multi-PCR for MRSA.In the comparative study of abscess model and injury infection model, two routes of infection resulted in different infection patterns. Subcutaneous injection allowed mice to form clear abscesses, while infection after needle damage made ulcers, with no abscesses formation. At the early-mid infection, the difference in size of abscesses and ulcers was highly significant (p<0.01). At the same period, the difference of CFU exacted from skin between groups was also significant, the4th day and10th day reaching to p<0.05and p<0.01respectively. Evident pathological alterations were observed. Skin of mice from subcutaneous injection group developed abscesses with limited inflammation, while no abscesses and diffuse inflammation from needle injury group. |
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