Establishment Of Mouse Bacterial Pneumonia Model And T Pharmacodynamic Evaluation Of Recombinant Lysostaphin For MRSA Pneumonia Treatment

Bacterial pneumonia composes up to80%of various pathogens pneumonia in hospitals.In the past half-century, a large number of broad-spectrum or super broad-spectrumantibiotics have been applied in clinical, which did not make pneumonia mortalitydecline, but constantly increased bacterial resistance. It has been reported thatapproximately15%of patients died during hospitalization were associated withpneumonia. The mortality rate of community-acquired pneumonia (CAP) is5%-10%,while the rate of hospital-acquired pneumonia (HAP) is as high as20%-50%.Bacterial infection is the most common reasons pneumonia and could result in evendeath when lack of timely and effective treatment. Antibiotics were widely used as themost powerful tools to control and prevent bacterial infections since they werediscovered. With the extensive use of antibiotics, the antibiotic resistance in a number ofmedically important bacterial pathogens increased, which limited the successfulapplication of antibiotics. Multi-drug resistant organisms including Methicillin-resistantStaphylococcus aureus (MRSA), pan-antibiotic resistant strain of Stenotrophomonasmaltophilia (SMA), Penicillin-resistant Streptococcus pneumonia (PRSP) andVancomycin-resistant Staphylococcus aureus(VRSA)are the main causes of nosocomialdiseases and caused numerous deaths because of the ineffectivity of antibiotic therapy.In this study, bacterial pneumonia mouse models with infections of clinical SAM andMRSA isolates were set up. Mice were immunosuppressed by injected cyclophosphamide and dexamethasone before the infection. Then the mice were givenan inoculum of fresh bacterial suspension intranasally. The clinical symptoms, bodyweight, temperature, lung weight, blood cells and histopathology changes of the micewere monitored at different time points. The results showed that compared with thecontrol group, the model group mice were listless and less active, with body weight andtemperature of mice decreased significantly and quickly, and lung weight increased.Immune cell (WBC, GRAN, LYM, and MONO) counts decreased to a very low levelafter infection. The model group also had a higher mortality rate than control group. Thelung histopathology of model group mice showed obvious abscess, hyperemia, bacterialcolony and loss of normal lung tissue structure, which indicated a significantinflammation symptom.To produce recombinant lysostaphin for the treatment, the sequence of lysostaphin wascloned in pQE30. After inducing and expressing, the protein was harvested and purified.Bactericidal activity of recombinant lysostaphin against Staphylococcus aureus wasconfirmed in vitro. The therapeutic effect of recombinant lysostaphin for mousepneumonia induced by methicillin-resistant Staphylococcus aureus (MRSA) wasevaluated. The results suggested that recombinant lysostaphin can reduce the loss ofbody weight and lung weight, and the increase of spleen weight of mice suffered frompneumonia. It also promote the recovery of body temperature and counts of immunecells, reducing the number of deaths in pneumonia mice. Lysostaphin treatmentextended the survival time diseased mice and made the survival curve shifted right,indicating that the recombinant lysostaphin protects animals from death in the late stageof infection. The therapeutic effect of recombinant lysostaphin for mouse MRSApneumonia was better than vancomycin which is a commonly used clinical antibioticsfor treatment of MRSA infection. The most significant curative effect was achieved withhigh doses of recombinant lysostaphin and treatment started at four hours after infection.There have been research data show that lysostaphin has good antibacterial activityagainst Staphylococcus aureus in vitro and in vivo. And lysostaphin has a potentialvalue of developing into anti-Staphylococcus aureus drug. However, there has beenrarely report about lysostaphin for Staphylococcus aureus pneumonia treatment. Thisexperiment conducted intensive research on treatment effect of recombinant lysostaphinfor MRSA pneumonia, found the effective treatment time and dose of drug. Ourfindings will bring development and application of MRSA pneumonia treatment withrecombinant lysostaphin in clinical to be promising.