| BackgroundStaphylococcus aureusis a worldwide pathogen that can causesuppurant, systematic, even generalized infections.Recently, Methicillin-resistant Staphylococcus aureus(MRSA), which can be resistant to multiple drugs (MDR), increased and spread dramatically, and becomes the cosmopolitanmajor nosocomialpathetic bacteria per saltum.Moreover, carrier rates among healthy people also increased by the time. Due to unrestrained clinical and personal use of antibiotics, China has a high prevalence on MRSA.While studies that focused on hospital-acquired MRSA are extensive, community epidemic MRSA in healthy people is unnoticed. Through the study of drug resistance, molecular typing, and virulence gene tests on community acquired S. aureus and MRSA isolated from urban and rural samples in Shandong province, we can acquire knowledge of epidemiological characteristics of MRSA carried by healthy adults, and help revising better clinical drug usage, infection controllingstrategies, and finally provide evidences to meet the purpose of postponing and reducing drug resistance rate.Objectives1. Describe the resistant and genetic characteristics of S. aureus and MRSA that isolated from urban and rural healthy adults in Shandong province. Provide evidences to infection treatments to S. aureus and MRSA infections in Shandong.2. Discuss the differences and relations of resistance, spa types andpvl gene carrying between urban and rural samples;3. Discover resistance differences among different spa types, and find the molecular basis of resistance characters.Methods1. ScreenedS.aureusand MRSA isolates by using screening agar plates, and verifiedS. aureus by Maldi-TOF and verifiedMRSA by mecA gene.2. Took the minimal inhibitory concentration test by using the 96-hole plate dilution method, and got the MIC values of clinical common use antibiotics, such as Penicillin (PEN), Oxacillin (OXA),Cefoxitin (FOX),Vancomycin (VAN),Daptomycin (DAP),Ciprofloxacin (CIP),Paediatric Compound Sulfamethoxazole (SXT)etc. Results showed in sensitive (S), intermediate sensitivity (I) and resistant (R). Isolates which show resistance to three and more antibiotics were identified as multiple drug resistance (MDR). Compared results by urban and rural resources.3. Tookspa typing by PCR, comparedspa types between urban and rural resources and built relations between drug resistance and spa types.4. Tookpvl test by PCR, and comparedspa types between urban and rural resources.5. Collected and sorted out data by Excel 2016 and analyzed and plotted by STATA 13.0.Results1. Research collected 1241 nasal samples, including 473 samples from urban population and 768 samples from rural area. S. aureusrate was about 20.23% and MRSA rate was approximately 2.66%, which was about 13.15% in S.aureus.Results showed no significant difference between urban and rural samples on S. aureusratesnor MRSA rates.2.87.88% isolates were identified as MDR in MRSA. MRSA resistant rates for PEN, Erythromycin (ERY), Clindamycin (CLI),OXA,Tetracycline (TCY),FOX,Chloramphenicol (CHL), CIP,Gentamicin (GEN),Streptomycin500 (SM500),SXT,DAP,VAN were about 100.00%、93.94%、78.79%、60.61%、57.58%、 57.58%、39.39%、36.36%、33.33%、27.27%、3.03%、0.00%、0.00%, separately. Intermediate sensitivity rate for CHL was about 51.52%.56.88% isolates were identified as MDR in S. aureus. S. aureus resistant rates to former antibiotics were89.45%、62.84%、41.74%、3.21%、25.69%、4.59%、15.60%、23.85%、10.09%、 5.96%、22.48%、0.00%、0.00%,separately.Intermediate sensitivity rate for CHL was about 63.30%.MRSA resistant rates were higher than S. aureus on OXA, CLI, ERY, FOX, SM500 and ERY/CLI. Rural MRSA showed significantly high resistant rate onCIP than urban ones, and no significant difference found to other drugs. Rural MSSA showed significantly high resistant rate on OXA, TCY, CHL, CIP, SXT and FOX, and significantly low on SM500 and GEN, and no significant difference found on other drugs.3. Relatively common spa types in S. aurewsweret437、t002 and t899, and with the rates of 16.33%、14.74%、7.17%. Other more than 50 types such as t011、t078、 t368 were also detected in S. aureus. Major type in urban MRSA was t437, t437 and t899 in rural MRSA, and t002 in urban and rural MSSA.More than 80% isolates were identified as MDR in 3 major spa types, and all showed high resistance to PEN, ERY and CLI. Type of t899 showed generally higher resistance, and t437took the second place. Type of t002 showed lower resistance, only performed higher resistance on GEN and CIP.4. Positive rate of pvl gene in S. aureuswas about 15.94%, which was about 3.88% in urban S. aureus and significantly lower than that of 22.97% in rural. Positive rate of pvl gene in MRSA was about 66.67%, significantly higher than that of 8.65% in MSSA.Discussions1. Study showed that S. aureuspositive rate in samples taken from urban and rural areas of Shandong province was about 20.23%, and that was about 2.33% in MRSA.2. When use antibiotics as treatment to infectious diseases, Penicillin, Erythromycin, Chloramphenicoland other traditional drugs are not good choices. Clindamycin, Oxacillin, Tetracycline and Cefoxitin might have less effects to MRSA infections, but Ciprofloxacin and Paediatric Compound Sulfamethoxazole are generally better. Daptomycin and vancomycinshowed inhibition to MRSA and MSSA isolates, which remain the last line of defense to MRSA infections. Resistance of urban and rural MRSA showed little difference, but rural MSSA showed significantly higher resistance than urban ones.3. S. aureuspresented strong sequence repeatability and high polymorphism on spa gene spot. Study showed that the polymorphism did not only exist between MRSA and MSSA, but also detected between urban and rural samples. What is more, different spa types showed different characters in drug resistance, which indicated that spa types might be the source of the different resistance of different samples.4. The pvl gene carrier rate is significantly higher in MRSA than in MSSA and higher in rural S. aureusthan in urban ones, which cause worse clinical symptoms and prognosis to infectious patients.ConclusionsCommunity healthy adults showed high carrier rate in S. aureusin Shandong province, but MRSA carrier rate was not significantly high and was consistent with the rate in hospitals. The MRSA carrier rate showed no difference between urban and rural areas, while MSSA carrier rate was higher in rural samples.The major spa types were t437, t899 and t002, and the former two mainly existed in MRSA and the later one existed in MSSA. Since the antibiotics resistance differences between urban and rural MRSA and MSSA were consistent with difference in spa types, study inferred that the difference in spa types may be the reason of resistance differences.Isolates showed high resistance to Penicillin, Erythromycin and Clindamycin, while remain sensitivity to Daptomycin and Vancomycin.When comes to clinical treatment with antibiotics, Penicillin, Erythromycin and Clindamycin are no longer good options, and other common drugs like Cefoxitin also need to be used appropriately. Daptomycin and vancomycin remain the last line of defense to MRSA infections. |
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