Liver cancer is a malignant tumor with the characteristics of high morbidity and mortality.However,the routine detection methods for the liver cancer such as imaging tests and pathological detection are with low specificity and sensitivity.And it's also hard to detect the condition of patients dynamically.Cell-free DNA (cfDNA) is the DNA fragment that is away from the extracellular and exists in the blood,which contains genetic information from the organism.The related disease information could be reflected on the cfDNA in patients with liver cancer,indicating that cfDNA has great potential in the screening,diagnosis,treatment and prognosis of liver cancer.The clinical applications of cfDNA can make up for the deficiency of existing detection methods and achieve noninvasive and dynamic monitoring of liver cancer.This article will present a review on the progress of clinical applications of cfDNA in liver cancer.

Objective To test the antimicrobial susceptibility of Staphylococcus aureus from children with impetigo,and to assess the differences in randomly amplified polymorphic DNA profiles between sensitive and resistant Staphylococcus aureus strains.Methods Secretion specimens were obtained from the impetiginous lesions of 178 children,and subjected to bacterial culture.The susceptibility of 162 Staphylococcus aureus isolates against 21 antibiotics was tested.Randomly amplified polymorphic DNA PCR(RAPD-PCR)was performed to characterize the genotype of Staphylococcus aureus.Results Totally,180 bacterial strains were isolated from 178 children with impetigo in Chengdu,including 162(90.00％)Staphylococcus aureus strains.Of the 162 Staphylococcus aureus strains,148 were methicillin sensitive Staphylococcus aureus(MSSA),14 methicillin resistant Staphylococcus aureus(MRSA).The most active antibiotic was minocycline,followed by teicoplanin,quinupristin,vancomycin and nitrofurantoin,while the resistance rate to penicillin was highest,followed by that to erythromycin,clindamycin,compound sulfamethoxazole and tetracycline.All the Staphylococcus aureus isolates were sensitive to fusidic acid,nitrofurantoin,vancomycin,minocycline and teicoplanin.According to RAPD-PCR,the 162 Staphylococcus aureus strains were divided into 8 genotypes,with the three most prevalent genotypes being Ⅲ(31.48％),Ⅱ(26.54％)and Ⅵ(25.93％),which accounted for 65.43％(106/162)in all the strains.The 148 MSSA strains fell into 8 genotypes,with genotype Ⅲ(50 strains,33.78％),Ⅵ(39 strains,26.35％)and Ⅱ(33 strains,22.30％)being the most prevalent genotypes;the 14 MRSA strains fell into 3 genotypes,i.e.,genotype Ⅱ(10 strains,71.43％),Ⅵ(3 strains,21.43％),and Ⅲ(1 strain,7.14％).Conclusions Staphylococcus aureus is the most prevalent pathogenic bacteria in children with impetigo in Chengdu area,which is highly sensitive to minocycline,teicoplanin and quinupristin,and falls into 8 genotypes according to RAPD-PCR with genotype Ⅲ being the most common genotype.