Mastitis is a cost effective disease and a source of heavy economical losses to dairyindustry, worldwide.We aimed to detect the prevalence of sub-clinical and clinicalcoliform mastitis in east China and to check the causative organism of mastitis theirantimicrobial sensitivity profile as well as molecular epidemiology of major mastitispathogens including Staphylococcus aureus from contagious mastitis and Escherichia colifrom environmental mastitis.Milk samples were collected from 299 cows infected withclinical mastitis to evaluate the prevalence of coliform mastitis and 1660 quarters milksamples randomly collected from 415 lactating cows for detection of subclinical mastitis(SCM) at selected dairy farms in eastern China during March to November 2011.A total of103/299 (34.44％) E.coli identified from clinical mastitis milk samples.Hangzhou mastitistest (HMT) carried out to detect the subclinical mastitis and the results showed 217(52.28％) cows and 336 (20.24％) quarters were positive for SCM.Occurrence of SCM inleft rear quarter was high (26.74％).Statistical analysis of risk factors showed, cows with 6-9 years age (P=0.046; Odds ratio (OR), ±1.414; 95％ confidence interval (CI)=1.006-1.988and 60.7％), cows with 4-7 calves (P=0.028; OR, ±1.502; 95％ CI=1.044-2.160 and 62.2％)and cows in late stage of lactation (P=0.039; OR, ±1.947; 95％ CI=1.023-3.702 and 68％)were more susceptible to SCM.All the 115 (34.22％) organisms from SCM milk samplesand 103 Escherichia coli from CM samples were confirmed by PCR techniques (16SrDNA).Some other gram-negative organisms like Pseudomonas, Klebsiella were alsofound in mastitic cattle milk and showed variable resistance against used antimicrobials.MIC results ofS.aureus revealed that all the isolates were sensitive against cefquinome butwere resistant to erythromycin, however isolates showed resistance to penicillin G (47％),ampicillin (91％), methicillin (29％), chloramphenicol (32％) and (59％) againstoxytetracycline.Furthermore, 13 virulence factors genes and 07 antimierobial resistancedeterminants including mecA and blaZ genes of S.aureus isolates were investigatedthrough PCR.Among all the tested virulence genes spaX gene was found in all isolates butother genes cna, spaIg, nuc, clfA,fnbpB, hlA, hlB and sea were also present in 35％, 79％,85％, 59％, 35％, 85％, 71％ and 38％ isolates, respectively.The macrolide resistancedeterminants ermB and ermC were found in all isolates.Moreover blaZ and tetK weredetected in 82％ and 56％ isolates, respectively.The statistical analyses showed anunconditional but potentially association of co-presence between clfA, fnbpB, hlB and seawith penicillin G, ciprofloxacin, methicillin, chloramphenicol, trimethoprim andoxytetracycline (P≤0.05).Genotyping of S.aureus isolates through REP-PCR showed 7distinct genotypes prevalent in this region.Furthermore, phenotypically methicillin resistantS.aureus (MRSA) isolates were also prevailing in subclinical mastitis infection withoutbearing mecA gene, which were multi drug resistant and more pathogenic than MSSAisolates.Besides, E.coli prevalence was higher in clinical mastitis milk samples but no anyisolate found in SCM milk samples.All the 103 E.coli isolates were investigated for theirserotypes, genotypes, virulence and antimicrobial resistance genes.Minimum inhibitoryconcentration (MIC) results of E.coti showed (93 to 99％) of isolates were resistant to betalactam, (40 to 74％) to fluoroquinolones, (54 to 66％) to cephalosporins, (91％) tooxytetracycline, (82％) to gentamicin, (88％) to SUL-TRM and were sensitive to florfenicol.Of the sixteen serotypes characterized through serum agglutination test, O39 followed byO92 and O123 were the most predominant serovars in this region.Most prevalent virulencegenes in E.coli isolates were TraT, FimH, papC, iucD, F4 (K88) and sfa.Among allinvestigated resistance genes, 48％ isolates carried CTX-M and qnrS.In addition tetA, tetB,sul1, sul2 were also found in high frequency.Statistic analysis revealed an unconditionalassociation between virulence and resistance genes on the basis of their co-presence.ERIC-PCR used for genotyping ofE.coli isolates which showed 10 distinct genotypes prevailingin this region.Moreover, different serotype bearing isolates were genetic similar.This studyreports that coliform mastitis is increasing in this region and emergence of multi drugresistance in S.aureus, E.coli and other gram-negative organisms limits the treatmentoptions for mastitis and also poses threat of spreading antibiotic resistant isolates fromcattle milk to human.This is first up to date report on the prevalence of bovine mastitis, itsvarious types, its causative organisms their serotypes and genotypes plus prevalentvirulence factors and antimicrobial sensitivity patterns which will obviously helpful indesigning strategic measures to control bovine mastiffs in this region of eastern China.