ABSTRACT
We investigated the contamination,antimicrobial resistance and the virulence genes carriage of Salmonella spp. in duck slaughter chain.Suspected strains were isolated from slaughterhouse samples according to GB 4789.4-2010 and identi-fied by duplex PCR,and then the positive strains were used for serotype analysis.Subsequently,positive strains were tested against 10 different antimicrobial agents using Kirby-Bauer disk diffusion method,the results were determined on the basis of CLSI standard.Finally,9 virulence genes were detected among positive strains by PCR.The results showed that 9 9 Salmonella isolates were recovered from 343 samples and total isolation rate was 28.86%.The prevalence of Salmonella before slaughte-ring,at depilation stage,at evisceration stage,in duck meat and after slaughtering was 45.71%,22.68%,24.72%, 38.33% and 25.81%,respectively.Seven serotypes were de-tected and most of them were S.Indiana,S.Newlands,S. Anatum.The Salmonella isolates were most frequently re-sistant to nalidixic acid(91.92%),the resistance rates of tet-racycline (43.43%),ampicillin (42.42%),trimethoprim-sulfamethoxazole (34.34%),ciprofloxacin (29.29%),ceftri-axone (27.27%),gentamycin (24.24%),and kanamycin (22.22%)were at a medium level.The resistance rates of amoxicillin-clavulanic acid (9.09%)and minocycline (6.06%)were relatively low.The multi-drug resistance rate of Salmonella isolates,which was 47.47%,showed a high especially in S.Indi-ana,S.Typhi and S.Typhimurium.It was notable that the harboring rates of virulence gene spvR(94.95%),avrA (93.94%),ssaQ(90.91%),mgtC(87.88%),sopB(83.84%),bcfC(80.81%),siiD(77.78%)among Salmonella isolates were at high level,in contrast to the lower carriage rates of spvB(29.29%),spvC (11.11%).In summary,the results indica-ted that the duck slaughter chain was easily contaminated by Salmonella spp.with different serotypes,different antibiotic re-sistant patterns and high virulence genes harboring rate.Relevant slaughterhouse and departments should strengthen supervi-sion in sanitation and manage the use of antimicrobial agents,to guarantee food safety and public health．
ABSTRACT
The phyA(m) gene encoding acid phytase and optimized neutral phytase phyCs gene were inserted into expression vector pPIC9K in correct orientation and transformed into Pichia pastoris in order to expand the pH profile of phytase and decrease the cost of production. The fusion phytase phyA(m)-phyCs gene was successfully overexpressed in P. pastoris as an active and extracellular phytase. The yield of total extracellular fusion phytase activity is (25.4+/-0.53) U/ml at the flask scale and (159.1+/-2.92) U/ml for high cell-density fermentation, respectively. Purified fusion phytase exhibits an optimal temperature at 55 degrees C and an optimal pH at 5.5~6.0 and its relative activity remains at a relatively high level of above 70% in the range of pH 2.0 to 7.0. About 51% to 63% of its original activity remains after incubation at 75 degrees C to 95 degrees C for 10 min. Due to heavy glycosylation, the expressed fusion phytase shows a broad and diffuse band in SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). After deglycosylation by endoglycosidase H (EndoH(f)), the enzyme has an apparent molecular size of 95 kDa. The characterization of the fusion phytase was compared with those of phyCs and phyA(m).