The objective of this study was to determine the effect of sodium lactate on the survival of Listeria monocytogenes, Escherichia coli O157: H7, and Salmonella spp. in cooked ham during storage at refrigerated and abus...The objective of this study was to determine the effect of sodium lactate on the survival of Listeria monocytogenes, Escherichia coli O157: H7, and Salmonella spp. in cooked ham during storage at refrigerated and abuse temperatures. Cooked ham was added with 0% - 3% lactate, inoculated with a multiple-strain mixture of L. monocytogenes, E. coli O157: H7, or Salmonella spp. and stored at 4oC - 15oC for up to 35 day. The growth of the three pathogens was inhibited in ham containing 3% lactate, and no growth of E. coli O157: H7 and Salmonella spp. occurred at the lowest storage tem- peratures of 6 and 8oC, respectively. In ham containing no lactate, the average growth rates were 0.256 - 0.380 log CFU/day for L. monocytogenes at 4oC - 8oC, 0.242 - 0.315 log CFU/day for E. coli O157: H7 at 8oC - 15oC, and 0.249 - 0.328 log CFU/day for Salmonella spp. at 10oC - 15oC. The addition of 1% or 2% lactate significantly (P < 0.05) reduced the growth rates of the three pathogens, and the effect was more profound at lower temperatures. Salmonella spp. were more sensitive to the effect of lactate than L. monocytogenes and E. coli O157: H7. Polynomial models were developed to describe the growth rates of the three pathogens as affected by the lactate concentration and storage tem- perature. Results from this study demonstrate the effect of lactate on the growth of L. monocytogenes, E. coli O157: H7, and Salmonella spp. in cooked ham and indicate the effective lactate concentrations and storage temperatures that can be used to enhance the microbiological safety of ready-to-eat ham products.展开更多
Almond pudding is a common traditional Iranian complementary food for infants after starting solid foods. Escherichia coli O157:H7 is one of the leading pathogenic microorganisms that cause serious foodborne disease i...Almond pudding is a common traditional Iranian complementary food for infants after starting solid foods. Escherichia coli O157:H7 is one of the leading pathogenic microorganisms that cause serious foodborne disease in different populations including infants. The large intestine of breast-fed infants is colonized predominantly by bifidobacteria, which have a protective effect against acute diarrhea. The study objective of this research was to screen the survival characteristics of E. coli O157:H7 as well as four strains of Bifidobacterium subspecies (spp.) in almond pudding. The bacterial strains were studied after three and six hours of incubation at 37℃ in-vitro. Luria-Bertani (LB) broth was used as a basic medium for both Bifidobacterium spp. and E. coli experiments in anaerobic and aerobic conditions, respectively. The viability of Bifidobacterium spp. increased from 2.46 ± 0.2 to 6.57 ±1.3 log10 CFU/ml in low inoculum and from 4.53 ± 0.7 to 7.2 ± 0.4 in high inoculum experiments in 6 hours. However, the growth of E. coli O157:H7 from 3.12 ± 0.2 to 4.99 ± 0.1 log10 CFU/ml was significantly (P < 0.05) lower compared to Bifidobacterium spp. The results illus- trate impaired growth of E. coli O157:H7 and enhanced growth of Bifidobacterium spp. in almond pudding. The finding demonstrated that almond pudding in infant’s diet may indirectly enhance the protection against survival and growth of E. coli O157:H7 by increasing the Bifidobacterium spp. populations in infant’s gastrointestinal system.展开更多
To construct and express the fusion protein Stx2B-IntiminC300 of EHEC O157 ： H7, and to further investigate its immunoprophylactic potential, the gene of Stx2B （stx2b） from EHEC O157：H7 chromosome was cloned into ...To construct and express the fusion protein Stx2B-IntiminC300 of EHEC O157 ： H7, and to further investigate its immunoprophylactic potential, the gene of Stx2B （stx2b） from EHEC O157：H7 chromosome was cloned into pMD18-T vector. Thereafter, the amplified gene was cloned into prokary- otic expression plasmid pET-28a （ ＋ ）-eaeC300, which was constructed previously. The recombinant pasmid pET-28a（ ＋ ）-stx2b-eaeC300 was transformed into E. coli BL21 （DE3）. After inducement, the protein Stx2B-IntiminC300 was successfully expressed and analyzed with sodium dodecyl sulfate polyacrylamide gel electrophoresis （SDS-PAGE）, Western blotting and N-terminal amino acid residual sequencing. To evaluate its immunoprophylactic potential, it was primarily purified by ion-exchange chromatography and injected into 30 BALB/c mice with AI（OH）3 in the subscapular region. Ten days after the last booster vaccination, 20 mice were attacked with EHEC O157：H7 lysate and the protective efficacy was observed. In the present study, the gene of Stx2B-intiminC300 was successfully cloned into pET-28a （ ＋ ） vector. The results of SDS-PAGE and Western blotting assay showed that the fusion protein was successfully expressed in the inclusion body form, accounting for 25 % of total expression products, and its molecular weight was about 43 kDa. The result of the N-terminal amino acid residual sequencing showed that it was identical to that of the molecular designed. The purity was about 75 % after primary purification. Animal tests revealed that the fusion protein Stx2B-intiminC300 has elicited high titer of protective antibody relatively. These results demonstrate that the fusion protein Stx2B-IntiminC300 is successfully expressed in prokaryotic expression system and shows certain immunoprophylactic potential.展开更多
文摘The objective of this study was to determine the effect of sodium lactate on the survival of Listeria monocytogenes, Escherichia coli O157: H7, and Salmonella spp. in cooked ham during storage at refrigerated and abuse temperatures. Cooked ham was added with 0% - 3% lactate, inoculated with a multiple-strain mixture of L. monocytogenes, E. coli O157: H7, or Salmonella spp. and stored at 4oC - 15oC for up to 35 day. The growth of the three pathogens was inhibited in ham containing 3% lactate, and no growth of E. coli O157: H7 and Salmonella spp. occurred at the lowest storage tem- peratures of 6 and 8oC, respectively. In ham containing no lactate, the average growth rates were 0.256 - 0.380 log CFU/day for L. monocytogenes at 4oC - 8oC, 0.242 - 0.315 log CFU/day for E. coli O157: H7 at 8oC - 15oC, and 0.249 - 0.328 log CFU/day for Salmonella spp. at 10oC - 15oC. The addition of 1% or 2% lactate significantly (P < 0.05) reduced the growth rates of the three pathogens, and the effect was more profound at lower temperatures. Salmonella spp. were more sensitive to the effect of lactate than L. monocytogenes and E. coli O157: H7. Polynomial models were developed to describe the growth rates of the three pathogens as affected by the lactate concentration and storage tem- perature. Results from this study demonstrate the effect of lactate on the growth of L. monocytogenes, E. coli O157: H7, and Salmonella spp. in cooked ham and indicate the effective lactate concentrations and storage temperatures that can be used to enhance the microbiological safety of ready-to-eat ham products.
文摘Almond pudding is a common traditional Iranian complementary food for infants after starting solid foods. Escherichia coli O157:H7 is one of the leading pathogenic microorganisms that cause serious foodborne disease in different populations including infants. The large intestine of breast-fed infants is colonized predominantly by bifidobacteria, which have a protective effect against acute diarrhea. The study objective of this research was to screen the survival characteristics of E. coli O157:H7 as well as four strains of Bifidobacterium subspecies (spp.) in almond pudding. The bacterial strains were studied after three and six hours of incubation at 37℃ in-vitro. Luria-Bertani (LB) broth was used as a basic medium for both Bifidobacterium spp. and E. coli experiments in anaerobic and aerobic conditions, respectively. The viability of Bifidobacterium spp. increased from 2.46 ± 0.2 to 6.57 ±1.3 log10 CFU/ml in low inoculum and from 4.53 ± 0.7 to 7.2 ± 0.4 in high inoculum experiments in 6 hours. However, the growth of E. coli O157:H7 from 3.12 ± 0.2 to 4.99 ± 0.1 log10 CFU/ml was significantly (P < 0.05) lower compared to Bifidobacterium spp. The results illus- trate impaired growth of E. coli O157:H7 and enhanced growth of Bifidobacterium spp. in almond pudding. The finding demonstrated that almond pudding in infant’s diet may indirectly enhance the protection against survival and growth of E. coli O157:H7 by increasing the Bifidobacterium spp. populations in infant’s gastrointestinal system.
文摘To construct and express the fusion protein Stx2B-IntiminC300 of EHEC O157 ： H7, and to further investigate its immunoprophylactic potential, the gene of Stx2B （stx2b） from EHEC O157：H7 chromosome was cloned into pMD18-T vector. Thereafter, the amplified gene was cloned into prokary- otic expression plasmid pET-28a （ ＋ ）-eaeC300, which was constructed previously. The recombinant pasmid pET-28a（ ＋ ）-stx2b-eaeC300 was transformed into E. coli BL21 （DE3）. After inducement, the protein Stx2B-IntiminC300 was successfully expressed and analyzed with sodium dodecyl sulfate polyacrylamide gel electrophoresis （SDS-PAGE）, Western blotting and N-terminal amino acid residual sequencing. To evaluate its immunoprophylactic potential, it was primarily purified by ion-exchange chromatography and injected into 30 BALB/c mice with AI（OH）3 in the subscapular region. Ten days after the last booster vaccination, 20 mice were attacked with EHEC O157：H7 lysate and the protective efficacy was observed. In the present study, the gene of Stx2B-intiminC300 was successfully cloned into pET-28a （ ＋ ） vector. The results of SDS-PAGE and Western blotting assay showed that the fusion protein was successfully expressed in the inclusion body form, accounting for 25 % of total expression products, and its molecular weight was about 43 kDa. The result of the N-terminal amino acid residual sequencing showed that it was identical to that of the molecular designed. The purity was about 75 % after primary purification. Animal tests revealed that the fusion protein Stx2B-intiminC300 has elicited high titer of protective antibody relatively. These results demonstrate that the fusion protein Stx2B-IntiminC300 is successfully expressed in prokaryotic expression system and shows certain immunoprophylactic potential.
