DNA aptamers selection and characterization for development of impedimetric aptasensor for Bacillus cereus at different growing stages

The physiology(membrane integrity,intracellular esterase and redox activity)of individual pathogenic bacteria is various in different growing phase,which has a profound significance for food safety testing and control.In this work,the aptamers against B.cereus in different growing phase was firstly selected based on whole bacterium-SELEX screening approach.Out of 32 candidate aptamers screened,aptamer B15 and B16 showed relatively high binding affinity with an apparent dissociation constant(Kd value)of 16.134.98 nM and 20.675.23 nM,respectively.A label-free impedance based aptasensor was further fabricated based on the screened aptamer,immobilized onto the GCE/Au surface.With the addition of B.cereus,the electron transfer process was prevented and exhibited a significant decrease in the electron-transfer resistance.Under optimal conditions,the fabricated aptasensor can achieve high sensitive detection of B.cereus as low as 10 cfu/mL.A satisfactory recovery of 90.5%–105.3%was achieved for the B.cereus detection in spiked milk samples,exhibiting its prospect in the sensitive detection of B.cereus in daily life.

Development of a Multiplex PCR for Diagnosis of Staphylococcus aureus, Escherichia coli and Bacillus cereus from Cows with Endometritis

Staphylococcus aureus, Escherichia coli and Bacillus cereus are the major agents of cow endometritis in dairy cows. A multiplex PCR （SEB-mPCR） was established based on the conserved genes of S. aureus, E. coli and B. cereus, and the detection limits were 103, 102 and 103 CFU mL-1, respectively. SEB-mPCR could not amplify genomic DNA of pathogenic bacteria of other common bovine diseases. A total of 309 vaginal discharge samples from cows with endometritis were tested by SEB-mPCR. Of the samples, 23.95% had the three kinds of bacteria detected, 17.15% had S. aureu and E. coli, 9.39% had E. coli and B. cereus, and 9.71% had S. aureus and B. cereus. The rates of infections with S. aureus, E. coli and B. cereus were 11.35, 16.18 and 9.06%, respectively. Therefore, SEB-mPCR has a potential as a diagnosis tool for endometritis in dairy cows.

Microbial populations,sensory,and volatile compounds profling of local cooked rice

Objectives:This study is designed to investigate the microbial populations,sensory,and volatile compounds profling of locally cooked rice stored at room temperature(30°C)on days 0,1,2,and 3(D0,D1,D2,and D3)for the determination of specifc spoilage organisms(SSOs).Materials and Methods:Microbiological,physicochemical,sensory evaluation,and volatile organic compounds(VOCs)analyses were conducted for samples of cooked rice stored at room temperature on days 0,1,2,and 3.SSO of cooked rice was then identifed by linking present organisms with the changes occurring throughout the storage period.Results:Microbiological analysis revealed the presence of spore-forming bacteria,yeast,and moulds,which survived the cooking process.While total viable count exceeded the microbiological limit at 6.90 log CFU/g on D3,panellists deemed cooked rice unacceptable for consumption on D2 at a total sensory score of 11.00,which indicates that D2 was the day cooked rice spoiled.Through culture-dependent and cultureindependent methods,Bacillus cereus was identifed as the sole bacteria observed throughout the storage period,confrming that the bacteria were SSOs.The VOC analysis proposed several metabolites,3-eicosene,1-heptadecene,hexacosane,phenol,4,4ʹ-(1-methylethylidene)bis-,n-nonadecanol-1,and cyclohexanone,as potential spoilage markers of cooked rice.Conclusions:B.cereus is confrmed to be the SSO of cooked rice,in which spoilage occured after 48 h of storage at room temperature.The organoleptic rejection in cooked rice was shown to be linked to the production of various compounds by B.cereus which could be proposed as potential spoilage markers for cooked rice.