INFECTIOUS AGENTS - Food Microbiology Flashcards
What is microbiological sampling of food?
Microbiological sampling of food is the process of collecting and analysing samples of food products to detect the presence of pathogens
What are the four purposes of food microbiological sampling?
Verification of hygienic food production and handling
Determine shelf life performance
Investigate food suspected to be the cause of food poisoning outbreaks
To verify the quality of imported food
What are the two main methods used to process and analyse food microbiological samples?
Culture
PCR
What are the six steps used to culture food microbiological samples?
Sample collection
Sample homogenising
Pre-enrichment
Selective enrichment
Isolation on selective agar
Biochemical or serological confirmation of colonies
How often should sampling collection be carried out within a meat plant?
At least weekly
How many carcasses should be sampled within a meat plant at least one a week?
Five carcasses
For poultry, how many carcasses should be sampled at least one a week?
Fifteen carcases
In a meat plant, what size samples should be taken using destructive sampling techniques (i.e. tissue sampling)?
Four 20cm2 tissue samples
In a meat plant, what size samples should be taken using non-destructive sampling techniques (i.e. swabs and sponge)?
100cm2 samples
What are the three main methods of microbiological sample collection?
Sponge
Swab
Tissue sample
What should be always used when sampling directly from the carcass?
10cm templates
What is homogenisation?
Homogenisation is the process of breaking down and mixing food samples to ensure that the pathogens present in the food are evenly distributed throughout the sample
What machine is used to carry out homogenisation?
Stomacher
What solution is used for pre-enrichment in food microbiology?
Buffered peptone water
What solution is used for selective enrichment in food microbiology?
Selective broth
How long are microbiological food samples left to incubate in pre-enrichment and selective enrichment solutions?
Overnight for both pre-enrichment and selective enrichment
Which microbiological test should always be carried out when culturing microbiological food samples?
Total viable counts (TVC)
Describe how to carry out a total viable count (TVC)
Carry out serial dilution and plate a portion of each dilution onto a sutiable selective agar plate. Count the number of colonies and calculate the total viable count through multiplying the number of colonies with the dilution factor
Which four factors can often cause damage to pathogens on food prior to microbiological sampling?
Heat
Storage
Chilling
Disinfectants
Give two examples of specialised media that can be used to restore damaged pathogens
Tryptone
Buffered peptone water
What are the seven main species of bacteria found in food?
Salmonella
Campylobacter
E.coli 0157
Clostridium perfringens
Staphylococcus aureus
Listeria monocytogenes
Clostridium botulinum
Which anatomical region of the chicken is used for sampling for salmonella and campylobacter?
Chicken neck
Why should Campylobacter be cultured in conditions with increased carbon dioxide (CO2) and decreased oxygen (O2)?
Campylobacter is microaerophillic
Which biochemical test should be used to confirm the presence of campylobacter?
Analytical profile index (API)
Which specific agar should be used to culture E.coli 0157?
Sorbitol MacConkey Agar (SMAC)
Why is sorbitol MacConkey agar (SMAC) used to culture E.coli 0157?
Sorbitol MacConkey agar (SMAC) contains sorbitol as a fermentable sugar and a pH indicator which helps to differentiate E.coli 0157 from other strains of E.coli as E.coli 0157 is unable to ferment sorbitol, resulting in translucent colonies