Food Microbiology - The Basics
-
Upload
scott-colbourne -
Category
Documents
-
view
271 -
download
2
Transcript of Food Microbiology - The Basics
RIGHT S O L U T I O N S | RIGHT PARTNER
Food Microbiology – The basicsScott ColbourneBusiness Manager NSW – ALS Food & Pharmaceutical
Food Microbiology - The Basics 2
Contents
• Common Microbiological Tests - what and why
• Method Turn Around Times (TAT)
• The Confirmation Process
• Causes of counts being high initially, then low when retested
Food Microbiology - The Basics 3
Common Tests – what and why?
• Standard Plate Count (SPC)What?A generic count of micro-organisms present. The results are non-specific Why?Gives a general indication of the level of micro-organisms present in the sample testedCan be referred to as…Total Microbial Count (TMC), Total Aerobic Microbial Count (TAMC), TVC, TVAC
Food Microbiology - The Basics 4
Common Tests – what and why?
• Yeast and MouldWhat?Generic test for the levels of these present. Non-specific.Why?• They cause biodegradation of natural materials, which
may become food spoilage• Some yeasts are useful in fermentation (e.g. Bread and
Beer) • However some (e.g. Candida albicans) are opportunistic
pathogens and can cause infections
Food Microbiology - The Basics 5
Common Tests – what and why?
• SalmonellaWhat?Pathogen found in cold/warm blooded animals and the environment
Why?• It causes food poisoning, such as gastrointestinal issues• To ensure there is no presence of pathogens
Food Microbiology - The Basics 6
Common Tests – what and why?
• ListeriaWhat?A genus of bacteria that contains 10 species, the most important genus, L. monocytogenes is a serious human pathogen.
Why?Healthy people and pregnant women may have mild or no symptoms, but Listeria infection may still result in miscarriage, premature birth or stillbirth.In people at risk, Listeria infection can result in serious illnesses including meningitis and septicaemia.
Food Microbiology - The Basics 7
Common Tests – what and why?
• E. coli and coliformsWhat?Coliforms can be found in the aquatic environment, in soil and on vegetation; they are universally present in large numbers in the faeces of warm-blooded animals and humans.
Why?• Commonly used bacterial indicators of hygiene and sanitary quality of
foods and water. • E. coli are almost exclusively of faecal origin and their presence is thus an
effective indicator of faecal contamination. • Most strains of E. coli are harmless, but some can cause serious illness in
humans.
Food Microbiology - The Basics 8
Common Tests – what and why?
• Staphylococcus (coagulase positive)What?A common bacterium that lives on the skin or in the nose of humans.
Why?Coagulase positive species of Staphylococcus can produce toxins in foods.
Food Microbiology - The Basics 9
Common Tests – what and why?
• Bacillus cereusWhat?A common bacterium found in the environment; typically associated in soil as well as a variety of foods.
Why?The toxin producing spore forming bacterium can cause vomiting and diarrhoea. Bacillus cereus spores are able to survive harsh environments which include normal cooking temperatures.
Food Microbiology - The Basics 10
Method Turn Around Times
MethodTurnaround Time (Days)
If Clean If Confirmation is Required
Standard Plate Count 3 N/a
Yeast and Mould 5 – 7 N/a
SalmonellaELISA (Automated rapid method) 2 5
Australian Standard (manual method) 4 7
ListeriaELISA (Automated rapid method) 2 7
Australian Standard (manual method) 5 7
Food Microbiology - The Basics 11
Method Turn Around Times
MethodTurnaround Time (Days)
If Clean If Confirmation is Required
Standard Plate Count 3 N/a
Yeast and Mould 5 – 7 N/a
SalmonellaELISA (Automated rapid method) 2 5
Australian Standard (manual method) 4 7
ListeriaELISA (Automated rapid method) 2 7
Australian Standard (manual method) 5 7
The ELISA method (e.g. DS2) is quicker, more reliable and cheaper
The confirmation process is identical to the Australian Standard method
The next slide has more details…
Food Microbiology - The Basics 12
Pathogens:ELISA is superior to the Australian Standard
Comparing Listeria and Salmonella test methodologiesParameter ELISA Australian Standard
Price High level of automation Labour intensive
Speed - negative 2 days 4-5 daysSpeed – confirmed positive 5-7 days 7 days
Interpretation of results Automated Labour intensiveHuman interaction Low High
NATA accreditation Yes YesInternationally recognised e.g. AFNOR Yes Yes
Client preference 95% 5%
Food Microbiology - The Basics 13
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Food Microbiology - The Basics 14
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Advantages:- Quick- Generally, no confirmation
step for coliforms
Disadvantages:- Sample matrix sensitive- Cannot use for samples with:
- High colour - High micro background- High acidity
Food Microbiology - The Basics 15
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Advantages:- Quantitative- Can report to low levels (0.3)- Australian standard
Disadvantages:- Labour intensive- Statistical value – most
probable number
Food Microbiology - The Basics 16
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Advantages:- Great if not detected
Disadvantages:- Qualitative only
Food Microbiology - The Basics 17
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Advantages:- Quick- Quantitative
Disadvantages:- Not available for E.Coli
Food Microbiology - The Basics 18
Method Turn Around Times
MethodTurnaround Time TAT (Days)
If Clean If Confirmation is Required
Coliforms
Petrifilm 2 N/a
MPN 2 4
Presence/Absence 2 4
Plate Count 1 N/a
E.Coli
Petrifilm 2 N/a
MPN 2 6
Presence/Absence 2 6
Enterobacteriaceae
Plate Count 1 3
Alternative to Coliforms as a faecal contamination indicator
Advantages:- Quick- Quantitative- Salmonella is included
Disadvantages:- Generic and positive results
may require specific testing
Food Microbiology - The Basics 19
Method Turn Around Times
MethodTurnaround Time (Days)
If Clean If Confirmation is Required
Staphylococcus
Plate Count 2 4-6
Presence/Absence 4 6
Food Microbiology - The Basics 20
Confirmation Process
• What is a suspect or presumptive result?• What is confirmation or follow up?
Hi John,Please note that the below sample is suspect for E.Coli:
Lot: 12345 Food sample A, DOM 15/05/2015
The sample is under confirmation and the final result will be updated once complete
Thank you and best regards
Jenny BloggsMicrobiologist
• Have you ever received an email like this?
Food Microbiology - The Basics 21
Confirmation Process
• What is a suspect or presumptive result?• What is confirmation or follow up?
Hi John,Please note that the below sample is suspect for E.Coli:
Lot: 12345 Food sample A, DOM 15/05/2015
The sample is under confirmation and the final result will be updated once complete
Thank you and best regards
Jenny BloggsMicrobiologist
• Have you ever received an email like this?
What is a suspect result?
For a number of microbiological tests the initial test is generic and any positive or SUSPECT result requires more testing.
A suspect may be:- The micro-organism being analysed- Other micro-organisms present that
interfere- Matrix interference
Synonyms: Presumptive
Food Microbiology - The Basics 22
Confirmation Process
• What is a suspect or presumptive result?• What is confirmation or follow up?
Hi John,Please note that the below sample is suspect for E.Coli:
Lot: 12345 Food sample A, DOM 15/05/2015
The sample is under confirmation and the final result will be updated once complete
Thank you and best regards
Jenny BloggsMicrobiologist
• Have you ever received an email like this?
What is confirmation?
Carrying out further steps of a test for identifying a particular type of bacteria.Therefore CONFIRMING its presence.
When the steps have been completed we say that the test has been “Confirmed”.
After confirmation, the result will be finalised.
Synonyms: Follow up
Food Microbiology - The Basics 23
Confirmation Process
• What tests can require confirmation?– Coagulase Positive Staphylococcus– E.coli and Coliforms– B. cereus
– Salmonella– Listeria– Clostridium perfringens
– Enterobacteriaceae
Food Microbiology - The Basics 24
High to Low Counts
• How can a result be high in one test and then low when retested?
• This can be caused by a number of factors.– The sample may not be completely homogenous.– Lab error– The sample has anti-bacterial properties.– Natural sample variation – e.g. due to the make-up and/or
components of the sample.
Food Microbiology - The Basics 25
High to Low Counts: Sample Not Homogeneous
• The laboratory generally uses 10g of the sample in the required media, e.g. 90g
• Of that 100g, 0.1g to 1.0g is removed for each test
• A reported result of 500 cfu/g, may only be 5 colonies on an agar plate. This is a low number and with repeat testing small variations will affect the result by 100’s of cfu/g
• In general, acceptable variation would be within half a log, e.g.
Result Possible Variation
5,000 (or 5 x 103) ± 500
3,000,000 (or 3 x 106) ± 500,000
Food Microbiology - The Basics 26
High to Low Counts: Anti-Bacterial Properties
• The sample may contain substances that are anti-bacterial
• Some samples have the capacity to kill bacteria, e.g. cinnamon, vinegar, salt and preservatives
• Samples are stored for 3-5 days from initial testing & before a retest generally occurs. Substances in the sample itself may lower the bacterial count e.g water activity, available nutrients & temperature
• Therefore possible high levels upon initial testing have been killed off or had their numbers lowered before the retest.
Food Microbiology - The Basics 27
High to Low Counts: Lab Error
• This is always a possibility and our quality procedures and controls minimise this risk. However it can never be 100% removed.
• If we believe lab error is a possibility we will try to look for a pattern, e.g.• Do all the similar samples have a high count?• Does the sample have a history of high counts?• Do unrelated samples tested concurrently have high counts?
• We also look at other factors, e.g.• Experience of the technician• Environmental monitoring results• Media testing, including daily positive/negative controls
Food Microbiology - The Basics 28
End.
• Thank you very much for your attention
• If you would like more information on ALS Food, please visit our website or contact one of our team