Download Food Microbiology The basics

Food Microbiology – The basics
Scott Colbourne
Business Manager NSW – ALS Food & Pharmaceutical
R IG H T S O L U T I O N S | R I G H T PA RT N E R
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
2
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 tested
Can be referred to as…
Total Microbial Count (TMC), Total Aerobic Microbial Count
(TAMC), TVC, TVAC
Food Microbiology - The Basics
3
Common Tests – what and why?
• Yeast and Mould
What?
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
4
Common Tests – what and why?
• Salmonella
What?
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
5
Common Tests – what and why?
• Listeria
What?
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
6
Common Tests – what and why?
•
E. coli and coliforms
What?
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
7
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
8
Common Tests – what and why?
• Bacillus cereus
What?
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
9
Method Turn Around Times
Turnaround Time (Days)
Method
If Clean
If Confirmation
is Required
3
N/a
5–7
N/a
Standard Plate Count
Yeast and Mould
Salmonella
ELISA
(Automated rapid method)
2
5
Australian Standard
(manual method)
4
7
ELISA
(Automated rapid method)
2
7
Australian Standard
(manual method)
5
7
Listeria
Food Microbiology - The Basics
10
Method Turn Around Times
Turnaround Time (Days)
Method
If Clean
If Confirmation
is Required
3
N/a
5–7
N/a
Standard Plate Count
Yeast and Mould
Salmonella
ELISA
(Automated rapid method)
2
5
Australian Standard
(manual method)
4
7
ELISA
(Automated rapid method)
2
7
Australian Standard
(manual method)
5
Listeria
7
Food Microbiology - The Basics
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…
11
Pathogens:
ELISA is superior to the Australian Standard
Comparing Listeria and Salmonella test methodologies
Parameter
ELISA
Australian Standard
Price
 High level of
automation
 Labour intensive
Speed - negative
 2 days
 4-5 days
Speed – confirmed
positive
 5-7 days
 7 days
Interpretation of results
 Automated
 Labour intensive
Human interaction
 Low
 High
NATA accreditation
 Yes
 Yes
Internationally
recognised e.g. AFNOR
 Yes
 Yes
Client preference
 95%
 5%
Food Microbiology - The Basics
12
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
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
13
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
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
Advantages:
- Quick
- Generally, no confirmation
step for coliforms
Disadvantages:
- Sample matrix sensitive
- Cannot use for samples with:
- High colour
- High micro background
- High acidity
3
Food Microbiology - The Basics
14
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
Coliforms
Petrifilm
2
N/a
MPN
2
4
Presence/Absence
2
4
Plate Count
1
N/a
Advantages:
- Quantitative
- Can report to low levels (0.3)
- Australian standard
E.Coli
Petrifilm
2
N/a
MPN
2
6
Presence/Absence
2
6
Disadvantages:
- Labour intensive
- Statistical value
probable number
–
most
Enterobacteriaceae
Plate Count
1
3
Food Microbiology - The Basics
15
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
Coliforms
Petrifilm
2
N/a
MPN
2
4
Presence/Absence
2
4
Plate Count
1
N/a
Advantages:
- Great if not detected
E.Coli
Petrifilm
2
N/a
MPN
2
6
Presence/Absence
2
6
Disadvantages:
- Qualitative only
Enterobacteriaceae
Plate Count
1
3
Food Microbiology - The Basics
16
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
Coliforms
Petrifilm
2
N/a
MPN
2
4
Presence/Absence
2
4
Plate Count
1
N/a
Advantages:
- Quick
- Quantitative
E.Coli
Petrifilm
2
N/a
MPN
2
6
Presence/Absence
2
6
Disadvantages:
- Not available for E.Coli
Enterobacteriaceae
Plate Count
1
3
Food Microbiology - The Basics
17
Method Turn Around Times
Turnaround Time TAT (Days)
Method
If Confirmation is
Required
If Clean
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
Alternative to Coliforms as a
faecal contamination indicator
Advantages:
- Quick
- Quantitative
- Salmonella is included
Disadvantages:
- Generic and positive results
may require specific testing
Enterobacteriaceae
Plate Count
1
3
Food Microbiology - The Basics
18
Method Turn Around Times
Turnaround Time (Days)
Method
If Clean
If Confirmation is
Required
Staphylococcus
Plate Count
2
4-6
Presence/Absence
4
6
Food Microbiology - The Basics
19
Confirmation Process
• Have you ever received an email like this?
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 Bloggs
Microbiologist
• What is a suspect or presumptive result?
• What is confirmation or follow up?
Food Microbiology - The Basics
20
Confirmation Process
• Have you ever received an email like this?
Hi John,
Please note that the below sample is suspect for E.Coli:
Lot: 12345 Food sample A, DOM 15/05/2015
What is a suspect result?
The sample is under confirmation and the final result will be updated once complete
Thank you and best regards
Jenny Bloggs
Microbiologist
• What is
• What is
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
a suspect or presumptive
- Other result?
micro-organisms present that
interfere
confirmation or follow
up?interference
- Matrix
Synonyms: Presumptive
Food Microbiology - The Basics
21
Confirmation Process
• Have you ever received an email like this?
Hi John,
Please note that the below sample is suspect for What
E.Coli:is confirmation?
Lot: 12345 Food sample A, DOM 15/05/2015
Carrying out further steps of a test for
The sample is under confirmation and the final result
will be a
updated
oncetype
complete
identifying
particular
of bacteria.
Therefore CONFIRMING its presence.
Thank you and best regards
Jenny Bloggs
Microbiologist
• What is a suspect or
When the steps have been completed we
say that the test has been “Confirmed”.
After confirmation, the result will be
presumptive
result?
finalised.
• What is confirmation or followSynonyms:
up? Follow up
Food Microbiology - The Basics
22
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
23
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
24
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
25
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
26
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
27
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
Food Microbiology - The Basics
28