Food Microbiology The basics - · PDF fileFood Microbiology –The basics Scott...

RIGHT S O L U T I O N S | RIGHT PARTNER

Food Microbiology – The basics

Scott Colbourne

Business Manager NSW – ALS Food & Pharmaceutical

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

2Food Microbiology - The Basics

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

3Food Microbiology - The Basics


• 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


• 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



• 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.



• 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.



• 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.




• 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.

Method Turn Around Times


Method

Turnaround Time (Days)

If CleanIf Confirmation

is Required

Standard Plate Count 3 N/a

Yeast and Mould 5 – 7 N/a

Salmonella

ELISA (Automated rapid method)

2 5

Australian Standard (manual method)

4 7

Listeria


2 7


5 7



Method


If CleanIf Confirmation

is Required

Standard Plate Count 3 N/a

Yeast and Mould 5 – 7 N/a

Salmonella


2 5


4 7

Listeria


2 7


5 7

The ELISA method (e.g. DS2) isquicker, more reliable andcheaper

The confirmation process isidentical to the AustralianStandard method

The next slide has moredetails…

Pathogens:ELISA is superior to the Australian Standard

Comparing Listeria and Salmonella test methodologies

12

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

Internationallyrecognised e.g. AFNOR

Yes Yes

Client preference 95% 5%

Food Microbiology - The Basics



Method

Turnaround Time TAT (Days)

If CleanIf 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


Enterobacteriaceae

Plate Count 1 3



Method



Coliforms

Petrifilm 2 N/a

MPN 2 4


Plate Count 1 N/a

E.Coli

Petrifilm 2 N/a

MPN 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



Method



Coliforms

Petrifilm 2 N/a

MPN 2 4


Plate Count 1 N/a

E.Coli

Petrifilm 2 N/a

MPN 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



Method



Coliforms

Petrifilm 2 N/a

MPN 2 4


Plate Count 1 N/a

E.Coli

Petrifilm 2 N/a

MPN 2 6


Enterobacteriaceae

Plate Count 1 3

Advantages:- Great if not detected

Disadvantages:- Qualitative only



Method



Coliforms

Petrifilm 2 N/a

MPN 2 4


Plate Count 1 N/a

E.Coli

Petrifilm 2 N/a

MPN 2 6


Enterobacteriaceae

Plate Count 1 3

Advantages:- Quick- Quantitative

Disadvantages:- Not available for E.Coli



Method



Coliforms

Petrifilm 2 N/a

MPN 2 4


Plate Count 1 N/a

E.Coli

Petrifilm 2 N/a

MPN 2 6


Enterobacteriaceae

Plate Count 1 3

Alternative to Coliforms as afaecal contamination indicator

Advantages:- Quick- Quantitative- Salmonella is included

Disadvantages:- Generic and positive results

may require specific testing



Method



Staphylococcus

Plate Count 2 4-6


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 Bloggs

Microbiologist

• Have you ever received an email like this?





Hi John,





Jenny Bloggs

Microbiologist


What is a suspect result?

For a number of microbiological tests theinitial test is generic and any positive orSUSPECT result requires more testing.

A suspect may be:- The micro-organism being analysed- Other micro-organisms present that

interfere- Matrix interference

Synonyms: Presumptive





Hi John,





Jenny Bloggs

Microbiologist


What is confirmation?

Carrying out further steps of a test foridentifying a particular type of bacteria.Therefore CONFIRMING its presence.

When the steps have been completed wesay that the test has been “Confirmed”.

After confirmation, the result will befinalised.

Synonyms: Follow up


• What tests can require confirmation?

– Coagulase Positive Staphylococcus

– E.coli and Coliforms

– B. cereus

– Salmonella

– Listeria

– Clostridium perfringens

– Enterobacteriaceae


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.


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

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.


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


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


http://www.alsglobal.com/en/Our-Services/Life-Sciences/Food/Food-Capabilties/Australia-Capabilities

mailto:[email protected]?subject=Request from Food Microbiology - The Basics

Date post:	07-Feb-2018
Category:	Documents
Upload:	phamanh
View:	215 times
Download:	0 times

Food Microbiology The basics - · PDF fileFood Microbiology –The basics Scott...

Documents