Food Microbiology – The basics Scott Colbourne Business Manager NSW – ALS Food & Pharmaceutical RIGHT SOLUTIONS | RIGHT PARTNER
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 Confirmation If Clean is Required Standard Plate Count 3 N/a Yeast and Mould 5 – 7 N/a Salmonella ELISA 2 5 (Automated rapid method) Australian Standard 4 7 (manual method) Listeria ELISA 2 7 (Automated rapid method) Australian Standard 5 7 (manual method) Food Microbiology - The Basics 10
Method Turn Around Times Turnaround Time (Days) Method If Confirmation If Clean is Required Standard Plate Count 3 N/a Yeast and Mould 5 – 7 N/a Salmonella The ELISA method (e.g. DS2) is ELISA 2 5 quicker, more reliable and (Automated rapid method) cheaper Australian Standard 4 7 (manual method) The confirmation process is identical to the Australian Listeria Standard method ELISA 2 7 (Automated rapid method) The next slide has more Australian Standard details … 5 7 (manual method) Food Microbiology - The Basics 11
Pathogens: ELISA is superior to the Australian Standard Comparing Listeria and Salmonella test methodologies ELISA Australian Standard Parameter High level of Labour intensive Price automation 2 days 4-5 days Speed - negative Speed – confirmed 5-7 days 7 days positive Automated Labour intensive Interpretation of results Low High Human interaction Yes Yes NATA accreditation Internationally Yes Yes recognised e.g. AFNOR 95% 5% Client preference Food Microbiology - The Basics 12
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean 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 13
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean Required Coliforms Advantages: Petrifilm 2 N/a - Quick MPN 2 4 - Generally, no confirmation Presence/Absence 2 4 step for coliforms Plate Count 1 N/a E.Coli Disadvantages: - Sample matrix sensitive Petrifilm 2 N/a - Cannot use for samples with: MPN 2 6 - High colour Presence/Absence 2 6 - High micro background - High acidity Enterobacteriaceae Plate Count 1 3 Food Microbiology - The Basics 14
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean Required Coliforms Petrifilm 2 N/a Advantages: MPN 2 4 - Quantitative Presence/Absence 2 4 - Can report to low levels (0.3) - Australian standard Plate Count 1 N/a E.Coli Disadvantages: Petrifilm 2 N/a - Labour intensive MPN 2 6 - Statistical value – most Presence/Absence 2 6 probable number Enterobacteriaceae Plate Count 1 3 Food Microbiology - The Basics 15
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean Required Coliforms Petrifilm 2 N/a MPN 2 4 Presence/Absence 2 4 Advantages: - Great if not detected Plate Count 1 N/a E.Coli Petrifilm 2 N/a Disadvantages: - Qualitative only MPN 2 6 Presence/Absence 2 6 Enterobacteriaceae Plate Count 1 3 Food Microbiology - The Basics 16
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean Required Coliforms Petrifilm 2 N/a MPN 2 4 Advantages: Presence/Absence 2 4 - Quick Plate Count 1 N/a - Quantitative E.Coli Petrifilm 2 N/a Disadvantages: - Not available for E.Coli MPN 2 6 Presence/Absence 2 6 Enterobacteriaceae Plate Count 1 3 Food Microbiology - The Basics 17
Method Turn Around Times Turnaround Time TAT (Days) Method If Confirmation is If Clean Required Coliforms Alternative to Coliforms as a Petrifilm 2 N/a faecal contamination indicator MPN 2 4 Advantages: Presence/Absence 2 4 - Quick Plate Count 1 N/a - Quantitative E.Coli - Salmonella is included Petrifilm 2 N/a Disadvantages: MPN 2 6 - Generic and positive results Presence/Absence 2 6 may require specific testing Enterobacteriaceae Plate Count 1 3 Food Microbiology - The Basics 18
Method Turn Around Times Turnaround Time (Days) Method If Confirmation is If Clean 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 For a number of microbiological tests the initial test is generic and any positive or Jenny Bloggs SUSPECT result requires more testing. Microbiologist A suspect may be: - The micro-organism being analysed What is a suspect or presumptive result? • - Other micro-organisms present that interfere What is confirmation or follow up? • - Matrix interference 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 E.Coli: What 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 updated once complete identifying a particular type of bacteria. Therefore CONFIRMING its presence. Thank you and best regards Jenny Bloggs When the steps have been completed we Microbiologist say that the test has been “Confirmed” . After confirmation, the result will be What is a suspect or presumptive result? • finalised. What is confirmation or follow up? • Synonyms: Follow up Food Microbiology - The Basics 22
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