Lectures advanced food microbiology
Most common food borne pathogens and their characteristics
Listeria (gram positive)
- high mortality rate
- facultative anaerobic
- growth temperature: 1-45 degrees (grow in refrigerator)
- highly persistent (PH, UV salt)
- Food: raw and processed vegetables/fruit, sausages, deli meats, fish, unpasteurised cheeses and milk
Bacillus cereus
- Temperature rate = 10-50 degrees
- Toxin producer (2 types)
- Spore former (heat resistant)
- Food: rice, pasta, potatoes, beans, spices
Clostridium perfigens
- Temperature growth = 15-55 degrees
- Toxin producer
- Anaerobic
- Fast doubling time
- Food: meat, gravy, pork, milk
Salmonella
- Growth temperature: 6-46 degrees
- Facultative anaerobic
- Food: chicken, beef, eggs, fruit and vegetables
E-coli
- Growth temperature: 20-49 degrees
- Facultative anaerobic
- Food: raw meat products, raw milk and cheeses, contaminated fruit and vegetables
Knowledge clip 1.1a Food safety – introduction microbiology and food safety
Food microbiology consists 3 domains:
1. The good → example: fermentation
2. The bad → cause illness (diarrhoea/vomiting)
3. The ugly → spoilage of food (example: moulds)
Food safety: pathogens (bacteria and viruses)
Food quality: spoilage (bacteria, yeasts and moulds)
Food quality: fermentation (taste, shelf life, health)
WHO estimates of the global burden of foodborne diseases
YLDS = years lived with disability
YLL = years life lost
DALY = disability adjusted life years
Magnitude of the issues in food safety
>200 diseases transmitted trough food: viruses, bacteria, parasites, metals, toxins enc…
,US estimated microbiological food borne illness per year
1:6 = people get sick
1:2300 = get hospilized
1:1000,000 = die due to food diseases
Foodborne diseases are not the most important sources of human deaths, but it does play a role
Knowledge clip 1.1a Food safety – the bad guys
Organisms responsible for illness, hospitalisation and death
For example: Listeria does not occur that often but when people get sick due to Listeria 20% dies, this is why Listeria
is still a very important microorganism looking at food safety
Some organisms → only really dangerous for some people (the YOPI)
The most important micro-organisms that cause diseases:
- Campylobacter
- Clostridium Perfringens
- Listeria
- Salmonella
- Toxoplasma (parasite/oocysten)
- Norovirus (virus)
Products related to causing organisms
Product relation (Hald) → Hald, a scientist has developed a procedure to look al all kinds of types of microorganisms
that she could find in al kinds of food in human cases
- She developed a equation:
Control: HACCP
1. Hazards → identify the hazards (experiments, literature, expert knowledge)
2. CCPs → these are the processes that clearly influence the risks (e.g. cooling, pasteurization)
3. Limits → critical limits (time and temperature of the processes)
, 4. Monitor → monitoring and define the corrective actions if the monitoring results and values are outside the
critical limits (e.g. reprocessing)
5. Corrective actions → actions that will lower the prevalence of the hazard (example; longer heating time)
6. Verification → verification of the system
7. Documentation → important for procedures
For defining CCps and limits a global analysis can be used or more specific analysis or by extensive quantitative
risk assessments
- Quantitative risk assessments are more generally carries out by the governments and by international
authorities like the FAO
Long life learning → prevent stupid errors
The risks cannot be reduced to zero but one can reduce by intelligent interventions an structured food safety
management systems
Knowledge clip 1.2a – food safety: the FSO concept
FSO concept (Food Safety Objective): one of the concepts that are used to manage food safety
- Norm set by the government
This concept assumes that the contaminant in the food chain starts at an initial level H0
H0 = initial level contamination
R = stage of reduction (for example during storage or baking)
G & C = increase growth (for example during the evening of the dough) or additional contamination due to for
example dirty hands of a person in the factory
- G = growth
- C = contamination
All these factors have to be eventually below the FSO norm
Left side = more relevant for the industry
Right side = more relevant for the consumer, government
, ALOP = appropriate level of protection (illness per year)
FSO = the maximum level of micro-organism that can be present in the food product (cfu/g or prevalence)
You can extend this to several parts of the food chain (example 3 stages):
In every stage of the food chain there can be growth, contamination or reduction
- For example consumer stage: The consumer can also cause in or decreasing of the growth by heating the
product of recontamination
Level during a step in the food chain/process (except before consumption) → has to be below the performance
objective
Final level before consumption → has to be lower than the FSO norm
Performance criteria = the effect in frequency and/or concentration of a hazard in a food that must be achieved by
the application of one or more control measures to provide or contribute to a PO or an FSO
Performance objective = The maximum frequency and/or concentration of a (microbial) hazard in a food at a
specified step in the food chain (except before consumption)
Food safety objective = The maximum frequency and/or concentration of a (microbial) hazard in a food before
consumption
Knowledge clip 1.2.b microbiological food safety: research
For quantitative methods the prevalence, initial concentration, growth, inactivation and recontamination is relevant
Calculation to estimate the contamination level:
Rc = Cair x Vs x A x t
Rc = recontamination
Cair = concentration in the air
Most common food borne pathogens and their characteristics
Listeria (gram positive)
- high mortality rate
- facultative anaerobic
- growth temperature: 1-45 degrees (grow in refrigerator)
- highly persistent (PH, UV salt)
- Food: raw and processed vegetables/fruit, sausages, deli meats, fish, unpasteurised cheeses and milk
Bacillus cereus
- Temperature rate = 10-50 degrees
- Toxin producer (2 types)
- Spore former (heat resistant)
- Food: rice, pasta, potatoes, beans, spices
Clostridium perfigens
- Temperature growth = 15-55 degrees
- Toxin producer
- Anaerobic
- Fast doubling time
- Food: meat, gravy, pork, milk
Salmonella
- Growth temperature: 6-46 degrees
- Facultative anaerobic
- Food: chicken, beef, eggs, fruit and vegetables
E-coli
- Growth temperature: 20-49 degrees
- Facultative anaerobic
- Food: raw meat products, raw milk and cheeses, contaminated fruit and vegetables
Knowledge clip 1.1a Food safety – introduction microbiology and food safety
Food microbiology consists 3 domains:
1. The good → example: fermentation
2. The bad → cause illness (diarrhoea/vomiting)
3. The ugly → spoilage of food (example: moulds)
Food safety: pathogens (bacteria and viruses)
Food quality: spoilage (bacteria, yeasts and moulds)
Food quality: fermentation (taste, shelf life, health)
WHO estimates of the global burden of foodborne diseases
YLDS = years lived with disability
YLL = years life lost
DALY = disability adjusted life years
Magnitude of the issues in food safety
>200 diseases transmitted trough food: viruses, bacteria, parasites, metals, toxins enc…
,US estimated microbiological food borne illness per year
1:6 = people get sick
1:2300 = get hospilized
1:1000,000 = die due to food diseases
Foodborne diseases are not the most important sources of human deaths, but it does play a role
Knowledge clip 1.1a Food safety – the bad guys
Organisms responsible for illness, hospitalisation and death
For example: Listeria does not occur that often but when people get sick due to Listeria 20% dies, this is why Listeria
is still a very important microorganism looking at food safety
Some organisms → only really dangerous for some people (the YOPI)
The most important micro-organisms that cause diseases:
- Campylobacter
- Clostridium Perfringens
- Listeria
- Salmonella
- Toxoplasma (parasite/oocysten)
- Norovirus (virus)
Products related to causing organisms
Product relation (Hald) → Hald, a scientist has developed a procedure to look al all kinds of types of microorganisms
that she could find in al kinds of food in human cases
- She developed a equation:
Control: HACCP
1. Hazards → identify the hazards (experiments, literature, expert knowledge)
2. CCPs → these are the processes that clearly influence the risks (e.g. cooling, pasteurization)
3. Limits → critical limits (time and temperature of the processes)
, 4. Monitor → monitoring and define the corrective actions if the monitoring results and values are outside the
critical limits (e.g. reprocessing)
5. Corrective actions → actions that will lower the prevalence of the hazard (example; longer heating time)
6. Verification → verification of the system
7. Documentation → important for procedures
For defining CCps and limits a global analysis can be used or more specific analysis or by extensive quantitative
risk assessments
- Quantitative risk assessments are more generally carries out by the governments and by international
authorities like the FAO
Long life learning → prevent stupid errors
The risks cannot be reduced to zero but one can reduce by intelligent interventions an structured food safety
management systems
Knowledge clip 1.2a – food safety: the FSO concept
FSO concept (Food Safety Objective): one of the concepts that are used to manage food safety
- Norm set by the government
This concept assumes that the contaminant in the food chain starts at an initial level H0
H0 = initial level contamination
R = stage of reduction (for example during storage or baking)
G & C = increase growth (for example during the evening of the dough) or additional contamination due to for
example dirty hands of a person in the factory
- G = growth
- C = contamination
All these factors have to be eventually below the FSO norm
Left side = more relevant for the industry
Right side = more relevant for the consumer, government
, ALOP = appropriate level of protection (illness per year)
FSO = the maximum level of micro-organism that can be present in the food product (cfu/g or prevalence)
You can extend this to several parts of the food chain (example 3 stages):
In every stage of the food chain there can be growth, contamination or reduction
- For example consumer stage: The consumer can also cause in or decreasing of the growth by heating the
product of recontamination
Level during a step in the food chain/process (except before consumption) → has to be below the performance
objective
Final level before consumption → has to be lower than the FSO norm
Performance criteria = the effect in frequency and/or concentration of a hazard in a food that must be achieved by
the application of one or more control measures to provide or contribute to a PO or an FSO
Performance objective = The maximum frequency and/or concentration of a (microbial) hazard in a food at a
specified step in the food chain (except before consumption)
Food safety objective = The maximum frequency and/or concentration of a (microbial) hazard in a food before
consumption
Knowledge clip 1.2.b microbiological food safety: research
For quantitative methods the prevalence, initial concentration, growth, inactivation and recontamination is relevant
Calculation to estimate the contamination level:
Rc = Cair x Vs x A x t
Rc = recontamination
Cair = concentration in the air
