Microbiology 4, 5, 6

Question 1

What is meant by chemorganotrophic microbes? What is their ideal growth medium?

Answer 1

Chemorganotrophic microbes = microbes that use organic compounds for energy

Question 2

How many people suffer from food bourne illnesses per year?

Answer 2

1 million people suffer from foodbourne illnesses per year

Question 3

What is the most common food poisoning?

Answer 3

Campylobacter = most common food poisoning

Question 4

What is meant by pathogenicity?

What microbe has high pathogenicity?

Answer 4

The number of microbes needed to cause illness

Salmonella has high pathogenicity - large no. of microbes needed to cause illness

Question 5

How do microbes cause illness?

Answer 5

Producing toxins - endotoxins and exotoxins

Producing toxic waste products

Question 6

What are exotoxins? Give examples

Answer 6

Exotoxins = toxins released extracellulary e.g. enterotoxins, cytolytic toxins, neurotoxins

Question 7

Define enterotoxins

Answer 7

Enterotoxins - act on intestinal mucosa causing diarrhea

Question 8

Define cytolytic toxins

Answer 8

Cytolytic toxins - kill host cells e.g. Cl. perfringens

Question 9

Define neurotoxins

Answer 9

Neurotoxins - interfere with neural transmission e.g. Botulinum

Question 10

What are endotoxins?

Answer 10

Gram negative bacteria undergo lysis - release lipopolysachharides from the plasma memeberane
e.g. Salmonella

Question 11

What happens when you ingest a pre-formed toxin?

Answer 11

Very short incubation period - show symptoms very quickly.
Toxin does not require person to person spread
Toxin is heat resistant

Question 12

What is an non-invasive infection? Give examples

Answer 12

Non-invasive infection - cells colonize the intestinal lumen and epithelial surface
e.g. E-coli, Cl. Perfingens

Question 13

What is an invasive infection? Give examples

Answer 13

Invasive infection - cells in the intestinal epithelium are invaded and then this infection can pass through to the lamina
e.g. salmonella

Question 14

What is meant by a D value?

Answer 14

Time required to reduce the number of cells by 90%

Question 15

What is campylobacter caused by?

Answer 15

80% caused by raw poultry
Milk
Untreated water

Question 16

Describe the microbiological features of campylobacter

Answer 16

Campylobacter:
Gram negative
Non-spore forming
Mesophile
Microaerophillic - grows at O2 conc lower than in air

Question 17

How can camylobacter be reduced in chicken?

Answer 17

Freezing it with nitrogen

Question 18

Describe the infective dose of campylobacter

Answer 18

LOW infective does needed

Question 19

Where is salmonella found?

Answer 19

Salmonella is found in the intestinal tract of birds and animals

Question 20

What are the main sources of salmonella

Answer 20

Raw chicken, milk, eggs, meat

Question 21

What type of organism is salmonella?

Answer 21

Zoonotic organism - salmonella is transferred from animals to humans

Question 22

Describe the microbiological features of salmonella

Answer 22

Salmonella:
Non spore forming
Motile rods
Facultative anaerobe
Can grow at pH's as low as 3.8
4-48 hr incubation period

Question 23

What is the most common salmonella infection?

Answer 23

S.Enteritis - a gastrointestinal infection

Question 24

Can salmonella become a systematic disease?

Answer 24

Yes, salmonella is a host adaptive serotype.

Question 25

What is the most lethal food bourne illness?

Answer 25

Listeria Monocytogenes

Question 26

What is listeria carried by?

Answer 26

Humans or animal gut

Question 27

Where is listeria found?

Answer 27

Unpasteurised milk, meat (salami and pate), reheated cook to chill meals

Question 28

Describe the microbiological features of listeia

Answer 28

Grows at LOW temperatures - grows in fridge Gram Positive Non-spore forming Facultative anaerobe 2.5-45 degree growth range Destroyed by acidic food, cooking and pasteurization

Question 29

What preservatives is listeria tolerant to?

Answer 29

Salt and sodium nitrite

Question 30

What is listeriosis?

Answer 30

1-70 day incubation period High mortality rate (death) Can have asymptomatic carriers neonates and pregnant people at risk

Question 31

What percentage of people hospitlaised with listeriosis die?

Answer 31

1/3

Question 32

Describe the pathogenicity of E-coli

Answer 32

Only a small number of cells needed to cause illness

Question 33

Where is ecoli found?

Answer 33

Ecoli is found in the intestinal tract of warm blooded animals

Question 34

What food sources is ecoli found in?

Answer 34

E-coli is found in diary and beef

Question 35

How is ecoli spread?

Answer 35

Direct contact to animals, faecal to oral route, cross contamination

Question 36

Describe some food outbreaks of e-coli in the past

Answer 36

Undercooked beef - 1993, 4 children in USA die | Unpasteurized apple juice

Question 37

Describe the microbiology of e-coli

Answer 37

``` E-coli: Non spore forming Gram negative Produces verotoxins Facultative anaerobe Can grow in pH 4.5 - acid is not an effective control Mesophile Resistant to freezing - frozen burgers still contain E-coli Favours fatty mediums ```

Question 38

Describe illness caused by E-coli

Answer 38

``` Mild diarrhea Haemorrhagic colititis Uraemia - often young in children Fatal in young and old High infectivity ```

Question 39

What is meant by the z value?

Answer 39

The temperature required to reduce number of cells by a further 90%

Question 40

List all spore forming bacteria

Answer 40

Spore forming: Clostridium perfingens Clostridium botulinum Bacillus cereus

Question 41

What are the sources of clostridium perfringens?

Answer 41

Gastrointestinal tract of mammals Soil Dust

Question 42

How is clostridium perfingens transmitted?

Answer 42

Contaminated meat and poultry

Question 43

Describe the microbiology of Cl. perfingens

Answer 43

Cl. Perfringens: Spore forming - spores survive low temperature cooking Gram Positive Anaerobic High nutritional requirement - needs 13 amino acids

Question 44

Describe the illness/symtpoms of Cl. perfringnes

Answer 44

Large number of cells needed for illness | Cells produce enterotoxins in the intestines

Question 45

What are the sources of Cl. Botulinum?

Answer 45

Soil, environment

Question 46

What foods contain Cl. Botulinum?

Answer 46

Raw, undercooked or under processed food | Home preservation techniques

Question 47

Describe the growth conditions of Cl. Botulinum Group 1

Answer 47

Anaerobic - grows in cans Cannot grow in refrigerators Grows at 10-12 degrees Spores survive severe heat processes - cans need to be sterilized in a botulinum cook at 121 degrees for 3 mins

Question 48

What is a botulinum cook?

Answer 48

Heats cans to 121 degrees for 3 mins

Question 49

Describe the growth conditions of Cl. Botulinum Group 2

Answer 49

Grows at chilled temperature/ in fridge - 3-5 degrees Spores are less heat resistant More likely to grow in chilled vacuum packed foods

Question 50

Where is bacillus cereus found?

Answer 50

Bacillus Cereus is found in the environment, soil, sediment and human gut

Question 51

Describe the microbiology of B. Cereus

Answer 51

``` Spore forming Gram positive Motile rods Facultative anaerobe 28-35 degree optimum temp ```

Question 52

What toxins are produced by B. Cereus? Can they be destroyed?

Answer 52

Pre-formed Emetic toxin - HEAT RESISTANT | Diarrhoeal eneterotoxin - can be destroyed by heat

Question 53

Describe the emetic form of B. Cereus

Answer 53

Ingestion of pre-formed heat stable toxin Vomitiing, Nausea 1-5 hr incubation period Duration of symptoms - 6-24 hrs

Question 54

What foods do B. Cereus spores grow on?

Answer 54

Spores can grow on surfaces because they are very hydrophobic - resist cleaning Found on dry food - cereals, spices, flour e.g. Vannilla sauce in Norway thickened with cornflour containing spores - heat treatment did not deactivate