Food born diseases Flashcards
describe a few ways in which food used to be preseved
salted; dried; vinegar; sugared
cool caves; smoked;fermented
Name some times in food processing where it may become contaminated
primary production, slaughterhouse, storage conditions, bacteriocidal step taken at all
Name 2 types of ‘goof’ bacteria, with regard to food microbiology
probiotics
fermentation agents
There are 4 phases of bacterial growth; name them
- lag
- log
- stationary (depletion of nutrients and accum of toxic products. prolif = death
- death
what is the D-value
time req to destroy 90% of bacterial population at a given temperature
what is the Z-value
number of degrees req for the D value to decrease by 1 log cycle (10x)
Name 3 bacteria who’s D60
Salmonella; Campy; Enterococcus faecalis
what is the D value for clostridium botulinum spores
D100
Does substrate of the feedstuff have an effect on D value
Yes!
name 3 main factors that affect microbial growth
intrinsic - properties of the food
extrinsic - storage
implicit - properties of the MO
name some intrinsic factors
nutrients available for MOs; pH; buffering capability; redox potential
what is the preffered pH range for MOST bacteria?
6-8
what is the prefered pH for most yeasts?
4.5-6
what is the natural pH of meat
5.6 - perfect range for most things!
Name a alkali tolerant bacteria
Vibrio (Cholera)
Name a acidic tolerant bacteria
Lactobacilli
what is redox potential (Eh)
tendancy for the medium to accept or donate electrones
what type bacteria like high redox potential mediums
obligate aerobes (pseudomonas)
Obligate anaerobes like low redox potentials, name one
clostridia
Name a food product with a:
A) high Eh
B) low Eh
A) lemon and raw meat
B) cooked meat
HIgh water activity can increase ability of bacteria to proliferate. NAme a few ways to reduce this
dry
add salt (NaCl)
freeze
What type of bacteria like high NaCl concentrations
Halophilic MOs
What are Xerophillic MOs good at
growing in dry places
Name some natural antimicrobial factors found in food
ovotransferrin (egg white)
Lactoferrin
egg shell
nitrites (added to meat for red-ness) - inhib C.botul
What colour mould does penecillin give
blue
name a bacteria which only affects the surface of the meat
sporotrichum carnis
Why is CO2 and N2 used in meat packagings
to inc pH
red surface contamination
red enzyme availability to prevent bdown
What does facultative anaerobe mean
it can grow in both aerobic and anaerobic conditions
What temperatures are thermophiles (clost botul) happy in?
40-90
What are the 2 types of bacteria important in the preserving food
mesophiles
psychrotrophs
- both grow at temp most food stored at (inc fridge)
What environment does Salmonella like?
aerobic
low pH
low water avail
What does Staffy A like?
aerobic
low pH
VERY low water avail
What environ does E coli like?
Aerobic and v low pH but high water
What environment does LIsteria monocytogenes like?
v low temperature and very high O2 and water availability
What temperature must a freezer reach before no MO can grow?
-12+ and rapidly is best
Name some of the implicit factors affecting bacterial growth
growth rate
mutalism
antagonism (lactobac and paths)
adaptation and competition
What is the stress response of bacteria (60% of the Salmonella genome!)
a change in the environment (temp change etc) causes a response from the bacteria
- fast growing
- virulent
- resistant
- adaptable
Name 6 gram negative bacteria which cause food born diseases
Salmonella Campy E coli Shigella Yersinia enterocolitica Vibrio spp
Name 5 gram positive food born pathogens
listeria monocytogenes staffy a clost perffringens clost botulinum bacillus cereus
What are the 2 types of food born infection
- Toxico-infection
2. INvasive infection
Name the 2 toxins types which can cause toxicoinfectionsq
entero
neuro
name the 2 types of invasive infection
enteric
systemic
What is foodborn intoxication?
when host ingests toxins/toxic metabolites the bacteria had produced in the food
Name a pathogen which causes intoxication in adults
C. botulinum
What syndrome does B cereus cause
emetic syndrome
what type of toxin does staff a produce?
thermostable enterotoxin
describe what an invasive infection actually is
when bacteria is ingested and it penetrates intestinal mucosa. it can be local or systemic
describe what a toxicoinfection actually is
bacteria is ingested and the organism produces toxins in the GIT
Name 3 bacteria which cause invasive infections
Campy
Salmonella
Listeria mono
Name 5 bacteria which cause toxicoinfections
E coli Vibrio C perfring B cereus C botulinum
What gram negative bacteria involved in food born disease are not facultative anaerobes
campy - micro-aerophillic
what agar type is used to isolate entericobacteria
MacConkey
- lactose fermenting –> pink; other stay orange
Name an agar selective for Salmonella
Brilliant green
salmon –> red
Name an agar selective for E coli
EMB
Name an agar selective for CAmpy
blood agar under reduced oxygen tension conditions
What serotypes are different in salmonella and e coli?
antigen K which is for capsule. not in salmonella
how do you subtype salmonella?
phage-typing. put bacteria against different lytic enzymes
Name the 5 types of E coli enteric infection
Entero __________ E. coli
- pathogenic
- toxigenic
- invasive
- haemorrhagic
- aggregative
what properties of E coli allow UTI
capsule
pili
fibriae
what is the most serious toxin
shiga-like toxins –> destroy b vessels
