18) Biological Control of Foodborne Bacteria Flashcards
Define biopreservation
what does this definition exclude?
using MO and/or their metabolic pdts to preserve food
excludes fermentation
what is an exception of fermentation that is considered biopreservation?
controlled acidification where acid is produced by LAB in temp-abused foods
what are 3 methods of acid production in controlled acidification
- adding organic acids to food
- producing organic acids via fermentation
- LAB producing lactic acid in situ
describe microGARD
what does it include?
- pdts that can be added to refrigerated food to improve shelf life protection when temperature abuse occurs
- includes: (1) fermentable CHOs and (2) bacterial culture combined to offer protection for food pdts
what are key benefits of microGARD?
- protect shelf life
- maintain organoleptic qualities of food
- meet consumers’ demand for natural pdts
when microGARD is present in food, what does bacteria do if food is temp abused?
bacteria (LAB) grows and produces lactic acid, acetic acid, propionic acid and bacteriocins to ensure safety of the pdt
effectiveness of in situ acidification of MicroGARD depends on what?
the products:
- pH
- buffering capacity
- target spoilage MO
- concentration of fermentable CHOs
describe the original experiment using microGARD
- two sets of test food were prepared: (1) one set was inoculated with LAB and C. bot (2) second was only inoculated with C. bot
- conditions were set to simulate temp abuse (prepared food was left for extended period at 30C)
- results:
- in absence of LAB, samples became toxic
in presence of LAB, very few samples became toxic
what is the wisconsin process
what is the result of this?
preparing bacon and cured meats with less nitrites and addition of LAB starter culture to avoid production of carcinogenic nitrosamines from nitrites
a FDA approved process
what can be formed from nitrites in cured meats?
this resulted in what?
carcinogenic nitrosames
lead to search for nitrite substitute
what are bacteriocins?
- antimicrobial peptides of bacterial origins
- lethal to some bacteria (but not the host that produced them) and can inhibit pathogens
- not antibiotics
- produced by all bacterial species
- food industry uses bacteriocins produced by LAB
describe class 1 bacteriocins
contains unusual AAs produced by post-translational modification; includes lantibiotics (bacteriocins with lanthionine rings)
in class 1 of bacteriocins, how is thioether lanthionine produced?
dehydro AAs + cysteine –> thioether lanthionine
what is a lantibiotic?
bacteriocin with lanthionine rings
included in class 1 bacteriocin
What is Nisin? how is it obtained? what is it used for?
- class 1 bacteriocin
- obtained from culturing L. lactis on natural substrates
- used to extend shelf life by suppressing gram-pos spoilage and pathogenic bacteria in processed cheese, meats and beverages
what is subtilin? what is it used in?
- class 1 bacteriocin
- lantibiotic
- effective protease
- used in food, laundry detergent, contact lens cleaners
describe class 2 bacteriocins
how does it function?
- small and heat stable proteins
- has a consensus leader sequence that signals to producing cell that protein must be exported
what are 3 subclasses of class 2 bacteriocins?
2a: active against L. monocytogenes
2b: requires 2 diff peptides for activity
2c: requires reduced cysteine for activity
describe class 3 bacteriocins
larger heat liable antimicrobial proteins
describe class 4 bacteriocins
have lipid and CHO moietites
the non-protein portions have unknown functions
what is the most common method for bacteriocin discovery
- overlay colony of putative bacteriocin producer w/ agar medium containing the bacterium being tested for sensitivity
- inhibition zone will be formed by: bacteriocin producers, or organic acid, bacteriphage or H2O2
- verication test: poke hole in center of inhibition zone where the colony is, then fill hole with proteolytic enzyme. As enzyme moves out, it cleaves the bacteriocin and inactivates it, allowing the bacteria to grow where it once inhibited
describe the inhibition zones produced by:
a) organic acids
b) bacteriophage
c) bacteriocin producers
a) organic acids: fuzzy edges
b) bacteriophage: no colony at center
c) bacteriocin producers: sharp edges of zone
how do bacteriocins produced by LAB affect the cytoplasmic membrane?
what does this result in?
- disrupts it
- results in rapid and non-specific efflux of pre-accumulated ions, AAs and ATP which dissipates chemical and electrical gradients
- cells can’t regenerate proton motive force = permeability increases = membrane can’t protect cytoplasm from environment = cell inhibition and death
although bacteriocins have varying biochemical attributes, they all act by _____ mechanisms
common
what do bacteriocins use to insert into the membrane?
what 2 models represents how this is done?
they have amphiphillic cationic peptides to insert
1) pore formation model: bacteriocins bind, insert into membrane, then oligomerize to form a pore
2) membrame solubilization model: bacteriocin acts as detergents resulting in lysis of the cell
describe the bacteriocin mechanism of action in spores
nisin allows spores to germinate but inhibits outgrowth of pre-emergent spore (which is less resistant to environmental stresses than spores)
describe colicins
proteins produced by and are toxic for strains of E.coli which carry a colicinogenic plasmid that bears genetic determinants for:
1) colicin synthesis
2) immunity
3) release
how do colicins function?
- expressed under SOS regulation; then released into extracellular medium
- binds to specific receptors on outer membrane
- translocated through outer membrane through periplasm by the tol or TonB system
- reaches lethal target. Acts by (1) forming a voltage dependent channel into inner membrane or (2) by using endonuclease activity on DNA, rRNA or tRNA
what is the SOS response?
response to DNA damage in which the cell cycle stops
first step in colicin mechanism
what are two types of colicins?
- enzymatic colicins
2. pore forming colicins
what are 4 modes of action of enzymatic colicins?
- peptidoglycan synthesis block (M)
- protein synthesis block by cleavage of tRNA (D and E5)
- protein synthesis block by cleavage of 16S rRNA (E3, E4, E6)
- DNA degradation (E2, E7, E9)
what are 3 approved methods to add bacteriocins to foods?
- purified bacteriocins added directly to food
- bacteriocinogenic cultures added to non-fermented food so bacteriocins can be produced in situ
- starter cultures encode bacteriocins chosen for fermentation rxns
describe an appliction of how purified bacteriocins can be added directly to the food pdt?
what are examples of products it is added to?
- directly adding nisin, which has anti-listerial properties to sensitize spores to heat which reduces thermal processing times
- commonly used in pdts where botulism is a concern
- nisin is used in a multiple barrier inhibitory system (includes modified atmosphere storage to delay toxin or bacterial production)
- added to milk, cheese, dairy, canned foods, baby foods
what kind of pdts is nisin used in?
pdts where botulism is a concern
describe an application of how bacteriocinogenic cultures can be added to non-fermented food pdts
- using pediocin producing cultures as a dried powder or culture liquid to be added to pdts such as salad dressings, cream, cottage chese
what is pediocins active against? what is it no active against?
active against vegetative L. monocytogenes cells
not active against spores
describe an application of using starter cultures that encode bacteriocins in fermentation rxns
- used in fermented meat and veg pdts where indigenous communities are not inactivated (ie. pasteruization)
- thus, using a starter that produces a bacteriocin can inactivate bacteria already there and give the fermentation rxn more success
- this can also add “added value: to the final pdt
what causes resistance mechanisms to bacteriocins?
changes in membrane permeability and generalized mechanisms
what are 4 types of mechanisms of resistance to bacteriocins?
describe their specificity
- destruction: specific or general
- modification: specific
- altered receptors: specific
- membrane composition: general
what is are suggestions used to overcome MOs resistant to bacteriocins? when is this effective?
- using combination of bacteriocins, but is only effective if resistance to each bacteriocin is conferred by different mechanisms
- using hurdle technology, which inhibits bacterial growth in food, but may also make bacteriocin resistant cells sensitive again
where are bacteriophages found?
naturally in food microbiota
it is routinely consumed in our diet
commercial bacteriopahges control what?
growth of salmonella, E. coli, Listeria
what are 2 challenges associated w/bacteriophage use in foods?
- possible resistance
2. low numbers of bacteria in food
how does resistance to bacteriophages occur?
by changes in bacteriophage receptor site (which consists of proteins, LPS or lipoproteins)
what is the most effective way to control resistance to bacteriophages? why?
- use multiple strains and types of phages at once
- if a bacteria is resistance to one type, other types should still be functional
