18) Biological Control of Foodborne Bacteria

Question 1

Define biopreservation

what does this definition exclude?

Answer 1

using MO and/or their metabolic pdts to preserve food

excludes fermentation

Question 2

what is an exception of fermentation that is considered biopreservation?

Answer 2

controlled acidification where acid is produced by LAB in temp-abused foods

Question 3

what are 3 methods of acid production in controlled acidification

Answer 3

1. adding organic acids to food
2. producing organic acids via fermentation
3. LAB producing lactic acid in situ

Question 4

describe microGARD

what does it include?

Answer 4

• 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

Question 5

what are key benefits of microGARD?

Answer 5

1. protect shelf life
2. maintain organoleptic qualities of food
3. meet consumers’ demand for natural pdts

Question 6

when microGARD is present in food, what does bacteria do if food is temp abused?

Answer 6

bacteria (LAB) grows and produces lactic acid, acetic acid, propionic acid and bacteriocins to ensure safety of the pdt

Question 7

effectiveness of in situ acidification of MicroGARD depends on what?

Answer 7

the products:

• pH
• buffering capacity
• target spoilage MO
• concentration of fermentable CHOs

Question 8

describe the original experiment using microGARD

Answer 8

1. 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
2. conditions were set to simulate temp abuse (prepared food was left for extended period at 30C)
3. results:
   - in absence of LAB, samples became toxic
   in presence of LAB, very few samples became toxic

Question 9

what is the wisconsin process

what is the result of this?

Answer 9

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

Question 10

what can be formed from nitrites in cured meats?

this resulted in what?

Answer 10

carcinogenic nitrosames

lead to search for nitrite substitute

Question 11

what are bacteriocins?

Answer 11

• 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

Question 12

describe class 1 bacteriocins

Answer 12

contains unusual AAs produced by post-translational modification; includes lantibiotics (bacteriocins with lanthionine rings)

Question 13

in class 1 of bacteriocins, how is thioether lanthionine produced?

Answer 13

dehydro AAs + cysteine –> thioether lanthionine

Question 14

what is a lantibiotic?

Answer 14

bacteriocin with lanthionine rings

included in class 1 bacteriocin

Question 15

What is Nisin? how is it obtained? what is it used for?

Answer 15

• 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

Question 16

what is subtilin? what is it used in?

Answer 16

• class 1 bacteriocin
• lantibiotic
• effective protease
• used in food, laundry detergent, contact lens cleaners

Question 17

describe class 2 bacteriocins

how does it function?

Answer 17

• small and heat stable proteins

- has a consensus leader sequence that signals to producing cell that protein must be exported

Question 18

what are 3 subclasses of class 2 bacteriocins?

Answer 18

2a: active against L. monocytogenes
2b: requires 2 diff peptides for activity
2c: requires reduced cysteine for activity

Question 19

describe class 3 bacteriocins

Answer 19

larger heat liable antimicrobial proteins

Question 20

describe class 4 bacteriocins

Answer 20

have lipid and CHO moietites

the non-protein portions have unknown functions

Question 21

what is the most common method for bacteriocin discovery

Answer 21

1. overlay colony of putative bacteriocin producer w/ agar medium containing the bacterium being tested for sensitivity
2. inhibition zone will be formed by: bacteriocin producers, or organic acid, bacteriphage or H2O2
3. 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

Question 22

describe the inhibition zones produced by:

a) organic acids
b) bacteriophage
c) bacteriocin producers

Answer 22

a) organic acids: fuzzy edges
b) bacteriophage: no colony at center
c) bacteriocin producers: sharp edges of zone

Question 23

how do bacteriocins produced by LAB affect the cytoplasmic membrane?

what does this result in?

Answer 23

1. disrupts it
2. results in rapid and non-specific efflux of pre-accumulated ions, AAs and ATP which dissipates chemical and electrical gradients
3. cells can’t regenerate proton motive force = permeability increases = membrane can’t protect cytoplasm from environment = cell inhibition and death

Question 24

although bacteriocins have varying biochemical attributes, they all act by _____ mechanisms

Answer 24

common

Question 25

what do bacteriocins use to insert into the membrane? what 2 models represents how this is done?

Answer 25

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

Question 26

describe the bacteriocin mechanism of action in spores

Answer 26

nisin allows spores to germinate but inhibits outgrowth of pre-emergent spore (which is less resistant to environmental stresses than spores)

Question 27

describe colicins

Answer 27

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

Question 28

how do colicins function?

Answer 28

1. expressed under SOS regulation; then released into extracellular medium 2. binds to specific receptors on outer membrane 3. translocated through outer membrane through periplasm by the tol or TonB system 4. 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

Question 29

what is the SOS response?

Answer 29

response to DNA damage in which the cell cycle stops first step in colicin mechanism

Question 30

what are two types of colicins?

Answer 30

1. enzymatic colicins | 2. pore forming colicins

Question 31

what are 4 modes of action of enzymatic colicins?

Answer 31

1. peptidoglycan synthesis block (M) 2. protein synthesis block by cleavage of tRNA (D and E5) 3. protein synthesis block by cleavage of 16S rRNA (E3, E4, E6) 4. DNA degradation (E2, E7, E9)

Question 32

what are 3 approved methods to add bacteriocins to foods?

Answer 32

1. purified bacteriocins added directly to food 2. bacteriocinogenic cultures added to non-fermented food so bacteriocins can be produced in situ 3. starter cultures encode bacteriocins chosen for fermentation rxns

Question 33

describe an appliction of how purified bacteriocins can be added directly to the food pdt? what are examples of products it is added to?

Answer 33

- 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

Question 34

what kind of pdts is nisin used in?

Answer 34

pdts where botulism is a concern

Question 35

describe an application of how bacteriocinogenic cultures can be added to non-fermented food pdts

Answer 35

- using pediocin producing cultures as a dried powder or culture liquid to be added to pdts such as salad dressings, cream, cottage chese

Question 36

what is pediocins active against? what is it no active against?

Answer 36

active against vegetative L. monocytogenes cells not active against spores

Question 37

describe an application of using starter cultures that encode bacteriocins in fermentation rxns

Answer 37

- 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

Question 38

what causes resistance mechanisms to bacteriocins?

Answer 38

changes in membrane permeability and generalized mechanisms

Question 39

what are 4 types of mechanisms of resistance to bacteriocins? describe their specificity

Answer 39

1. destruction: specific or general 2. modification: specific 3. altered receptors: specific 4. membrane composition: general

Question 40

what is are suggestions used to overcome MOs resistant to bacteriocins? when is this effective?

Answer 40

1. using combination of bacteriocins, but is only effective if resistance to each bacteriocin is conferred by different mechanisms 2. using hurdle technology, which inhibits bacterial growth in food, but may also make bacteriocin resistant cells sensitive again

Question 41

where are bacteriophages found?

Answer 41

naturally in food microbiota it is routinely consumed in our diet

Question 42

commercial bacteriopahges control what?

Answer 42

growth of salmonella, E. coli, Listeria

Question 43

what are 2 challenges associated w/bacteriophage use in foods?

Answer 43

1. possible resistance | 2. low numbers of bacteria in food

Question 44

how does resistance to bacteriophages occur?

Answer 44

by changes in bacteriophage receptor site (which consists of proteins, LPS or lipoproteins)

Question 45

what is the most effective way to control resistance to bacteriophages? why?

Answer 45

- use multiple strains and types of phages at once | - if a bacteria is resistance to one type, other types should still be functional