Exam 4 SG

BIO 220

3 types of mechanisms for exchanging genetic information in bacteria:

1. Transformation

2. Conjugation

3. Transduction

Transformation

absorption of DNA from the environment. EX: heat-killed bacteria with a capsule released DNA into the environment

Conjugation

exchange of plasmid DNA between two bacteria;

Gram negative: conjugate through formation of a sex pilus

Gram positive: form a sticky surface called glycocalyx

Transduction

bacterial DNA is transferred to another cell by a bacteriophage, or phage; inserted DNA segments are incorporated into bacterium’s genome, and the genes are transcribed

Similarities between the 3 types of mechanisms:

1. they all transfer genetic material from one bacterium to another

2. all create new combinations of genes

3. all can change bacterial traits

Transposon(jumping genes)

pieces of DNA that can excise out of the chromosomes and reinsert back into a different part of the chromosome

Transposon jumps inside a promoter:

would interfere with transcription which may result in the gene not being transcribed properly

Transposon jumps inside of a terminator:

terminator is involved in ending transcription, if disrupted transcription may not stop correctly

Transposon jumps inside of an operon:

operon controls the expression of genes, as a result of disruption the genes controlled may not be expressed correctly

Plasmids

small, circular, autonomous(independent) pieces of DNA found in the cytoplasm of some bacteria

F factor (type of plasmid)

produces the sex pillus, only found in G- bacteria

Dissimilation plasmids

produce enzymes to catabolize carbohydrates and hydrocarbons (oil); used to degrade oil spills and pollution

Pathogenic plasmids

produce toxins and other proteins that increase the pathogenicity of the bug

Resistance factors (type of plasmid)

produce enzymes to break down antibiotics, toxins and heavy metals

Restriction enzyme

used to cut the plasmid DNA; very specific to where they cut in the DNA sequence

2 types of cuts restriction enzymes make:

1. Sticky-ended cut

2. Blunt end cut

Methods for integrating a plasmid back inside a bacterial cell:

1. Weaken the cells with calcium chloride, then heat shock to absorb plasmid from the media

2. Digest the cell wall with enzymes to form protoplasts

3. Use a gene gun with high pressure to shoot the plasmids into the protoplasts

Protoplasts

bacterial cells that have had their outer cell wall removed by enzymatic digestion; very delicate with only a plasma membrane as protection

Electroporation

when protoplasts are treated with an electrical current to poke holes in the plasma membrane

Intrinsic

physical and chemical properties of the food

Extrinsic

properties of the storage environment

Nutrient content (Intrinsic)

chemical composition of the food determines the type of microorganisms that will grow

pH and Organic acids (Intrinsic)

foods with a pH below 4.5 are not readily spoiled by bacteria but are susceptible to molds and yeasts

Water activity (Intrinsic)

the amount of water available for microorganisms to use for growth

Time and Temp (Intrinsic)

for every 10°F increase in storage temperature there is a doubling in growth rate of bacteria, and for every 10°F decrease in storage temperature the growth rate is cut in half.

Oxygen (Intrinsic)

removing or reducing oxygen in food packages (by vacuum packaging or canning) or exchanging it with other gases (by using controlled atmosphere or modified atmosphere packaging) stops the growth of most spoilage microorganisms

Storage temp (Extrinsic)

different bacteria have optimum growth temperatures.

Relative humidity of environment (Extrinsic)

an increase in relative humidity could increase an microorganism's aw value, causing it to grow

Gasses (Extrinsic)

increasing the concentration of CO 2 can slow down the growth

Temperature danger zone

when bacteria can double in number every 15 to 20 minutes, especially in the temperature range of 41°F to 135°F; microorganisms multiply quickly within this range

Staphylococcal food poisoning (staphylococcal enterotoxicosis)

Caused by enterotoxin produced by S.aureus; bug is resistant to environmental stress, heat (vegetative cells can survive 60C for 30 min), drying, radiation, osmotic pressure.

Salmonellosis (Salmonella gastroenteritis)

inhabit intestines of humans and animals; meat is very susceptible

Cholera

caused by Vibrio cholerae; ingested through contaminated seafood, infects small intestines; produces enterotoxin that causes cells to release chlorine, water, and bicarbonates—electrolyte imbalance.

E. coli gastroenteritis (travelers diarrhea)

Causes hemorrhagic colitis, inflammation of colon with bleeding, maybe hemolytic uremic syndrome (blood in urine leading to kidney failure, called HUS).

Campylobacter gastroenteritis

causes diarrhea, intestinal/stomach cramping; most likely to contract Campylobacter when consuming undercooked chicken

Botulism

Caused by Clostridium botulinum; produces neurotoxin in anaerobic environment such as canned foods

Norovirus

leading cause of viral disease outbreaks from contaminated food in the United States; highly contagious

Cheese (dairy fermentation)

use lactic acid bacteria to give aroma and flavors; longer the cheese is aged, stronger the flavor.

Buttermilk (dairy fermentation)

use lactic acid bacteria to form lactic acid and diacetyls which give the flavor and aroma

Yogurt (dairy fermentation)

evaporated low-fat milk inoculated with Streptococcus thermophilus (acid production) and Lactobacillus bulgaricus (flavor, aroma); the slightly acidic pH also decreases the growth of spoilage bacteria

Bean fermentations:

soy sauce, tofu

Grain fermentations:

Beer, bread, sake, sourdough, rice wine, malt whiskey (made only from malted barley), grain whiskey (from both malted and unmalted barley and other grains), Vodka (from rye or wheat)

Vegetable fermentations:

Pickles (cucumbers), olives, sauerkraut (cabbage), Vodka (potatoes or sugar beets), gin (juniper berries), tequila (agave plant)

Fruit fermentations:

wine, cider, vinegar

Meat fermentations:

salami, prosciutto

Alcohol fermentation

cereal grains (barley, oats, rice, etc) are malted, which means they are allowed to partially germinate (sprout) and then are quickly heated to stop germination. Malting allows the development of enzymes that will convert starch into glucose and other sugars.

Ways an antibiotic can have side effects:

1. Drug may be toxic to certain organs (liver, kidneys, nervous system)

2. Allergic responses to drug

3. Changes to the normal flora (diarrhea, nausea and vomiting can all be side effects of these drugs)

Ways and antibiotic may not be effective and how it can affect the patient:

1. The drug cannot diffuse into the area where the infection is located (such as the brain, joints, or skin).

2. A few resistant cells are present, meaning some pathogens are not affected by the antibiotic.

3. The infection is caused by more than one pathogen, and some of those pathogens are resistant to the drug.

Kirby-Bauer technique

an agar diffusion test that will show antimicrobial sensitivity to various drugs

Susceptible

microorganism is affected by the antibiotic, meaning the drug is effective at inhibiting or killing it

Intermediate

microorganism shows a response between susceptible and resistant; the antibiotic may have limited effectiveness

Resistant

microorganism is not affected by the antibiotic, meaning the drug will not effectively treat the infection

MIC (minimum inhibitory concentration)

determines the smallest effective dose of a drug that will kill the organism; tests different drug concentrations to find the lowest effective amount