BIOL 2401 Week 8 Unit 6: Growing microbes in the lab & Measuring bacterial growth

Commerical sterilization

Heat treatment aimed at killing endospores in canned foods

Disinfection

Destroying vegetative pathogens on surfaces and objects (fomites)

Fomite

Inanimate object that can become contaminated with infectious agents

Antiseptic

Disinfectant for living tissue

Degerming

Mechanical removal of microbes from living tissue

Sanitization

Lowering microbial counts to safe levels

Biocide

Treatment that can kill microorganisms

Bacteriostatic

Treatment that only stops division or growth of bacteria

AMA

Anti-microbial agent

Critical items

Sterile items. E.g. surgical forceps

Semi-critical items

Highly disinfected items. E.g. CPAP mask

Non-critical items

Lightly disinfected items. E.g. glasses

D-value

Expresses the efficiency of anti-microbial agents. Time needed to kill 90% of bacteria. Smaller D-value = stronger AMA

Most resistant microbe

Prions

Least resistant microbe

Lipid-enveloped viruses, since their fatty membrane is fragile

Physical damage to microbes

Changing membrane permeability, causing cellular contents to leak out and cause death

Chemical damage to microbes

Causing protein or DNA/RNA damage, disrupting the cell’s funtion

What microbes does boiling not kill?

Boiling does not kill endospores

Autoclave

Use of heated steam under pressure to sterilize

Dry heat

Flaming contaminants (flaming loops!). Burns them

Hot-air sterilization

High temperatures for longer periods of time, such as for lab glassware

Pasteurization

Use of mild heat to kill pathogens without changing taste of food. E.g. wine or milk

How does freezing kill bacteria/parasites?

By damaging proteins and cell structure, rupturing cells

Phenols and phenolytics

Disrupts lipids and denatures enzymes, killing microbes. E.g. lysol or triclosan

Heavy metals (disinfectant)

Denatures proteins, killing microbes. E.g. silver, copper, and zinc

Halogens (disinfectant)

Oxidizes proteins and cell membranes. E.g. Iodophors and chlorine

Iodophor

Combination of iodine and an organic molecule, used as an antiseptic. Effective against endospores

Alcohol (disinfectant)

Denatures proteins and disrupts membrane. May induce endospore formation

Surfactant

Decreases surface tension of water, mechanically removing (but not killing) microbes

Detergents (disinfectant)

Cationic detergents that disrupt plasma membranes, particularly effective against gram-positive bacteria

Alkylating agents

Denatures proteins and damages DNA. E,g, Glutaraldehyde and formaldehyde

Gaseous alkylating agents

Kills all microbes and endospores at room temperature. E.g. ethylene oxide and propylene oxide

Oxidizing agents

Reactive oxygen forms that oxidize proteins and cell membranes. E.g. hydrogen peroxide and ozone

Why is hydrogen peroxide not optimal for wounds?

Because bodt cells frequently contain catalase, converting hydrogen peroxide into other forms

Antibiotic

Antimicrobial agent produced derived from organisms

Narrow spectrum antibiotics

Highly specific towards certain types, only killing targetted ones. Requires lab testing before prescription

Broad spectrum antibiotics

Affects many microbes, can be immediately prescribed. May harm normal flora and increase risk of a superinfection

Inhibition of cell wall synthesis (antibiotics)

Weakens cell wall (peptidoglycan), making bacteria susceptible to lysis. E.g. penicillin

Disruption of the plasma membrane (antibiotics)

Changing plasma membrane permeability, impacting cell metabolism. Bactericidal. E.g. Polymyxin B

Inhibition of protein synthesis (antibiotics)

Inhibits protein production, targeting ribosome. Bacteriostatic. E.g. Tetracycline

Inhibition of nucleic acid synthesis

Prevents DNA & RNA replication. Broad spectrum, bactericidal. E.g. Rifamycin (rifampin)

Block the production of essential metabolites

Inhibits production of required substances, such as folic acid. Broad spectrum, bacteriostatic

Superbug

Bacteria resistant to many antibiotics. E.g. Staphylococcus aureus

Why are antimicrobial drugs for eukaryotic pathogens difficult to safely treat with?

Since eukaryotic cell structure is closer to ours, making selective treatment more challenging. Can also cause side effects

Antifungals

Targets ergosterols in fungi, disrupting ergosterol synthesis. E.g. miconazole

Atovaquone

Anti-protozoan drug that blocks the ETC in protozoa

Ivermectin

Anti-helminthic drug that blocks neuronal transmission in worms, leading to paralysis and death of worms.