Microbiology Exam 2

Sepsis

Bacterial contamination

Asepsis

absence of significant contamination

Sterilization

removing and destroying all microbial life using temp and pressure

Commercial Sterilization

killing Clostridium botulinum endospores from canned goods

Disinfection

destroying harmful microorganisms on non-living things

Antisepsis

Destroying harmful microorganisms on living things

Degerming

the mechanical removal of microbes from a limited area

Sanitization

removal of pathogens from objects to meet public health standards

Biocide (Germicide)

Treatment that kills microbes

Bacteriostasis

Inhibiting microbes (not killing)

What does the effectiveness of treatment depend on?

Number of microbes, environment (organic matter, temperature, biofilms), time of exposure, microbial characteristics

Microbial Control Agent Actions

Altercation of membrane permeability; damage to proteins (enzymes); damage to nucleic acids

What are the physical methods of microbial control?

Heat, low temp, desiccation, osmotic pressure, radiation

How does heat control microbial growth?

Denatures enzymes

What is the Thermal death point (TDP)?

lowest temperature at which all cells in a liquid culture are killed in 10 min

What is the Thermal death time (TDT)?

minimal time for all bacteria in a liquid culture to be killed at a particular temperature

What is the Decimal reduction time (DRT)?

Minutes to kill 90% of a specific population of bacteria at a given temperature

Moist Heat Sterilization

Autoclaving; Pasteurization; Boiling

Autoclave

Steam under pressure; 121 degrees C, 15 psi, 15 minutes; kills all organisms and endospores

Pasteurization

reduces spoilage organisms and pathogens

High-temperature short-time (HTST)

most common form of pasteurization; uses metal plates and hot water to raise milk temperatures to at least 72° C for 15 seconds, followed by rapid cooling

Dry Heat Sterilization

kills by oxidation (removal of electrons); flaming; incineration; hot-air sterilization

Filtration Sterilization

a "cold" method of sterilization that removes microbes instead of killing them; used for heat-sensitive materials;

HEPA (high-efficiency particulate air) filter

remove microbes > 0.3μm in diameter

Membrane filters

remove microbes >0.22 μm

How does low temperature control microbial growth?

Refrigeration, deep-freezing, lyophilization (freeze drying)

Desiccation

Absence of water prevents metabolism; drying out an organism

How does osmotic pressure control microbial growth?

uses high concentrations of salts and sugars to create hypertonic environment

Ionizing radiation

Includes X-Rays, gamma rays, electron beams; Ionizes water to create reactive hydroxyl radicals; Damages DNA by causing lethal mutations

Nonionizing radiation

Includes ultraviolet, 260 nm; Damages DNA by creating thymine dimers

Microwaves

kill by heat; not especially antimicrobial

Radiant Energy Spectrum

- Wavelength increases as you go from gamma rays to radio waves

- Energy increases as you go from radio waves to gamma rays

Principles of Effective Disinfection

Concentration of disinfectant; Organic matter; pH; Time

Use-Dilution Tests

-Metal cylinders are dipped in test bacteria and dried

-Cylinders are placed in disinfectant for 10 min at 20°C

-Cylinders are transferred to culture media to determine whether the bacteria survived treatment

Disk-Diffusion Method (Kirby-Bauer test)

-Evaluates efficacy of chemical agents

-Filter paper disks are soaked in a chemical and placed on a culture

-Look for zone of inhibition around disks

If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference?

Sneeze is watery and vomit has food so the two are completely different

Phenol (Phenolics)

Injure lipids of plasma membranes, causing leakage

Bisphenols

-Contain two phenol groups connected by a bridge

-Example: Hexachlorophene and triclosan

-Disrupt plasma membranes

Biguanides

- Example: Chlorhexidine

- Used in surgical hand scrubs

- Disrupt plasma membranes

Essential Oils (EOs)

-Mixtures of hydrocarbons extracted from plants

-Examples: Peppermint oil, pine oil, orange oil

-Used for centuries in traditional medicine and for preserving food

-Microbial action primarily due to phenolics and terpenes

-Stronger activity against gram-positive bacteria; effectiveness against viruses not studied to date

Halogens

Iodine and Chlorine

Iodine

-Tincture: solution in aqueous alcohol

-Iodophor: combined with organic molecules

-Impairs protein synthesis and alters membranes

Chlorine

- Oxidizing agents; shut down cellular enzyme systems

- Bleach: hypochlorous acid (HOCl)

- Chloramine: chlorine + ammonia

Alcohols

- Denatures proteins and dissolves lipids

- No effect on endospores and nonenveloped viruses

- Ethanol and isopropanol- Require water

Heavy Metals and their Compounds

-Oligodynamic action: very small amounts exert antimicrobial activity; a biocidal effect of metals, especially heavy metals, that occurs even in low concentrations

-Denature proteins

-Ag, Hg, Cu, Zn

Silver Nitrate

used to prevent ophthalmia neonatorum

Mercuric chloride

prevents mildew in paint

Copper sulfate

algicide

Zinc chloride

found in mouthwash

Surface-Active Agents

soap, acid-anionic sanitizers, quaternary ammonium compounds (quats)

Soap

Degerming; emulsification (breaks down lipids)

acid-anionic sanitizers

Anions react with plasma membrane

quaternary ammonium compounds (quats)

Cations are bactericidal, denatureproteins, disrupt plasma membrane

Chemical Food Preservatives

-Sulfur dioxide prevents wine spoilage

-Organic acids: inhibit metabolism; Sorbic acid, benzoic acid, and calcium propionate prevent molds in acidic foods

-Nitrites and nitrates prevent endospore germination

Bacteriocins

proteins produced by one bacterium that inhibits another

Nisin and natamycin (pimaricin)

prevent spoilage of cheese

Aldehydes

- Inactivate proteins by cross-linking with functional groups (-NH2, OH, -COOH, -SH)

- Used for preserving specimens and in medical equipment (Formaldehyde and ortho-phthalaldehyde) (Glutaraldehyde is one of the few liquid chemical sterilizing agents)

Chemical Sterilization

-Gaseous sterilants cause alkylation—replacing hydrogen atoms of a chemical group with a free radical

-Cross-links nucleic acids and proteins

-Used for heat-sensitive material (Ethylene oxide)

Plasma

- Fourth state of matter, consisting of electrically excited gas

- Free radicals destroy microbes

- Used for tubular instruments

Supercritical Fluids

-CO2 with gaseous and liquid properties

-Used for medical implants

Peroxygens and Other Forms of Oxygen

-Oxidizing agents

-Used for contaminated surfaces and food packaging (O3, H2O2, and peracetic acid)

Is Betadine an antiseptic or a disinfectant when it is used on skin?

antiseptic

What chemical disinfectants can be considered sporicides?

Nitrate and nitrite prevent endospore germination

The presence or absence of endospores has an obvious effect on microbial control, but why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria?

Gram-negative has two plasma membranes and a liposaccharide covering and when it's broken down, Lipid A is released which is a toxin

Selective toxicity

selectively finding and destroying pathogens without damaging the host

Chemotherapy

the use of chemicals to treat a disease. Paul Ehrlich coined the term "chemotherapy"

Antibiotic

a substance produced by a microbe that, in small amounts, inhibits another microbe

Antimicrobial drugs

synthetic substances that interfere with the growth of microbes

Who coined the term chemotherapy?

Paul Ehrlich coined the term "chemotherapy"

More than half our antibiotics are produced by a certain genus of bacteria. What is it?

Streptomyces genus

Narrow spectrum of microbial activity

drugs that affect a narrow range of microbial types

Broad-spectrum antibiotics

affect a broad range of gram-positive or gram-negative bacteria

Superinfection

overgrowth of normal microbiota that is resistant to antibiotics

Identify at least one reason why it's so difficult to target a pathogenic virus without damaging the host's cells.

Because the virus lives inside the host cell so it's difficult to get to it and can affect the host cells

Why are antibiotics with a very broad spectrum of activity not as useful as one might first think?

They destroy many normal microbiota of the host

Bactericidal

Kill microbes directly

Bacteriostatic

Prevent microbes from growing

The Action of Antimicrobial Drugs

1. Inhibition of cell wall synthesis

2. Inhibition of protein synthesis

3. Inhibition of nucleic acid replication and transcription

4. Injury to plasma membrane

5. Inhibition of synthesis of essential metabolites

Inhibiting cell wall synthesis example

Penicillins prevent the synthesis of peptidoglycan

Inhibiting protein synthesis

-Target bacterial 70S ribosomes

-Examples: Chloramphenicol, erythromycin, streptomycin, tetracyclines

Injuring the plasma membrane examples

- Polypeptide antibiotics change membrane permeability.

- Antifungal drugs combine with membrane sterols.

- Ionophores antibiotics allow uncontrolled movement of cations (not for human use)

What cellular function is inhibited by tetracyclines?

Protein Synthesis

Inhibiting nucleic acid synthesis

Interfere with DNA replication and transcription

Inhibiting the synthesis of essential metabolites

- Antimetabolites compete with normal substrates for an enzyme

- Example: Sulfanilamide competes with para-aminobenzoic acid (PABA), stopping the synthesis of folic acid

Penicillin

- Contain a β-lactam ring: Types are differentiated by the chemical side chains attached to the ring

- Prevent the cross-linking of peptidoglycans, interfering with cell wall construction(especially gram-positives)

Natural penicillins

- Extracted from Penicillium fungi cultures: Penicillin G (injected) and Penicillin V (oral)

- Narrow spectrum of activity

- Susceptible to penicillinases (β-lactamases)

β-lactamases

inactivate beta-lactam antibiotics

Semisynthetic penicillins

- Contain chemically added side chains, making them resistant to penicillinases

- Oxacillin: Narrow spectrum; only gram-positives; resistant to penicillinases

- Ampicillin: Broad spectrum; mostly gram-negatives

Penicillinase-resistant penicillins

Methicillin and oxacillin

Extended-spectrum penicillins

- Effective against gram-negatives as well as gram-positives

- Example: ampicillin, amoxicillin

Penicillins plus β-lactamase inhibitors

Contain clavulanic acid, a noncompetitive inhibitor of penicillinase

Carbapenems

modified to make broad spectrum

Monobactam

- Synthetic; single ring instead of the β-lactam double ring

- Low toxicity; works against only certain gram-negatives

Cephalosporins

- Work similar to penicillins

- β-lactam ring differs from penicillin

- Grouped according to their generation of development

Polypeptide antibiotics

-Bacitracin: Topical application; works against gram-positives

- Vancomycin: Last line against antibiotic-resistant MRSA

- Teixobactin: A new class of antibiotics; worksagainst gram-positives

Antimycobacterial Antibiotics

- Isoniazid (INH): Inhibits the mycolic acid synthesis in mycobacteria

- Ethambutol: Inhibits incorporation of mycolic acid into the cell wall

One of the most successful groups of antibiotics targets the synthesis of bacterial cell walls; why does the antibiotic not affect the mammalian cell?

No cell walls in mammals

What phenomenon prompted the development of the first semisynthetic antibiotics, such as methicillin?

Staphylococcus became resistant to penicillin so methicillin was discovered

What genus of bacteria has mycolic acids in the cell wall?

Microbacteria

Nitrofurantoin

- Converted to intermediates that attack bacterial ribosomal proteins

- Synthesized chemically

- Treatment for urinary bladder infections