Microbial Growth and Control Mechanisms

Microbial growth

Increase in number of cells NOT cells size

Biofilm

Community of mixed microbes living together.

Lag Phase

Initial phase of microbial growth where there is no increase in cell number.

Exponential Phase (log phase)

Phase of rapid cell division and growth.

Stationary Phase

Phase where growth rate slows and cell division equals cell death.

Death Phase

Phase where the number of dying cells exceeds the number of new cells formed.

Psychrophile

Organisms that grow best at low temperatures.

Mesophile

Organisms that grow best at moderate temperatures.

Thermophile

Organisms that grow best at high temperatures.

Psychotroph

Organisms that can grow at low temperatures but have a higher optimal temperature.

Halophiles

Thrive in high-salt environments (> 3% NaCl).

Obligate aerobe

Grows only in the presence of oxygen.

Facultative anaerobe

Can use oxygen or grow without oxygen; WILL USE oxygen if present.

Obligate anaerobes

Grow only in the absence of oxygen and lack enzymes to breakdown harmful oxygen species.

Differential media

Media formulated to visually distinguish one microbe from another.

Selective media

Ingredients foster the growth of certain bacteria and suppress the growth of others.

Decontamination

Removes or reduces microbial populations to render an object safe for handling.

Sterilization

Eliminates all bacteria, viruses, and endospores.

Pasteurization

HIGH HEAT/SHORT TIME process to kill pathogens.

CIDE

Refers to agents that KILL.

STATIC

Refers to agents that INHIBIT growth.

Competitive Inhibitors

Bind the active site of an enzyme and block the substrate from binding.

Non-competitive Inhibitors

Bind to a regulatory site of an enzyme, changing the shape of the active site.

Holoenzyme

Protein plus one or more cofactors.

Apoenzyme

Not active, has protein but no cofactors.

Catabolism

Reactions that break down large molecules to small molecules, generating ATP.

Anabolism

Reactions that combine small molecules to larger ones, using ATP.

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

Opportunistic pathogens

Only cause disease when their host is weakened.

True pathogen

Does not require a weakened host to cause disease.

Epidemic

A widespread disease outbreak in a particular region during a specific time frame.

Pandemic

Occurs if an epidemic spreads to numerous countries.

Zoonotic diseases

Spread from animals to humans.

Virulence

Describes severity of disease following infection.

Pathogenicity

The general ability of an infectious agent to cause disease.

Infectious dose-50 (ID50)

Number of cells or virions needed to establish an infection in 50% of exposed hosts.

Endotoxins

Released when cell wall is broken; Lipid A region of LPS.

Exotoxins

Secreted from cell

Adhesins

Virulence factors used to stick to host cells in a specific or nonspecific manner

BSL-1 agents

Examples: Bacillus subtilis

BSL-2 agents

Examples: Staphylococcus aureus

BSL-2+ agents

HIV

BSL-3 agents

Examples: Mycobacterium tuberculosis

BSL-4 agents

Examples: Ebola

Alexander Fleming

Discovered penicillin in 1928

Bacteriostatic

Prevent bacteria from growing (INHIBIT)

Bactericidal

Kill bacteria

Penicillin

Inhibits by inhibiting enzyme that forms peptide bridges

Isoniazid

Inhibits mycolic acid

Streptomycin

Binds 30S Ribosome, causes misreading of mRNA

Tetracycline

Binds 30S Ribosome, Inhibits tRNA from binding to A site of ribosome

Erythromycin

Binds 50S ribosome, inhibits translocation of ribosomes

Sulfonamides

TMP/Sulfanilamide inhibit folic acid synthesis

Ciprofloxacin

Inhibits DNA Gyrase

Rifamycin

Inhibits RNA Polymerase

Polymyxins

Interacts with membrane phospholipids; distort the cell surface and cause leakage of protein and nitrogenous bases

Azoles

Class of antifungal drugs targeting fungal plasma membranes

Allyamines

Class of antifungal drugs targeting fungal plasma membranes

Polyenes

Class of antifungal drugs targeting fungal plasma membranes

Intrinsic resistance

Natural resistance to antimicrobial drugs

Acquired resistance

Resistance comes from genetic mutation or by acquisition of resistance genes

Generation time

Time it takes for a cell to divide

Log Phase (Exponential Phase)

Period of rapid exponential growth

Psychrophiles

Thrive between -5 C-20 C

Psychrotrophs

Grow at about 0 C-30 C; associated with foodborne illness

Mesophiles

Grow best between 20 C-50 C; associated with most pathogens

Thermophiles

Grow 50 C-80 C; associated with compost piles and hot springs

Hyperthermophiles

Grow above 80 C

Superoxide dismutase

Converts reactive superoxide ions to hydrogen peroxide

Catalase

Converts the hydrogen peroxide to water and oxygen

Obligate aerobes

Require oxygen to grow

Microaerophiles

Use only small amounts of oxygen

Facultative anaerobes

Grow with and without oxygen and will use oxygen if present

Aerotolerant anaerobes

Grow with or without oxygen, but do not use oxygen to grow

Defined media

Chemically defined or precisely known composition

Mannitol salt agar (M S A)

An example of selective media

Eosin methylene blue agar (E M B)

An example of selective media

Disinfection

Reduces microbial numbers

Microbiocidal

Germicides that kill microbes

Microbiostatic

Germicides that only inhibit microbial growth

Disinfectants

Used to treat inanimate objects

Antiseptics

Applied to living tissue

Alcohols

Intermediate-level disinfectants that denature proteins and attack lipid membranes

Halogens

Oxidize cell components

Ethylene oxide

Sterilant that damages proteins and nucleic acids; colorless gas

Amphibolic pathways

Have a dual role, and can be used for both breaking down and building substances

Effects of temperature on enzymes

Lowering temperature will lower enzyme activity, causing cells to grow slower; warmer temperatures can increase enzyme activity.

pH effects on enzymes

pH above or below optimal pH will alter enzyme structure by disrupting bonds; extreme changes in pH can also lead to protein denaturation.

Coenzymes

Enzymes carrying out redox reactions usually rely on coenzymes like NAD+ and FAD to act as electron shuttles.

Infectious disease

An illness caused by a pathogen.

Epidemiology

The monitoring and controlling disease occurrence to promote public health.

Latent infection

Patients experiencing a latent infection are usually asymptomatic.

Reservoirs

An animate or inanimate habitat where the pathogen is naturally found.

Dysbiosis

Microbiota disruption.

Virulence factors

Mechanisms pathogens use to overcome our defenses.

Attenuated

A pathogen that is still infectious, but weakened.

Infectious dose-50

Number of cells or virions needed to establish an infection in 50% of exposed hosts.

Lipid A

The lipid portion of lipopolysaccharide (LPS) that is toxic to us and other animals.

Transferrin

Binds to iron and shuttles it to tissues.