Microbio lab practical- section 6 control of growth and death of microorganisms

bactericidal effect

kills the microbes

bacteriostatic effect

inhibits the reproductive capacities of the cells and maintians the microbial population at a constant size

methods for control of microbial growth

- cell-wall injury

- cell membrane damage

- alteration of the colloidal state of cytoplasm

- inactivation of enzymes

- interference with the structure and function of the DNA molecules

cell wall injury

- lysis of cell wall

- inhibit cell wall synthesis which is needed for rell reproduction

cell membrane damage

lysis of membrane which causes immediate cell death

alteration of the colloidal state of cytoplasm

certain agents cause denaturing of cytoplasmic proteins, produces irreversible cell damage

inactivation of enzymes

Due to the activity of certain physical and chemical agents,s cell cannot perform essential life functions

interference with the structure and function of the DNA molecule

breakage or distortion of molecule DNA, interfering with replication and role in protein synthesis

antiseptics

chemical substances used on living tissue that kills or inhibits the growth of vegetative microbial forms

disinfectants

chemical substances that kill or inhibit the growth of vegetative microbial forms on nonliving materials

chemotherapeutic agents

chemical substances that destroy or inhibit the growth of microorganisms in living tissues

factors that influence efficiency of disinfectants and antiseptics

- concentration

- length of exposure

- type of mcirobial population to be destroyed

- environmental conditions: temperature, pH, type of material n which the microorganism exist

- mode of growth

- concentration of organisms

efficiency factor- concentration

higher concentrations produce a more rapid death. concentration cannot be determined arbitrarily, the toxicity of the chemical to the tissues being treated and the damaging effect on nonliving materials must be considered

efficiency factor- length of exposure

sensitive forms are destroyed more rapidly than resistant ones. longer the exposure, the greater its antimicrobial activity

efficiency factor- type of microbial population to be destroyed

bacterial spores are the most resistant forms. capsulated bacteria are more resistant than non-capsulated forms. acid-fast bacteria are more resistant than non-acid fast. older, metabolically less active cells are more resistant than younger cells

efficiency factor- temperature

increasing temp increases rate of chemical reactions. application of heat during disinfection markedly increases rate that the population is destroyed

efficiency factor- pH

can change potency of an agent and impact cell survivial

efficiency factor- type of material on which the mciroorganisms exist

destructive power of the compounds on cell is due to its combination with organic cellular molecules. if the material is primarily organic like blood, tissue fluids, pus, the agent witll combine with these organic molecules and the antimicrobial activity will be reduced

efficiency factor- concentration of organisms

too many cant kill them all

narrow spectrum activity

effective only against a subset of bacteria, usually gram negative or gram positive

broad spectrum activity

effective against both gram positive and gram negative

B-lactam

inhibit peptidoglycan synthesis

glycopeptide

inhibit peptidoglycan chain elongation

intracellular

inhibit peptidoglycan subunit synthesis

antibiotics

synthesized and secreted by some bacteria, actinomycetes, and fungi that destroy or inhibit the growth of other microorganisms. some antibiotics are laboratory synthesized or modified, however origins are living cells

synthetic drugs

synthesized in laboratory

competative inhibition

active compenent of drug competes with the essential metabolite during synthesis

what agent uses competative inhabition

sulfadiazine (a sulfonamide)

anti-metabolite

class of drug that mimics natural cell compounds used in cell metabolism and interferes with their processes including DNA replication

essential metabolite

small molecule produced during cell metabolism that is vital for growth, development, and reproduction

Kirby-Bauer antibiotic sensitivity test

test to see drug susceptibility of microorganisms

zone of inhibition

region around the filter paper disc that results from the diffusion of the agent into the medium surrounding the disc

autoclaving

free-flowing steam under pressure

tyndallization

free flowing steam at 100 C

- kills all vegetative cells

- using this for three consecutive days ensures that all spores are destructed

pasteruization

exposes thermolabile products like milk, wine, beer for a given period of time, high enough to destroy pathogens and spoilage-causing microorganisms

gamma radiation

originating from unstable atomic nuclei

x-ray

originating from outside of atomic nucleus

ionizing radiation

gamma and x radiation- transfer energy through photons, causing excitation and loss of electrons from molecules. this injurous effect is nonspecific

free radicals

form HO2 free radicals due to radiation breakdown. the free radicals combine with oxygen to form H2O2 which is highly toxic

ultraviolet light

has a lower energy content than ionizing radiation, but can produce a lethal effect in cells exposed to the low penetrative wavelengths

thymine dimerization

covalent bonding of two adjacent thymine molecules on one nucleic acid strand in the DNA molecule. this dimer formation distorts the DNA configuration and interferes with DNA replication and transcription during protein synthesis

transient microbes

microorganisms that are not normally found on skin, organisms that temporarily colonize the body but don't establish permanent residence

native microbiota

microorganism that normally inhibit the hosts body, like gut microbiota

chromosomal resistance

mutation of the chromosomal DNA- spontaneous or induced

extrachromosomal resistance

bacteria acquire resistant plasmids that carry resistant genes by conjugation or transduction

genetic transformation

change caused by genes, involves the insertion of a gene or set of genes into an organism in order to change the organisms trait

mechanisms of resistance

- blocking entry

- enzymes

- alteration of targets

- alteration of membrane permeability

- alteration of metabolic pathways

blocking entry

alteration of porins in gram negative bacteria (only applies to gram negative)

enzymes

enzymes that destroy or inactivate antimicrobial agents

alteration of targets

alteration of antibiotic targets like ribosomes where the tareted portion is altered and formerly inhibited reaction occurs

alteration of membrane permeability

change the nature of proteins in the membrane, like efflux pumps, so the antibiotic is pumped out of the cell at a higher rate

alteration of metabolic pathway

bacteria are able to by-pass the reaction inhibited by the antimicrobial

selection

selection is accomplished by growth on plates containing the antibiotic

selective agent- antibiotic

heat shock

rapidly increase then decrease the sample temperature to increase permeability of the cell membrane to DNA