Bio Sci 106N Micropara Lec Midterms

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Bio Sci 106N (LEC):

Microbiologyand

Parasitology(MIDTERM NOTES)

_______________________Lennon D. Ponta-oy, RMT

UNIT 4. MICROBIAL GENETICS

GENETICS Study of the inheritance of biological characteristics by

living things (heredity) Examines:

o The transmission of biological properties (traits) from parent to offspring

o The expression and variation of those traitso The structure and function of the genetic materialo How this material changes or evolves

Several levels:o Organismal genetics – observes the transmission

and expression of genetic factors in the whole organism or cell

o Chromosomal genetics – examines the characteristics and actions of chromosomes

o Molecular genetics – deals with the biochemistry of gene function

LEVELS OF STRUCTURE & FUNCTION OF THE GENOMEGENOME – sum total of genetic material carried within a cell

Includes the chromosomes and the plasmidsCHROMOSOME – discrete cellular structure composed of a neatly

packaged DNA molecule; contains the geneGENE

in classic genetics, it refers to the fundamental unit of heredity responsible for a given trait in an organism

in the molecular and biochemical sense, it is a portion of the chromosome that provides information for a given cell function

specific segment of DNA (or RNA in some viruses) that contains the necessary codes for functional products

“Pursue excellence, and success will follow, pants down.” – 3 Idiots

COVERAGE:Unit 4. Microbial GeneticsUnit 5. Control of Microbial GrowthUnit 6. Drugs, Microbes, Host – the

Elements of ChemotherapyUnit 7. Infection, Infectious Diseases and

EpidemiologyUnit 8. Principles of Immunology

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directs all functions of the cell, providing it with its own particular traits and individuality

falls into three categories: Structural Genes – code for proteins Genes that code for the RNA Regulatory Genes – control gene expression

GENOTYPE – Also the genome Complete collection of genes Genetic makeup, the information that codes for all

the particular characteristics of an organism

PHENOTYPE – all the physical traits or characteristics of an organism PHENOTYPE is the manifestation of GENOTYPE.

CONSTITUTIVE GENES – genes that are expressed at all timesINDUCIBLE GENES – expressed only when needed

PACKAGING OF DNA Packing the mass of DNA into the cell involves compacting

the DNA molecule by means of supercoils or superhelices. In prokaryotes, the circular chromosome is packaged by the

action of topoisomerase (specifically DNA gyrase).o Bacteria package DNA in bacterial chromosomes

(single circular DNA) and plasmids. In eukaryotes, more complex:

o Formation of nucleosomes (linear DNA + histone)o Folding of nucleosomes in a spiral formationo Supercoiling of the spiral to form an even greater

spiral Eukaryotes package DNA in chromatin and chromosomes.

STRUCTURE & COMPOSITION OF THE GENETIC MATERIAL NUCLEOTIDES – building blocks of nucleic acids: DNA

(deoxyribonucleic acid) and RNA (ribonucleic acid) Consist of three subunits:

o Nitrogenous Bases Purines – have two rings

Adenine (A) Guanine (G)

Pyrimidines – have single ring Thymine (T) (in DNA) Cytosine (C) Uracil (U) (in RNA)

o Pentose (5-Carbon sugar) Ribose (in RNA) Deoxyribose (in DNA)

o Phosphate group


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3 Parts to Every Nucleotide

Four DNA Nucleotides

Four RNA Nucleotides

1) Nitrogen Base Adenine (A)Guanine (G)Cytosine (C)Thymine (T)

Adenine (A)Guanine (G)Cytosine (C)Uracil (U)

2) Pentose Deoxyribose Ribose3) Phosphate Group Phosphate Group Phosphate Group

DNA STRUCTURE Double-stranded helix Sugar-phosphate backbone: each deoxyribose sugar bonds

covalently in a repeating pattern with two phosphates Complementary base pairs (in DNA: A and T, G and C) are held

together by hydrogen bonds. Chargaff’s Rule

The number of purines is equal to the number of pyrimidines (A=T and G=C, thus A+G=C+T)

Antiparallel arrangement: one side of the helix runs in the opposite direction of the other (one helix runs from 5’ to 3’, the other helix runs from 3’ to 5’)


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NOTE: Adenine (A) forms two H-bonds with thymine (T). Cytosine (C) forms three H-bonds with guanine (G). The bases are attracted to each other in this pattern

because each has a complementary three-dimensional shape that fits together with its pair.

THE SIGNIFICANCE OF THE DNA STRUCTUREThe arrangement of the N-bases has two essential effects:

1. Maintenance of the genetic message during reproduction The constancy of base-pairing guarantees that the

correct order of the DNA bases will be retained during cell division.

When the two strands are separated, each one provides a template (pattern or model) for the replication (exact copying) of a new molecule.

Because the sequence of one strand provides the correct pattern for its complementary strand, the codes can be duplicated with accuracy.

2. Providing variety The order of bases along the length of the DNA strand

provides information needed to produce RNA and protein molecules, which in turn are responsible for the phenotype of the cell.

RNA STRUCTURE It is a single-stranded molecule that can assume secondary

and tertiary levels of complexity due to bonds within the molecule, leading to specialized forms of RNA (mRNA, tRNA, and rRNA).

RNA contains uracil, instead of thymine, as the complementary base-pairing mate for adenine. This does not change the inherent DNA code in any way because the uracil still follows the pairing rules.

Although RNA, like DNA, is structured with a backbone of alternating sugar and phosphate molecules, the sugar in RNA is ribose rather than deoxyribose.

DNA REPLICATION One “parental” double-stranded DNA molecule is converted

to two identical “daughter” molecules Requires unwinding the double helix and exposing the

nucleotides to serve as templates for synthesis of 2 identical molecules by DNA polymerase.

Is semiconservative (each new double-stranded DNA molecule contains one original or conserved strand and one new strand) and proceeds in the 5’ to 3’ direction of the newly synthesized DNA .

Replication fork – point in the DNA molecule at w/c replication occurs

Origin of Replication – site that serves as the site where replication will be initiated

Some Enzymes Involved in DNA Replication and their FunctionsEnzyme Function

Helicase Unzipping the DNA helixPrimase Synthesizing an RNA primerDNA Polymerase III Adding bases to the new DNA

chain; proofreading the chain for


Johann Friedrich Miester – discovered DNA (“nuclein”)James Watson and Francis Crick – discovered the double-

helix structure of DNAOswald Avery, Colin MacLeod and Maclyn McCarty

– purified DNA and demonstrated that it was indeed the blueprint for life.

Erwin Chargaff – Chargaff’s Rule

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mistakesDNA Polymerase I Removing RNA primers,

replacing gaps between Okazaki fragments with correct nucleotides, repairing mismatched bases

Ligase Final binding of nicks in DNA during synthesis and repair

Gyrase Supercoiling

DNA replication by some bacteria, such as E. coli, goes bidirectionally around the chromosome.


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THE CENTRAL DOGMA Proposed by Francis Crick in 1957 to explain the flow of

genetic information within the cell Also known as the “one gene-one protein hypothesis” States that:

o The genetic information contained in one gene of a DNA molecule is used to make one molecule of mRNA by a process known as transcription.

o The genetic information in that mRNA molecule is then used to make one protein by a process known as transcription.

THE GENE-PROTEIN CONNECTION The language of DNA exists in the order of groups of three

consecutive bases, or triplets, on one DNA strand. Each triplet represents a code for a particular amino acid. When the triplet code is transcribed and translated, it

dictates the type and order of amino acids in a polypeptide (protein) chain.

Key points that connect DNA and protein function:o DNA is a blueprint that indicates which kinds of

proteins to make and how to make them. This blueprint exists in the order of triplets along the DNA strands.

o The order of triplets directs a protein’s primary structure—the order and type of amino acids in the chain—which determines its characteristic shape and function

o Proteins contribute significantly to the phenotype by functioning as enzymes and structural molecules.

THE GENETIC CODE Set of rules specifying the relationship between the

sequence of bases in a DNA or mRNA molecule and the order of amino acids in the polypeptide chain encoded by that DNA or mRNA.


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The genetic code is a triplet code – that is, a code in which three base pairs in double-stranded DNA are required to specify each amino acid in a polypeptide.

The genetic code is a degenerate code – that is, a given AA can be specified by more than one nucleotide triplet.

The genetic code is nonoverlapping – that is , each nucleotide is part of one, and only one triplet.

Nucleotide triplets in mRNA, called CODONS, are the actual coding units read by the translational machinery during protein synthesis.

The genetic code is unambiguous – that is, every codon has one and only one meaning.

Start Codon (AUG) – initiates the process of protein synthesis

Stop Codon (UAA, UAG, and UGA) – instructs the cell to terminate synthesis of the

polypeptide chainMajor Types of RNA Involved in Protein SynthesisRNA type Contains codes

for:Function Translated

Messenger (mRNA)

Sequence of AA in proteins

Carries the DNA master code to the ribosomes

Yes

Transfer (tRNA) A cloverleaf tRNA to carry AA

Brings AA to ribosomes during translation

No

Ribosomal (rRNA)

Several large structural RNA molecules

Forms the major parts of the ribosomes and involved in protein synthesis

No

Primer An RNA that can begin DNA replication

Primes DNA No

TRANSCRIPTION It is the synthesis of an RNA molecule whose base sequence

is complementary to the base sequence of a template DNA strand.

During transcription, an RNA molecule is synthesized using the codes on DNA as a guide or template.

Enzyme involved: RNA Polymerase It proceeds in three stages:

o Initiation – requires the RNA polymerase to recognize a region on a gene called the promoter region

o Elongationo Termination

*promoter site – determines where RNA synthesis starts and which DNA strand is to serve as the template strand

*Sigma factor – guides the RNA polymerase to the correct position on the promoter

*template strand – one strand of DNA that is transcribed*nontemplate strand – sometimes called the sense, or

coding strand because its sequence is the same order as mRNA (although it will have thymine and uracil); not transcribed


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TranscriptionSequence of Bases in the DNA

TemplateSequence of Bases in the mRNA

TemplateA UT AG CC GC GG CA UA UT A


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TRANSLATION (Protein Synthesis) It refers to the synthesis of polypeptide chains on ribosomes

using a process that employs mRNA to determine the AA sequence.

Decoding the “language” of nucleic acids and converting that information into the “language” of proteins

Language of mRNA is in the form of codons, groups of three nucleotides, such as AUG, GGC, or AAA.

o The sequence of codons on an mRNA molecule determines the sequence of amino acids that will be in the protein being synthesized.

o Each codon “codes” for a particular amino acid. This is the genetic code.

o Of the 64 codons, 61 are sense codons, and 3 are nonsense codons.

o Sense codons – code for AAo Nonsense (stop) codons – do not code for AA;

signal the end of the protein molecule’s synthesis (UAA, UAG, UGA)

o Start codon – initiates protein synthesis; AUG codes for formylmethionine in bacteria (in eukaryotes, methionine)

The codons of an mRNA are “read” sequentially; and, in response to each codon, the appropriate amino acid is assembled into a growing chain.

The three-base sequence of the codon determines which tRNA brings its specific AA to the ribosome, because the tRNA molecule contains an anticodon (a 3-base sequence complementary to the code of the mRNA).

Key Components:o rRNA component of the ribosome helps position the

mRNA and catalyzes peptide bond formation.o tRNA molecules – align AA in the correct order

along the mRNA template

o aminoacyl-tRNA synthetases – attach AA to their appropriate tRNA molecules

o mRNA molecules – encode the AA sequence information for the polypeptides being synthesized

o protein factors - facilitate several steps in the translation process

Mechanism:o Translation involves initiation, elongation and

termination stages.o During the initiation stage, initiation factors trigger

the assembly of mRNA, ribosomal subunits and initiator aminoacyl tRNA into an initiation complex.

o Chain elongation involves sequential cycles of aminoacyl tRNA binding, peptide bond formation, and translocation (enzyme-directed shifting of the ribosome to the next position on the mRNA strand, which causes the blank tRNA to be discharged from the ribosome at the E site). The net result is that aminoacyl tRNAs add their AA to the growing polypeptide chain in an order specified by the codon sequence in mRNA.

o Chain termination occurs when a stop codon in mRNA is recognized by release factors, which cause the mRNA and newly formed polypeptide to be released from the ribosome.

Example:DNA template mRNA (codon) tRNA

(anticodon)Amino Acid

G C GProlineG C G

C G C


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GENETIC REGULATION OF PROTEIN SYNTHESIS AND METABOLISM

Control mechanism ensures that genes are active only when their products are required.

Major form of gene regulation in prokaryotes is through systems called operons

Operon – section of DNA that contains one or more structural genes along with a corresponding operator gene that controls transcription

o Inducible operons - the operon is turned on (induced) by the substrate of the enzyme for which the structural genes code; e.g., catabolic operons, lactose (lac) operon in bacteria

o Repressible operons -several genes in series are turned off (repressed) by the product synthesized by the enzyme; often contain genes coding for anabolic enzymes

MUTATION Changes in the base sequence of a DNA molecule

It can involve the loss of base pairs, the addition of base pairs, or a rearrangement in the order of base pairs.

Wild type/strain - A microorganism that exhibits a natural, nonmutated characteristic

Mutant strain – A microorganism that bears a mutation- show variance in morphology, nutritional

characteristics, genetic control mechanisms, resistance to chemicals, temperature preference, and nearly any type of enzymatic function

- very useful for tracking genetic events, unraveling genetic organization, and pinpointing genetic markers

SPONTANEOUS MUTATION random change in the DNA arising from errors in replication

that occur without a known causeINDUCIBLE MUTATION

result from exposure to known mutagens, which are primarily physical or chemical agents that damage DNA and interfere with its functioning

Selected Mutagenic Agents and Their EffectsAgent EffectChemicalNitrous acid, bisulfite Remove an amino group from

some basesEthidium bromide Inserts between the paired

basesAcridine dyes Cause frameshifts due to

insertion between base pairsNitrogen base analogs Compete with natural bases for

sites on replicating DNAPhysical (primarily types of radiation)Ionizing (gamma rays, X rays) Form free radicals that cause

single or double breaks in DNA


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Ultraviolet Causes cross-links between adjacent pyrimidines

Categories of Mutations: Point (base) mutations

o Involve addition, substitution or deletion of bases Missense mutation

o If the base substitution results in an amino acid substitution in the synthesized protein

Nonsense mutationo changes a normal codon into a stop codon that

does not code for an amino acid and stops the production of the protein wherever it occurs

Silent mutationo alters a base but does not change the amino acid

and thus has no effect Back-mutation

o occurs when a gene that has undergone mutation reverses (mutates back) to its original base composition

Frameshift mutationo occurs when one or more bases are inserted into or

deleted from a newly synthesized DNA strando so named because the reading frame (specific order

of nucleotides or codons provided by the mRNA formed during transcription) has been changed

Repair of Mutations: Proofreading mechanism of the DNA Photoactivation or light repair

o Fix DNA damaged by UV radiationo requires visible light and a light-sensitive enzyme,

DNA photolyase, which can attach to sites of

abnormal pyrimidine bonding and restore the original DNA structure

Excision repairo Mutations can be excised by a series of enzymes

that remove the incorrect base and add the correct ones.

Mismatch Repairo Targets errors made during DNA replication, when

improperly base-paired nucleotides sometimes escape the normal proofreading mechanisms

o Because mismatched base pairs do no hydrogen-bond properly, their presence can be detected and corrected

BACTERIAL RECOMBINATION An event in which one bacterium donates DNA to another

bacterium End result of which is a new strain different from both the

donor and the original recipient strain


Ames Test A mutant strain of Salmonella is used to learn

whether a particular chemical (e.g., a food additive or a chemical used in some type of cosmetic product) is a mutagen

If exposure to the chemical causes a reversal of the organism’s mutation (back mutation), then the chemical has been shown to be mutagenic.

If the chemical is mutagenic, then it might alse be carcinogenic (cancer-causing) and should be tested using laboratory animals or cell cultures.

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In general, any organism that has acquired genes that originated in another organism is called a recombinant

Depends largely on the bacteria’s extreme versatility in acquiring and expressing the genetic material of other bacteria and even other organisms

Are generally beneficial: They can provide additional genes for resistance to drugs and metabolic poisons, new nutritional and metabolic schemes, increased virulence, and adaptations to changing environmental conditions

Ways in Which Bacteria Acquire New Genetic Information1. Mutations – involve changes in the base sequence of genes2. Lysogenic Conversion

Involves bacteriophages and the acquisition of new viral genes

While the prophage is integrated into the bacterial chromosome, the bacterial cell can produce gene products that are coded for by the prophage genes.

3. Transduction Means “to carry across” Involves bacteriophages and the acquisition of new

bacterial genes Process by which a bacteriophage serves as the

carrier of DNA from a donor cell to a recipient cell Although it occurs naturally in a broad spectrum of

bacteria, the participating bacteria in a single transduction event must be the same species because of the specificity of viruses for host cells

Only small segments of DNA are transferred from cell to cell

4. Transformation Involves the uptake of “naked” DNA


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This nonspecific acceptance by a bacterial cell of small fragments of soluble DNA from the surrounding environment.

Cells that are capable of accepting genetic material through this means are termed competent.

5. Conjugation

Involves the transfer of genetic information from one cell to another through a hollow sex pilus

Discovered by Joshua Lederberg and Edward Tatum in 1946 while experimenting with E. coli.

Involves a specialized type of pilus called the sex pilus (F pilus or conjugation bridge)

A bacterial cell (donor cell or F+ cell) possessing a sex pilus attached by means of the sex pilus to another bacterial cell (recipient or F- cell). Some genetic material (plasmid) is then transferred through the hollow sex pilus from the donor cell to the recipient cell.

Has great biomedical importance:o Special resistance (R) plasmids, or

factors, that bear genes for resisting antibiotics and other drugs are commonly shared among bacteria through conjugation. Transfer of R factors can confer multiple resistance to antibiotics such as tetracycline, chloramphenicol, sulfonamides, and penicillin.

oOther types of R factors carry genetic codes for resistance to heavy metals (nickel and mercury) or for synthesizing virulence factors (toxins, enzymes, and adhesion molecules) that increase the pathogenicity of the bacterial strain.


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GENETIC ENGINEERING Manipulation of an organism’s genome and is often used in

conjunction with biotechnology, the use of an organism’s biochemical and metabolic pathways for industrial production of proteins

Plasmids are frequently used as vectors or vehicles for inserting genes into cells

Bacteria, yeasts, human leukocytes, macrophages, and fibroblasts have been used as genetically engineered “manufacturing plants” for proteins such as human growth

hormone (somatotropin), somatostatin, plasminogen-activating factor, insulin and interferon.

Applications:o Therapeutic applications

Synthetic genes linked to the β-galactosidase gene (lacZ) in a plasmid vector were inserted into E. coli, allowing E. coli to produce and secrete the two polypeptides used to make human insulin

Cells and viruses can be modified to produce a pathogen’s surface protein, which can be used as a vaccine.

DNA vaccines consist of recombinant DNA cloned in bacteria.

Gene therapy can be used to cure genetic diseases by replacing the defective or missing gene.

o Genome Projects Nucleotide sequences of the genomes over

1000 organisms, including humans, have been completed.

This leads to determining the proteins produced in a cell.

o Scientific Applications DNA can be used to increase understanding

of DNA, for genetic fingerprinting, and for gene therapy

DNA sequencing machines are used to determine the nucleotide base sequence of restriction fragments in shotgun sequencing.

Bioinformatics is the use of computer applications to study genetic data; proteomics is the study of a cell’s proteins


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DNA probes can be used to quickly identify a pathogen in body tissue or food

Forensic microbiologists use DNA fingerprinting to identify the source of bacterial or viral pathogens

Bacteria may be used to make nano-sized materials for nanotechnology machines.

o Agricultural Applications Cells from plants with desirable

characteristics can be cloned to produce many identical cells. These cells can then be used to produce whole plants from which seeds can be harvested.

Incorporating nitrogen-fixing capabilities into additional soil microorganisms

Make plants that are resistant to insects, as well as to bacterial and fungal diseases.

Increase the size and nutritional value of foods.

UNIT 5. CONTROL OF MICROBIAL GROWTH

Definition of Terms: Sterile

Free of life of every kind Sterilization

Complete destruction or removal of all forms of microbial life including endospore.

Usually done by steam under pressure, sterilizing gas, or ethylene oxide.

Disinfection Destruction of vegetative pathogens on inanimate

objects Partial destruction through physical and chemical

methods Antisepsis

Destruction of vegetative pathogens on living tissue Treatment is almost always by chemical antimicrobials

Sanitization Treatment intended to lower microbial counts on eating

and drinking utensils to safe public health levels. May be done with high temperature washing or by

dipping into a chemical disinfectant. Degermining

Removal of microbes from a limited area, such as the skin around an injection site.

Mostly mechanical removal by an alcohol-soaked swab Microbicidal

Property of destroying microbes Bactericidal, fungicidal, etc.

Microbiostatic Property of inhibiting microbial growth and

multiplication Bacteriostatic, fungistatic, etc.


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Disinfectant Chemical agents applied on inanimate surface, too

toxic to be applied on living tissues Antiseptic

Chemical agents which could have a –cidal or –static effect, applied topically on living tissues.

Septic Condition characterized by presence of pathogens

(particularly on living tissues) Aseptic

Condition characterized by the absence of pathogens

Thermal death time Minimum time required to kill suspension of

microbes in a given temperature in a specified environment

Thermal death point Maximum temperature in a given time to destroy all

microbes present

Several Factors that Influence the Rate at which Antimicrobial Agents Work:

Exposure time of the agent Numbers of microbes present Relative resistance of microbes (for example, endospores

versus vegetative forms) Activity of the agent (microbicidal versus microbiostatic)

2 General Methods of Microbial GrowthA. Physical methods - control is achieved by modifying

environmental condtionsa. Scrubbing with soap and water

Washing based on standard operating procedure before and after an activity

b. Filtration Used to remove microbes for liquids or gases,

with use of filters – 0.2 to 0.45µm pore. Filters most bacteria, while viruses and small

bacteria pass through them. For antibiotic solutions, CHO solutions,

vaccines, culture media which cannot be heated

Liquid: pulling solution through cellulose acetate or cellulose nitrate medium with vacuum

Air: HEPA filters (removes organisms > 0.3µm)c. Sedimentation

Allowing solid or solutes or particulate matter to settle at bottom of liquid

d. High temperaturei. Pasteurization

Use brief exposures to moderately high temp to reduce & eliminate pathogens, w/o eliminating viable beneficial microbes and w/o altering chemical nature of food.

Kills non-sporeforming organisms in heat sensitive materials (milk products, wine, etc.)

Batch/LTH – 63⁰C for 30 mins Flash/HTST – 72⁰C for 15 secs

ii. Moist Heat Denatures bacterial proteins; water

hastens breaking of H-bonds which hold proteins in their 3 dimensional configurations; more penetrating

Boiling 100⁰C for 15 mins or 30 mins


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Kills vegetative cells but not spores

For sterilization of apparatus that are heat resistant

Suitable in situations from which endospores and hepatitis virus are known to be absent

Autoclaving Steam under pressure Most effective method 121⁰C at 15lbs psi for 15mins Destroys spores For sterilization of culture media

and surgical instruments Biologic indicator: Bacillus

stearothermophilus Tyndallization

Also Fractional/Discontinuous/ Intermittent Sterilization

For heat labile, spore-containing material

100⁰C for 30 mins for 3 consecutive days; 60⁰C for 1hr for 5-6 days

Inspissation 75⁰C - 80⁰C for 2 hrs for 3

consecutive days Principle: Thickening through

evaporation For high protein content media

e. Dry Heat Denatures proteins; kills organisms by

oxidation; requires higher temperature and

long exposure to ensure complete sterilization

Passing through a flame For loops needles, mouth of

tubes as well as plates Hot Oven

For sterilization of glasswares 160⁰C - 170⁰C for 1.5 to 2 hrs

Incineration For infectious wastes; burning

wastes into ashes 870⁰C - 980⁰C (800⁰C to 6500⁰C) Banned in the Philippines

Cremation Burning dead bodies (with

communicable disease) to ashesf. Low Temperature

Limits rate of microbial reproduction Microbiostatic Commonly used to preserve food, media,

and cultures 5⁰C for refrigeration temperature; 0⁰C or

subzero; freeze drying through sublimationg. Radiation

Ionizing Radiation Short wavelength, high energy

gamma rays and x-rays For plastic syringes, catheter or

gloves Has deep penetrating power and

works by causing breaks in the DNA of target organisms

Non-ionzing Radiation Long wavelength low E UV light


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Very little penetrating power Works by creating dimers

between adjacent pyrimidines, which interferes with replication

B. Chemical Methodsa. Halogens

Chemicals based on elements from group VII of the periodic table

i. Chlorine Kills microbe by disrupting the plasma

membrane Chlorine gas, hypochlorites,

chloramines all work by disrupting disulfide bonds

Na hypochlorite or bleach (1:10)ii. Iodine

Reactive by precipitating proteins and oxidizes essential enzymes

I2 + detergent = iodophor I2 in alcohol = I2 tincture

iii. Fluorides In toothpaste, H2O supply

b. Phenolic Compounds Act by disrupting lipid containing

membranes, resulting in leakage of cellular contents

Carbolic acid, Lysol, cresol-o-polyphenol Standard disinfectant in the lab

c. Detergentsi. Anionic Detergents (Soaps)

Removing grease and soil that contains microbes

ii. Quaternary Ammonium Compounds (QUATS) Cationic detergents

Act as surfactants that alter the membrane permeability of some bacteria and fungi

Benzalkonium chloride (Zephiran) For digestion and decontamination of

sputum Inactivated by ORGANIC SUBSTS Disadvantage: Nonsporicidal;

Nontuberculoidald. Alcohols

Most effective and most used Act as surfactants, dissolving membrane

lipids and coagulating proteins of vegetative bacterial cells and fungi

Non-sporicidal Used on skin (as antiseptic) and on

thermometers and injection vial rubber septum (as disinfectant)

Evaporates easilyi. Ethanol

70% is more effective than 95% EtOH 70% EtOH kills nearly 90% of

cutaneous microbiota w/in 2 minsii. Isopropanol

Highest bactericidal activity at 70-80% Less activity against endospores, fungi

and virusese. Aldehydes

Denature proteins and DNA by alkylation Used for disinfecting surgical

instruments Formaldehyde and Glutaraldehyde (pH

7.5 kills Staphylococci in 5 mins, tubercle


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bacilli in 10 mins and endospore for 12 mins

f. Acids – destroy or inhibit microbial cellsi. Organic Acids

widely used in food preservation because they prevent spore germination and bacterial and fungal growth and because they are generally regarded as safe to eat

Acetic acid, Lactic acid, Benzoic acid, Sorbic acid

Vinegar (household disinfectant)g. Alkalis – inactivates proteins

i. Ammonium hydroxide `reliably destroys prions

h. Dyes antimicrobial effects are apparently due to

the way they insert into nucleic acids and cause mutations

interfere with cell wall synthesisi. Hydrogen peroxide

produces highly reactive hydroxyl free radicals that damage protein and DNA while also decomposing to O2 gas, which is toxic to anaerobes

3 to 6% solutions – antiseptic 6 to 25% solutions – for sterilization

mixtures, disinfects implants, prostheses and contact lenses

Strong solutions are sporicidalj. Ethylene oxide

Colorless gas, soluble in water and organic solvents used for heat sensitive items

Used for sterilizing aircrafts for space explorations

Can be used for sterilizing disposable utensils, instruments and prostheses

k. Ozone Strong oxidizing agent Oxidizes cellular biochemical Disinfect drinking water

l. Heavy Metals Acts with sulfhydryl groups of proteins, thus

inactivates them Inactivated by organic materials (e.g.,

blood) Mercury-containing compound is no longer

recommended – toxic to the environment Silver Nitrate eyedrop – used to prevent N.

gonorrhoeae infection in newbornsm. Chlorhexidine

surfactant and protein denaturant with broad microbicidal properties, although it is not sporicidal

Solutions of chlorhexidine are used as skin degerming agents for preoperative scrubs, skin cleaning, and burns

n. Antibiotics Antimicrobial substances produced by

microbes, used for treating humans and animals

Modes of action: inhibits CW synthesis, inhibits CM function, inhibits protein synthesis, inhibits nucleic acid synthesis


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Bio Sci 106N Micropara Lec Midterms

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