Microbiology exam two

Sterilization

Removes/kills all life, including bacterial endospores. Is difficult to attain.

Disinfection

Reduces number of potentially pathogenic microbes.

Disinfectants

used on non-living objects

Antiseptics

used on living tissue

Bacteriostatic

agents inhibit bacterial growth

Bactericidal

agents kill bacteria but not necessarily endospores

Protein denaturations

action for antimicrobials

membrane disruption

action for antimicrobials

alkylating agents add alkyl groups to proteins and nucleic acids, disrupting structure

action for antimicrobials

Number of microbes, exposure time

Factor influencing agent antimicrobial effectiveness

Microbial characteristics. could form endospores

Factor influencing agent antimicrobial effectiveness

Environmental influences. Temperature and presence of organic material

Factor influencing agent antimicrobial effectiveness

Sufactants

Soap, detergents. Aide removal most are not bactericidal

Alcohol

Dissolves membranes, denatures proteins

Heavy metals

copper or silver. Bind to and denature proteins

Halogens

bleach. Oxidize/denature proteins, damage membranes

Alkylating agents

ethylene oxide. Denature proteins, disrupt nucleic acids

Heat

Autoclaves. commonly used for sterilization

pasteurization

kills pathogens in liquid with heat. Exposes liquids to specific temperature for specific time, normally does not sterilize

irradiation

high energy ionizing. common for heat sensitive products

filtration

membrane pore size excludes microbes. air filters

Anti-microbial drug therapy

most antibiotics are naturally produced by soil bacteria or fungi

Seletice toxicity

is critical. Goal is high toxicity to microbe, low toxicity to patient. Max does tolerated is high and therapeutic dose is low

spectrum of activity

can be brand or narrow. Determined by antibiotic’s mechanism of action or how it affects bacteria

Cell wall mechanisms of action

synthesis inhibitors is the most common. Penicillin, bacitracin and vancomycin does this.

Cell membrane mechanisms of action

Disruption of peptogiycan. polymyxins and gramicidin does this. Mainly targets gram negative

protein Synthesis mechanisms of action

Inhibitors of protein synthesis. streptomycin, neomycin, and tetracycline do this

Nucleic acid mechanism of action

Synthesis inhibitors. inhibits DNA gyros. Quinolones (ciprofloxacin) inhibit DNA synthesis

Antimetabolites

inhibit specific metabolic pathways. Sulfa drugs are competitive inhibitors of colic acid synthesis. B9

B-lactam ring

critical for inhibition of transpeptidase. Basic structure of cell wall synthesis inhibitor antibiotic that inhibits transpeptidase enzyme.

Gramicindin

a peptide that forms an ion channel across membranes, compromises membrane integrity. For topical use only. Would insert into good membranes also which is why only topical use.

Antibiotics that inhibit protein synthesis

inhibit normal function of bacterial ribosomes

Sulfa drugs

are antimetabolites that competitively inhibit folic acid synthesis.

PABA

normal substrate. Used for folic acid synthesis in prokaryotes.

Sulfanilamide

a sulfa drug. Structure is similar to PABA, acts as competitive inhibitor of folic acid synthesis

Desirable antimicrobial characteristics

soluble, stable in body fluids. Selectively toxic, little resistance, non-allergenic, low cost, easy storage

Mechanism of microbial drug resistance

acquired via spontaneous mutation or gene exchange

Prevention of drug accumulation within cell

enzymes that destroy drug

(B-lactamase hydrolyzes penicillin)

Pump drug out of cell using efflux pump

Decrease membrane permeability

Modify drug target so drug no longer binds

Mutation increases enzyme specificity

Mutation in rRNA or ribosomal proteins, antibiotic no longer binds/inhibits modified ribosome

Antibiotic resistance

Enzyme inactivates antibiotic: B-lactamase breaks a bond in the B-lactamase ring of penicillin to disable the molecule. Bacteria with this enzyme can resist the effects of penicillin and some other B-lactam antibiotics.

Principles of antibiotic resistance

Antibiotics do not induce (cause) initial resistance, but they do select and amplify pre-existing resistance

Factors contributing to antibiotic resistance

insufficient exposure time

overuse/misuse of antibiotics amplifies overall resistance

last resort antibiotics exist but how long will they be effective?

Spontaneous antibiotic resistance

lung is infected with an antibiotic susceptible pathogen—→ replication happens spontaneous antibiotic-resistant mutant —→ antibiotic is administered and patient starts to recover ——→ mutant replicates while antibiotic is still present and patient relates

Prokaryotic Genetics: Chromosomes and Genomes

Double strandar DNA

chromosomes usually circular

single chromosome

Genomes increasingly sequenced and used to identify species

plasmid with multiple resistance genes

A sinle palms can carry genes to resist many antibiotic. pLW1043 plasmid

MDR strains

multiple resistant drug pathogen

Gene expression

represents a universal central dogma of biology

DNA —→ RNA polymerase——→ RNA —→ Ribosome ——> protein

DNA replication uses transcription and translation

genetic code

ultimately read by ribosome as a triplet code of codons

DNA template strand ——> transcription (mRNA) —→ translation (protein)

Biotechnology

Recombinant DNA and genetic engineering

cloning and expression of human growth hormone

Plasmids

small, circular, self-replicating extrachromosomal DNA

often contain antibiotic resistance genes and virulence genes

important molecular biology tool

Microbial Gene transfer/exchange

1. Mutations in DNA

2. Horizontal gene transfer. Primary source of genetic diversity in bacteria. (can result in rapid acquisition of antibiotic resistance, virulence factors) transfer of DNA from donor cell to recipient cell produces recombinant cell with new genes. Prokaryotes are capable of 3 types on gene transfer

Transformation

Griffith first described this. Avery demonstrated DNA was crucial for this material in 1940s. This provided evidence that DNA and not protein was the long sought after genetic material. Only competent cells can take up DNA by this. Requires competence factor or chemical treatment. Commonly used in genetic engineering.

Transduction

Virus transferring DNA. Bacteriophage virus injects nucleic acid into host cell. Occurs as bacterial DNA from an infected donor cell is mistakenly packaged into new virus. Phage then transfers DNA to another recipient bacteria where it is integrated into recipient cell chromosome.

Virus life cycle

requires packaging of viral genome into new viruses. (transduction)

Conjugation

plasmid transfer requiring sex pills. Can transfer large amounts of DNA potentially entire plasmid. F+ cells transfer palms to F- cells. common method for transfer of antibiotic resistance genes.

Transposons

Jumping DNA sequences, move randomly between DNA of plasmids and chromosome. Cane carry antibiotic resistance genes.

what is transposes composed of

Transposes gene which allowed transportation from one site in DNS to another site

Insertion sequences define transposon ends where transposes enzyme blinds and cuts

Often include antibiotic resistance genes

Order of horizontal transformation

donor—> (DNA)——> recombinant cell (virulent cell)