Microbio Exam 2

removes/kills all life, including bacterial endospores

reduces number of potentially pathogenic microbes

Disinfectants: are used on non-living objects
Antiseptics: disinfect living tissue
Bacteriostatic agents: inhibit bacterial growth
Bacteriocidal agents: kill bacteria (but not always endospores)

1. Protein denaturation
2. Membrane disruption
3. Alkylating agents

Number of microbes, exposure time
Microbial characteristics
Environmental influences

1. Surfactants (soaps, detergents) aide removal,
-most not bactericidal
2. Alcohol (typically ~70% ethanol in H2O)
-dissolves membranes, denatures proteins
3. Heavy metals (e.g. silver, copper)
-Bind to and denature proteins
4. Halogens (e.g. chlorine [bleach], iodine)
-Oxidize/denature proteins, damage membranes
5. Alkylating agents (e.g. formaldehyde, glutaraldehyde, ethylene oxide [gas] can sterilize)
-Denature proteins, disrupt nucleic acids

1. Heat: Autoclave (steam under pressure) commonly used for sterilization
-Pasteurization kills pathogens in liquid
-Exposes liquids to specific temperature for
specific time, normally does not sterilize
2. Irradiation (high energy ionizing typically used)
-Common for heat-sensitive products, some foods
3) Filtration (of liquids, air)
-Membrane pore size excludes microbes (E.g. HEPA air filters in clinical/surgical units)

lowers microbial numbers in liquids (not designed to sterolize)

Goal is high toxicity to microbe, low toxicity to patient (host)
Chemotherapeutic index = max dose tolerated/theraputic dose

Can be broad or narrow
Determined by antibiotic's mechanism of action

1. Cell wall synthesis inhibitors (penicillin, vancomycin, bacitracin)
2. Disruption of cell membrane (polymyxins, gramicidin)
3. Protein synthesis inhibitors (streptomycin, neomycin, tetracycline)
4. Nucleic acid synthesis inhibitors (quinolones)
5. Antimetabolites inhibit specific metabolic pathways (sulfa drugs are competitive inhibitors of folic acid synthesis)

A peptide that forms an ion channel across membranes, compromises membrane integrity

50S subunit: oxazolidinones; prevent 70S subunit formation
macrolides; prevent peptidyltransferase activity and location
30S subunit: aminoglycosides; inhibit translocation and cause misreading of mRNA
tetracyclines; prevent aminoacyl-tRNA entry into the A site

Antimetabolites that competitively inhibit folic acid synthesis
(PABA is the normal substrate)

Soluble, stable in body fluids
Selectively toxic, little resistance
Non-allergenic
Low cost, easy storage

1. Prevent drug accumulation within cell
a. Enzymes that destroy drug (beta-lactamase hydrolyzes penicillin)
b. Pump drug out of cell using efflux pump
c. Decrease membrane permiability
2. Modify drug target so drug no longer binds
-E.g. mutation inceases enzyme specificity

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

Insufficient exposure time
Overuse/misuse of antibiotics

Double-stranded DNA
Chromosomes usually circular
Single chromosome
Genomes increasingly sequenced and used to identify species

DNA --(RNA polymerase/[Transcription])--> RNA --(Ribosome/[Translation])--> Protein

By ribosomes as a triplet code of codons

Small, circular, slef-replicating extrachromosomal DNA
Often contain antibiotic resistance genes and virulence genes
Important molecular biology tool

1. Mutations in DNA
2. Horizontal (lateral) gene transfer

Primary source of genetic diversity in bacteria
Transfer DNA from donor cell to recipient cell produces recombinant cell with new genes

Transformation
Transduction
Conjugation

Recipient cell takes in donor DNA from environment, integrates into it's chromosome
Griffith first described transformation
Only competent cells can take up DNA by transformation
OR
Transfers less than 1% of cell's DNA
Requires competence factor; changes certain characteristics of an organisim, depending on which genes are transferred

Require conpetence factor expression by recipient cell or chemical treatment
-Commonly used in genetic engineering to introduce DNA into bacteria cells

Virus transfers DNA
Occurs as bacterial DNA from donor (infected) cell is mistakenly packaged into new virus
Phage then transfers DNA to another (recipient) bacteria, where it is integrated into recipient cell chromosome
OR
Transfer is effected by a plasmid
Generalized transduction transfers any random fragment of bacterial DNA, while specialized transduction transfers only specific bacterial genes

virus injects nucleic acid into host cell

requires packaging of viral genome into new viruses

Plasmid transfer requiring conjugation (sex) pilus
Can transfer large amounts of DNA, potentially entire plasmid
F+ cells transfer plasmid to F- cells
Common method of transfer of antibiotic resistance genes

"Jumping" DNA sequences, move randomly between DNA of plasmids and chromosomes
Carry antibiotic resistance genes

Transposase gene allows transposition from one site to another site
Insertion sequences define transposon ends, where transposase binds and cuts
Often inculde resistance gene(s)

largely beneficial (e.g. prevent pathogen colonization, educate immune system, provide beneficial vitamins, enzymes)

1. Host is immunosuppressed
2. Introduced to abnormal (e.g. sterile) body sites
3. Normal microflora disturbed/eliminated

1. Attatchment of pathogen to host tissue is crucial
-adhesions on cell wall, pili, capsule, flagella...
2. Avoidance of host defences
3. Colonization of host tissue
4. Invasiveness (penetration/persistance in host tissue), pathology/immunopathology
5. Exit from host/transmission to next host

Rigid, non-retractable primarily used by bacteria for adhesion to host cells or surfaces, important in infections like UTI

Flexible, retractable involved in both bacteria adhesion and twitching motility, also play a role in DNA uptake and surface movement

Allows pathogen invasion of deeper host tissues

extracellular, intracellular

host phagocytes and antibodies

Capsule to prevent phagocytosis
Coagulase sheilds bacteria from white blood cells
Leukcidin enzymes kill white blood cells
Antigenic variation changes surface coat proteins at regular intervals

Survive in harsh phagolysome environment
Inhibit fusion of phagosome to lysosome
Escape from phagosome

Secreted proteins from gram positive bacteria

Extremely potent at low doses
Target-specific effects
Cause tissue damage/pathology, often involving benefit to pathogen survival and/or transmission
Can cause intoxication if ingested
Some exotoxins can be made into vaccines

Plasma membrane disruption (hemolysis)
Protein synthesis disruption (diptheria toxin)

caused by hemolysin exotoxins
method of action is plasma membrane disruption

AB type toxin that inactivates eukaryotic ribosomes (protein synthesis disruption), causes cell death
A subunit: acts as a toxin, inhibits vital cell function
B subunit: attatchment, entry into host cell
B subunit peramiter surrounds A subunit

(LPS) gram negative outer membrane component
Released upon bacterial cell death
Toxic in high doses
Systemic effects: can cause hyper-inflammation, fever, rashes
Dramatic vasodilation, blood vessel leakiness, clotting, blood pressure drop, shock, possible death

Used by clinics, public health and other government agencies to provide:
-Information and statistics on pathogens, disease frequency and transmission in populations
-Advice on interventions, treatment during outbreaks

First epidemiology study in London 1854, cholera in the water

Organism: virulence factors, invasiveness
Reservoir: animal, human, environment
Transmission: person to person, inanimate objects, air, vector borne
Susceptible host: portal of entry, immuno-competence

total active cases in population

new cases in a population/time period

always present in a population (rhinoviruses, west nile in US)

describes disease cause and source

sudden incidence rise in region (cholera in Haiti 2010)

spreads worldwide (COVID-19)

single contaminated source (typically short duration)

transmitted easily person to person (typically longer duration)

Acquired from healthcare provider or facility
Affect 5-10% of hospital patients

Susceptible individuals
Presence of many pathogens
Extensive antibiotic useessitance
Lack of proper preventative actions

Urinary tract (20-30%, catheter-associated)
Pneumonia (15-20%, ventilator-associated)
Surgical wounds (20-30%, surgical site-associated)
Septicemia (5-10%, central line-associated)
Diarrhea (15-20%, antibiotic-associated)