microbiology exam 4

disease

a condition where normal structure and/or function are damaged or impaired

infection

invasion of pathogn or parasite that leads to disease

signs (evidence for infection)

things that can be directly measured by a clinician (e.g. blood count)

symptoms (evidence for infection)

things felt by patient that cannot be clinically measured (e.g. nausea)

syndrome

groups of signs and symptoms that help indicate a particular disease

• some symptoms may be asymptomatic = meaning that only signs can be observed through correct testing

  • e.g. patient w/ herpes and no symptoms

infectious (classification for diease)

disease is directly affected by pathogen(s)

communicable (classification for disease)

capable of spreading person-to-person

latrogenic (classifications of disease)

acquired as result of a medical procedure

nosocomial (classification for disease)

acquired from a hospital setting

zoonotic (classifications of disease)

acquired from animal, usually vertebrate

non-communicable (classification of disease)

obtained from non-living thing such as soil of contaminated object

non-infectious (classification of disease)

not caused by pathogen

WHO’s international classification of disease (ICD)

used globally to classify and monitor diseases

healthcare professionals (doctors, nurses, researchers, epidemiologists, etc.)

ICD used by

periods/stages of disease

1. incubation

2. prodromal

3. illness

4. decline

5. convalescence

incubation (stage one of disease)

initial entry of pathogen; replication begins

prodromal (stage 2 of disease)

replication continues; host starts to show signs and symptoms

illness (stage 3 of disease)

signs and symptoms are most severe in host

decline (stage 4 of disease)

pathogen now starts to decrease; host’s immune system is weak and vulnerable to secondary infection

convalescence (stage 5 of disease)

host starts to recover

patient is contagious is which stages of disease?

all stages

koch’s postulates (developed in 1884)

set of standards that must be met

• The suspected pathogen must be found in every case of disease and not be found in healthy individuals

• The suspected pathogen can be isolated and grown in pure culture

• A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms of disease seen in postulate one

• The pathogen must be re-isolated from the new host and must be identical to the pathogen in postulate 2

koch’s wrong assumptions

1. pathogen are only found in diseased individuals

2. all subjects are equally susceptible to infection

3. all pathogens can be grown in culture

molecular koch’s postulates

• postulates improved with molecular methodologies

• overcame some of koch’s limitations

• identifies gene instead of pathogen

pathogenicity

ability of pathogen to cause disease

virulence

degree of pathogenicity

• continuum among many pathogen types

• ex. highly virulent - Bacillus anthracis induces severe signs and symptoms

• ex. low nutrient - rhinovirus induces low signs and symptoms

pathogens - primary and opportunistic

• some are automatic pathogens, some are not

• primary pathogen: enterohemorrhagic E. coli (mainly due to Shiga toxin)

• opportunistic pathogen: candida albicans; UTI caused by E. coli

• Drugs, resident microbiota, genetics, and age can all influence susceptibility to disease

acute v. chronic disease

• illness period can be variable

• acute disease: relatively short (hours, days, week)

• chronic disease - longer time (months, years, lifetime)

• latent disease - comes in episodes; pathogen replicates when disease is active

virulence curve

• virulence can be modelled in controlled experiments

• median infectious dose - no. of pathogens required to infect 50% of population

• median lethal dose - no. of pathogens required to kill 50% of the population

medican infectious dose (virulence curve)

how mant pathogens will infect 50% of the population?

median lethal dose (cirulence curve)

how many pathogens to kill 50% of the population?

virulence curve - brain training on reading graphs

The higher the value (more pathogens), the WORSE the infection is. (200 pathogens to infect/kill 50% of the population is worse than 400 pathogens to infect 50% of the population)

stages of pathogenicity

1. exposure to host

2. adhesion

3. invasion and colonization

4. infection

exposure to host (stage of pathonenicity)

can occur in many ways; pathogens must be exposed to portals of entry (eyes, nose, throat, mouth, vagina, anus, urethra, broken skin, needle, palcenta, insect bite, etc.) to begin adhesion (also known as trophism)

• some portals are worse than others (e.g. mucosa)

TORCH infections (infect pregnant women)

pathogens that can cross planential barrier as portal of entry

• Tocoplasmosis

• O (syphilis, chickenpox, hepatitis B, HIV, fifth disease - erythema infectiosum)

• Rubella (german measles)

• Cytomegalovirus

• Herpes

adhesion (step of pathogenicity)

pathogens have varying capability of colonization.

Adhesion factors:

• molecules/structures that bind to certain host receptors

• biofilm- production of community glycocalyx

invasion (step of pathogenicity)

occurs when colonization is established.

• pathogens generally produce toxins to allow further colonization into body/tissue

• virulence plays role in degree of invasion

  • Ex. Helicobacter pylori urease production

obligate intracellular invade via

endocytosis and evasion of host immune defenses

invasion mechanisms

1. effector proteins are secreted to trigger entry (e.g. salmonella and shigella spp.)

2. surface proteins allow for binding to host cell (trojan horse approach)

some pathogens are able to survive

lysosome that engulf (ex. Mycobacterium tuberculosis and listeria)

some pathogens can evade

phagocytosis of WBC

• listeria - can lyse phagosome before fusing with lysosome

• mycobacteria tuberculosis - prevent fusion of phagosome with lysosome

infection (stage of pathogenicity)

multiplication leads to established host infection.

types of infection

1. local infection

2. focal infectionp

3. systemic infection

local infection

small area on the body

focal infection

pathogen or toxin spreads to secondary location

systemic

occurs throughout body (ex. septicemia)

primary infections can lead to

secondary infection of different pathogen

• Ex. HIV lowers immune system and opens door for yeast and others; rhinoviruses can lead to bacterial pneumonia

virulence factors dictate how

severe and extensive a disease is.

some have more than one = more virulent

• examples

  • adhesion factors (adhesion)

  • exoenzymes (invasion)

  • toxins (invasion)

  • immune evasion (invasion)

adhesins - virulence factors

Proteins that aid in attachment to host cell receptors

• commonly found in fimbriae or pili

• can initiate biofilm formation in some species

  • Ex. Stereptococcus pyogenes produces Protein F to adhere to respiratory epithelia on the back of the throat (pharynx)

exoenzymes (virulence factors)

extracellular enzymes used to invade host tissues

• examples: glycohydrolases, nucleases, phospholipases, proteases

toxins (virulence factors)

poisons that cause host cell toxigenicity

• endotoxins - lipolysaccharides (only gram - ) that triggers host inflammatory responses; can cause severe fever and shock

• exotoxins - proteins mostly produces by Gram (+); targets receptors on specific cells

intracellular targeting (exotoxin)

with A and B regions for activity and binding; Ex. diptheria and botulinum toxin

Membrane disrupting toxin (exotoxin)

aka phospholipases that degrade bilayer membrane; Ex. Bacillus anthracis and rickettsia spp.

• S. pyogenes produces streptolysin, enhancing invasion to cells

superantigen toxin (exotoxin)

trigger excessive producation of cytokines by immune cells; Ex. staphylococcus auerus and toxic shock syndrome

host evasion (virulence factors)

mechanisms to evade phagocytosis

• examples:

  • capsules that enlarge bacterial cell so phagocytes cannot engulf pathogens

  • proteases digest host antibody molecules

  • mycolic acid in acid fast bacteria (M. tuberculosis) helps evade phagolysosomes

  • coagulase pos. microbes can coagulate blood cells to keep immune cells out of reach

  • alteration of cell surface proteins to hide from immune cell recognition

virulence in viruses

some properties are similar to bacteria (adhesions and antigenic variation)

• example:

  • HIV glycoprotein 20 for binding to CD4 T-cells

  • influenza virus’ high mutation of envelope spikes allows for antigenic variation

virulence in fungi

many properties are also similar to bacteria (adhesions, proteases, and toxins)

• example

  • capsule (+) cryptococcus spp. can cause pneumoniae and meningitis

  • mycotoxins produced by Claviceps purpurea and Aspergillus spp. that contaminate grains and other staple crops

virulence in protozoans

unique features for attachment-

• Giadfia lamblia uses adhesive disk of microtubules to attach to intestines

• plasmodium falciparum quickly changes adhesive protein fr RBC’s to avoid immune recognition; causes chronicity in malaria patients

virulence in helminths

• tissue penetration commonly achieves w/ proteases (e.g. worms that burrow into skin)

• roundworms produce cuticle to last longer against host defense assaults

• schistosoma mansoni degrades host antibodies to halt immune defense

focal infection

a localized infection that spreads to other parts of the body, potentially cuasing systemic disease.

local infection

an infection confines to a specific part of the body, like a urinary tract infection or a skin infection, and doesn’t spread throughout the body.

secondary infection

an infection that occurs during or after treatment for another primary infection

systemic infection

an infection that has spread throughout the body often through the bloodstream

causes of superinfections

the growth of resistant organisms (bacteria, lichens, or fungi) that are normally held in check by the forms of bacteria normally present in the oral and intestinal tracts of the host animals.

TORCH pathogens

infectious agents that can be transmitted from a mother to her fetus during pregnancy.

(Toxoplasmosis, Others (syphilis, Zika virus, malaria, HIV), Rubella, Cytomegalovirus, and Herpes sumplex virus)

ID50 vs. LD50

• ID50 is the infectious dose that will cause 50% of people exposed to a pathogen to become contaminated.

• LD50 is the lethal dose that will kill 50% of people.

Limulus amoebocyte lysate (LAL) test and endotoxins

LAL test is widely used in vitro assay for detecting bacterial endotoxins. It relies on the coagulation of amebocyte lysate from horseshoe crabs in the presence of endotoxins, a process that can be measured quantitatively or qualitatively

facultative intracellular pathogens

microorganisms, primarily bacteria, that can replicate both inside and outside host cells.

obligate intracellular pathogens

microorganisms that can only survive and reproduce inside the cells of a host.

what makes up a DNA nucleotide

a phosphate group, a five-carbon sugar called deoxyribose, and a nitrogenous base. the four nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T).

what makes up a DNA nucleoside

a five-carbon sugar called deoxyribose and a nitrogenous base (A, G, C, T).

NO PHOSPHATE GROUP

parts of DNA

• deoxyribose sugar backbone

• nitrogenous bases

2 functions of DNA

• info for cell functions

• info for cell replication

• main player in cellular (central dogma)

purines

adenine and guanine

• double-ring structures

pyrimidines

cytosine, thymine, and uracil

• have a single-ring structure

binding location of DNA binding proteins

major groove of DNA because it exposes more functional groups for recognitions of specific base pairs.

• they can also bind to the minor groove or interact with other DNA features like origins of replications, centromeres, and telomeres.

phenotype

observable characteristics resulting from genotype interaction

• expression of a set of genes

genotype

an organism’s genetic makeup.

• collection of all genes in a cell

steps of PCR

• denaturation

  • DNA is heated to 95 celsius to separate it into a single strand, breaking the hydrogen bonds between base pairs.

• annealing

  • the temperature is loweres to 55-72 celsius to allow short DNA sequences calles primers to bind to a single-stranded DNA at specific target locations

• extension

  • the temperature is raised again to 72 celsius allowing the DNA polymerase enzyme to extend the primers by adding nucleotides and synthesizing new DNA strands, complementary to the template

vertical gene transfer

the passing of genetic information from a parent organism to its offspring during sexual or asexual reproduction

horizontal gene transfer

the movement of genetic material between organsims, not through reproduction from parent to off-spring.

DNA v. RNA

• DNA is double-stranded, with a stable long-term storage role

• RNA is typically single=stranded and more involved in the process of protein synthesis

RNA synthesis and ribosome assembly location

nucleolus, a specialized region within the nucleus.

super coiling

the winding and unwinding of the DNA double-helix beyond its typical helical structure, creating a higher-order structure

peptidyl transferase

a ribozyme, meaning it’s an RNA molecule with enzymatic activity, located in the ribosome.

• plays a crucial role in protein synthesis by catalyzing formation og peptide bonds between amino acids.

• facilitates the transfer of a growing polypeptide chain from a tRNA molecule in the P site to the amino acid attached to a tRNA in the A site.

differences between RNA types

mRNA: linear, single-stranded that carries genetic information from DNA to the ribosome

rRNA: forms a major compoenent of ribosomes and plays a structural and catalytic role in protein synthesis

tRNA: smaller, L-shaped molecule that carries specific amino acids to the ribosome for protein synthesis

ribosomal RNA (rRNA)

make up ribosomes with proteins

messenger RNA (mRNA)

carries message from DNA to ribosome

transfer RNA (tRNA)

carries amino acid to growing peptide chain at ribosome

Joachim Hammerling- discovery of the nucleus (hereditary information)

Used single cell agla to show important of nucleus in propagation and survival.

• showed that the nucleus in the foot and would kill algal cell if removed.

• proposed nucleus was source of herediary information.

A. mediterranea foot was grafted with cap of other species A/ crenulata but did not take on new algal traits.

Beadle and Tatum (1941)- one gene-one enzyme hypothesis

• used mold Neurospora crassa

• mutant spores were induced with x-ray exposure

• mutants were examines to determine which amino acid(s) they could/couldn’t produce

• later was revised to one gene-one enzyme polypeptide (because not all code enzymes).

frederick griffith (1928)- hereditary info can be horizontal and vertical

• showed heredditary info can be shared to cells of same generation by demonstrating bacterial transformation - bacteria pick up external DNA

• his model worked with pathogenis (S) and non-pathogenic (R) strains of Streptococcus pneumoniae

• DNA was picked up by (R) strain after (S) strain was heat killed

Avery, MacLeod, McCarty (1941)- DNA was transforming component

• expanded on Griffith experiment by degrading specific enzymes

• then attempted a transformation to see the component responsible (protein, RNA, or DNA)

• transformation ONLY occurred when DNA was available after heal killing the (S) strain

Alfred Hershey and Martha Chase (1952)- DNA as genetic material

• used bacteriophage with radioactive sulfur (proteins) or phosphorus (DNA) to infec E. coli.

• phosphhorus labelled phages created new phages with the label in E. coli.

• sulphur labelled phased remained outside E. coli. phage inside had no labelled sulphur

conjugation

use of pilus to transfer genes cell-to-cell

tranformation

naked DNA is taken up by cell

transduction

genes are transferred via virus

central dogma

describes the flow of genetic information from DNA to RNA to proteins.

DNA > transcription > RNA > translation > proteins

okazaki fragments

used for lagging strand (3’ to 5’) in DNA replication.

• short, newly synthesized strands of DNA formed on the lagging strand during DNA replication.

• they are created discontinuously and are later joined together by the enzyme DNA ligase to form a complete, continous DNA strand.

transcription in eukaryotes

1. RNA polymerasses

2. Addition of 5’ cap and poly A tail

3. removal of introns (mRNA splicing)