Microbiology Exam 3

Selective Media

allows for growth of only certain orgamisms

differential

produces particular colony morphologies for target organisms

To get a pure culture:

streak an isolated colony from a mixed culture

the first step after isolation is

differential staining

examples of differential staining

• gram stain

• endospore stain

• acid-fast stain

enzyme activities

• tests detect for the presence of one particular enzyme or metabolic pathways (look for -ase)

• differential

Fermentation of carbohydrates

• acid and/or gas production

• differential

oxidase

• Cytochrome C oxidase

• Part of the electron transport chain

• Reduces O2 to H2O

• Oxidase positive organisms can use aerobic respiration

Catalase

• protects from host defences

• 2H2O2 → 2H2O + O2

coagulase

clotting (coaggulation) to protect from host immune system

hemolysis

• break down of red blood cells

• damages immune system and gives access to iron

urease

• raises pH (more basic)

Ornithine decarboxylase

L-ornithine → putrescine

Indole production (IMViC)

tryptophan → indole using tryptophanase

methyl red test (IMViC)

mixed acid fermentation with acidic end products

voges-proskauer (IMViC)

acetoin production

Citrate utilization (IMViC)

• Citrate permease allows for transport of citrate into the cell

  • Citrate → pyruvate + acetate + CO2

  • CO2 + sodium → sodium carbonate (alkaline)

IMViC panels are for gram-_____ bacteria

negative

Biochemical identification require

multiple tests

Benefits of a dichotomous key

• only perform necessary tests

• fewer resources

disadvantages to a dichotomous key

• limited # of possible organisms

• time consuming

Numerical identification (rapid identification method)

• Simultaneously performs many biochemical tests

• Results produce a code number

• Linked to a database for species identification

problems of rapid identification method

• requires pure culture

• limited testing

• limited results

• intraspecies variation

• databases infrequently updated

phage typing

Differentiation of bacteria based on infection by bacteriophage (virus)

• receptors not present= bacteria not infected

serology

highly specific use of antibodies for identification of species and strains of microbes

antiserum

Solution of antibodies used for identification of microorganisms

• serology

antibodies are ______

highly specific (will only recognize one antigen from the microbe)

Latex agglutination test (serological)

• antibodies attach to latex beads

• binding to microbes causes clumping

• differentiates serotypes and stains

Enzyme-linked immunosorbent assay (ELISA)

• detects antigens in patient sample (current infection)

  • antibodies adhere to plate wells

  • antigens from patient sample bind to primary antibodies

  • secondary antibodies bind to antigens

    • color change

lateral flow assay

• detects antigens in patient sample (current infection)

  • Labeled antibodies are present in test strip

  • Antigen from patient sample binds to labeled antibodies

  • Liquid is pulled across test strip by capillary action

  • Test line contains antibodies that bind antigen

  • If present, antigen binds to antibodies in test line

  • Labeled antibodies show color change in test line when antigen is bound (positive test)

  • Control line contains antibodies that bind extra labeled antigens

    • Control line always shows color change

organisms with similar _____ may be related

g + c ratios

Nucleic acid hybridization

complete: identical

partial: related

none: unrelated

___% DNA-DNA hybridization means same species

70

DNA chips (nucleic acid hybridization test)

• DNA probes with specific sequences are bound to chip

• DNA sample is denatured and labeled

• DNA sample is allowed to hybridize with DNA probes on the chip where sequences are complementary

• Fluorescence is detected where sample DNA is bound

flourescent in situ hybridization (FISH) (nucleic acid hyrbidization)

• Cells are treated with a fluorescent DNA probe

• Probe binds to complementary DNA or RNA in the cell

• Allows for visualization of cells in their natural environment

• Can allow for differentiation of organisms in a mixed population

Restriction fragment length polymorphisms (RFLP) (DNA fingerprinting)

• Restriction enzymes cut DNA at specific places to produce fragments of different sizes

• DNA fragments are separated by size, using gel electrophoresis

• Look for similar banding patterns

  • Indicates similarities between nucleotide sequences because restriction sites are the same locations

Nucleic acid amplification

Polymerase chain reaction

• Use primers for a target organism or gene

• Amplification will only occur if target sequence is present

• Identification of organism specific genes

• Amplification of DNA for further analysis

16S ribosomal DNA sequencing

gene encoding the 16 rRNA

same species = ___% sequence identity in 16S ribosomal DNA

98.65

whole genome sequencing

all DNA in organism

same species in whole genome sequencing = __% nucleotide identity

95%

cladograms

show evolutionary relationships by calculating percent identity

shorter horizontal branch = more closely related

symbiosis

relationship btw two organisms where at least one benefits

mutualism

both organisms benefit (e.g., intestinal E. coli)

commensalism

one benefits; one unaffected (e.g, staphylococcus epidermidis)

parasitism

one benefits; one is harmed (parasitic microorganisms)

normal microbiota establish a _____ residence and ____ cause disease

permanent, do not

transient microbiota are present for ______ and _____ cause disease

• several days, weeks, or months, than disappear

• may or may not cause disease

microbial antagonism/competative exlusion

members of the microbiome protect the host from colonization by pathogens

types of competitive exclusion

• nutrient and space competition (gut microbiome)

• harmful substance production (e.g., bacteriocins in the intestine by E. coli)

• pH and oxygen availability effects in surrounding environment

infections

• invasion/colonization of body with pathogenic microorganisms

• microorganisms carry out at least part of life cycle in the host

disease

any change in health caused by an infection (so need to have symptoms!)

pathology

scientific study of disease

etiology

causative agent of disease

pathogenesis

how disease develops

koch’s postulates

shows that a specific infectious disease is associated with a particular microorganism

rules of koch’s postulates

1. same pathogen must be present in every disease case

2. pathogen must be isolated from diseased host and grown in pure culture

3. pathogen from pure culture must carry same disease when inoculated into healthy, susceptible host

4. pathogen must be isolateted from inoculated animal and must be shown to be the original organism

Koch’s postulates exceptions

culture requirements (ability to grow in pure culture on artificial media)

multiple pathogens have same signs and symptoms

pathogens can cause multiple disease conditions

can lack non-human host (HIV)

symptoms

subjective (what you feel)

signs

objective changes in body fxn (can be observed & measured)

syndrome

specific group of signs and/or symptoms that may always accompany a particular disease

communicable disease

infected person transmits an infectious agent to another person

• flu, tb

contagious disease

highly communicable disease that can spread easily and quicky, host to host

• chickenpox, measles

noncommunicable disease

not spread host to host

• tetanus

contact transmission

spread of disease agent by contact

direct contact transmission

physical contact with infected person (kissing, touching, sex)

indirect contact transmission

transmission by nonliving object (fomite)

droplet transmission (contact)

droplet nuclei less than 1 meter away

vector

animal carries pathogen from one host to another

mechanical transport (vector)

passive transport of pathogen on body

biological transmission

active process

• insect vector bites host and ingests infected blood

• pathogen replicates in the vector

• insect passes pathogen to new host

vehicle transmission

spread of disease by medium

• waterborne: contaminated water

• foodborne: consumption of contaminated food

• airborne: droplet nuclei more than 1 meter away

acute disease

rapid development, lasts a short time

chronic disease

develops slowly, less severe, continues for long period of time

latent disease

causative agent remains inactive for a time, but then becomes active to produce the disease symptoms

subclinical disease

no noticeable illness

local infection

infection in which the invading microorganisms are confined to a relatively small area of the body

systemic infection

infection in which the invading microorganisms are spread throughout the body (blood or lymph)

septicema

• response to bloodstream infection

• bacteremia, toxemia, viremia

primary infection

acute infection that causes the initial illness

secondary infection

infection caused by opportunistic pathogen after the body’s defenses have been weakened by a primary infection

disease development

1. incubation period

2. predromal period

3. period of illness

4. period of decline

5. period of convalescence

incubation period

• between initial infection and the appearance of signs and symptoms

• # of microbes increases, but no signs or symptoms

predromal period

• period of early, mild symptoms in some diseases

• relatively short

period of illness

• disease is most severe

• overt signs and symptoms

• ends when host immune system starts to overcome the pathogen

  • unsuccessful = patient dies

period of decline

• signs and symptoms subside, but still present

• vulnerable to secondary infections

period of convalescence

• body → predisease state

• no more signs or symptoms

• microbes eliminated

epidemiology

study of where and when diseases occur and how they are transmitted

john snow

mapped illnesses of a cholera outbreak and linked it to a singular water pump

descriptive epidemiology

collecting all data to describe the occurence of the disease

• affected individuals

• time and location

• retrospective

incidence

number of people who develop a disease at particular time

• new cases

prevelance

number of people in a population who have a disease at a specific time regardless of when it first appeared

• accounts for old and new cases

sporatic disease

a disease that occurs only occasionally

endemic disease

constantly present

epidemic

many people in a given geographic area acquire a disease in a short period of time

pandemic

a worldwide epidemic

analytical epidemiology

analysis of a particular disease to determine the probable cause

• case-control method

• cohort method

case-control method (analytical)

compare ill people to unaffected people (non sick vs. sick)

• stats to determine which factors may have contribute to illness

cohort method (analytical)

compare a group of people who had contact with disease agent and one group that hasnt been

• exposed vs. not exposed

experimental epidemiology

• begins with a hypothesis about a particular disease

• test hypothesis with a group of people

• e.g., drug effectiveness