CHARACTERISTICS OF MICROBES (WEEK 4)

Why do we classify bacteria?

• compare and contrast bacteria

• bacteria identification

How do we classify bacteria?

• visual methods

• biochemical tests

• serological tests

• DNA tests

What is cell morphology?

• size and shape

• coccus (round)

• bacillus (rod)

What are the cell arrangements?

• species of coccus and bacillus can exist in different cellular arrangements

What are some common cell arrangements?

• streptococcus (cocci chain)

• staphylococcus (cocci cluster)

• streptobacillus (rod chain)

How do we identify bacteria with flagella?

• flagella number and arrangement are constant within species

What are examples of flagella?

• peritrichous (distributed flagella)

• monotrichous (one flagella)

• lophotrichous (tuft of flagella)

• amphitrichous (flagella at both ends)

What is a colony?

• visible mass of microbial cells arising from one cell of the same organism

What does colony appearance rely on?

• species type

• type of media bacteria grows on

What characteristics should always be included in colony morphology?

• size (mm)

• shape (circular irregular, rhizoid, punctiform)

• pigmentation (white, grey, yellow)

• margin (filamentous, lobate, undulate, serrate, entire)

• elevation (raised, umbonate, flat, convex, crateriform)

• texture (rough or smooth + dull or shiny)

What is a gram stain?

• differential stain

• reacts differently between bacteria due to cell wall features

What is a gram positive bacteria?

• thick peptidoglycan layer

• has teichoic acids

• stains purple

What is a gram negative bacteria?

• thin peptidoglycan layer

• has lipopolysaccharides

• stains pink

What is the process of gram staining?

1. crystal violet to stain purple or blue

2. iodine adheres to cell walls

3. decolourizer alcohol makes gram negative cells colourless

4. safranin gives gram negative cells pink or red colour

What is oxygen tolerance?

• bacteria vary in oxygen use and tolerance in their environment

What are the different types of bacterial growth in oxygen-free mediums?

• obligate aerobes (grow at top)

• obligate anaerobes (grow at bottom)

• facultative anaerobes (grow throughout, denser at top)

• aerotolerant anaerobes (grow evenly, can survive without O2)

• microaerophiles (grow just below surface; only need low O2)

What is a fermentation test?

• breakdown of carbs like glucose or mannitol to make ATP

What are the two types of fermentation tests?

• ph indicator with phenol red (neutral pH = red, acidic pH = yellow)

• inverted tube to detect gas formation like CO2

What is a gelatinase test?

• whether an organism can use proteins

• checks for extracellular protease presence

• bacterial culture + gelatin

What is a deamination test?

• tests if organism can use amino acids

• bacterial culture + phenol red + amino acids

What is a urease test?

• tests if organism can use urea

• bacterial culture + phenol red + urea

How do we identify unknown bacteria?

• we can use found classifications

• subject bacteria to multiple tests

• compare characteristics using bergeys manual

How does rapid identification for bacteria work?

• pre packaged tests decrease labour and contamination

• several tests at once

• results are analyzed together to ID bacteria

What is serology?

• study of blood serum which contains antibodies

What are antigens?

• markers found outside pathogens that stimulate an immune response

What are antibodies?

• proteins produced by immune system that target antigens

• very specific

What are serological tests?

• based on antibody to antigen interaction

• use antibodies as tools to identify bacteria species and strain

• antibody-antigen binding = positive

What are serotypes?

• strains with different antigens

What is agglutination?

• clumping of cells or particles by antibodies

How do slide agglutination tests work?

• use latex beads

  • can be coated with antigen to detect specific antibodies or vice versa

What is the enzyme linked immunosorbent assay?

• use of specific enzyme linked antibodies to detect pathogen presence (Ag) or exposure (Ab)

What is a direct ELISA?

• detects antigen in sample using known antibody

• used for drugs or hormones in urine

What is an indirect ELISA?

• detects antibody in sample (using known antigen)

• checks presence of antibodies in the serum of a patient

How does a direct ELISA work?

1. primary antibody binds to well

2. blocking agent is added

3. sample is added; binds to antibody if antigen is present

4. unbound sample is washed away

5. antibody enzyme conjugate is added

6. unbound secondary antibody enzyme conjugate is washed

7. substrate is added; present = converts substrate to coloured product

How does an indirect ELISA work?

1. antigen is bound to well

2. blocking agent is added

3. sample added; antibody present = bind

4. unbound sample washed

5. antihuman enzyme linked antibody added

6. unbound antihuman antibody washed

7. substrate added; present = converts substrate to coloured product

What is DNA sequencing?

• DNA or full genome nucleotide sequence determined

• compared tod atabase of microbial genomes

• most accurate way of determining species