Bacterial Systematics Flashcards
Which discipline of taxonomy is responsible for giving an organism a scientific name?
Nomenclature
What is an obligate aerobe?
An organism that requires O2 to grow and survive
Give an example of an obligate aerobe (Genus and species)
Mycobacterium tuberculosis
What is an obligate anaerobe?
An organism that requires an complete lack of O2 to grow and survive
Give an example of an obligate anaerobe (Genus and species)
Clostridium botulinum
What is a facultative organism?
An organism that can grow in Increase or decreased O2 environments
Give an example of a facultative organism (Genus and species)
Escherichia coli
What does microaerophilic mean
AN organism that requires low levels of O2 to grow and survive
Name a genus of bacteria that has the characteristic of a microaerophile
Haemophilus sp.
What is a capnophile?
An organism that grows and survives in CO2 rich environments.
Name a genus of bacteria that has the characteristic of a capnophile
Neisseria sp.
List the Genus and species of an organism that is acid fast?
Mycobacterium tuberculosis
Which genera of bacteria produce spores?
Bacillus and Clostridium
Why do you have to be careful when performing a catalase test on a colony taken from BA?
A weak positive reaction occurs if inoculum is contaminated with RBC from BA
What precautions do you need to take when performing an oxidase test?
Need to be careful not to use iron containing loop or wires and this results in a false positive reaction
Explain the principle of the Gram stain (how/why it works).
The dyes used during the staining process stain the peptidoglycan layer of the cell wall of the bacteria showing either purple or pink after the decolourizing stage which then separates the bacteria into two different groups, Gram Positive or Gram Negative.
List the colour of both Gneg and Gpos cells at the completion of each staining step
- Fixation - Both GN and GP are colourless.
- Crystal violet stage both are purple
- Lugol’s iodine stage - both purple
- Decolourization with alcohol - GP are purple and GP are colourless
- Carbol fuchsin stage GP is purple GN is pink
Explain the principal of action of the catalase test? (how does it work? what is happening?)
Catalase is an enzyme which catalyses the breakdown of hydrogen peroxide to produce oxygen and water.
The Catalase test uses hydrogen peroxide as the reagent, the inoculum is scooped up with a tooth pick from the BA plate and inserted into the 2H2O2. An almost instant reaction of bubbles in the reagent occurs if the organism is positive for producing catalase.
Explain how to interpret the OF test
The OF test is used to detect the presence of acid from the utilisation of glucose through fermentation or oxidation.
Results for Oxidation - O2 tube yellow, paraffin tube green
Results for Fermentation - both yellow
Negative results for both - both green
In C&S phenotypic tables for bacteria, what exactly does a “+” , “-“ and “d” represent?
"+" = 85-100% of strains are positive "-" = 0-15% of strains are positive "d" = 16-84% of strains are positive
What are the thee interrelated disciplines of taxonomy?
- Classification
- Nomenclature
- Identification
What is Systematics?
The scientific process of characterising micro-organisms in an orderly manner with the aim of providing an identification.
The process of classifying and Identifying organisms is based upon three traits, what are they?
- Morphologic traits
- Physiological traits
- Genetic traits
what do Morphological traits of classification and identification include?
- size, shape, colour, texture of colonies
- size, shape, arrangement microscopically
- staining characteristics
What do Physiological traits of classification and identification include?
- Nutritional requirements (ability to use carbon, nitrogen sources)
- Environmental preferences (temp, pH, O2, ANO2, CO2, ions, salts)
- Antibiotic resistance profiles
- Presence of antigenic structures/properties (spores, capsules, fimbriae, pili, cell wall proteins)
- Virulence factors (enzymes, haemolysins, toxins)
- Bacteriophage typing
What do Genetic traits of classification and identification include?
- DNA sequence analysis (similarity - homology)
- DNA base composition ratio
- Plasmid content (dsDNA).
What are the characteristics we look at when identifying bacteria?
- Colony morphology
- Gram reaction
- Atmospheric requirements
- Motility
- Biochemical tests
- Serological tests
What are the Primary ID tests and results by Genera for bacteria?
- Shape by Gram stain
- Acid Fastness
- Spore stain
- Motility
- Growth in air
- Growth anaerobically
- Catalase
- Oxidase
- Glucose (acid)
- OF test
What is another name for the Acid Fast stain?
Ziehl-Neelson stain
What colour are positive Acid fast organisms?
Red/pink
What genera are positive for the Acid fast test?
Mycobacterium and Nocardia
What colour do spores come out in the spore stain?
Malachite green
What do you use for the counterstain in a spore stain?
Safranin
What genera are positive for the spore stain?
Bacillus and Clostridium
What tests are conducted for motility?
- Hanging drop (coverslip suspended above the slide)
- Wet preparation
- Motility medium
What genera is always positive for motility?
Proteus sp.
What are the three Proteus species that swarm due to peritrichous flagella?
Proteus mirabilis
Proteus vulgaris
Proteus penneri
What are the spot tests conducted to identify Proteus sp. from each other?
Spot indole and rapid maltose test.
Name the genera of bacteria used as a positive control for catalase testing.
Staphylococcus sp.
Name the genera of bacteria used as a negative control for catalase testing.
Streptococci sp. and enterococci sp.
What does the Oxidase Test do?
Detects the presence of the enzyme cytochrome oxidase in the bacteria
What are the clinically significant genera that are oxidase positive?
- Pseudomonas sp.
- Vibrio sp.
- Campylobacter sp.
- Aeromonas sp.
- Pasteurella sp.
- Neisseria sp.
- Moraxella sp.
What genera are used as positive control for Oxidase test?
- Moraxella catarrhalis
- Pseudomonas sp.
What does the Glucose (acid production) test do?
Detects the presence of acid from the utilisation of glucose through fermentation or oxidation.
What colour change is detected in a positive reaction for the glucose (acid production) test?
The pH indicator bromthymol blue (green) to yellow means acid production is present.
What does the Oxidation-Fermentation test do?
Detects whether an organism metabolises glucose by oxidation or fermentation.
what does Oxidation require for a positive reaction?
Oxygen
What does a positive test for fermentation indicate?
anaerobic metabolism of glucose
API Strep panel is for which type of organism?
GPC - catalase neg
API20E panel is for which type of organism?
GNB - Oxidase neg
What must we have done, and already know, before setting up secondary tests such as an API panel?
- Primary stage testing must have been done first
- We must have a reasonable idea of what type of organism an unknown isolate will be in order to select the correct ID panel.
