Bacterial classification and identification (midterm) Flashcards
What are the taxonomic ranks of bacterial classification?
Kingdom/domain
Phylum/division
Class
Order
Family
Genus
species
What methods are used to identify bacteria?
Phenotype: morphology, microscopy, biochemistry
Immunological/serological tests: specific Ig
Genotype: PCR
Bacteriophage typing
What microscopic techniques are used to identify bacteria?
Hanging drop method (motility)
Simple staining, e.g. methylene blue
Gram stain (G+ and G–)
Ziehl–Neelsen stain (acid fast)
What macroscopic techniques are used to identify bacteria?
Hemolysis
Pigment production
Colonial morphology
Describe hemolysis on blood agar
β (complete): Staphylococcus aureus, Streptococcus pyogenes
α (partial): Streptococcus viridans, Streptococcus pneumoniae (pneumococcus)
γ (none): Enterococci
Which bacteria perform complete (β) hemolysis?
Staphylococcus aureus
Streptococcus pyogenes
Which bacteria perform partial (α) hemolysis?
Streptococcus pneumoniae (pneumococcus)
Streptococcus viridans
Which bacteria perform no hemolysis (γ)?
Enterococci
Describe pigment production
Endopigment: Staphylococcus aureus (yellow), Staphylococcus epidermidis (white)
Exopigment: Pseudomonas aeruginosa (green)
Which bacteria release yellow endopigment?
Staphylococcus aureus
Which bacteria release white endopigment?
Staphylococcus epidermidis
Which bacteria release green exopigment?
Pseudomonas aeruginosa
Outline colonial morphology
Colony form: pinpoint, circular, filamentous, irregular
Colony elevation: flat, raised, convex
Colony margin: smooth, irregular
Outline microscopic colonial morphology
Diplococci: pairs
Streptococci: chains
Staphylococci: bundles/clusters
Sarcina: tetrads
Bacillus: like E. coli
Vibrio: comma shaped
Spirillum: spiral
Actinomyces: filamentous
What types of diseases do spiral bacteria tend to cause?
Systemic diseases
What types of diseases to filamentous bacteria tend to cause?
Chronic diseases
What types of diseases do G+ bacteria tend to cause?
Skin infections
Describe the Durham test
Glucose broth with Durham tubes
Red → yellow: acid fermentation
Red → yellow with gas: acid fermentation with gas production
Red: no acid fermentation
Describe the IMViC/indole test
Production of indole from Trp, detected with Kovac’s reagent
Red/pink ring: positive
Yellow ring: negative
What bacteria give a positive indole test?
E. coli
What bacteria give a negative indole test?
Klebsiella
Describe the methyl red reaction (MR) test
Detection of acid fermentation using methyl red
Yellow → red: positive
Yellow: negative
What bacteria give a positive MR test?
E. coli
What bacteria give a negative MR test?
Klebsiella
Describe the Voges–Proskaur reaction (VP) test
Detection of acetyl methyl carbinol from glucose fermentation using KOH
Yellow → pink: positive
Yellow: negative
What bacteria give a positive VP test?
Klebsiella
What bacteria give a negative VP test?
E. coli
Describe the H2S test
Detection of sulfur reduction to H2S using sulfide-indole-motility (SIM medium) and triple sugar iron agar (TSIA)
Blackening: positive
No blackening: negative
What bacteria give a positive H2S test?
Enterobacteriaceae, especially Salmonella, Francisella, Proteus
What bacteria give a negative H2S test?
Most G– bacilli
Describe the citrate utilization test
Detection of the enzyme citrase (citrate → OAA + acetate) using Simmons citrate agar
Green → blue: positive
Green: negative
Which bacteria are differentiated by the citrate utilization test?
Presence of species of the Enterobacteriaceae family
Describe the urease test
Detection of the enzyme urease (urea → NH3) by change in pH
Yellow → pink: positive
Yellow: negative
What bacteria give a positive urease test?
Proteus vulgaris
What bacteria give a negative urease test?
E. coli
Describe the oxidase test
Detection of the enzyme oxidase using the oxidase reagent
Colorless → purple: positive
Colorless: negative
What bacteria give a positive oxidase test?
Pseudomonas
What bacteria give a negative oxidase test?
All Enterobacteriaceae members
Describe the catalase test
Detection of the enzyme catalase (H2O2 → H2O + O2) using hydrogen peroxide
Bubbling: positive
No bubbling: negative
What bacteria give a positive catalase test?
Staphylococci
What bacteria give a negative catalase test?
Streptococci
Describe the coagulase test
Detection of the enzyme coagulase (fibrinogen → fibrin) by adding fibrinogen and smearing with a slide or test tube
Clot formation: positive
No clot formation: negative
What bacteria give a positive coagulase test?
Staphylococcus aureus
What bacteria give a negative coagulase test?
Most Staphylococci except S. aureus
