dichotomous key
TRANSCRIPT
Characteristics of Microbes
• Prokaryote• microscopic, unicellular organisms• lack nuclei and membrane-bound organelles
Chapter 4
Bacterial Structures• Flagella • Pili• Capsule• Plasma Membrane• Cytoplasm• Cell Wall• Lipopolysaccharides• Teichoic Acids• Inclusions• Spores
How to Make a Dichotomous Key From a Table of Bacterial
Characteristics
(for use in running the minimum number of tests in identifying an
unknown bacterium)
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Dichotomous Key to Identifying Eight Bacteria
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight BacteriaTable of Characteristics for Eight Bacteria
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight BacteriaTable of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negativeAlcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
positive
Dichotomous Key to Identifying Eight Bacteria
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
positive
Dichotomous Key to Identifying Eight Bacteria
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negativeAlcaligenes faecalis
Aeromonas hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negativeAlcaligenes faecalis
Aeromonas hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkalineCitrobacter freundii
Pseudomonas fluorescens
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negativeAlcaligenes faecalis
Aeromonas hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkalineCitrobacter freundii
Pseudomonas fluorescens
acid fast
Acid-fast staining
not acid fastMycobacterium smegmatis Corynebacterium xerosis Mycobacterium leprae Streptococcus pneumoniae
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negativeAlcaligenes faecalis
Aeromonas hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkalineCitrobacter freundii
Pseudomonas fluorescens
acid fast
Acid-fast staining
not acid fastMycobacterium smegmatis Corynebacterium xerosis Mycobacterium leprae Streptococcus pneumoniae
positive
Catalase produced
negativeMycobacterium smegmatis
Mycobacterium leprae
Organism Characteristics
Alcaligenes faecalis Gram negative bacillus, acid-fast negative, ferments galactose, catalase positive, motile, alkaline with litmus milk, not hemolytic, H2S negative
Citrobacter freundii Gram negative bacillus; acid-fast negative, does not ferment galactose, catalase positive, non-motile, acid produced in litmus milk, not hemolytic, H2S negative
Pseudomonas fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose, catalase positive, non-motile, alkaline in litmus milk, hemolytic, H2S negative
Streptococcus pneumoniae
Gram positive oval coccus found as streptococci, acid-fast negative, galactose fermentation negative, catalase negative, non-motile, acid in litmus milk, hemolytic, H2S negative
Mycobacterium smegmatis
Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-negative,, non-motile, alkaline in litmus milk, catalase positive, not hemolytic, H2S negative
Mycobacterium leprae Gram positive club-shaped bacilli, acid-fast positive, galactose fermentation negative, catalase-positive, non-motile, alkaline in litmus milk not hemolytic, H2S negative
Corynebacterium xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose fermentation positive, non-motile, acid from litmus milk, catalase positive, not hemolytic, H2S negative
Aeromonas hydrophila Gram negative bacilli, acid-fast negative, ferments galactose, catalase positive, motile, acid from litmus milk, not hemolytic, H2S positive
Table of Characteristics for Eight Bacteria
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisStreptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatisCitrobacter freundii Mycobacterium lepraePseudomonas fluorescens Corynebacterium xerosisAeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negativeAlcaligenes faecalis Citrobacter freundii Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negativeAlcaligenes faecalis
Aeromonas hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkalineCitrobacter freundii
Pseudomonas fluorescens
acid fast
Acid-fast staining
not acid fastMycobacterium smegmatis Corynebacterium xerosis Mycobacterium leprae Streptococcus pneumoniae
positive
Catalase produced
negativeMycobacterium smegmatis
Mycobacterium leprae
positive
Hemolysis
negativeCorynebacterium
xerosisStreptococcus pneumoniae