Dichotomous key

1. Characteristics of Microbes

2. •Prokaryote
• microscopic, unicellular organisms
• lack nuclei and membrane-bound organelles

3. Chapter 4
Bacterial Structures
•Flagella
•Pili
•Capsule
•Plasma Membrane
•Cytoplasm
•Cell Wall
•Lipopolysaccharides
•Teichoic Acids
•Inclusions
•Spores

5. 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)

6. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

7. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Dichotomous Key to Identifying Eight Bacteria

8. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight BacteriaTable of Characteristics for Eight Bacteria

9. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight BacteriaTable of Characteristics for Eight Bacteria

10. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
positive
Dichotomous Key to Identifying Eight Bacteria

11. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

12. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
positive
Dichotomous Key to Identifying Eight Bacteria

13. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

14. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H
2
S production
positive negative
Alcaligenes
faecalis
Aeromonas
hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria

15. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

16. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H
2
S production
positive negative
Alcaligenes
faecalis
Aeromonas
hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkaline
Citrobacter
freundii
Pseudomonas
fluorescens

17. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

18. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H
2
S production
positive negative
Alcaligenes
faecalis
Aeromonas
hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkaline
Citrobacter
freundii
Pseudomonas
fluorescens
acid fast
Acid-fast staining
not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Mycobacterium leprae Streptococcus pneumoniae

19. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

20. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H
2
S production
positive negative
Alcaligenes
faecalis
Aeromonas
hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkaline
Citrobacter
freundii
Pseudomonas
fluorescens
acid fast
Acid-fast staining
not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Mycobacterium leprae Streptococcus pneumoniae
positive
Catalase produced
negative
Mycobacterium
smegmatis
Mycobacterium
leprae

21. Organism Characteristics
Alcaligenes faecalisGram negative bacillus, acid-fast negative, ferments galactose,
catalase positive, motile, alkaline with litmus milk, not hemolytic, H
2
S
negative
Citrobacter freundiiGram negative bacillus; acid-fast negative, does not ferment galactose,
catalase positive, non-motile, acid produced in litmus milk, not
hemolytic, H
2
S negative
Pseudomonas
fluorescens
Gram negative bacillus, acid-fast negative, does not ferment galactose,
catalase positive, non-motile, alkaline in litmus milk, hemolytic, H
2
S
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, H
2
S 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, H
2
S negative
Mycobacterium lepraeGram positive club-shaped bacilli, acid-fast positive, galactose
fermentation negative, catalase-positive, non-motile, alkaline in litmus
milk not hemolytic, H
2
S negative
Corynebacterium
xerosis
Gram positive club-shaped bacilli, acid-fast negative, galactose
fermentation positive, non-motile, acid from litmus milk, catalase
positive, not hemolytic, H
2
S negative
Aeromonas hydrophilaGram negative bacilli, acid-fast negative, ferments galactose, catalase
positive, motile, acid from litmus milk, not hemolytic, H
2
S positive
Table of Characteristics for Eight Bacteria

22. Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Streptococcus pneumoniae Aeromonas hydrophila
Gram stain
negative
positive
Alcaligenes faecalis Mycobacterium smegmatis
Citrobacter freundii Mycobacterium leprae
Pseudomonas fluorescens Corynebacterium xerosis
Aeromonas hydrophila Streptococcus pneumoniae
Galactose fermentation
negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H
2
S production
positive
negative
Alcaligenes
faecalis
Aeromonas
hydrophila
positive
Dichotomous Key to Identifying Eight Bacteria
Litmus milk
acid alkaline
Citrobacter
freundii
Pseudomonas
fluorescens
acid fast
Acid-fast staining
not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Mycobacterium leprae Streptococcus pneumoniae
positive
Catalase produced
negative
Mycobacterium
smegmatis
Mycobacterium
leprae
positive
Hemolysis
negative
Corynebacterium
xerosis
Streptococcus
pneumoniae