1. Characteristics of Microbes

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

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

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. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

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

8. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

9. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

10. Dichotomous Key to Identifying Eight Bacteria
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

11. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

12. Dichotomous Key to Identifying Eight Bacteria
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
positive negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens

13. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

14. Dichotomous Key to Identifying Eight Bacteria
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
positive negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H2S production
positive negative
Aeromonas Alcaligenes
hydrophila faecalis

15. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

16. Dichotomous Key to Identifying Eight Bacteria
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
positive negative
Alcaligenes faecalis Citrobacter freundii
Aeromonas hydrophila Pseudomonas fluorescens
H2S production Litmus milk
positive negative acid alkaline
Aeromonas Alcaligenes Citrobacter Pseudomonas
hydrophila faecalis freundii fluorescens

17. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

18. Dichotomous Key to Identifying Eight Bacteria
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 Acid-fast staining
positive negative acid fast not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Alcaligenes faecalis Citrobacter freundii
Mycobacterium leprae Streptococcus pneumoniae
Aeromonas hydrophila Pseudomonas fluorescens
H2S production Litmus milk
positive negative acid alkaline
Aeromonas Alcaligenes Citrobacter Pseudomonas
hydrophila faecalis freundii fluorescens

19. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

20. Dichotomous Key to Identifying Eight Bacteria
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 Acid-fast staining
positive negative acid fast not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Alcaligenes faecalis Citrobacter freundii
Mycobacterium leprae Streptococcus pneumoniae
Aeromonas hydrophila Pseudomonas fluorescens
H2S production Litmus milk Catalase produced
positive negative acid alkaline positive negative
Aeromonas Alcaligenes Citrobacter Pseudomonas Mycobacterium Mycobacterium
hydrophila faecalis freundii fluorescens leprae smegmatis

21. Table 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, H 2S
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 Gram negative bacillus, acid-fast negative, does not ferment galactose,
fluorescens catalase positive, non-motile, alkaline in litmus milk, hemolytic, H 2S
negative
Streptococcus Gram positive oval coccus found as streptococci, acid-fast negative,
pneumoniae galactose fermentation negative, catalase negative, non-motile, acid in
litmus milk, hemolytic, H2S negative
Mycobacterium Gram positive club-shaped bacilli, acid-fast positive, galactose
smegmatis fermentation negative, catalase-negative,, non-motile, alkaline in litmus
milk, catalase positive, not hemolytic, H 2S 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 Gram positive club-shaped bacilli, acid-fast negative, galactose
xerosis 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, H 2S positive

22. Dichotomous Key to Identifying Eight Bacteria
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 Acid-fast staining
positive negative acid fast not acid fast
Mycobacterium smegmatis Corynebacterium xerosis
Alcaligenes faecalis Citrobacter freundii
Mycobacterium leprae Streptococcus pneumoniae
Aeromonas hydrophila Pseudomonas fluorescens
H2S production Litmus milk Catalase produced Hemolysis
positive negative acid alkaline positive negative positive negative
Aeromonas Alcaligenes Citrobacter Pseudomonas Mycobacterium Mycobacterium Streptococcus Corynebacterium
hydrophila freundii fluorescens
faecalis leprae smegmatis pneumoniae xerosis