Classification of Bacteria
Taxonomy
The science of classification
Haeckel’s 3 Kingdoms
• Plant
• Animal
• Protista
Carl Woese’s 3 Domains
Based on rRNA nucleotide sequences
Why use this as a basis for classification?
Organisms in the 3 Domains
• Eukarya - kingdoms: plantae, animalia, fungi,
protists
• Archaea - prokaryotes
• Bacteria - prokaryotes
2 Types of Prokaryotic Cells
• Eubacteria
• Archaebacteria
– cell walls contain
peptidoglycan
– different nucleotide
sequences in rRNA
– different membrane
lipids
–
–
–
–
no peptidoglycan
rRNA
lipids
live in extreme
environments
ex. Thermoacidophiles
Extreme halophiles
Methanogens
http://www.ucmp.berkeley.edu/archaea/archaea.html
Comparison of Archaea, Bacteria & Eukarya
Naming organisms (nomenclature)
Binomial system uses 2 names
Genus
species
ex. Bacillus
subtilis
ex. Clostridium
tetani
ex. Staphylococcus
aureus
Is tubercle bacillus the scientific name of an
organism or a common name?
3. Phylogenetic Classification
• An evolutionary arrangement of species.
• Sharing a recent ancestor as in plants and animals
(fossil records)
• In bacteria?
• Possible by Molecular Methods
– Genetic Homology:
•
•
•
•
Base composition (GC ratio)
Nucleic acid hybridisation.
Ribosomal RNA (rRNA) sequence analysis
Protein profiles and amino acid sequences
• PURE CULTURE:
•
Populations of individuals all derived from the
same single organism.
• STRAIN:
•
A Group of Pure Cultures Derived from a
Common Source and Thought to be the Same.
• SPECIES:
•
A Group of Closely Similar Strains.
INTRASPECIES CLASSIFICATION
• Biotypes
– Biochemical properties.
• Serotypes
– Antigenic features.
• Phage Types
– Bacteriophage susceptibility.
• Colicin Types
– Production of bacteriocins.
Species of bacteria - “population of cells
with similar characteristics”
Strain of bacteria - “group of cells
derived from a single cell”
ex. Staphylococcus aureus 13578
• Naming of microorganisms.
• Governed by international rules
• Rules published in the International Code of
Nomenclature of Bacteria.
• The International Journal of Systematic
Bacteriology
Rules for the Nomenclature of Microorganisms
• There is only one correct name for an organism.
• Names that cause error or confusion should be rejected.
• All names in Latin or are latinized.
– The first word (genus) is always capitalized.
– The second word (species or specific epithet) is not capitalized.
– Both genus and species name, together referred to as species, are
either underlined or italicized when appearing in print.
– The correct name of a species or higher taxonomic designations is
determined by valid publication, legitimacy of the name with
regard to the rules of nomenclature, and priority of publication.
Nomenclature
• Casual or Common Name:
• e.g. "typhoid bacillus"
• Scientific or International Name:
•
•
•
•
•
•
Salmonella typhi
Salmonella london
Staphylococcus aureus
Clostridium tetani
Mycobacterium bovis
Borrelia burgdorferi
Classification vs. Identification
Techniques
Bergey’s Manual of Determinative Bacteriology uses:
• microscopic appearance
• biochemical reactions
• growth requirements
• serology
• phage typing
Classification or identification??
Biochemical Tests
Serology
Slide Agglutination Test
Phage Typing
Bergey’s Manual of Systematic Bacteriology
establishes phylogenetic relationships by:
• amino acid sequencing
• protein analysis
• rRNA sequencing – ribotyping
– Why is rRNA rather than other types of RNA used?
• Chapter 10
• nucleic acid hybridization
Classification or identification??
DNA Hybridization
Identification vs. Classification
Spirochetes
Axial filaments for motility
Examples:
Treponema pallidum - syphillis
Borrelia burgdorferi - Lyme
disease
Leptospira interrogans leptospirosis
Axial Filaments
Movement of spirochetes
Structure
Filament
Hook
Basal body
Ex. Treponema
pallidum
Bundles of fibrils that arise at the end of the cell beneath the
outer sheath & spiral around the cell
Campylobacter jejuni
•
•
•
•
•
•
microaerophilic
motile vibrio
Gram negative
animals esp poultry & cattle
grows @ 42oC
most commonly identified
bacterial cause of diarrhea in
world (CDC)
– unpasteurized milk
– food
Pseudomonas aeruginosa
• Gram negative aerobic
rod
• “bacillus of blue-green
pus”
– pyocyanin pigment
• fermented grape smell
• normal flora
– skin & intestine
• unusual carbon sources
• antibiotic resistant
• infections
– wound, ear, urinary,
respiratory, burns
Gram negative aerobic cocci
Neisseria meningitidis
Branhamella catarrhalis
Neisseria gonorrhoeae in pus
Enterobacteriales
Family- enterobacteriaceae
Non-pathogens
• Escherichia
• Klebsiella
• Proteus
• Serratia
• Etc.
Describe the microscopic appearance of these organisms.
Enterobacteriaceae cont’d
Pathogens
• Salmonella (typhi)
– typhoid fever
• Shigella (dysenteriae)
– bacillary dysentery
• Yersinia (pestis)
– bubonic plague
All members of Enterobacteriaceae are facultative anaerobes. Meaning?
Can you see why the family, enterobacteriaceae, has been
referred to as the Colon-typhoid-dysentery group?
Can you differentiate the pathogens from the nonpathogens microscopically?
Vibrionales
Vibrionaceae
Vibrio cholerae
Shape?
Facultatively
anaerobic
Hemophilus influenzae
• Aerobic Gram negative
rod
• Normal flora in intestine
and respiratory tract
• Most common cause of
meningitis in children
– Hib vaccine
• Also causes otitis media,
pneumonia, epiglottitis
Why is the name of this organism misleading?
What can you learn from the name?
Bacteroidaceae - Bacteroides fragilis
• Gram negative
anaerobic rods
• Found in the human
intestine & mouth
– 95% of the bacteria in
a stool specimen &
20% of the weight!
– One billion per gram of
feces!
• Most common
anaerobe isolated from
infections
– appendicitis,
peritonitis, complicate
abdominal surgery
Rickettsia & Chlamydia
Gram negative obligate intracellular parasites
Rickettsia
transmitted to humans by insects & ticks
Ex. Rickettsia rickettsii - Rocky Mountain spotted fever
Chlamydia
Not transmitted by insects
Chlamydia trachomatis
Causes:
1.Trachoma - world’s leading
infectious cause of blindness
Middle East, North Africa, India
2.Non-gonococcal urethritis
common std in U.S.
Chlamydia psittaci causes:
1. Psittacosis (“parrot fever”)
2. Ornithosis
Chlamydia pneumoniae - pneumonia
Mycoplasmas
• No cell wall
– pleomorphic
– penicillin sensitive or
resistant?
• Smallest free-living
organisms
• Microscopic fried-egg
colonies
• Ex. Mycoplasma
pneumoniae
Gram Positive Cocci
Staphylococcus
Streptococcus
Micrococcus luteus
Staphylococcus aureus
• Gram positive cocci, clusters
• Yellow pigment
• Causes
– common food poisoning
– surgical wound infections
• resistance
– toxic shock syndrome
Streptococcus pyogenes
• Gram positive cocci in chains
• Diseases
– pharyngitis (sore throat)
– scarlet fever *
– erysipelas *
* look for a description of this disease
Endospore-Forming Gram Positive Rods
• Bacillales - Bacillus
– aerobes or facultative anaerobes
– common in soil
– ex. Bacillus anthracis, Bacillus subtilis
• Clostridiales - Clostridium
– obligate anaerobes
– found in soil
– diseases
• tetanus (Clostridium tetani), botulism (C. botulinum),
gas gangrene (C. perfringens)
Spore-Forming Organisms
Bacillus cereus - spore stain
Clostridium tetani - Gram stain
Corynebacterium
Characteristics of
Corynebacterium sp.:
• pleomorphic Gram positive
rod
• metachromatic granules
• unusual arrangements
– palisades
– Chinese letters
• C.diphtheriae causes
diphtheria
Mycobacteria
Characteristics of
Mycobacterium sp.
• Gram positive small rods
• acid-fast
– mycolic acid complexed
with peptidoglycan (waxy)
• diseases:
Acid-fast stain of sputum showing
Mycobacterium tuberculosis
– tuberculosis
– leprosy (M. leprae)
Streptomycetes
Characteristics of
Streptomyces:
• mold-like bacteria
– branching, spores
• produce geosmin
– soil smell
• several species
produce antibiotics
– ex. streptomycin