Classification of Bacteria

Taxonomy

The science of classification

Haeckel’s 3 Kingdoms

• Plant

• Animal

• Protista

Carl Woese’s 3 Domains

Based on rRNA nucleotide sequencesWhy 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– cell walls contain

peptidoglycan

– different nucleotide sequences in rRNA

– different membrane lipids

• Archaebacteria– no peptidoglycan– rRNA– lipids– live in extreme

environments

ex. Thermoacidophiles

Extreme halophiles

Methanogenshttp://www.ucmp.berkeley.edu/archaea/archaea.html

Comparison of Archaea, Bacteria & Eukarya

Naming organisms (nomenclature)

Binomial system uses 2 names

Genus speciesex. Bacillus subtilis

ex. Clostridium tetani

ex. Staphylococcus aureus

Is tubercle bacillus the scientific name of an organism or a common name?

Taxonomic Categories

Order ends in –ales in fungi, plantae & bacteria

Family ends in- aceae infungi, plantae & bacteria

Species of bacteria - “population of cells with similar characteristics”

Strain of bacteria - “group of cells derived from a single cell”

ex. Staphylococcus aureus 13578

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

Bundles of fibrils that arise at the end of the cell beneath the outer sheath & spiral around the cell

Ex. Treponema pallidum

Structure

Filament

Hook

Basal body

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 gonorrhoeae in pus

Neisseria meningitidis

Branhamella catarrhalis

Enterobacteriales

Non-pathogens• Escherichia• Klebsiella• Proteus• Serratia• Etc.

Family- enterobacteriaceae

Describe the microscopic appearance of these organisms.

Enterobacteriaceae cont’dPathogens• Salmonella (typhi)

– typhoid fever

• Shigella (dysenteriae)– bacillary dysentery

• Yersinia (pestis)– bubonic plague

Can you see why the family, enterobacteriaceae, has been referred to as the Colon-typhoid-dysentery group?

Can you differentiate the pathogens from the non-pathogens microscopically?

All members of Enterobacteriaceae are facultative anaerobes. Meaning?

Vibrionales

VibrionaceaeVibrio 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 & ChlamydiaGram negative obligate intracellular parasites

Rickettsiatransmitted to humans by insects & ticks

Ex. Rickettsia rickettsii - Rocky Mountain spotted fever

ChlamydiaNot transmitted by insects

Chlamydia trachomatisCauses:

1.Trachoma - world’s leading infectious cause of blindnessMiddle 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:– tuberculosis– leprosy (M. leprae)

Acid-fast stain of sputum showing Mycobacterium tuberculosis

Streptomycetes

Characteristics of Streptomyces:

• mold-like bacteria– branching, spores

• produce geosmin– soil smell

• several species produce antibiotics– ex. streptomycin

The End!