Taxonomy

• Defined as the science of classification of organisms

• Taxonomic categories are arranged to show degree of similarities among organisms

• Relatedness through evolution

Three Domain System

• System of classification above the five kingdoms

• Based on molecular techniques of ribosomal RNA analysis

• Domains consists of the:– Eukarya – Bacteria– Archaea

Taxonomic Hierarchy

Prokaryote Classification

• Bacteria• Peptidoglycan in cell

wall• All pathogenic and

non-pathogenic bacteria

• Archaea• No peptidoglycan in

cell wall• Extreme

environments• Methanogens• Extreme halophiles • Hyperthermophiles

How could you classify bacteria?

• Gram reaction• Shape• Nutritional requirements• Oxygen requirements

– Aerobic - requires oxygen– Anaerobic - killed by oxygen– Facultative anaerobe - lives with or without oxygen

• DNA profiles – G+C ratios• Combination of all of the above

Prokaryotes

• Grouped into two Domains

• Domain Archaea

• Domain Bacteria – two major divisions– Proteobacteria – 5 classes– Gram positive bacteria – two groups

• High G+C ratios – phylum Firmicutes• Low G+C ratios – phylum Actinobacteria

Proteobacteria

• Five classes

• Very diverse group

• Most of the gram negative bacteria

• Alpha, beta, gamma, delta, and epsilon – proteobacteria

• General survey of some the better known and medically important members of this group

Alphaproteobacteria

• Genus Rickettsia • Obligate intracellular parasites• Transmission to human by bites of ticks and

insects• Spotted fever diseases• Epidemic typhus• Rocky Mountain Spotted Fever

Betaproteobacteria

Medically important genus:

• Genus Neisseria – aerobic G- cocci– mucous membranes of mammals– Neisseria gonorrhoeae – gonorrhoea – Neisseria meningitidis - meningococcal

meningitis

Figure 11.6

Gammaproteobacteria

• Largest sub-group of the Proteobacteria

• Many pathogenic orders and genera in this group

• Important groups:– Genus - Pseudomonas– Order Enternbacteriales (enteric bacteria)

Pseudomonas

• Pseudomonas aeruginosa is the important bacteria of this genus

• Motile, G- rod, aerobe – produces a blue-green pigment

• Highly antibiotic resistant

• Important bacteria in urinary tract infections and wound/burn infection

Figure 11.7

Order Enterobacteriales

• All members of this order are straight G- rods, facultative anaerobes

• Commonly found in the gut of humans and other animals – ENTERICS

• Fimbriae for surface attachment

• Sex pili for exchange of genetic information

Important genera of order Enterobacteriales

• Escherichia

• Salmonella

• Shigella

• Klebsiella

• Serratia

• Proteus

• Enterobacter

Escherichia

• E. coli • Common gut bacteria, usually non-

pathogenic• Used as indicator for fecal contamination

of water• Common cause of traveler’s diarrhea• Most toxic strain is called 0157:H7 -

foodborne disease

Salmonella

• Intestinal tracts of poultry and cattle

• Food contaminate

• Typhoid fever and gastrointestinal illness

• Almost all members of this genus are pathogenic

Shigella

• Found only in humans

• Causes bacillary dysentery

Klebsiella

• Common in soil and water

• Klebsiella pneumoniae can cause a serious pneumonia in humans

Serratia

• Serratia marcescens produces a red pigment when grown at room temperature

• Cause of urinary and respiratory infections in hospitals

Proteus

• Highly motile bacteria

• Shows swarming growth on agar plates

• Important in urinary tract and wound infections

Figure 11.9b

Enterobacter

• Widely found in humans and other animals, also found in sewage, water, and soil

• Two important pathogens are:

• Enterobacter aerogenes

• Enterobacter cloacae

• Urinary tract infections and nosocomial infections

Epsilonproteobacteria

• Slender G- rods that are helical or vibroid

• Two important genera:– Helicobacter

• Helicobacter pylori – common cause of peptic ulcers in humans and stomach cancer

– Campylobacter• Leading cause of food-borne intestinal disease

especially from chicken

Figure 11.12

FirmicutesLow G+C Gram + bacteria

• This group includes the following important groups of bacteria:– Clostridium– Bacillus – Staphylococcus– Streptococcus– Lactobacillus – Enterococcus

Clostridium

• Rod shaped, obligate anaerobes

• SPORE FORMERS

• Many medically important members of this genus– Clostridium tetani - tetanus– Clostridium botulinum - botulism– Clostridium perfringenes – gas gangrene– Clostridium difficile - diarrhea

Bacillus

• Rod shaped, facultative anaerobes

• SPORE FORMERS

• Common in the soil, few important pathogens– Bacillus anthracis - anthrax– Bacillus cereus – food poisoning

Staphylococcus

• Cocci usually occur in grape-like clusters

• Facultative anaerobe

• Grow well in high salt

• Found on human skin

• CATALASE POSITIVE - reaction with hydrogen peroxide

• Important pathogen:– Staphylococcus aureus

Figure 11.18

Lactobacillus

• Rod shaped, non-spore forming

• Aerotolerant, grow in the presence of oxygen, but poorly

• Important in production of lactic acid and also sauerkraut, pickles, buttermilk, and yogurt

• Commonly found in the vagina, intestinal tract, and oral cavity

Streptococcus

• Cocci, growing in chains• CATALASE NEGATIVE• Cause more illness than any other group of

bacteria• Two typical reactions on a media called blood

agar:• β- hemolytic streptococci

– Streptococcus pyogenes

• α- hemolytic streptococci– Streptococcus pneumoniae

Figure 11.19

Enterococcus

• Common hospital pathogen• Low oxygen requirement, catalase negative• Found in the GI tract, vagina, and oral cavity.

Also fecal matter.• Two important members of this genera:

– Enterococcus faecalis– Enterococcus faecium– Both are highly antibiotic resistant– Nosocomial infections

ActinobacteriaHigh G+C bacteria

• Genus Mycobacterium– Acid-fast bacteria; mycolic acid– Mycobacterium tuberculosis– Mycobacterium leprae

• Genus Mycoplasma– NO CELL WALL– Mycoplasam pneumoniae

• Genus Corynebacterium– Highly pleomorphic

• Genus Propionibacterium– Propionibacterium acne

• Genus Streptomyces– Filamentous bacteria; common in soil; antibiotics

Phylum Chlamydiae

• No peptidoglycan in the cell wall

• Intracellular parasites

• Spread through direct personal contact or air borne transmission

• Chlamydia trachomatis– Best known pathogen in this group– Common cause of blindness - trachoma– Most common STD in the US.