Bacteria

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Bacteria

• Professor Mark Pallen

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Outline

• Importance of bacteria
• Nature of bacteria
• Classification of bacteria

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Importance of Bacteria

• Life is microbial! (to the first approximation)
• Micro-organisms colonise every environment on
  earth
• gt80 of lifes history was bacterial
• You have more bacterial cells than human cells
• Microbes play a key role in the biosphere
• Pathogenic microbes globally are the most
  important cause of human disease and death

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Importance of Infection

• Decisive role in history
• Still major cause of death and misery worldwide
• Public anxieties
• Meningitis, Food poisoning
• Mad cow disease
• Emerging infections
• Hospital Infection
• Antibiotic-Resistant Superbugs

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Microbes in History
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Microbes in History
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Microbes in the News
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Microbes in the News
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Microbes in the News
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Microbes in the News
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Differences between Bacterial and Human Cells

• Bacterial cells
• No nucleus
• No intracellular organelles (but ribosomes)
• No introns (nearly)
• No junk DNA
• Plasmids, bacteriophage

• Human cells
• Nucleus
• Intracellular organelles (ribosomes subtly
  different)
• Introns
• Lots of junk DNA
• Viruses

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Tree of Life
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Size matters
Bacterial cells
Animal cell
1 micron
10 microns
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Bacterial cells
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Differences between bacteria and viruses

• Viruses
• Obligate intracellular parasites
• No ribosomes
• DNA or RNA, not both
• seen by EM
• 10-100s of genes
• Tangled phylogeny

• Bacteria
• Usually free-living, but can be parasites
• Ribosomes
• DNA and RNA
• seen by LM
• 100s-1000s of genes
• Natural phylogeny

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The Gram stain procedure
Developed in 1884 by the Danish physician Hans
Christian Gram An important tool in bacterial
taxonomy, distinguishing so-called Gram-positive
bacteria, which remain coloured after the
staining procedure, from Gram-negative bacteria,
which do not retain dye and need to be
counter-stained. Can be applied to pure cultures
of bacteria or to clinical specimens
Top Pure culture of E. coli (Gram-negative
rods) Bottom Neisseria gonorrhoeae in a smear of
urethral pus (Gram-negative cocci, with pus cells)
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The Gram Stain
Gram's
Crystal
iodine
violet
Decolorise with
acetone
Gram-positives
appear purple
Counterstain with
e.g. methyl red
Gram-negatives
appear pink
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Gram-positive rods
Gram-positive cocci
Gram-negative rods
Gram-negative cocci
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Anaerobic
Anaerobic
Gram-positive rods
Gram-positive cocci
Gram-positive
cocci
Anaerobic
Anaerobic
Gram-negative rods
Gram-negative cocci
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Bacterial Growth

• Solid media or liquid media
• Agar plates, slopes, broth culture
• Atmosphere
• Aerobic, anaerobic or microaerophilic
• Facultative or obligate anaerobes
• Usually at 37 degrees C
• Most clinically important bacteria grow
  overnight, or within a few days
• Mycobacteria can take months
• Some can not be grown

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Gram-Negative Rods

• Enteric Bacteria
• E. coli
• Salmonella
• Shigella
• Yersinia
• Pseudomonas
• Proteus
• Vibrio cholerae
• Klebsiella pneumoniae

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Gram-Negative Rods

• Fastidious GNRs
• Bordetella pertussis
• Haemophilus influenzae
• Campylobacter jejuni
• Helicobacter pylori
• Legionella pneumophila
• Anaerobic GNRs
• Bacteroides fragilis
• Fusobacterium

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Gram-Negative Cocci

• Neisseria gonorrhoeae
• The Gonococcus
• Neisseria meningitidis
• The Meningococcus
• Both Gram-negative intracellular diplococci

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Gram-positive Cocci

• Staphylococci
• Catalase-positive
• Gram-positive cocci in clusters
• Staphylococcus aureus
• coagulase-positive
• Staph. epidermidis
• and other coagulase negative staphylococci

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Gram-Positive Cocci

• Streptococci
• Catalase-negative
• Gram-positive cocci in chains or pairs
• Strep. pyogenes
• Strep. pneumoniae
• Viridans-type streps
• Enterococcus faecalis

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Gram-Positive Rods

• Clostridia
• Anaerobes
• C.perfringens
• C. tetani
• C. botulinum
• C. difficile
• Bacillus cereus
• Aerobe
• Listeria monocytogenes
• Faculative anaerobe

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Non-Gram-stainable bacteria

• Unusual gram-positives
• Spirochaetes
• Obligate intra-cellular bacteria

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Unusual Gram-positives

• Mycoplasmas
• Smallest free-living organisms
• No cell wall
• M. pneumonia, M. genitalium
• Mycobacteria
• Acid-fast bacilli, stained by Ziehl-Neelsen stain
• M. tuberculosis
• M. leprae
• M. avium

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Spirochaetes

• Thin spiral bacteria
• Viewable by phase-contrast microscopy or silver
  stain
• Treponema pallidum
• Borrelia burgdorferi
• Leptospira

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Obligate intracellular bacteria

• Rickettsia
• Coxiella burneti
• Chlamydias
• C. trachomatis
• C. pneumoniae
• C. psittaci

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Outline

• Importance of bacteria
• Nature of bacteria
• Classification of bacteria
• Gram-positive versus Gram-negative
• Rods and Cocci
• Aerobic versus anaerobic