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SGUL - Fundamentals of Pathology > Bacterial Morphology and Growth > Flashcards

Bacterial Morphology and Growth Flashcards

1
Q

List some structural components of bacteria.

A
  • haploid circular DNA
  • ribosomes in the cytoplasm
  • DNA in nucleoid region (NOT bound in a nucleus)
  • peptidoglycan membrane (a target for antibiotics)
  • no mitochondria
  • no membrane-bound organelles
  • may have a capsule
  • may have pilli/ flagella
  • may have spores
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2
Q

Describe the Gram stain, and how to apply it to bacteria.

A

It is a differential CELL WALL stain dividing bacteria into:
GRAM-POSITIVE - stained blue/purple. Thick peptidoglycan layer integral with lipo/teichoic acid
GRAM-NEGATIVE - stained pink. Extra outer membrane with integral lipopolysaccharides and periplasmic space

  • Fix the bacteria.
  • Add the crystal violet dye, then add iodine (to trap the crystal violet)
  • Add alcohol (this will remove traces of the dye from Gram-negative bacteria by dissolution so colour disappears if not strongly attached to cell wall), then you add another dye, such as Carbol Fuschin or Safranin.
  • The Gram-positive bacteria have thick cell walls which are able to hold onto the original dye.
  • The Gram-negative has a thinner cell wall, so the alcohol step damages the outer membrane and allows the blue/purple Crystal Violet dye to move out. The second Safranin/Carbol Fuschin dye then stains the cell wall red/pink.

At alcohol step, Gram-negative are white whereas Gram-positive are purple

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3
Q

Describe the Acid Fast stain.

A

It is used on bacteria with waxy cell walls because the Gram stain won’t stick to them.
STRUCTURE if acid-fast: Thick layer of mycolic acids linked by arabinogalactans integral with lipoarabinomannan

  • Fix the bacteria.
  • Add Carbol Fuschin(red) or Auramine(fluorescent).
  • Add an acid or an alcohol (which will remove the dye from non-acid-fast bacteria)
  • Add a background stain.

If a bacterium is non-acid-fast, they do not retain (keep fast) the Carbol Fuschin/Auramine stain on their cell surface when washed with acid/alcohol and so appear white. If acid-fast, appear red.

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4
Q

Give examples of the following.

  • Gram-positive cocci in pairs
  • Gram-positive cocci in chains
  • Gram-positive cocci in clusters
  • Gram-positive rods (bacillus)
  • Gram-positive rods with spores
  • Gram-negative rods (bacilli)
  • Gram-negative cocci (diplococci)
  • Spiral (helical) shaped bacteria
  • Acid-fast staining bacteria
A

Gram-positive cocci in pairs
- Streptococcus pneumoniae (pneumonia)

Gram-positive cocci in chains
- Streptococcus pyogenes (pharyngitis)

Gram-positive cocci in clusters
- Staphylococcus aureus (toxic shock syndrome)

Gram-positive rods (bacillus)
- Corynebacterium diptheriae (diphtheria)

Gram-positive rods with spores
- Clostridium tetani (tetanus)
- Clostridium perfringens (gangrene)
- Bacillus anthrax (anthrax)

Gram-negative rods (bacilli)
- Escherichia coli (colitis)
- Salmonella typhi (typhoid fever)

Gram-negative cocci (diplococci)
- Neisseria meningitidis (meningitis)
- Neisseria gonorrhoea (gonorrhoea)

Spiral (helical) shaped bacteria
- Treponema pallidum (syphilis)
- Helicobacter pylori (stomach ulcers)
- Vibrio cholerae (cholera)

Acid-fast staining bacteria
- Mycobacterium tuberculosis (TB)

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5
Q

What bacterium is an exception to the cell wall staining tests, and why?

A

Mycoplasma pneumoniae (atypical pneumonia)

  • No cell wall (therefore doesn’t have peptidoglycan), thus it cannot be stained
  • Only has a lipoprotein outer coat.
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6
Q

Describe how bacteria can be classified based on temperature

A
  • PSYCHROPHILES (-20°C to 20°C)
    eg. Camplyobacter jejuni (food poisoning)
  • MESOPHILES (2°C to 45°C)
    most animal pathogens
  • THERMOPHILES (42°c TO 80°C)
    eg. Bacillus stearothermophilus (used for sterilisation strips)
  • EXTREME (HYPER) THERMOPHILES (60°C TO 250°C)
    eg. Thermus aquaticus (source of Taq for PCR)
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7
Q

Describe how bacteria can be classified based on pH

A
  • ACIDOPHILE: thrives in acidic conditions e.g Helicobacter pylori
  • NEUTROPHILE: thrives in neutral conditions
  • ALKALIPHILE: thrives in alkaline conditions e.g Bacilus cereus

Most human pathogens are neutrophiles.

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8
Q

How can bacteria be classified?

A

Size
Gross structure
Cell wall structure
Differential stains
Morphology
Growth requirements (e.g pH, temperature)

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9
Q

What are the 8 factors that affect growth rate of bacteria?

A
  • division rate
  • lag phase time
  • oxygen availability
  • carbon availability
  • temperature
  • pH
  • inhibitors
  • growth factors
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10
Q

Give examples of the following
- rapid growers
- slow growers
- dormancy

A

Rapid growers
- Vibrio cholerae (a curved flagellate) - Division every 20-40 minutes

Slow growers
- Treponema pallidum (syphilis) - Division every 30 hours

Dormancy
- Mycobacterium tuberculosis (lung abscess) - Division every 18 hours (min) - 80 years

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11
Q

With examples, briefly describe the following
- Obligate aerobes
- Facultative anaerobes
- Aerotolerant annaerobes
- Obligate anaerobes

A

Obligate Aerobes
- Require SOME oxygen to make ATP (energy/growth) Most tolerate O2( Air = 21%O2: 0.04%CO2) eg Pseudomonas aeruginosa
- Some (Microaerophiles) only tolerate 5% O2 eg Helicobacter pylori i.e at certain amounts
- Some (Capnophiles) require O2 higher than in air (5-10%) eg. Neisseria gonorrhoeae

Facultative Anaerobes
- Use oxygen or fermention or anaerobic respiration eg. E.coli

Aerotolerant Anaerobes
- Cannot use oxygen but can tolerate it eg. Clostridium botulinum (botulism)

Obligate Anaerobes
- Oxygen is toxic eg. Clostridium tetani (tetanus)

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12
Q

What can bacteria with the Lac gene do?

A
  • Ferment lactose
  • Can be viewed in cell cultures as lactose can alter pH of the medium causing precipitation of bile salts and turns indicator red
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13
Q

Briefly describe Campylobacter jejuni

A
  • common cause of food poisoning
  • Grows between 0ºC to 45ºC.
  • Allows it to grow in cattle (humans 37ºC : cattle 42ºC) AND in badly prepared food while stored e.g in fridges
  • Very few faecal organisms grow at 42ºC
  • We use this to differentially isolate Campylobacter jejuni from stool samples
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14
Q

What is the significance of systemic classification when classifying bacteria?

A
  • Shows how much bacteria is present ( + culture : shows viability)
    Important from normally sterile samples (blood, CSF)
    Quantification can give a measure of risk
  • Pathogen Identification
    Not all bacteria are pathogens (Commensals)
    Commensals in one host can cause disease in another
  • Identification can indicate treatment options
    Clinico-pathological manifestations are often species-specific
    Antibiotic selectivity for bacterial targets (cell wall specificity)
  • Speciation enables epidemiological study
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SGUL - Fundamentals of Pathology (20 decks)

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