1. 3 × 10^29 bacteria in the oceans 1. 3 × 10^21stars in the universe Bacteria in a teaspoon of soil = Humans inAfrica (1 x 109)

W12 - Bacterial morphology Flashcards by Sharjeel Ahmad

Bacteria in numbers

3 × 10^29 bacteria in the oceans
3 × 10^21stars in the universe

Bacteria in a teaspoon of soil = Humans inAfrica (1 x 109)

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Number of bacterial species

Total: > 0.7 - 100 million?

In the human gut : 500 – 1000

Species causing human disease : <100

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Methods of classifying bacteria

Size

Gross structure

CW structure

Differential stains

Morphology

Growth requirements

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Size ranges

0.3μm - 3μm

(Virus = 0.02μm - 0.3μm)

(WBC = 7μm - 25μm)

(Plant Cell = 10μm - 100μm)

Thiomargarita namibiensis = 300,000 nm

Mycoplasma genitalium = 300 nm

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Structural components

Haploid (single chromosome) DNA (circular)

DNA in nucleoid region = NOT bound in a nucleus

Ribosomes in cytoplasm

Peptidoglycan membrane
No mitochondria

No membrane bound organelles
+/- Capsule
+/- Pilli / Flagella
+/- Spore

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CW gram -ve

Extra outer membrane with integral lipopolysaccharides Periplasmic space

Escherichia.coli

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CW gram +ve

Thick peptidoglycan layer integral with Lipo/teichoic acid

Streptococcus pyogenes

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CW acid fast

Thick layer of mycolic acids linked by arabino-galactans integral with lipoarabinomannan

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Gram stain

A differential cell wall stain dividing bacteria into
Hans Christian Joachim Gram 1882
Gram positive – BLUE/PURPLE Gram negative – RED/PINK

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Gram -ve means

Negative means the alcohol step damages the outer membrane and allows the BLUE/PURPLE Crystal Violet dye out.

The second Safranin/Carbol fuschin dye then stains the cell wall RED/PIN

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Gram stain proces

Fix (white) → crystal violet (blue) → iodine (purple) → alcohol →carbol fushcin or safranin

at alcohol -ve is white whereas +ve is purple

at last step +ve still purple whereas -ve pink

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Cell Wall & Acid Fast Stain

Acid Fast RED (Ziehl–Neelsen : ZN) or FLOURESCENT (Auramine)

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AFB+ and AFB-

Fix (white) → carbol fuschin or auramine (red) → acid + alcohol → background stain

+ve stays red

-ve white from acid + alcohol

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Gram positive cocci

in pairs (diplococci)

Streptococcus pneumoniae (pneumonia)

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Non Acid Fast

they do NOT retain (keep fast) the Carbol Fuschin/Auramine stain on cell surface when washed with acid

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Gram positive cocci

(in chains)

Streptococcus pyogenes (pharyngitis)

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Gram positive cocci in clusters

Staphylococcus aureus (toxic shock syndrome)

Gram positive rods

(bacillus)

Corynebacterium diphtheriae (diphtheria)
Pallisades
Chinese writing

Gram positive rods (with spores)

Clostridium tetani (tetanus) 
Clostridium perfringens (gangrene) Clostridium difficile (pseudomembranous colitis)
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

Treponema pallidum (syphilis) Helicobacter pylori (stomach ulcers) 
Vibrio cholerae (cholera)

Acid Fast Stains

Mycobacterium tuberculosis
Auramine
Ziehl-Neelsen

Cording colony

Cell wall deficient

Mycoplasma pneumoniae (atypical pneumonia)
No cell wall = no staining
Have only lipoprotein outer coat

Factors affecting growth

``` Division rate Lag phase time Oxygen availability Carbon availability Temperature pH Inhibitors Growth Factors ```

Rapid growers

``` Vibrio cholerae (a curved flagellate) Division every 20-40 minutes = 1,073,741,824 bacteria from 1 starting cell overnight ```

Slow growers

``` Treponema pallidum (syphilis) Division every 30 hours ```

Dormancy

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

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 Some (Capnophiles) require CO2higher 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)

Psychrophiles

extremophilic bacteria or archaea which are cold‐loving (-20ºC to 20ºC) eg. Campylobacter jejuni (food poisoning

Mesophiles

an organism that grows best in moderate temperature, neither too hot nor too cold (2ºC to 45ºC) eg. Most animal pathogens

Thermophiles

an organism—a type of extremophile—that thrives at relatively high temperatures (42ºC to 80ºC) eg. Bacillus stearothermophilus (used for sterilisation strips)

Extreme (hyper) thermophiles

(60ºC to 250ºC) eg. Thermus aquaticus (source of Taq for PCR)

Campylobacter jejuni

(a common cause of food poisoning) Grows between 0ºC to 45ºC. This allows it to grow in cattle (humans 37ºC : cattle 42ºC) AND in badly prepared food IN YOUR FRIDGE!!! Very few faecal organisms grow at 42ºC We use this to differentially isolate Campylobacter jejuni from stool samples

Acidophile

Helicobacter pylori (stomach ulcers)

Neutrophile

Most human pathogens

Alkaliphile

Bacillus cereus (food poisoning)

Carbon usage

Bacteria with the Lac gene can ferment Lactose

Why systemic classification?

1. Shows how much is present ( + culture : shows viability) Important from normally sterile samples (blood, CSF) Quantification can give a measure of risk 2. Pathogen confirmation Not all bacteria are pathogens (Commensals) Commensals in one host can cause disease in another 3. Indicates treatment options Clinico-pathological manifestations are often species specific 4. Speciation enables epidemiological study