W12 - Bacterial morphology Flashcards
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)
Number of bacterial species
Total: > 0.7 - 100 million?
In the human gut : 500 – 1000
Species causing human disease : <100
Methods of classifying bacteria
Size
Gross structure
CW structure
Differential stains
Morphology
Growth requirements
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
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
CW gram -ve
Extra outer membrane with integral lipopolysaccharides Periplasmic space
Escherichia.coli
CW gram +ve
Thick peptidoglycan layer integral with Lipo/teichoic acid
Streptococcus pyogenes
CW acid fast
Thick layer of mycolic acids linked by arabino-galactans integral with lipoarabinomannan
Gram stain
A differential cell wall stain dividing bacteria into
Hans Christian Joachim Gram 1882
Gram positive – BLUE/PURPLE Gram negative – RED/PINK
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
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
Cell Wall & Acid Fast Stain
Acid Fast RED (Ziehl–Neelsen : ZN) or FLOURESCENT (Auramine)
AFB+ and AFB-
Fix (white) → carbol fuschin or auramine (red) → acid + alcohol → background stain
+ve stays red
-ve white from acid + alcohol
Gram positive cocci
in pairs (diplococci)
Streptococcus pneumoniae (pneumonia)
Non Acid Fast
they do NOT retain (keep fast) the Carbol Fuschin/Auramine stain on cell surface when washed with acid
Gram positive cocci
(in chains)
Streptococcus pyogenes (pharyngitis)
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?
- Shows how much is present ( + culture : shows viability) Important from normally sterile samples (blood, CSF) Quantification can give a measure of risk
- Pathogen confirmation Not all bacteria are pathogens (Commensals) Commensals in one host can cause disease in another
- Indicates treatment options Clinico-pathological manifestations are often species specific
- Speciation enables epidemiological study
