Important microbes Flashcards
5 iconic bacterial genera
Mycobacterium Bacillus Streptomyces Escherichia Staphylococcus
Mycobacterium tuberculosis
Causative agent of Tuberculosis
> Consumption, pthisis, wasting disease
Ancient human disease
Evidence in stone age mummies, Egypt and Peru
Discovered by Robert Koch in 1882
When discovered, TB accounted for 14% of deaths in Europe ( 33% in young adults)
Phylogeny of M. tuberculosis
high G+C Gram +ve group
Family Mycobacteriaceae
Single genus Mycobacterium
Characteristic cell walls 60-90% mycolic acids
Tuberculosis today
Estimated to affect 20% of the World’s population.
Incidence increased by poverty, malnutrition, poor sanitation, and overcrowding.
Alarming re-emergence in Europe and N. America (AIDS / multidrug resistant strains).
Tuberculosis, the disease
The infection and the disease: clear cut distinction, only 5% of infections lead to disease.
Untreated it can last a life time.
Periods of health can be interspersed with morbidity.
85% of cases found in the lung but other organs can be affected :
lymph nodes, kidneys, long bones, genital tracts,
brain and meninges
Detection of Tuberculosis
Mantoux Test
0.1 ml of PPD injected into the forearm to produce a small bleb.
X-Ray test
Tubercles seen as radio-opaque patches in lower parts of lungs
Cell Morphology of M. tuberculosis
- Cells slightly curved or straight rods.
- Often filamentous but fragment easily unlike Actinomycetes.
- Samples from patients can appear as rope-like structures.
- Grown on selective egg-potato base media
- Colonies take ~ 6 weeks to grow and have a granular waxy morphology.
Other important members of the genus Mycobacterium:
M. bovis (Cattle) M. scrufulaceum (Scrofula) M. leprae (Leprosy) M phlei (Sputum and soil) M. smegmatis (Smegma and soil) M. marinum (sea)
Importance of Bacillus subtilis
Discovered in 1872 by Ferdinand Cohn, “subtilis” means slender (L.)
Model Experimental System:
Bacterial physiology and genetics
Cell division
Sporulation in prokaryotes
Microbial factory:
Industrial scale enzymes
Fine biochemicals
Antibiotics
Phylogenetic of Bacillus subtilis
and general
Member of the Low G+C Gram-Positive bacteria (Phylum Firmicutes).
Gram +ve rods: 2 to 3 uM long, 0.7 to 0.8 uM wide.
Heterotroph: primarily aerobic but weakly fermentative
Mesophile
G+C content 42-43 % (low)
Motile with lateral flagellae
Forms heat- and dessication-resistant endospores situated centrally- Endospores promote survival
Phylum Firmicutes - thr group includes the genera
- Clostridium (Obligately anaerobic spore forming rods)
- Lactobacillus
- Steptococcus
- Listeria
- Mycoplasmas (Obligate endoparasites of plant and animal cells, Lack cell walls
Bacillus subtilis as a Bio-Factory
Enzymes: amylases, proteases, lipases
Amino acids and vitamins
Bio-active peptides:
antibiotic – subtilisin
surfactant/anti-bacterial/viral antibiotic - surfactin
Bacillus subtilis sporulation can be triggered by
Carbon, nitrogen or phosphorus starvation
7 hours to complete
Can survive hours of boiling or baking, most cleaning agents including ethanol
veg cells vs spores
spores has
refractile microscopic appearance when none in veg cell
higher heat resistant
higher Dessication resistant
higher Radiation resistant
lower water content
higher calcium content
higher dipicolinic acid content while absence in veg cell
lower metabolic rate
has absent of marcomolecular synthesis while high in veg cell
Other important Bacillus species
Bacillus anthracis - cause of Anthrax
Bacillus cereus - food poisoning (enterotoxins) reheated rice
Bacillus larvae, popilliae - insect pathogens
Bacillus thuringiensis - insecticidal parasporal crystals (‘BT toxin’)
Bacillus licheniformis - antibiotic producer: Bacitracin and Polymyxin B
Bacillus stearothermophilus - thermophile: source of spores for autoclave testing
Streptomyces
Bacteria that look like fungi
Mainly live in soil
Produces geosmin to give soil its characteristic smell
Produce a wide range of antibiotics including streptomycin
David Hopwood, pioneering geneticist
Taxonomy of Streptomyces
History
which family
Gram / G+C / oxygen requirement
Initially thought to be intermediate between fungi and bacteria
Discovered it has no nuclear membrane
Phylum Actinobacteria
Family Streptomycetaceae
Gram positive bacterium
High G+C content DNA (70%+)
Strict aerobes
Unusual structure of Streptomyces
Apical spores
Spores produce germ tube that grow by apical growth
which bacterial genera used as Antibiotic producers
How many species used
for ?
Streptomyces
Around 500 species of Streptomyces
Form 1-20% of the culturable population of soil
Antibiotics used against competitors
Whopping 8700 antibiotics made – more than all other bacteria and fungi combined
Different species of Streptomyces
S. coelicolor – model organism S. griseus – antibiotic producer S. avermitilis – antibiotic producer S. scabies – potato scab S. somaliensis – human actinomycetoma S. albus – associated with human disease
Escherichia History
Discovered 1885 by German biologist Theodor Escherich
Gut (lower intestine) dweller = 100 billion-10 trillion in stools
Taxonomy of Escherichia
Phylum Proteobacteria
Class Gammaproteobacteria
Family Enterobacteriaceae
Gram negative rod
48-52% G+C
Optimum growth temperature is 37oC
Facultative anaerobes
E. coli used as a lab tool for
reason
which strain
Used in virtually every biology lab Propagating plasmids and phage Making proteins Model organism for many systems K12, classic strain
Pathogen types of E. coli
ET- Enterotoxin
EH- Enterohaemorrhagic
EA- Enteroaggregative
DA- Diffusely adhering
EP- Enteropathogenic
EI- Enteroinvasive
