Week 5:

Bacteria

Viruses

Monday, February 16, 2015

Biochemistry, Microbiology and Immunology

What are bacteria?

• Single celled organisms

• Very small

• Need a microscope to see

• Can be found on most

materials and surfaces

– Billions on and in your

body right now

E. Coli O157:H7

can make you

very sick.

Streptococcus

can cause strep

throat.

This E. coli helps

you digest food.USDA NIFSI Food Safety in the Classroom©

University of Tennessee, Knoxville 2006

Classification of Bacteria

Binomial nomenclatureGenus & species

Escherichia coli

Genus name is always capitalized

Species name is never capitalized coli

Both names are always either italicized or underlined

Abbreviation: E. coli

Strain or variety – a culture derived from a single

parent that differs in structure or metabolism from other cultures

of that species (biovars, morphovars)

Type – a subspecies that can show differences in:

• antigenic makeup (serotype or serovar),

•susceptibility to bacterial viruses (phage type)

•pathogenicity (pathotype)

Classification of Bacteria

Light microscope was the original tool for classification.

Initial classification was based on of the shape of the bacterial cells.

What do they look like?

• Three basic shapes– Rod shaped called bacilli

(buh-sill-eye)

– Round shaped called

cocci (cox-eye)

– Spiral shaped

• Some exist as single

cells, others

cluster together

Bacilli

Spiral

Cocci

Cluster of cocciUSDA NIFSI Food Safety in the Classroom©

University of Tennessee, Knoxville 2006

4 Main Shapes of Bacteria• Cocci

• Bacilli

• Spirilla

• Spirochetes

Medical Microbiologists said…

One bacterium = One disease

So to these scientists, bacteria were also

classified as to the disease they caused…

e.g. Mycoplasma pneumoniae

Four Groups Based on Cell Wall

Composition1. Gram-positive cells

2. Gram-negative cells

3. Bacteria without cell walls

4. Bacteria with chemically unique cell walls

Peptidoglycan• Macromolecule composed of a

repeating framework of long chains sugars cross-linked by short peptide fragments

– Unique to Bacteria

– Composed of 2 sugars: NAG & NAM

– Sugars alternate in the backbone

– Rows linked by polypeptides

• Provides strong, flexible support to keep bacteria from bursting or collapsing because of changes in osmotic pressure

N-acetylglucosamine

(NAG)

N-acetylmuramic

acid (NAM).

Gram Positive Cell Wall

• Consists of

– A thick, homogenous sheath of

peptidoglycan, 20 - 80 nm thick

– Tightly bound acidic polysaccharides,

– Retains crystal violet with iodine in culture

Gram Negative Cell Wall

• Consists of

– An outer membrane containing

lipopolysaccharide (LPS)

– Thin shell of peptidoglycan between inner and

outer membranes

– Loses crystal violet-iodine complex when cells

are exposed alcohol (decolorization step) and

stains red with safranin counterstain

Bacteria without Cell Walls - Mycoplasma

• Lack a rigid cell wall during their entire life cycle

• Smallest known organisms – smallest genomes (other than viruses)

– Diameter ranges from 0.15 m to 0.30 m

• Do not stain with the Gram stain

– Tiny cocci, short rods, short spirals

– Mycoplasma pneumoniae that causes a typical pneumonia in humans

Bacteria and their energy

• Autotrophs

• Chemotrophs

• Heterotrophs

Autotrophs

• Make their own

energy

• Using Solar energy

• E.g. Cyanobacteria

Chemotrophs

• Make own Energy

• Using Chemical

energy

• E.g. Archaebacteria

Heterotrophs

• Obtain food from

other organisms

• E.g. E-coli that

Infects meat products.

Respiration in Bacteria• Obligate Anaerobes: Live without Oxygen

• Facultative Anaerobes: Can live with or

without oxygen

• Obligate Aerobes: Cannot live without

oxygen.

Reproduction in Bacteria

• Binary Fission

• Conjugation

Cellular organism copies it’s genetic information then splits into

two identical daughter cells

Conjugation in Bacteria

Conjugation or genetic

transformation

• This process requires contact between living cells.

• One type of genetic donor cell is an F+; recipient cells are F-.

• F+ cells contain plasmids called F factors; these are transferred to the F- cells during conjugation.

• When the plasmid becomes incorporated into the chromosome, the cell is called an Hfr (high-frequency recombinant).

• During conjugation, an Hfr can transfer chromosomal DNA to an F-, usually, the Hfr chromosome breaks before it is fully transferred.

Cyanobacteria• Gram negative phototrophs

– Oxygenic photosynthesis 12H2O + 6CO2 C6H12O6 + 6H2O + 6O2

– Existed for 2.3 bya (billions years ago)

– Largest and one of the most important groups of bacteria on Earth

• Extremely diverse group

– Unicellular, colonial & filamentous form

– Some species fix N2

Most species are found in fresh water• Marine

• Damp soil

• Temporarily moistened desert rocks

• Endosymbionts in lichens, plants, various protists or sponges

Internal photosynthetic

membrane

vis-pc.plantbio.ohiou.edu/algaeimage/pages/anabaena.html

Spirulina sp.Merismopedia sp.

Oscillatoria sp.

Spirochetes• Long, helically coiled cells.

• Gram negative

• Axial filaments

– Running lengthwise between the cell membrane and cell wall

– Most spirochetes are free-living and anaerobic, but there are exceptions

• 3 families:

• Leptospira spp.

– Leptospirosis:

– Leptospirosis is a bacterial disease spread

– through contact with water, soil or

– food contaminated by urine from infected

– animals, or by direct contact with infected

– animals. The bacteria can live in the ground

– for days and favour humid and

– moist conditions.

• Borrelia burgdorferi

– Lyme disease:

– is an illness caused by a

– bacterium called Borrelia burgdorferi,

– which is transmitted by the bite of an

– infected tick

• Treponema pallidum

– Syphilus: is a highly contagious

– disease spread primarily by sexual activitywww.bbc.co.uk/.../stis_syphilis.shtml

www.microbeworld.org

Borrelia burgdorferi

Do you know about Leptospirosis? It is also known byvarious names such as disease Weil, feverIcterohemorrhage, Disease Swineherd’s, Fever farmers (Rice-field fever), fever Cutting sugar cane (Cane-cutterfever), Swamp fever , Jaundice Bleeding Stuttgart diseaseand fever Canicola.

www.surrey.ac.uk/SBMS/ACADEMICS_homepage/mcfadden_johnjoe/sbms243.html

Pyogenic cocci • Causes many suppurative infections

• Gram + cocci – Staphylococcus aureus, Streptococcus

pyogenes & Streptococcus pneumoniae,

• Gram - cocci– Neisseria gonorrhoeae & N. meningitidis

• ⅓ of all human bacterial infections – Food poisoning, strep throat,

pneumonia, various skin diseases, septic shock, gonorrhea (one of the most common diseases passed from one person to

another during sexual activity) & meningitis

Lactic Acid production in

Bacteria

• Fermentative bacteria that

produce lactic acid under

anaerobic conditions Convert

pyruvate to lactic acid• Also produce acetic acid & CO2

– Regenerate NAD+ for glycolysis

• Species of Streptococcus and

Lactobacillus

• Dairy industry

– Cheese, cottage cheese, yogurt

Endospore-forming Bacteria • Gram +

– Bacillus, Clostridium and Sporosarcina

• Survival structure– Resistant to heat, UV,

desiccation

• Pathogen– Bacillus anthracis

– Clostridium tetani

– C. perfringens (of the most common causes of food

poisoning)– C. botulinum (a serious form of

food poisoning that can cause death)

Endospore formation is usually triggered by a lack of nutrients, and usually occurs

in Gram-positive bacteria. In endospore formation, the bacterium divides within its cell

wall. One side then engulfs the other. Endospores enable bacteria to lie dormant for

extended periods, even centuries.

Purple and Green Bacteria

• A photosynthesis process

without oxygen and water:– 12H2S + 6CO2 C6H12O6 + 12S°

• Colors due to presence of

Chemical components of S:

– Green - deposit S° outside

– Purple - S° is inside the cell

• Anaerobic H2S-containing

mud and water

Vibrios • Gram -, slightly curved rods, flagellum

• Estuarine & marine environments

• Pathogenic and cooperative interactions with eukaryotic host

• Vibrio cholerae– Cholera

• Extreme watery diarrhea

– Only species that can survive in both fresh and salt water

– Potent toxin

• Vibrio fischeri– Bacterial bioluminescence

– Live in seawater but can also colonizes organs of squids and marine fish

Myxobacteria • Glide over surface

– No flagella

• The myxobacteria are a group of bacteria that predominantly live in the soil and feed on insoluble organic substances. The myxobacteria have very large genomes, relative to other bacteria,

• Dormant myxospores

• Spores “germinate” under favorable conditions

www.textbookofbacteriology.net

Actinomycetes• Filamentous, Gram + soil bacteria

• They are decomposers

• They produce Geosmin:

• an organic compound with a distinct earthy flavor and aroma that contributs to the strong scent that occurs in the air when rain falls after a dry spell of weather.

– Pathogens – Mycobacterium tuberculosis

– Corynebacterium diphtheriae

Radioresistant• Deinococcus radiodurans

– Gram +

• Survive a dosage of radiation that is 3,000 times greater than what would kill a human

• Survive DNA damaging chemicals, and high levels of ionizing and ultraviolet radiation, and dehydration

• Able to repair chromosome fragments within 12-24 hours– Repair chromosomes that have been

broken into 100 fragments

Deinococcus radiodurans

A radioresistant extremophile. It can survive cold, dehydration, vacuum, and acid, and is therefore known as a polyextremophile and has been listed as the world’s toughest bacterium.

Radiodurans First DiscoveredDeinococcus Radiodurans was discovered in 1956 at

the Oregon Agricultural Experiment Station in Corvallis by Arthur W. Anderson. An experiment was being conducted to investigate whether meat could be sterilized when treated with gamma radiation. The meat later spoiled despite the radiation treatment do to Deinococcus Radiodurans in the meat. Arthur isolated the bacteria in the can of spoiled meat.

Anderson, A W; H C Nordan, R F Cain, G Parrish, D Duggan (1956). “Studies on a radio-resistant micrococcus. I. Isolation, morphology, cultural characteristics, and resistance to gamma radiation”.

Food Technol. 10 (1): 575–577.

How can I avoid pathogens?

• Wash your hands often so you won’t

transfer bacteria to your mouth or

food

– Warm water with soap for 20 seconds,

rub hard between fingers and nails

USDA NIFSI Food Safety in the Classroom©

University of Tennessee, Knoxville 2006

• Cook food thoroughly to kill

any pathogens that may be

in your food

• Store food properly to limit

pathogen growth

– Cold temperatures (40F)

How can I avoid pathogens?

USDA NIFSI Food Safety in the Classroom©

University of Tennessee, Knoxville 2006

What are Viruses

A virus is a non-cellular particle made up of genetic material and protein that can

invade living cells.

The Structure Of a Virus

• Viruses are

composed of a core

of nucleic acid

• The Nucleic acid core

is surrounded by a

protein coat called a

capsid

• The Nucleic core is

either made up of

DNA or RNA but

never both

Retrovirus

• Change RNA into DNA.

• Example of a Retrovirus is HIV

Retroviruses

• Contain RNA and not DNA

- to be able to take over a host cell, the

retrovirus must be able to convert the RNA

into DNA.

- to accomplish the conversion, retroviruses

insert an enzyme called Reverse

Transcriptase into the host cell.

Bacteriophage• Bacteriophages are viruses that infect bacteria

- they are responsible for transduction in

bacteria

Transduction is the process by which DNA is transferred from

onebacterium to another by a virus.

Viruses have two life cycles

• Lytic Cycle-Viruses-immediately infect the

host cell

• Lysogenic Cycle - lay dormant in the cell

Lytic Cycle

Lysogenic Cycle

Lytic and Lysogenic Cycles

Small Pox- Lytic

Jenner developed first vaccine 1798

Small pox virus can only live in humans.

Spread person to person generally

through close contact with infected

person. Symptoms appear 12 –14 days

after exposure. 1st symptoms are fever,

tiredness, severe back pain, stomach

pain and vomiting. This last 2-3 days

and at this time the person is highly

contagious to others. Then over the next

5 days the bumps appear. Today we

have a vaccine for small pox. Today the

risk of the disease is less than the risk

from the vaccine so people do not get

vaccinated. Vaccine can be helpful if you

are exposed up to 4 days after exposure.

Herpes Simplex 1/Lysogenic

Shingles-Lysogenic/ Chicken pox virus

(herpes varicella-zoster)

Vocabulary

• Obligate intercellular parasite• Capsid• Envelope• bacteriophage• Lytic Cycle• Lysogenic Cycle• Phage• prophage• Retrovirus• Reverse Transcriptase