Bacteria - Identification

Microbiologists identify bacterial species by: Cell shape - sphere, rod, spiral Clumping styles - filaments, bunches Colony appearance – shape & texture Staining w/ dyes – based on cell wall composition Nutrition & respiration – food, O2

Surface/cell membrane molecules, such as proteins

** Sterile technique must be used to inoculate (introduce) bacteria into sterile

culture medium(agar or fluid) **

Sphere-Shaped Bacteria

One coccus, two cocci…

In chains - streptococcus

In twos –diplococcus

In bunches, staphylococcus

Rod-Shaped Bacteria

One bacillus, two bacilli…

Spiral-Shaped Bacteria

One spirillum, two spirilla…

Gram Stain

Uses two dies (blue and red) and two rinses: some bacteria retain both dies blue/purple

appearance = Gram-positive bacteria

Staphlococcus aureus Bacillus anthracis (anthrax) in cerebrospinal fluid

Gram Stain

Some bacteria retain only the red stain red/pink appearance = Gram-negative bacteria

Escherichia coli (E. coli)stained using the Gram method

Some strains of this bacterium cause food poisoning; others are harmless and help make vitamin K in our intestines.

Gram Stain

Some bacteria do not stain well with this method must use other diesEx.: tuberculosis bacteria

What can we infer about the physical and chemical characteristics of Gram-positive and Gram-negative bacteria? they must differ!

Lipopolysaccharide

Differences in Cell Wall Structure – Gram + vs. Gram - Bacteria

What kingdom and domain do these bacteria belong to?Prokarya/Bacteria, Eubacteria/Bacteria

Bacterial Colony Appearance

Inhibition Rings

Clear / clearer area where cell growth was inhibited

Anti-bacterial Substances

Higiene: Most germs are killed or removed with water & soap. Resistance: Germs may evolve resistance to drugs

Finish your antibiotic prescription as directed!

DisinfectantsDisinfectants::

UV light, bleach, lysol, UV light, bleach, lysol, etc.etc.

Used to disinfect objectsUsed to disinfect objects Skin irritant & highly toxic Skin irritant & highly toxic if ingested, inhaledif ingested, inhaled

AntisepticsAntiseptics::

hydrogen peroxide, hydrogen peroxide, alcohol, iodine, etc.alcohol, iodine, etc.

Used topically (on skin)Used topically (on skin) Toxic if ingested, inhaledToxic if ingested, inhaled

AntibioticsAntibiotics::

Drugs such as penicillin, Drugs such as penicillin, erythromycin, etc.erythromycin, etc.

Used internally, taken Used internally, taken orally or by injectionorally or by injection

Low toxicity, usually have Low toxicity, usually have side effectsside effects

How Antibiotics Work--Mechanisms of Action of Some Antibiotics

Penicillins:  Inhibits formation of the bacterial cell wall by blocking cross-linking of the cell wall structure. The cell wall is a needed protective casing for the bacterial cell. Bacitracin: Inhibits cell wall production by blocking the step in the process (recycling of the membrane lipid carrier) which is needed to add on new cell wall subunits.Cephalosporins: Similar to penicillins in their mode of action but they treat a broader range of bacterial infections. They have structural similarities to penicillins and many people with allergies to penicillins also have allergic reactions to cephalosporins.

Aminoglycosides: Inhibit protein synthesis by binding to a portion of the bacterial ribosome. Most of them are bacteriocidal (i.e., cause bacterial cell death).

Rifampin: Inhibits RNA synthesis by inhibiting one of the enzymes (DNA-dependent RNA polymerase) needed in this process. RNA is needed to make proteins.

Quinolones: Blocks DNA synthesis by inhibiting one of the enzymes (DNA gyrase) needed in this process.

Bacteria - Nutrition

Most are heterotrophs Some autotrophs

Photoautotrophs Photosynthetic, most have chlorophill

ex.: cyanobacteria Chemoautotrophs

Use ammonia or sulfur to make own foodex.: archaebacteria in hot springs / ocean vents

Saprophytic (decomposers)

Bacteria - Respiration

Aerobes – use oxygenex.: tuberculosis bacteria

Anaerobes – do not use oxygen, perform fermentationex.: tetanus bacteria

Obligate aerobe/anaerobe can only survive under the condition; ex.: obligate aerobes need oxygen

Facultative aerobes/anaerobe can live with or without the condition; ex.: facultative anaerobes grow better in anaerobic conditions, but can tolerate oxygen

Bacteria - Reproduction

Reproduce mostly asexually by binary fission

May reproduce sexually by conjugation Some form dehydrated spores, or

endospores survive hard conditions, start growing again when water/food available

http://www.cellsalive.com/ecoli.htm

Binary Fission vs. Mitosis

(prokaryote) (eukaryote)

Reproduction & Recombination(increase number of bacteria) (DNA from different

organisms combined)

Sexual or asexual?

Endospore FormationAnthrax

Recombination

Genetic Changes by three means:

1. Conjugation – exchange plasmids

2. Transformation – absorb DNA from environment

3. Transduction – DNA via viruses

1. Conjugation

Which Bac-t is the F+?

Which Bac-t is the F-?

Which Bac-t is donating the plasmid?

Which Bac-t is receiving the plasmid?

1

2

2

1

1

2

Is this an example of Bacterial Reproduction or Bacterial Recombination or Both?

Sex pilus

Transformation

Biotechnology techniques can be used to “transform” bacteria so that they will express a gene from another organism:

Copies of the desired gene are synthesized and added to the bacterial cultureex.: gene for insulin protein

Bacteria are exposed to an electrical current or other type of “stress” – this causes them to take in the pieces of DNA around them

The transformed bacteria are grown in culture and the new expressed protein can be isolated

Purified protein is used in research, medical treatment, etc.

2. Transformation

Smooth Strain(Virulent, causes Pneumonia)

Rough Strain(Harmless)

Capsules

l

Transformation of Bacteria

OUCH!

3. Transduction – virus takes some of Bacterial DNA

Step 1

Step 2

Step 3

Step 1

Step 2

3.Transduction – viral DNA inserted into bacterial DNA

How do bacteria cause disease? Exotoxins – secreted by living bacteria

Endotoxins – released when bacteria die

Stealing resources / nutrients from host

Interfering with proper functioning of body cells

Bacterial Disease Examples

Dental caries Food poisoning –

Salmonella, E. coli “Staph” – S. aureus “Strep” – S. pyogenes Tuberculosis Lyme disease Black plague Cholera

STDs – gonorrhea, siphilis, chlamydia

Gangrene – causes tissues to die, loss of limbs

Septicemia – blood infection

Anthrax Meningitis Tetanus The list goes on and

on and on…