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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
In twos –
diplococcus
In chains - streptococcus
One coccus, two cocci…
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:
bacteria retain both dies  blue/purple
appearance = Gram-positive bacteria
 some
Staphlococcus aureus
Bacillus anthracis (anthrax)
in cerebrospinal fluid
Gram Stain
bacteria retain only the red stain  red/pink
appearance = Gram-negative bacteria
 Some
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
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Some bacteria do not stain well with this method 
must use other dies
Ex.: tuberculosis bacteria
What can we infer about the physical and chemical
characteristics of Gram-positive and Gramnegative bacteria?
 they must differ!
Differences in Cell Wall Structure – Gram + vs. Gram - Bacteria
Lipopolysaccharide
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
Disinfectants:
UV light, bleach, lysol,
etc.
Used to disinfect objects
Skin irritant & highly toxic
if ingested, inhaled
Antiseptics:
hydrogen peroxide,
alcohol, iodine, etc.
Used topically (on skin)
Toxic if ingested, inhaled
Antibiotics:
Drugs such as penicillin,
erythromycin, etc.
Used internally, taken
orally or by injection
Low toxicity, usually have
side effects
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Higiene: Most germs are killed or removed with water & soap.
Resistance: Germs may evolve resistance to drugs 
Finish your antibiotic prescription as directed!
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.
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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 (DNAdependent 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
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Most are heterotrophs
Some autotrophs
 Photoautotrophs
 Photosynthetic,
most have chlorophill
ex.: cyanobacteria
 Chemoautotrophs
 Use
ammonia or sulfur to make own food
ex.: archaebacteria in hot springs / ocean vents
 Saprophytic
(decomposers)
Bacteria - Respiration
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Aerobes – use oxygen
ex.: tuberculosis bacteria
Anaerobes – do not use oxygen, perform fermentation
ex.: 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
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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
Reproduction & Recombination
(increase number of bacteria) (DNA from different
organisms combined)
Binary Fission vs.
(prokaryote)
Mitosis
(eukaryote)
Sexual or asexual?
Endospore Formation
Anthrax
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 donating the plasmid? 2
Which Bac-t is receiving the plasmid? 1
Which Bac-t is the F+? 2
1
Which Bac-t is the F-? 1
Sex pilus 
Is this an example of Bacterial
Reproduction or Bacterial
Recombination or Both?
2
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 culture
ex.: 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
Capsules
Smooth Strain
(Virulent, causes Pneumonia)
Rough Strain
(Harmless)
Transformation of Bacteria
OUCH!
l
3. Transduction – virus takes some of Bacterial DNA
Step 1
Step 2
Step 3
3.Transduction –
viral DNA inserted into bacterial DNA
Step 1
Step 2
How do bacteria cause disease?

Exotoxins – secreted by living bacteria
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Endotoxins – released when bacteria die
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Stealing resources / nutrients from host
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Interfering with proper functioning of body cells
Bacterial Disease Examples
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Dental caries
Food poisoning – Salmonella,
E. coli
“Staph” – S. aureus
“Strep” – S. pyogenes
Tuberculosis
Lyme disease
Black plague
Cholera
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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…