Antibiotic producers include
 fungi (Penicillium, Cephalosporium) and bacteria (Bacillus, Streptomyces) or may be synthetic.
To date, there are > 100 different antimicrobials in our arsenal.
Narrow-spectrum drugs are more desirable to use whenever possible because they target the pathogen more specifically and do less damage to the normal microbiota.
Broad-spectrum drugs are used when the cause of the infection is unknown or when other antibiotics are not effective.

Antibiotic resistance has evolved due to the misuse and over use of these drugs.  This is a major health concern since it is hard or impossible to treat infections caused by
microbes such as MRSA, the multidrug-resistant Staphylococcus aureus.

1910: Paul Ehrlich develops Salvarsan to treat individuals infected with Treponema pallidum that causes syphilis.
1928: Alexander Fleming observes Penicillium mold growing on agar plates was inhibiting
 bacterial growth.

procedure:
 disc diffusion method
(Kirby-Bauer method)
 tests the effectiveness of antibiotics by placing paper discs soaked in the test agent on an agar plate inoculated with bacteria.

a zone of inhibition
around the disc indicates the agent's effectiveness

materials:
1. Mueller-Hinton agar plates
2. liquid cultures of selected bacteria
3. sterile cotton swabs
4. antibiotic disk dispensers with antibiotic discs

procedure:
Work in a group of four. 
Use a sterile cotton swab to lawn inoculate one species of bacteria on the                 agar plates.
Use the disk dispenser to introduce antibiotic disks onto the plates.
Each disk that is introduced to the plate is stamped with a letter and a                 number which
           indicates the type of antibiotic as well as the concentration.
           ex: P10 = 10 units of penicillin
                 PIP-100 = 100 mcg (micrograms) of piperacillin.

Using your inoculation loop, gently push down on the disks to ensure                   that they are adhered to the agar surface.
           Be sure to FLAME your loop in between plates!
Incubate the Mueller-Hinton agar plates (inverted) until the next lab                   period.

Part 2:
Measure zones of inhibition for the antibiotics by measuring the diameter of the zone of inhibition in millimeters (mm).
Use the chart provided to look up the interpretation for each of the zones you measured. Record measurements and interpretations 

All antibiotics are NOT effective at killing ALL types of bacteria.
ex: Gram (-) bacteria are intrinsically resistant to vancomycin because the drug cannot penetrate the outer membrane of the gram (-) cell wall.

Bacteria that have been isolated can be tested for their antibiotic susceptibility so that health care clinicians can determine which drug should be used to treat the infection. 

Gram (+) bacteria are usually more susceptible to certain antibiotics because the thick peptidoglycan readily absorbs antibiotics.
Antibiotic resistance by Gram (+) bacteria is a growing concern...
MRSA = Methicillin-resistant Staphylococcus aureus
(resistant to most penicillin-related antibiotics)
and 
   VRE = Vancomycin-resistant Enterococcus
(resistant to vancomycin)

1. enzymes that degrade the antibiotic
2. reduction in the affinity of the antibiotic's target site
3. pumps that push antibiotics from the cell 

Newer antibiotics that combat Gram-positive bacteria are being developed:
daptomycin, tigecycline, dalbavancin, and oritavancin

Antibiotics can treat a variety of bacterial infections such as
strep throat, UTIs and bacterial pneumonia. They are
NOT EFFECTIVE
 against viral infections like the common cold or the flu virus.

Antibiotics are medicines that fight bacterial infections by
killing the bacteria = bactericidal
or by making it hard for the bacteria to grow and multiply = bacteriostatic 

There are different classes of antibiotics including the penicillins, cephalosporins, macrolides, & fluoroquinolones. 
Different classes fight infections differently such as
disrupting cell wall synthesis or protein production which prevents replication and eventually leads to the elimination of the infection. 

what is the purpose of the disc diffusion method?

                 quick recap of the disc diffusion method
1. inoculation: an agar plate is inoculated with a lawn of the target bacteria. 
2. agent application: each disc is soaked with test solution. 
3. disc placement: sterile filter paper discs are placed on the agar surface. 
4. incubation: the plate is incubated
5. zone of inhibition: a clear zone (zone of inhibition) around the disc indicates that the antimicrobial agent has inhibited the growth of the bacteria. 

what is the meant by the zone of inhibition? how does this zone relate to the effectiveness of

an antibiotic?

microbial control

​using antibiotics