Biol 104 lecture 2
Lecture 5: Bacterial Growth and Control
Growth = increase in cellular constituents.
In bacteria this results in an increase in _________________________________
Volume and mass increase to critical mass transverse binary fission
_____________________________________________________= time it takes for a bacterial cell (or population) to duplicate itself. Determined by genetic programming but influenced by _____________________
_________________ like: moisture and nutrient availability, temperature,
Under optimum conditions, generation time is a constant characteristic of a bacterial species. Results in _____________________________________________, in which cell numbers double after each generation time.
II. Exponential Growth:
Example: Unpasteurized milk with 10 bacteria / mL, and a generation time of 20
III. In vitro Control of Microbial Growth:
b. Methods of control:
__________________ methods of control (Table in text p 30, Lab 4):
Heat, cold, radiation, filtration, desiccation
__________________ methods of control (Table in text p 29, Lab 6):
______________________: antimicrobial chemical agent used to
carry out disinfection of inanimate objects only, may be harmful to tissues.
_____________________: antimicrobial chemical agent safe to
c. Microbial Targets for Control:
d. Spectrum of Activity:
- static = ________________________________________ the target cell
- cidal = ________________________________________
- _____________________ = kills all (would have to be sporocidal)
Examples: glutaraldehyde, ethylene oxide gas
e. Describe the attributes of an ideal disinfectant:
IV. Antimicrobial Chemotherapeutic Agents:
Definition: Chemical agents that can be used ____________________________
that can kill, or inhibit the growth of, other microbes.
ii. Synthetic agents:_____________________________________________
iii. Semisynthetic agents:_________________________________________
Antibiotics can be _______________________ (generally target metabolic
pathway or synthesis of cellular components) or ______________________
(generally target cell wall or membrane)
b. Spectrum of Activity:
Antibiotics can have a _____________________________________________; they are effective against a single group of bacteria. E.g. Vancomycin vs. Gram +; Colistin vs. Gram -. or they can be ________________________; active against a wide range of bacteria. E.g. Ampicillin, Tetracycline Narrow spectrum antibiotics produce less ‘collateral damage’ and are therefore a better choice than broad spectrum antibiotics. All antibiotics exhibit ________________________________: the ability to inhibit
or kill the pathogen without causing significant damage to the host.
They target _____________________ of the microbe’s __________________ or
________________________________, thereby limiting the side effects on the
Eukaryotic host’s cells. The greater the selective toxicity, the fewer the side
Virtually all antimicrobial chemotherapeutic agents have side effects:
Why is it more challenging to produce anti-fungal or anti-parasitic chemotherapeutic agents than antibacterial agents?
Why are these agents more likely to have side effects?
c. Lab Testing for Antimicrobial Susceptibility:
To determine the optimum antimicrobial agent to treat a patient’s pathogen, in vitro
tests are performed in the Clinical Microbiology Lab. (Lab 6 and Lab 9b)
_________________________: Measure the zone of inhibition around the
disks containing antibiotic and compare its size to a standard table.
MIC: ________________________________________determines the
smallest amount of drug that will inhibit the growth of the pathogen
___________________: contains a gradient of the antimicrobial agent.
The MIC is indicated by where the zone of inhibition intersects the strip.
d. Mechanisms of Antibacterial Drug Action:
Examples: Penicillins and Cephalosporins contain a _________________
Beta-lactam antibiotics bind to the bacterial enzyme that x-links PG during
cell wall synthesis, cell wall weakenslysis
Only effective on __________________________________.
FYI The semi-synthetic antibiotic Methicillin was designed to evade the action of beta-lactamase, but most Staph have developed resistance to it. Newer beta-lactam antibiotics are combined with a beta-lactamase inhibitor that binds to and inactivates the beta-lactase enzyme. Extended spectrum penicillins: ‘Natural’ penicillins are narrow spectrum antibiotics; they target Gram positives only. Ampicillin and Amoxicillin were developed as broad spectrum antibiotics active against Gram positives and negatives. ESBL: Extended spectrum beta-lactamases: 3rd generation Cephalosporins were originally resistant to beta-lactamase. In 1980’s a new type of beta-lactamase evolved, not affected by inhibitors. The gene that codes for this beta-lactamase is carried on a plasmid, often with resistance to other antibiotics. First ESBL producers were E.coli
and Klebsiella pneumoniae
, now produced in many other Gram negative bacilli. 2009 New Delhi metallo-β-lactamase (NDM-1)
Examples: Tetracycline, Erythromycin, Chloramphenicol
_____________________________ (concentration dependent)
Target: bacterial enzymes necessary for nucleic acid synthesis
Examples: Ciprofloxicin and other quinolones, Rifampin
Disrupts structure and permeability Examples: Polymyxin B (topical antibiotic) Cidal 5. ______________________________________ (Competitive Inhibitors, growth factor analogs) Target: mimics and competes with _______________________________
Examples: Sulfonamides (first effective antimicrobial drug), Isoniazid
Sulfa drugs as an example of Selective Toxicity:
All cells require folic acid for growth. Humans cannot synthesize folic acid, therefore we must obtain it from the food we eat. Bacteria are able to synthesize folic acid from p-aminobenzoic acid (PABA). Because of their similar chemical structure, Sulfa drugs compete with PABA, but since bacterial enzymes cannot recognize sulfonamides, bacteria cannot use it to manufacture folic acid.
e. Characteristics of an Ideal Antibiotic:
Not induce hypersensitivities in the host (no allergic reactions)
Not interfere with _________________________________________________
Not induce development of ____________________________
Venta y publicidad de medicamentos por Internet y la necesidad de una regulación homogénea Joaquín Catalán Socio Responsable del Área de Economía y Derecho Farmacéutico Marta Brosa Departamento Mercantil y Derecho Farmacéutico LA GACETA DE LOS NEGOCIOS. 7 de octubre de 2004 El hábito en el consumo de medicamentos está cambiando al igual que las exigencias de la demanda d
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