Biol 104 lecture 2

Lecture 5: Bacterial Growth and Control

I. Introduction:
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:
a. Terminology:
__________________________ __________________________ __________________________ __________________________ __________________________ __________________________ __________________________ __________________________ 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 ____________________________ ________________________________________________ a. Categories:
i. Antibiotics:__________________________________________________ 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:
1. ____________________________________________ Examples: Penicillins and Cephalosporins contain a _________________ Beta-lactam antibiotics bind to the bacterial enzyme that x-links PG during cell wall synthesis, cell wall weakenslysis 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) ii. _______________________________________ Examples: Tetracycline, Erythromycin, Chloramphenicol _____________________________ (concentration dependent) iii. _________________________________________________________ Target: bacterial enzymes necessary for nucleic acid synthesis Examples: Ciprofloxicin and other quinolones, Rifampin 4. __________________________________________ 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 ____________________________

Source: http://scotten.disted.camosun.bc.ca/biol104pdfs/104Lec5F10.pdf