Please enable JavaScript.
Coggle requires JavaScript to display documents.
Control of Microbial Growth - Coggle Diagram
Control of Microbial Growth
Fundamentals and Definitions
Chemotherapy: the use of chemical substances to treat a disease (NOT just associated with cancer)
Antimicrobial Drugs: interfere with the growth of microbes within a host, including examples such as anti-fungal, antiviral, and anti-parasitic
Antibiotics: a substance produced by microbes that in small amounts inhibits the growth of other microbes (bacteria ONLY)
Disinfectants: chemical substances that destroy or inactivate microorganisms on non-living surfaces
Efficacy and Microbial Action
Depends on factors such as the number of microbes, the environment (including organic debris, biofilms, and medium contents), time of exposure, and microbial characteristics (like acid-fast or endospore formation)
Most antibiotics are "broad spectrum" and take care of every type of infection
Bactericidal
: agent that achieves a 99.9% reduction in the number of viable bacteria, meaning that it directly kills bacteria
Bacteriostatic
: agent that prevents bacteria from reproducing but does not necessarily kill them, most agents keep bacteria in the stationary phase of growth
Mode of Action
(how the bacteria acts on the cell) for microbial control agents includes:
Alteration of membrane permeability (ex: penecillin acts on cell wall)
Damage of proteins (ex: staph infection)
Damage to nucleic acids (ex: TB meds)
Physical Methods of Microbial Control
Autoclave
: uses moist heat (followed by pressure) and is the preferred method of sterilization provided the material will not be damaged by heat or moisture. (Ideal Temp: 121C. 250F)
Dry heat methods, such as flaming or incineration, are also classified as bactericidal
Pasteurization
: uses mild heating to kill spoilage organisms. When used for milk, it involves heating to 72 degrees C for 15 seconds (low heat)
Kills pathogens in milk, but DOES NOT sterilize the milk, Thermoduric organims, such as Streptococcus spp. and Lactococcus spp. survive and cause spoilage
Filtration
: applicible to clear liquids and gases only, using filters with holes typically of 0.2 microns. HEPA filters are 0.3 micron. (relatively fast and sterilizes anything in the media)
Low temps are usually bacteriostatic and should not be used as a method to kill bacteria (slows down reproduction)
Listeriosis
: is caused by Listeria monocytogenes, is one of the few pathogens able to grown at refridgerator temperatures. Serious in pregnant women and can result in premature delivery, miscarriage, or stillbirth (infection can cross the placenta)
Osmotic Pressure
: a food preservation method using salt or sugar (often with "smoking") to cure meats and preserve fruits
Ionizing radiation
: (gamma and x-rays) destroys bacterial DNA
Non-Ionizing Radiation
: (UV light) damages DNA by producing thymine dimers but has the limitation that does not penetrate well.
History, Spectrum, and Safety
Ehrlich (1910)
, coined the term chemotherapy and used Salvarsan (an arsenic compound) against syphilis. Speculated about a "magic bullet"
Fleming (1928)
discovered penicillin, produced by Penicillium notatum, which inhibited the growth of Staphylococcus aureus
Goal of Chemotherapy:
Selective Toxicity, which means killing the microbes without damaging the host (patient)
Fungi, protozoans, and helminths are hard to treat because they are eukaryotes and resemble human cells.
Florey and Chain (1940)
1st clinical trials of Penecillin
Broad Spectrum antimicrobial:
saves time but destroys normal flora. This can result in a super-infection, where opportunistic pathogens like Candida albicans or Clostridium difficile flourish (C diff). Adv: save time without ID
Narrow Spectrum Drugs:
(specific and targeted) such as Penicillin G, are most likely to affect Gram (+) cells.
Antimicrobial substances that affect Gram-negative cells have to contend with the lipopolysaccharides and porins in the outer membrane. (ex: streptomycin)
Resistance and Specific Agents
Methods of Antibiotic Resistance:
enzymatic destruction (ex:beta lactamase, prevention of penetration in the cell, alteration of the drug's target site, and rapid ejection via an efflux pump)
A variety of mutations: antimicrobial resistance
Resistance genes are often found on plasmids or transposons that can be transferred between bacteria
Streptomyces spp
. are filamentous, soil bacteria that produce 50% of antibiotics (Actinomycetes: soil microbes)
Antifungal drug
Polyenes
(ex: amphotericin B) treat systematic fungi but are nephrotoxic
Neuraminidase inhibitors
: used to treat influenza include Zanamivir (Relenza) and Oseltamivir Phosphate (Tamiflu)
Zidovudine (AZT) and Acyclovir are examples of nucleotide analogs used to treat HIV and genital herpes, respectively
Bisphenol
agents like Hexachlorophenol were effective against Staph infections in infants but could cause neurological damages.
Triclisan
works best against Gram + bacteria
Iodine
in an alcohol base is an antiseptic. Iodophors, like Betadine (water base), are used as a surgical scrub and are classified as a disenfectant
Quaternary Compounds like
Zephiran
are widely used in medications used to treat acne
Norovirus
Norovirus causes Gastroenteritis and is transmitted via the fecal/oral route
Can survive termperatures as high as 140 degress F
Recommended prevention method: using a solution of 25T tablespoons of bleach per gallon of water
Tests and Doses:
Broth Dilution Test:
can estimate the MIC (Minimal Inhibitory Concentration: min concen required to inhibit the growth of 80% of the org) and the MBC (Minimal Bacteriocidal Concentration: min concen for death)
Kirby-Bauer Test:
(Disc Diffusion Method) is simple and inexpensive and determines effectiveness by measuring the zone of inhibition (means that antibiotic is good at killing organism on plate)
Theraputic Dose:
the amount of medication needed to have the desired effect (as low or little as possible)
Toxic Dose:
is the amount of medication administered before undesirable heath side effects are noticed and the health of the patient is impaired. (HIGH dose: as much as possible)
Selective Toxicity
: target things on bacteria that our cells don't have (ex: cell wall)
Theraputic Index
: the ratio of the toxic dose divided by the theraputic dose. The LARGER the index, the safer the medication.
No growth: organism is SENSITIVE (choose this one) Growth in all wells: RESISTANT