Control of Microorganisms

Asepsis:

the absence of significant contamination. Aseptic technique is used in surgery to lower contamination from the instruments, operating personnel, & the patient.

Tests for effectiveness of antiseptics & disinfectants: Phenol coefficiant test:

A comparison of other disinfectants containing phenol. Phenol coefficient = the reciprocal of the last dilution to inhibit the growth by drug B. If a disinfectant with phenol coefficiant of 1.0 the effectiveness is the same. If it is less than 1.0 then the effectivesness is less. If the disinfectant has greater than 1.0 the effects are more.

Physical methods of control: Incineration:

An effective way to sterilize & dispose of contaminated paper cups, bags & dressings. Part of Dry heat. Burning to ashes.

Nucleic acid analogs & others: Antifungal agents:

Antifungal treatment causes toxic side effects. Imidazoles & Triazoles comprise a large group of fungicides. Affect fungal plasma membranes by interrupting the biosynthesis. Topical creams for Candida yeast infections of the skin, nails, mouth, & vagina. Inhibition of ergosterol biosynthesis is the basis for the selective toxicity of many antifungals, which include members of the polyene, azole, & allylamine groups.

General methods of control: Bactericidal vs. bacteriostatic

Bacteriostatic are growth interfering by: 1. bacteria protein production. 2. bacteria DNA production. 3. bacteria cellular metabolism. Bactericidal will prevent or inhibit the growth of microbes. High concentration may be bactericidal & low concentration bacteriostatic.

Chemical agents: Heavy metals:

Can be biocidal or antiseptic, like silver, mercury, & copper. Small amounts of metal inhibit the growth of bacteria. Silver is used as an antiseptic. Copper is an algicide to destroy green algae. Denaturation of enzymes & other essential proteins. Silver nitrate may be used to prevent opthalmia neonatorum; silver-sulfadiazine is used for burns. Silver & mercury are biocidal.

Chemical agents: Phenols:

Carbolic acid - control surgical infections in the OR. Rarely used due to the odor & irritates the skin. Used in throat lozenges for local anesthetic, but has little antimicrobial effect at low concentration. A concentration above 1% a good antimicrobial effect.

Antibiotic resistance:

Farmers use antibiotics in the feed because the drugs lower the number of bacterial infections. Resistance to anitmicrobial drugs in bacteria results from mutations.

Factors influencing success of control methods: Number & nature of microorganisms:

Gram-negative bacteria are generally more resistant than gram-positive bacteria to disinfectants & antiseptics. Mycobacteria, endospores, & protozoan cysts & oocyst are very resistant to disinfectants & antiseptics. Nonenveloped viruses are generally more resistant than enveloped viruses to disinfectants & antiseptics. Prions are resistant to disenfections & autoclaving.

Antibiosis & Chemotherapy:

In 1928 Alexander Fleming observed a growth of bacterium staphylococcus aureus in the area surrounded by mold. The mold was Penicilliumnotatum, which was named penicillin later. The mechanism of inhibition is called antibiosis. Antibiosis inhibits another microorganism. Chemotherapy: "magic bullet" discovered by Paul Ehrlich that would find and destroy pathogens, but not harm the host.

Modes of actions: Inhibiting synthesis of essential metabolites:

Inhibition of essential metabolite synthesis: Sulfanilamide, trimethoprim. Antimetabolites are substances that affect the utilization of metabolites & prevent a cell from doing its metabolic reactions. Ex: competitive inhibition the relationship between antimetabolite sulfanilamide & para-aminobenzoic acid PABA. PABA is the substrate for an enzymatic reaction for the synthesis of folic acid.

Modes of actions: Inhibition of nucleic acid synthesis:

Inhibition of nucleic acid replication & transcription: quinolones, rifampin. Several antibiotics interfer with the processes of DNA replication & transcription in microorganisms.

Nucleic acid analogs & others: Antiparasitic agents:

Protozoan parasites cause intestinal or UTIs. Several antiprotozoan agents are successful in controlling or even curing most protozoan infections, with bad side effects. Quinine, from the bark of the cinchona tree, used to treat malaria. Chinese scientist discovered artemisinin-based combination therapies ACTs to be the principal treatment for malaria. Artemisinin used for controlling fever. ACTs act by killing the asexual stages of Plasmodium spp. in the blood & also affect the sexual stages that transmit the infection by mosquitos. Quinacrine drug of choice for treat giardiasis. Metronidazole (Flagyl) most widely used antiprotozoan drugs. Works against parasitic protozoa & obligate anaerobic bacteria.

Time, temp, & pH:

Temp: Heat kills microorganisms by denaturing their enzymes; changing the 3-dimensional shapes of these proteins inactivates them. Increase the temp by 10C doubles the rate of chemical reactions & increase the potency of the chemical agent. Time: Chemical antimicrobials often require extended exposure to more-resistant microbes or endospores. pH: Acidic or alkaline pH can increase or decrease the agent's potency. A pH that increases the degree of ionization of chemical agent often increase its ability to penetrate a cell.

Antibiotics: Penicillin & others: Antibiotic sensitivity:

The appropriate antibiotic to treat infection should be determind prior to antibiotic been given. A sensitivity can happen without warning to any medication.

Test for effectiveness: Use-Dilution Test:

The current standard test to evaluate the effectiveness of disinfectants & antiseptics. Glass cylinders are dipped into standardized culteres of bacteria grown liquid media. They are dried & then placed in a soluction of disinfectant & left for 10 minutes. then transferred to a medium that allows surviving bacteria to grow. The effectiveness of the disinfectant is measured by the number of cultures that grow. Many microbiologist believe this test is more reliable than the penol coefficient test.

Factors influencing success of control methods: Strength & control agent

The plasma membrane of a mocroorganism located inside the cell wall is the target for microbial control agent. Damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak & interfers with the growth of the cell. The nucleic acids DNA & RNA carry the cells genetic information. Damage to the nucleic acid by heat radiation, or chemicals is frequently lethal to the cell. The cell can't replicate or carry out normal metabolic functions like the synthesis of enzymes.

Sanitiation:

Treatment to lower microbial counts on eating & drinking utensils in public places. This is done in high temp washing & dipping into a chemical disinfectant.

Radiation:

Ultraviolet a good example of nonionizing radiation. UV light is damaging to DNA. UV light damages DNA by causing bonds to form between adjacent pyrimidine bases, usually thymines, in DNA chains. Thymine dimers inhibit correct replication of the DNA. The UV wavelengths that kill microorganisms are about 260nm; are absorbed by cellular DNA. Also used to control microbes in the air. The radiatin from the UV light is not very penetrating, so the organisms have to be directily exposed to be killed. Ionizing radiation: like gamma rays, X-rays, or high-energy electron beams--- has a wavelength shorter than about 1 nm. It carries more energy. They can dislodge electrons from atoms creating ions. Used to sterilize pharmaceuticlas & medical & dental supplies.

Modes of actions: Inhibition of protein synthesis:

chloramphenicol, erythromycin, tertacyclines, streptomycin. Notable difference between eukaryotes & prokaryotes structure of their ribosomes. Eukaryotes cells have 80S ribosomes; prokaryotes have 70S ribosomes. The difference in structure accounts for toxicity of antibiotics that affect protein synthesis. *Translation!!!

Disinfection & antisepsis:

disinfection destroy harmful microorganisms; like non-endospore-forming pathogens. A disinfectant is a chemical that is used to treat a surgace or substance. When the treatment is directed to living tissue then it is call antisepsis & the chemical is antiseptic. In practice a chemical might be called a disinfectant for one thing & an antiseptic for another. In reality a chemical to clean a surface will be to harsh to clean living tissue.

Chemical agents: alcohols:

effectively kill bacteria & fungi but not endospores & nonenveloped viruses. The action is protein denaturation, but can also disrupt membranes & dissolve lipids, including enveloped viruses. They act & evaporate fast leaving no residue. When using hand sanitizers rub over the surface of hands & fingers until dry. When it says 99.9% killing action, that is seldom reached. Certain pathogens like C-diff & viruses that lack a lipid envelope, are resistant to alcohol-based sanitizers.

Chemotherapetic agents: nucleic acid analogs & others: Antiviral agents:

inhibit some phase of viral replication, but done kill the viruses. A nucleoside analogs, acyclovir is widely used, best known for treating genital herpes or most herpes virus infections. Purine & pyrimidine analogs are effective antiviral agents. Interfere with the replication of viruses. Drugs include azidothymidine (AZT), ribavirin, ganciclovir. Amantadine prevents influenza A viruses from penetrating cells. Can be given to a week after exposure and decrease incidence and severity of symptoms.

Chemical agents: Gases

inhibits vital cellular functions. Used to sterilize thing that heat would damage.

Chemical methods of control: Chemical agents: Halogens:

iodine & chorine are effective antimicrobial agents, alone & together of inorganic or organic compounds. Iodine is active against bacteria, endospores, fungi, & viruses. Iodine is a tincture--- a solution in alcohol & an iodophor is a combination of iodine & an organic molecule, where the iodine is released slowly. A good example is Betadine Chlorine, as a gas or in combo with other chemicals is used as a disinfectant. It has a germicidal reaction when added to water.

Dry Heat:

kills by oxidation effects. Direct flaming: burning contaminants to ashes; very effective method of sterilzation used for inoculating loops. Hot-air sterilization: action of oxidation. Requires temps of 170C for 2 hours. Use for empty glasware, istruments, needles, & glass syringes.

Moist Heat:

kills microorganisms by coagulating proteins (denaturation), caused by breaking the hydrogen bonds that hold the proteins in their structure. Boiling water: kills vegetative bacterial & fungi pathogens & almost all viruses within 10 minutes; less effective on endospores. Autoclave: about 15 psi of pressure (121C), kills all vegetative cells & their endopores in 15 minutes. Pasteurization: Heat treatment for milk 72C for 15 seconds that kills all pathogens & most nonpathogens.

Chemical agents: Detergents:

mechanical removal of microbes through scrubbing. Used for skin degerming & removal of debris. Antibacterial soaps contain antimicrobials.

Chemical agents: Peroxides:

oxidation is the action. Used on contaminated surfaces; they are very effective against oxygen-sensitive anaerobes.

Chemotheerapeutic agents & antibiotics: Modes of actions: Inhibition of cell wall synthesis:

penicillins, cephalosporins, bacitracin, vancomycin. Inhibiting cell wall synthesis damages bacterial & fungi cells.

Modes of actions: Injury to plasma membrane:

polymyxinB. Certain antibiotics, especially polypeptide antibiotics, change the permeability of the plasma membrane. These changes result in the loss of metabolites from the microbial cell.

Chemical agents: Aldehydes:

protein denaturation. They inactivate proteins by forming covalent bond with several organic groups on protein. Glutaraldehyde (Cidex) is less irritating than formaldehyde & is used for disinfecting medical equipment. Very effective antimicrobials.

Sterilization:

removal or destruction of all living microorganisms. Heating is the most common of killing microbes, such as endospores. High-level germicides kill endospores. Bacillus stearothermophilis, as the name suggests, loves heat. If the heat sterilization has killed this bacterium, it's very effective. Sterilization can also be achieved by chemicals, irradiation, or filtration. A sterilizing agent is called a sterilant.

Antibiotics: Penicillin & others: The problem of antibiotics resistance:

the ability of a microorganism to withstand the effects of an antibiotic. Genetic differences happen d/t mutations. These mutational differences can spread horizontally among bacteria by processes like conjugation or transduction. Once the mutation is transmitted, by normal reproduction, the progeny carry the genetic characteristics of the parent microbe. Because bacteria reproduce rapidly the resistance to the antibiotic only takes a short time. When bacteria are resistant to a large number of antibiotics are popularly designated as superbugs. Ex: MRSA - a range of both gram - positive & gram - negetive bacteria. There is only limited treatment.

Filtration:

the passage of liquid or gas through a screenlike material with pores to catch microorganisms. Used to sterilize culture media, enzymes, vaccines, & antibiotic solutions. Burn patients receive filtered air through a High-efficiency particulate air (HEPA) filters to remove all microorganisms.