Control Of Microorganisms By Physical And Chemical Agents Pdf

Labs performing very large numbers of susceptibility tests frequently use the automated methods but the equipment is quite expensive. Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols do. Think About It What are two advantages of ionizing radiation as a sterilization method? The fluoroquinolones norfloxacin, lomefloxacin, fleroxacin, ciprofloxacin, enoxacin, trovafloxacin, gatifloxacin, etc. Fruits were preserved by adding sugar, making jams and jellies.

Chemical Methods of Control

More than likely, the potatoes were canned using boiling water, a method that allows endospores of Clostridium botulinum to survive. Iodine also denatures microbial proteins.

The term moderately susceptible is usually applied to those situations where a drug may be used for infections in a particular body site, e. The macrolides erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.

Bacterial growth subsequent to endospore germination can be monitored by biological indicator spore tests that detect acid metabolites or fluorescence produced by enzymes derived from viable G. Macrolides are used against Gram-positive bacteria and some Gram-negative bacteria. An example of an alkali is lye sodium hydroxide. The process of pasteurization was first developed by Louis Pasteur in the s as a method for preventing the spoilage of beer and wine. Aminoglycosides may also interfere directly or indirectly with the function of the bacterial cytoplasmic membrane.

Drugs that are effective against a variety of both Gram-positive and Gram-negative bacteria are said to be broad-spectrum e. Hydrogen peroxide is useful on inanimate objects and in foods, but on the skin surface, it is quickly broken down by the enzyme catalase, liberating oxygen.

Chemical Methods of Control

These agents prevent bacteria from synthesizing structural proteins and enzymes. Name two chemical agents that are reliable for sterilization. Drying, also known as desiccation or dehydration, is a method that has been used for millennia to preserve foods such as raisins, prunes, and jerky.

Because of their toxicity, aminoglycosides are generally used only when other first line antibiotics are not effective. However, certain microbes, such as molds and yeasts, tend to be more tolerant of desiccation and high osmotic pressures, and, thus, may still contaminate these types of foods. Sorbic acid is used in a number of acidic foods, including cheese, to prevent microbial growth. Make sure you reflame the glass rod between plates.

Unfortunately, some rare risks include oxygen toxicity and effects on delicate tissues, such as the eyes, middle ear, and lungs, which may be damaged by the increased air pressure. Which of the following terms is used to describe the time required to kill all of the microbes within a sample at a given temperature?

Mercury compounds mercurochrome, metaphen, merthiolate are only bacteriostatic and are not effective against endospores. The key to autoclaving is that the temperature must be high enough to kill endospores to achieve complete sterilization.

An in vitro test is one done under artificial, controlled laboratory conditions. Boiling is one of the oldest methods of moist-heat control of microbes, b167-08 pdf and it is typically quite effective at killing vegetative cells and some viruses. Pasteurization is a form of microbial control for food that uses heat but does not render the food sterile. Antimicrobial chemotherapy is the use of chemicals to inhibit or kill microorganisms in or on the host. Incineration at very high temperatures destroys all microorganisms.

Peracetic acid is a disinfectant that kills microorganisms by oxidation and subsequent disruption of their cytoplasmic membrane. Filtration is a method of physically separating microbes from samples. Various physical methods used for microbial control are described in this section.

For example, they may be found in vacuum cleaners, heating and air-conditioning systems, and air purifiers. Bisphenols, biguanides, and chloroxylenol alter membrane permeability. However, they are usually ineffective against endospores and non-enveloped viruses. Certain types of laboratory cultures can be preserved by refrigeration for later use.

Chemical agents to control microorganisms

Bactericide, fungicide, virucide, sporicide, etc. Selinium sulfide kills fungi and their spores. Generally, the lower the temperature, the longer it takes to disinfect or decontaminate. Semisynthetic broad-spectrum penicillins combined with beta lactamase inhibitors such as clavulanic acid and sulbactam. Using your wax marker, divide each plate into thirds to guide your streaking.


They appear to i nhibit elongation of the protein by preventing the enzyme peptidyltransferase from forming peptide bonds between the amino acids. Because air is more completely eliminated, the steam can more easily penetrate wrapped items. Polymyxins and colistins act as detergents and alter membrane permeability in Gram-negative bacteria. If the organism is a Staphylococcus or is fastidious and grows unpredictably in broth like the streptococci, suspend the colonies is saline, Mueller Hinton broth or trypticase soy broth.

Physical agents to control microorganisms

Another gas that is used as a sterilant is chlorine dioxide which denatures proteins in vegetative bacteria, bacterial endospores, viruses, and fungi. During the examination, she began to experience abdominal cramping, nausea, paralysis, dry mouth, weakness of facial muscles, and difficulty speaking and breathing. To produce antibiotics, manufacturers inoculate large quantities of medium with carefully selected strains of the appropriate species of antibiotic-producing microorganism.

Chemical Methods of Control2. low temperature

Endospore producers such as Bacillus species, Clostridium species, and acid-fast bacteria like Mycobacterium tuberculosis are harder to eliminate. Because of this, antibiotic susceptibility testing is often essential in order to determine which antimicrobial agent to use against a specific strain of bacterium. Mode of action of the agent vii.

Interpret the results of a Bauer-Kirby antimicrobial susceptibility test when given a Mueller-Hinton agar plate, a metric ruler, and a standardized zone-size interpretation table. Removal of bacteria from heat-sensitive solutions like vitamins, antibiotics, and media with heat-sensitive components. Set tubes in a test tube rack at room temperature. Moreover, they traced the source of the outbreak to a potato salad made with home-canned potatoes.

For thousands of years, humans have used various physical methods of microbial control for food preservation. State why chemical agents are usually unreliable for sterilization. Ethylene oxide is one of the very few chemicals that can be relied upon for sterilization after hours exposure.

Since it is explosive, it is usually mixed with inert gases such as freon or carbon dioxide. Hyperbaric oxygen therapy helps increase oxygen saturation in tissues that become hypoxic due to infection and inflammation. Using the appropriate antibiotic disc dispenser, place Gram-positive antibiotic-containing discs on the plates of S. High-pressure processing can be used to kill microbes in food.