MICROBIOLOGY

G) QUATS (QUATERNARY AMMONIUM  COMPOUNDS) :            They are germicidal, cationic detergents.  They are bactericidal against Gran positive bacteria & Gram negative bacteria & are also effective against fungi to certain pathogenic protozoa. Virus appear to be more resistant than bacteria. The two popular quats are  Zephiran, a brand mane of benzalkonium chloride & Cepacol, a brand name of cetylpyridinium chloride.Eg Cetrimide . Please visit this link;http://en.wikipedia.org/wiki/Disinfectant Uses:  They are used as skin disinfectant, preservatives in ophthalmic solution,& cosmetic preparations. They are widely used for control of mos on  floors & walls of hospitals & public places. They are also used to sanitize food & beverage utensils in the restaurant & in food processing plants.  Mode of Action: They denature protein, interfere with glycolysis ...

F) DYES :  They are important as staining reagents & in lab media. Two classes of dyes that have antimicrobial properties are; 1) Triphenyl Methane Dyes :   It includes Malachite green, brilliant green, & crystal violet. These dyes are more toxic to Gram positive than Gram negative bacteria.  It is used in certain media to make it selective( especially crystal violet is used in Mac Conkey agar  as selective substances).  Crystal violet has been used as fungicide & used to treat thrush caused by  Candida albicans .   The actual mechanism of mode of action is unclear. However, they may interfere with cellular oxidation process. Please visit this links; http://en.wikipedia.org/wiki/Triphenylmethane.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC373988/                                        ...

E) ALDEHYDES:                                  They have general formula (R-CHO) . The commonly used aldehydes are formaldehyde & glutaraldehyde.They inactivate proteins by forming covalent bond  cross-links with several organic functional groups on proteins(-NH2, -OH, -COOH, -SH). Formaldehyde(HCHO):   It is gas at high temperature & solid at room temperature.  It is also marked as aqueous Formalin, used which contains 37-40% of formaldehyde. Formalin was extensively used to preserve biological specimens & inactivate bacteria & viruses in vaccines.  Uses: Formaldehyde in solution is used to sterilize certain instruments. However,they may leave a residue & instruments should be rinsed  before use. Formaldehyde in gaseous form is used to disinfect & sterilize the enclosed area. MODE OF ACTION:   It is alkylating ag...

D) HEAVY METALS & THEIR COMPOUNDS :                                                                                              Heavy metals have larger atomic weight & complex electronic configuration. The detrimental effect of small amount of heavy metals on microorganisms is called "Oligodynamic Effect".  This action can be seen when we place a coin or other clean piece of metal containing silver or copper on a culture media on an inoculated Petri Plate. The most effective metals are Hg,Ag, &  Cu.                                                Fig: Oligodynamic Effect Mercury(Hg):  It is in th...

C. HALOGENS: 2) IODINE:   It is slightly larger than chlorine atom & more germicidal & reactive. It is slightly soluble in  water & readily soluble in alcohols & aqueous solution of sodium & potassium iodide. It is used in several forms like;  Tincture of iodine: It consists of 2% iodine & sodium iodide dissolved in ethanol. It is used for the disinfection of water, & as antiseptics for wounds.  Iodophors: It is iodine detergent complex that release iodine over a long period of time & hence added advantage of non-staining tissues or fabrics. The detergent complex portion of complex looses the organism from the surfaces & halogens kills them. Examples: Beta dine which is a povidone-iodine. Povidone is  a surface active iodophor that improves the wetting action  & serves as reservoir of free iodine. It is used for local wound cleaning.  Wescodyne is us...

C) HALOGENS :                Halogens is any of the five elements( Iodine, Bromine,Chlorine, Fluorine, Astatine ) in Group VII A of periodic table. They are highly reactive elements which contains seven electron in their outer shell in normal state. Iodine & chlorine are more commonly used as disinfectants. Chlorine:  Chlorine is applied as chlorine gas, sodium hypochlorite & calcium hypochlorite . Since chlorine gas is difficult to handle, different compounds are used which are effective & easy to handle like;  Hypochlorite: Hypochlorite release free chlorine in solution. Eg:  Sodium hypochlorite calcium hypochlorite. Sodium hypochlorite's 5% solution is called bleach. Calcium hypochlorite is known as chlorinated lime. To know about halogens as disinfectants please visit this link http://en.wikipedia.org/wiki/Halogen. Chloramines : The organic compounds that contains chlorine like chloroamine-T. They a...

B) ALCOHOLS :                        Alcohols are effective skin aspetics & valuable disinfectant for medical treatment. For practical, the preferred alcohol is ethanol & iso-propyl alcohol .Ethyl alcohol is generally used in the concentration of 70% . It is active against vegetative bacterial cells including Tubercule bacillus  but has no effect on spores. Ethanol is a strong dehydrating agent. Methanol is poisonous & less bactericidal than ethyl alcohol. Higher alcohol like propyl & others are more germicidal than ethanol & germicidal power increases with increase in molecular weight.              Ethanol & isopropanol  are often used to enhance the effectiveness of other chemical agents. For eg; an aqueous solution of Zephiran kills about 40% of the population of test organism in 2 minutes, whereas a tincture of Zephiran kills about 85% in sa...

PHENOL COEFFICIENT: Phenol Coefficient    is a measure of the bactericidal activity of a chemical compound in co relation to phenol. To calculate phenol coefficient, the concentration of phenol at which the compound kills the test organism in 10 minutes, but not in 5 minutes, is divided by the concentration of the test compound that kills the organism under the same conditions (or, probably more common, dividing the dilution factor at which the tested substance shows activity by the dilution factor at which phenol shows comparable activity). The phenol coefficient may be determined in the presence of a standard amount of added organic matter or in its absence. A related way to express the bactericidal activity of an agent (at a given concentration) is by employing the formula k = N/C·T where N is the number of surviving cells, C is the concentration of agent applied and T is the time for which the agent is applied, so k is inversely proportional to...

CHEMICAL METHODS : A). PHENOLS & PHENOLICS :                                        Phenols & phenolics compounds are very important disinfectants. A 5% aqueous solution of phenol rapidly kills vegetative cells but spores are most resistant. Phenol was used( first) by Joseph Lister(1880s) to reduce infection in surgical incisions  & surgical wounds.  Phenols remains the standard against another antiseptics & disinfectants are evaluated by Phenol Coefficient Techniques. But, phenol is expensive,has pungent small & is irritating to skin. So, several phenol derivatives are used like;     Cresol:  It is phenol derivatives containing methyl group. It has germicidal activity & lower toxicity than the parent compound. Mixture of or-tho, para, & meta cresol  are used commercially as wood preservatives.  Hex...

4)  DESSICATION :  It is effective for preventing microbial reproduction but don't kills the mos. Some mos required water for growth & bacteria will not generally grow below water activity below 0.9. Similarly, fungi will not grow at water activity below 0.05. So, maintenance of water activities below 0.65 prevents microbial growth.  Therefore, drying or dessication can be used  for food preservation. Eg In powder milk over 85% water is generally removed. 5) OSMOTIC PRESSURE:   The use of high concentrations of salts & sugars to preserve food is based on the effects of osmotic pressure . High concentrations of these substances create a hyper tonic environment that causes water to leave the microbial cell. This process resembles preservation by dessication; in both methods deny the cell moisture it needs growth. The principle of osmotic pressure is used in the preservation of foods. Eg; Concentrated salts solutions are used to cure meats ...

FILTRATION:           It is passage of gases or liquids via a screen like materials with pores size small enough to retain mos. Generally, filtration decontaminate heat sensitive liquids or gases like beverages,intravenous solution, bacteriological media, serum etc. Filtration removes mos rather than destroying them. Effectiveness of filter proportional to size of the pores. However, other factors like electric charge of filter, charge of organisms & nature of fluids can influence the efficacy of filtration. TYPES OF FILTER: Inorganic Filter: It consists of pad of procleain or ground glass mounted in filter flask. It is used in sterilization of serum during media preparation.  Eg: Seitz Filter   Organic Filter: It consists of organic molecules or filter that attracts the organic component of mos. It has large pores. Breke field filter which uses a substance called diatomaceous earth. It is used in swimming pool.   ...

2) RADIATION:          Radiation is the energy transmitted through the space in the varieties of forms. Major types of radiations includes ionizing radiation; UV radiation, Ultrasonication. i) Ionizing Radiation : It has high energy & can ionize the atoms. They have energy above 10eV. On such radiation pass via cells they create unstable ions & free radicals(H- radicals, OH-radicals, & some peroxides). This radical causes different types intracellular damage whereas ions combines & destroys proteins & nucleic acids causing death. Some of the common ionizing radiation are Gamma rays, X-rays, alpha & beta particles.    X-rays : They are electromagnetic waves with wavelength smaller than 10nm. X-rays are lethal to mos & higher organisms. However, they are impracticable  for controlling mos because they are expensive to produce, difficult to handle efficiently & since radiations are given o...

 1.)  TEMPERATURE:               A.) HIGH TEMPERATURE : b) DRY HEAT :  Dry heat dehydrates the cell, reduces water molecules & bounds intracellular components. Dry heat is not as effective as compared to moist heat. The lab apparatus or methods designed to use dry heat for sterilization are; Hot Air Oven: It is used to sterilize glassware like pipettes, flasks, dry powder etc. It is operated at a temperature 160 c for 1 hours. The above figure shows a typical hot air oven.  Flaming: Here Bunsen burner is used for few seconds to sterilize bacteriological loop before removing a sample from culture tubes & after preparing a smear. Flaming is also used to sterilize tips of tube & flasks, needles, forceps, & scalpels.  Incineration: It is used for destruction of corpses, infected lab animal & other infected  materials like hospital gowns, plastic apparatus. It is simply b...

PHYSICAL METHODS : MOIST HEAT(CONTD..) MOIST HEAT BELOW 100C:  It is used in Pasteurization process in which moist heat is used below 100c to kill only organisms that may cause spoilage & human diseases.ie Pasteurization kills only certain microorganisms but not all mos. Spores are not affected by Pasteurization. Pasteurization is carried out on milk, cream, & certain alcoholic beverages, the methods of Pasteurization are as shown in the following table; Fig: Inspissation tank  Vaccine Bath: The contaminating bacteria in vaccine preparation can be inactivated by heating in a water bath at 60c for an hour. Only the vegetative bacteria are killed spores survive.  Serum Bath:  The contaminating bacteria in a serum preparation can be inactivated by heating in water at 56c  for an hour on successive days. Proteins in the serum will coagulate at higher temperature. Only vegetative bacteria are killed spores survive.  Inspissation: Thi...

A) PHYSICAL METHOD FOR CONTROLLING MOS:  1) HEAT:   i) High Temperature:  Growth of microorganisms depends upon metabolic activities which depends upon different chemical reactions. These reactions are influence by temperature. Each organism has their cardinal temperature for their growth ie minimum,optimum, & maximum temperature. Heat is employed either at moist heat or dry heat. Moist Heat : Moist  heat kills mos by denaturation of proteins. It is more effective than dry heat because moist heat penetrates materials more rapidly than dry heat. Therefore, moist heat requires low temperature & short exposure because water molecules conducts heat better than air. Eg Clostridium botulinum are killed in 4- 20 minutes by moist heat at  120 c whereas these spores are killed in 2 hours by dry heat at same temperature.   Moist heat can be used or classified as; At temperature above 100c   At temperature below 100c  At temperature at ...

DISINFECTION & STERILIZATION  TECHNIQUES IN MICROBIOLOGY: Sterilization is the complete destruction or removal of all forms of life including viruses & spore forming bacteria. The term 'Sterile' therefore refers to complete absence or destruction of all microorganisms.             Disinfection is the process by which causative, pathogenic & harmful microorganisms are killed or inhibited. This process is usually carried by chemical agents. Disinfectants are agents used to carry out disinfection on inanimate objects.           Different Terminology Used in Microbes Control: Antiseptics:  It is an agent used to carry out disinfection on living objects like tissue of human body. It prevents sepsis or growth of pathogens on the tissues. Asepsis: It is the employment ( such as  usage of gloves, air filters, UV rays etc)  to achieve microbes free environment, Sanitization: ...

Glycogenolysis :             Glycogen degradation requires the following two reactions: Removal of glucose from the non reducing ends of glycogen: Glycogen phosphorylase uses inorganic phosphate (Pi) to cleave the (1,4) linkageson the outer branches of glycogen to yield glucose-1-phosphate. Glycogen phosphorylase stops when it comes within four glucose residues of a branch point.      Hydrolysis of the a(1,6) glycosidic bonds at branch points of glycogen:  Amylo-(1,6)-glucosidase, also called debranching enzyme, begins the removal of (1,6) branch points by transferring the outer three of the four  glucose residues attached to the branch point to a nearby non reducing end. It then removes the single glucose residue attached at each branch point. The product of this latter reaction is free glucose. Glucose-1-phosphate, the major product of glycogenolysis, is diverted to glycolysis in muscle cells ...

GLYCOGEN METABOLISM:                       Glycogen is the storage form of glucose. The synthesis and degradation of glycogen are carefully regulated so that sufficient glucose is available for the body’s energy needs. Both glycogenesis and glycogenolysis are controlled primarily by three hormones: insulin, glucagon, and epinephrine. GLYCOGENESIS : Glycogen synthesis occurs after a meal, when blood glucose levels are high. It has long been recognized that the consumption of a carbohydrate meal is followed promptly by liver glycogenesis. The synthesis of glycogen from glucose-6-phosphate involves the following set of reactions: 1.)  Synthesis of glucose-1-phosphate:   Glucose-6-phosphate is reversibly converted to glucose-1-phosphate by phosphoglucomutase, an enzyme that contains a phosphoryl group attached to a reactive serine residue.The enzyme’s phosphoryl group is transferred to glucose-6-phosphate, forming...

GLUCONEOGENESIS: Gluconeogenesis, the formation of new glucose molecules from noncarbohydrate precursors, occurs primarily in the liver. Precursor molecules include lactate, pyruvate, glycerol, and certain -keto acids (molecules derived from amino acids). Under certain conditions (i.e., metabolic acidosis or starvation) the kidney can make small amounts of new glucose. Between meals adequate blood glucose levels are maintained by the hydrolysis of liver glycogen. When liver glycogen is depleted (e.g., owing to prolonged fasting or vigorous exercise), the gluconeogenesis pathway provides the body with adequate glucose. Brain and red blood cells rely exclusively on glucose as their energy source. Gluconeogenesis Reactions: The reaction sequence in gluconeogenesis is largely the reverse of glycolysis. Recall, however, that three glycolytic reactions (the reactions catalyzed by hexokinase, PFK-1, and pyruvate kinase) are irreversible. In gluconeogenesis, alternate reac...

TRICARBOXYLIC ACID CYCLE AMPHIBOLIC IN NATURE:   TCA cycle is embelished  with  the name Amphibolic because there is catabolism & anabolism. The term Amphibolic was proposed by B.Davis in 1961 to emphasize dual metabolic role of such pathway. The citric acid cycle is an good example of amphibolic pathway. In first step of TCA cycle, Oxaloacetate( 4-Carbon compound) combines with acetate to form Isocitrate(6-carbon compound) is anabolic. TCA cycle serves as catabolism of carbohydrates,fatty acids,& amino acids, also cycle provides precursors for many biosynthetic pathways, through  reactions that served the same purpose in anabolism. a-Ketoglutarate & Oxaloacetate  can for eg serves  for precursors of amino acid Aspartate & Glutamate by simple transamination. Through aspartate & glutamate, the carbons of oxaloacetate & a-Ketoglutarate  are then used for synthesis of amino acids, as well as purine ...