ABSTRACT
Saprophytic microorganisms feed on dead organic matter. The pathogenic (infectious) microorganisms grow in/on humans, animals, or plant tissue and can cause diseases in macroorganisms. Opportunistic pathogens have the potential to be pathogens in debilitated or immune-compromised organisms. The diseases may be conventionally distinguished as airborne, waterborne, soilborne, and foodborne infectious diseases. When an infectious agent is spread by an insect, such as a mosquito, flea, lice, biting fly, or tick, they are referred to as vectors. Sources of pathogens in water are sewage outlets, wildlife watersheds, farm lots, garbage dumps, and septic tank systems. The indicator microorganisms are detected in water to indicate the possible presence of disease-causing constituents. There are over 100 known waterborne human enteric viruses such as infectious hepatitis A, poliovirus, and rotaviruses. Control of unwanted microbial growth can be performed by inhibition of growth, killing the microorganisms, or removing them from an environment. Antimicrobial (“cidal”) agents kill microbes, thus the terms bactericidal, fungicidal, and virucidal agents are used. The most sensitive targets of the microbial cell are the integrity of the cytoplasmic membrane, active centers and structures of enzymes, and structures of nucleic acids. Physical sterilization is the process of killing, by heat, microwaves, ultraviolet radiation, X-rays, gamma rays, UV radiation, or filtration, all living organisms and viruses present in the sample. Pasteurization kills the vegetative cells of bacteria, fungi, and protozoa in the liquid. Disinfectants (chlorine gas, chloramine, ozone, quaternary ammonium compounds) are chemical antimicrobial agents that are used on inanimate objects. Antiseptics (iodine, 3% solution of hydrogen peroxide, 70% solution of ethanol) are chemical antimicrobial agents used on living tissue. Antibiotics are microbial or synthetic substances that are used to treat infectious diseases because of the specific inhibition of microbial species in low concentration. The resistance of different groups of microbes to disinfection increases in the following order: vegetative bacteria, enteric viruses, spore-forming bacteria, protozoan cysts. Ferrous ions, nitrites, hydrogen sulfide, and various organic molecules exert a demand for oxidizing disinfectants such as chlorine. Suspended solids significantly reduce the inactivation of microorganisms during disinfection. A tutorial with solutions and a quiz bank are added to this chapter.
