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Introduction to Bacteriology Early theories of the cause of diseases Theurgical theory. According to this theory it is said that the disease is due to the wrath of the divine spirit because of the individual sin. It is governed by the superstition followed by a community. Miasmatic theory: this theory explains that all diseases originate from the earth under the influence of stars, the moon, wind, water and season of the year. Germ theory: Jacob Henle explained that minute organism not visible to the naked eyes causes the disease. This theory was based on the finding of Leeuwenhook who made the visualisation of microbe possible by inventing the first microscope. F. A. Brauell demonstrated that anthrax could be transmitted to healthy animal by injecting blood from anthrax infected anuimals. Koch formulated rules that came to be known as Koch’s rule, and that the disease if caused by microbes must follow this sequence. Koch’s rules: Organism must be found in each case. Be able to isolate organism from diseased individual Must reproduce same disease when isolated organism is used on healthy animal. This lead to the study of microorganism by various scholars, which later on led to the origin of bacteriology. Bacteriology: Is the branch of biology that deals with the study of minute organisms called bacteria (singular bacterium). Microbial growth "Because individual cells grow larger only to divide into new individuals, microbial growth is defined not in terms of cell size but as the increase in the number of cells, which occurs by cell division." This emphasis has practical application since it is typically far easier to measure increases in cell number than it is to measure increases in cell size. Bacterial organisms multiply by a process called binary fission. Binary fission The majority of bacteria reproduce by a mechanism termed binary fission. Binary fission is much simpler than the mechanisms of cell division seen in eucaryotic cells. 1 Factors affecting bacterial growth "The kinds of organisms found in a given environment and the rates at which they grow can be influenced by a variety of factors, both physical and biochemical. Physical factors include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation. Nutritional (biochemical) factors include availability of carbon, nitrogen, sulfur, phosphorus, trace elements, and, in some cases, vitamins." Classification of bacterial organism Based on the utility to humankind Industrial bacteriology: is the study of bacterial organisms and their action involved in various industries. Alcohol production, curing of leather. Agricultural bacteriology: deals with bacterial organisms involved in relation to soil fertility and those related to diseases in agricultural plants. Dairy bacteriology: deals with study of microbes involved in manufacture of dairy products. Eg cheese production. Human bacteriology: is the branch of medical bacteriology that deals with organisms affecting the human health. Veterinary bacteriology: Branch of medical bacteriology that deals with microbes affecting the health of domestic animals. Based on pH requirements The pH scale measures hydrogen ion (H+) concentration and that low pH correspond with high concentrations of hydrogen ion, neutral pH with equal numbers of hydrogen and hydroxyl ions (OH-), and high pHs correspond to low concentrations of hydrogen ion Optimum pH Optimum pH is that pH at which a given organism grows best. The range over which most organisms can grow tends to vary over no more than a single pH unit in either direction (e.g., from pH 6 to pH 8 for an organism whose pH optimum is pH 7) Acidophiles Organisms whose optimum pH is relatively to highly acidic, which means growing best in acidic pH 2 Neutrophiles Organisms whose optimum pH ranges about pH 7, plus or minus approximately 1.5 pH units Alkaphiles Organisms whose optimum pH is relatively to highly basic, which grow best in high pH Based on temperature requirement Optimum temperature Optimum temperature is the temperature at which an organism grows best Typically the range in temperature over which a bacterium can grow is about 30ºC Psychrophile Cold-adapted organisms are called psychrophiles. The cut-off temperature for a psychrophile is a 20ºC or colder. Psychrophiles may additionally be termed obligate or facultative with obligate psychrophiles unable to grow above 20ºC, but facultative psychrophiles are able to grow above 20ºC. Mesophile Organisms whose optimum growth temperature is found between 20ºC to 40ºC are termed mesophiles. Human and animal pathogens, which must be able to grow at the approximately 37ºC body temperature, are mesophiles Thermoduric Mesophilic organisms that can endure brief exposures to relatively high temperatures are termed thermoduric These are one category of the organisms that survive following inadequate heating of foods and may thereby contribute to the spoilage of foods that have been heated (e.g pasteurization) to kill microorganisms Thermophil High-temperature-adapted organisms are called thermophiles. Examples organism that grow in hot springs Based on Oxygen requirements Organisms differ in their requirements of molecular oxygen (i.e., O2) as well as other atmospheric gasses (e.g., carbon dioxide). Categories of organisms as per their oxygen requirements include: Obligate aerobe Organisms that are unable to grow in the absence of oxygen or they require oxygen for their growth. Some times this group of organism may be called strict aerobes as they can not grow without oxygen. 3 Facultative aerobe Organisms that can grow in the absence normal level of oxygen that is other wise required. Microaerophile These are organisms that grow best when small amounts of oxygen are present That is, less than atmospheric concentrations, but more than those concentrations tolerable by obligate anaerobes Obilagate anarobe Organisms that are strict anaerobe and require complete absence of oxygen for their growth, which mean they cannot grow in the presence of oxygen. Facultative anaerobe Facultative anaerobes can grow either in presence or absence of oxygen. These organisms tend to exist in environments in which oxygen concentrations are uncertain. Aerotolerant anaerobe These are organisms that are able to grow in the presence of oxygen though they do not require it for their growth. Capnophiles These are organisms whose optimum growth requires relatively high concentrations of carbon dioxide Effect of Osmotic pressure The concentration of dissolved substances in the environment can impact on the growth and survival of bacterial cells Plasmolysis Environments containing large concentrations of dissolved substances draw water out of cells, causing shrinkage of the cytoplasm volume, a phenomenon termed plasmolysis. Plasmolysis interferes with growth and this is why highly osmotic environments prevent bacterial growth (e.g., brine, the high sugar concentrations in jellies and jams, salting of meats) Halophiles Organisms that require high concentrations of dissolved salts to grow are termed halophiles. Depending on organism, the salt concentrations required range from those of seawater on up to those of brine Based on gram staining Gram staining uses two dyes and based on the type of dye an organism takes It is classified as gram positive or gram negative. Gram-positive organisms get blue stained while gram negative organism get red stained. 4 Based on presence of Capsule: Covering over the cell membrane present in certain bacteria. When capsule is present the bacteria is called capsulated eg anthrax bacilli when capsule is absent it is called uncapsulated. 1. Virulence factors, protecting bacteria from phagocytosis by immune cells. 2. Permit bacteria to adhere to cell surfaces 3. Capsules can be a source of nutrients and energy to microbes. 4. Prevent cell from drying out (desiccation) 5. Polysaccharides from certain capsules can be the targets of protective immune responses and have therefore been included in 'conjugated' vaccines. Based on ability to produce spore Is the inactive form of bacteria formed under unfavourable condition to tide over this condition. E.g. Clostridium tetani. Such organisms are called spore forming while those that does not produce spore are called non-spore forming bacteria. Spores are resistant to: heat: withstand boiling for over one hour, desiccation: for a long period of time, UV radiation, chemical disinfectants the resistance of these spores has serious consequences and some very pathogenic bacteria have the ability to produce such spores. Shapes of bacteria: Bacterial organisms are grouped according to their shape into the following: Group name Shape of bacteria Appearance Coccus (cocci) Spherical / round °°° ° °°•• Bacillus (bacilli) Straight rod −-_-==- -Spirillum (spirilla) Curved rods ∼∼∼ιι, Filamentous Elongated thread like ⁄ √ ζ⎞ ⎞ ⎠ ⎠ Coccobacillus Not perfectly round but ◘ ◘ ◘ have blunted Vibrio Comma shaped cells ‚’ ‘ “ Names in brackets mean plural term for each. Groupings of cocci include: Diplococci: pairs of cocci Streptococci: chains of cocci. Staphylococci: clusters of geometrically arranged cocci. Tetrads: packets of 4 cells Sarcinus: packet of 8 cocci Groupings of bacilli include: Diplobacilli : bacilli in pair 5 Streptobacilli : bacilli in chain Toxin Are the substance released by certain bacteria during their multiplication and growth, which produces adverse effect on the host animal and other bacteria. Exoenzymes These are enzymes employed to break down nutrients found outside of bacterial cells (extracellularly) so that the breakdown products may be taken up into the bacterial cell and used. Many of these enzymes are harmful and represent exotoxins produced by disease-causing microorganisms, especially Gram-positive bacteria Endoenzymes To some extent equivalent to the exoenzymes used by Gram-positive bacteria, Gram-negative bacteria employ enzymes secreted into their periplasm to break down large molecules before those molecules are brought across the plasma membrane and into the cytoplasm of bacterium. This is in a way endotoxin that is released after the death of bacterium. Conditions affecting disease-producing ability of an organism: Virulence of organism: when the organism is very virulent disease will be produced very rapidly and when the organism is not virulent it will take long time to produce disease in the host. Resistance of host: resistance of the host can also influence the out come of an infection. When the resistance of the host is good it will take longer time for the infecting organism to produce disease on the contrary when the resistance of the host is low or poor the organism produces disease rapidly. Host barrier to infection: Skin: covers the body and act as the barrier to infection. Mucous membrane: internal organs are line by mucous membrane to protect from infection. Hairs in nostril: act as the filter and hold back dust and organism that are present in the air. Hair on animal body: act as the first barrier against the invasion by microbes and parasites. Tear: in the eyes tear is produced to wash away the microbes. 6