A. Cell Biology of Bacteria

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TAXONOMY OF BACTERIAInstructor Terry WisethMICROBIOLOGYNorthland Community & Technical College


TAXONOMYTaxonomic classification based on: gram staining gram positive gram negative mode of respiration aerobic anaerobic cell wall shape cocci bacilli spiral


TAXONOMYGram Positive Bacilli Gram Positive Cocci Gram Negative Bacteria Spirochetes Rickettsia Chlamydia


GRAM-POSITVE BACILLIClinically important genus Aerobic Bacillus Lactobacillus Listeria Erysipelothrix Corynebacterium Mycobacterium Anaerobic Clostridium Propionibacterium




BACILLUSgenus of Gram-positive bacteria ubiquitous in nature (soil, water, and airborne dust) Some species are natural flora in the human intestines most species are harmless saprophytes two species are considered medically significant B. anthracis B. cereus


B. anthraciscauses anthrax in cows, sheep, and sometimes humans Anthrax is transmitted to humans via direct contact with animal products or inhalation of endospores Anthrax can be treated with penicillin or tetracycline


B. anthracisThe anthrax bacteria can live in the soil for many years Man may become infected with anthrax by inhaling contaminated soil particles or by handling wool or hair from diseased animals Infection of the intestinal tract can occur by eating undercooked meat from diseased animals


B. cereuscan cause toxin-mediated food poisoning It is known to inhabit many kinds of food including stew, cereal, and milk


B. cereusThe toxins released lead to vomiting and diarrhea toxin production usually takes place after the infected foods are cooked proper cold storage of food is recommended immediately after preparation


LACTOBACILLUSferment glucose into lactose hence the name Lactobacillus most common application of Lactobacillus is industrial specifically for dairy production yogurt, sauerkraut, pickles, buttermilk L. acidophilus


LACTOBACILLUSmake up part of the natural flora of the human vagina create an acidic environment which inhibits growth of many bacterial species leads to urogenital infections Lactobacillus is generally harmless to humans


LISTERIASpecies of human pathogenic significance L. monocytogenes found in soil and water


L. monocytogenesVegetables can become contaminated from the soil or from manure used as fertilizer Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products


L. monocytogeneshas been implicated in several food poisoning epidemics (Listeriosis) normal inhabitant of the gastrointestinal tract and of animal feces infected suffer from vomiting, nausea, and diarrhea those at high risk include newborns, pregnant women and their fetuses, the elderly, and persons lacking a healthy immune system


ERYSIPELOTHRIXbetter known as a veterinary pathogen than as a human pathogen This ubiquitous microbe has been found in many farm animals such as pigs, horses, and turkeys can infect a human host and cause Erysipeloid, an inflammatory skin disease


CORYNEBACTERIUMubiquitous in nature normally saprophytic and harmless to humans exception is the bacterium C. diphtheriae produces the toxin that causes diphtheria a disease of the upper respiratory system in humans unique in its exotoxin formation


MYCOBACTERIUMM. tuberculosis M. leprae


M. tuberculosiscausative agent of tuberculosis


M. tuberculosisTubercle bacilli that reach the alveoli of the lung are ingested by macrophages but often survive


M. tuberculosisTubercle bacilli multiplying in macrophages cause a chemotactic response that brings additional macrophages into the area, forming and early tubercle


M. tuberculosisAfter a few weeks many of the macrophages die, releasing tubercle bacilli and forming a caseous center in the tubercle, which is surrounded by a mass of macrophages and lymphocytes. The disease may become dormant after this stage.


M. tuberculosisIn some individuals, a mature tubercle is then formed as a firm outer layer surrounds the mass of macrophages and lymphocytes. The caseous center enlarges in the process of liquefaction, forming and air-filled tuberculous cavity in which the bacilli multiply extracellularly


M. tuberculosisLiquefaction continues until the tubercle ruptures, allowing bacilli to spill into a bronchiole and thus be disseminated throughout the respiratory system and to other systems


M. tuberculosis


M. lepraecausative agent of leprosy

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Last Updated: 8th March 2018

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