good response of the bone marrow. The primarybacteria-destroying cells (known as phagocytes)are the neutrophils, and the bone marrow shouldsupply large numbers of these to combat theinfection. The greater the “shift to the left”(increase in immature neutrophils), the moresevere the infection. The appearance ofnumerous juvenile cells (metamyelocytes)indicates irritation of the bone marrow withregeneration. If the infection continues and thepatient’s resistance declines, the shift advancesfurther to the left. If improvement ensues, theshift declines and recedes to normal.A falling white cell count with the number andmaturity of neutrophils progressing towardnormal indicates recovery.A continued “shift to the left” with a falling totalwhite cell count indicates a breakdown of thebody’s defense mechanism and is a poorprognosis.The percentage of eosinophils, lymphocytes,and monocytes generally decreases in acuteinfections.In tuberculosis, an increase in monocytes(monocytosis) indicates activity in the infectedarea. An increase in lymphocytes (lympho-cytosis) indicates healing.Eosinophils increase in parasitic infections andallergic conditions.BACTERIOLOGYLEARNING OBJECTIVE:Recallbacteria classifications, common bacteria,and procedural steps for making smears,Gram staining, and reading and reportingsmears.Bacteriology is the study of bacteria. Of primaryinterest to Hospital Corpsman is medical bacteriology,which deals with the bacteria that cause disease in man.Bacteria are prokaryotic microorganisms of thekingdom Protista. They reproduce asexually bytransverse binary fission in which the cell divides intotwo new cells. Bacteria are found almost everywhere,and the human body harbors vast numbers. Manybacteria are beneficial and essential to human life; onlya few are harmful to man.BACTERIA CLASSIFICATIONSince there are thousands of types of bacteria, amethod of classification is essential. Bacteria areclassified according to their respectivedisease-producing ability,growth requirements,morphologic characteristics,colonial morphology,toxins produced, andGram’s stain reaction.Disease-Producing AbilityThe disease-producing ability of bacteria isreferred to as either pathogenic or nonpathogenic.Pathogens are bacteria that cause diseases, andnonpathogens are harmless bacteria. Bacteria that areessential to our body are, in their proper environment,called common or normal flora. For example, alphastreptococcus in the throat is common flora, but whenit is found elsewhere (such as in the blood stream,possibly as a result of tooth extraction), it may causediseases such as septicemia and endocarditis.Growth RequirementsThe four growth requirements for bacteria aretemperature,oxygen,nutrition, andmoisture.TEMPERATURE REQUIREMENTS . —Temperature requirements are divided into thefollowing three categories.Psychrophilic—bacteria that reproduce best at15EC to 20ECMesophilic—bacteria that reproduce best at20EC to 45ECThermophilic—bacteria that reproduce best at50EC to 55ECOXYGEN REQUIREMENTS.—The amount ofoxygen needed for an organism to grow or reproducevaries with the type of organism.Aerobes areorganisms that reproduce in the presence of oxygen.Obligate aerobes are organisms that grow only in the7-25
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