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CHAPTER 2

CHAPTER 2. MEDICAL MICROBIOLOGY. Introduction. Medical microbiology: study of collecting and identifying pathogenic organisms and suggesting medical management Numerous specialties (e.g., bacteriology, virology, mycology, parasitology) This chapter focuses on bacteriology

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CHAPTER 2

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  1. CHAPTER 2 MEDICAL MICROBIOLOGY

  2. Introduction Medical microbiology: study of collecting and identifying pathogenic organisms and suggesting medical management Numerous specialties (e.g., bacteriology, virology, mycology, parasitology) This chapter focuses on bacteriology Insight into prevention of health care–associated infections (HAIs) through methods such as proper hand washing by health care providers and patients 2-3

  3. History of Microbiology Antonie van Leeuwenhoek (1600–1670s) Developed the microscope; able to view the motility of “wee beasties”; kept much of the knowledge to himself; given credit for starting science of microbiology Remember Louis Pasteur is known for understanding the importance of pasteurization; also developed immunization techniques 2-4

  4. History of Microbiology Epidemiology-study of disease patterns and spread of diseases Present day Numerous classifications of microbes Numerous classifications of antibiotics Numerous vaccines against disease 2-4

  5. “Science” of Microbiology Science: an idea used to develop a theory Scientific inquiry: planned and deliberate investigation Scientific theory: information based on natural and physical phenomena; able to be tested by unaffiliated researchers 2-5

  6. Bacteriology Binary fusion: process of bacteria reproduction; cell copies DNA and organelles, divides cytoplasm, splits in half Asexual reproduction: cells make identical copies of themselves; no involvement of another cell 2-6

  7. Naming Bacteria Binomial nomenclature Genus: first (family) name; capitalized; italicized; groups bacteria with similar characteristics Species: second name; lowercase; italicized; represents specific characteristics of a particular group of bacteria 2-7

  8. Bacterial Structure and Morphology Bacteria Anucleate Nucleoid (stores DNA) Glycocalyx (protection around cell wall: capsular, or slime layer increasing resistance to antibacterial agents) Some have no locomotion; others have cilia or flagella Spores (produced by inactive bacteria; difficult to kill) (Continues) 2-8

  9. Bacterial Structure and Morphology Three basic shapes Cocci (round or spherical) Bacilli (rod-shaped) Spirella (spiral) 2-9

  10. Cocci Grouped by formation Mono (bacteria in single formation) Diplo (paired bacteria) Strepto (chain-like formation) Staphylo (clustered formation) 2-10

  11. Bacilli Rod-shaped May possess flagella Pairs (diplobacillus) and chains (streptobacillus) E. coli (normal flora of intestinal tract; may migrate to urinary tract causing UTI or to blood stream causing bacteremia) May form spores 2-11

  12. Spirella Spirochetes Gram negative Spiral-shaped For example, syphilis, Lyme disease 2-12

  13. Guidelines for Specimen Collection Collect before administration of antibiotics Collect without contaminating specimen Obtain sufficient quantity of specimen from site, not surrounding tissue Place specimen in appropriate container or transport media (Continues) 2-13

  14. Guidelines for Specimen Collection • Label each specimen properly • Transport to lab within allotted time • Safe collection and handling lead to • Accurate results • Prevention of spread of disease to other health care workers or patients 2-14

  15. Bacterial Staining • Dyes/stains • Lend color to bacteria allowing ease in viewing/identification • Provide information about classification and arrangement of bacterial cells • Simple stains (illustrate structure and arrangement of bacterial cells) • Differential stains (supply information on composition of bacterial walls) 2-15

  16. Gram Stain Technique • Place specimen on slide • Stain with crystal violet resulting in purple hue of organisms • Wash slide with water • Flood with Gram’s iodine aiding adherence of stain • Apply alcohol decolorizing rinse (Continues) 2-16

  17. Gram Stain Technique Bacteria retaining purple color are gram positive Counter-stain with red dye (safranin) Bacteria retaining red or pink are gram negative (more difficult to treat due to three layers with tough cell wall) 2-17

  18. Acid-Fast (Ziehl-Neelsen) Stain Used on genus Mycobacterium testing causative agents of TB and leprosy Acid-fast organisms resist staining due to presence of glycolipid and mycolic acid layer Acid-fast bacteria retain carbolfuchsin stain; appear red against blue background 2-18

  19. Growing and Testing Bacteria • Culture and Sensitivity Test (C&S) • After obtaining specimen, inoculate into proper culture media containing nutrients allowing for growth of microbes • Place in incubator, maintaining stable temperature and humidity level • Test growth organisms with antibiotics to determine best options for treatment 2-19

  20. Culturing • Medium (liquid broth, semisolid, or solid agar) varies with specific bacteria • Use Petri dish • Clear (allowing visualization of growth) • Specimen is spread/streaked on dish, pattern dividing plate into four quadrants • Place bottom up in incubator, preventing the dripping of condensation onto colonies (Continues) 2-20

  21. Culturing • Primary (first) culture: usually available after 24–48 hours of incubation • Mixed culture: identification of more than one microorganism; must separate to yield pure culture of only one species • After isolation of microbes, examine to identify pathogens (Continues) 2-21

  22. Culturing • Pathogens identified by • Appearance • Growth requirements • Biochemical tests • DNA • These identifications may require several days 2-22

  23. Susceptibility Testing • After identification of microbes, determine susceptibility to treatment with antibiotics • Disk diffusion (Bauer-Kirby test) • Provides qualitative information; shows zone of inhibition • Broth dilution • Quantitative • Identifies concentration of drug needed; MIC 2-23

  24. MIC and MBC Testing • Minimal inhibitory concentration (MIC) • Does not identify if organism is killed • Minimum bactericidal concentration (MBC) • Determines whether the organism is killed or just inhibited in growth • Testing with FDA-approved machines • Expensive • Unable to detect some resistant bacteria 2-24

  25. Empiric Antibiotic Therapy • Treatment begins before C&S results • Determination of prescribed antibiotic • Type or location of suspected infection • Usual bacteria noted with this type of infection • Local bacterial resistance patterns • After C&S results, antibiotic therapy may need modification 2-25

  26. Bacterial Disease • Bacteria cause disease by • Destroying infected tissue • Release of toxins into the body • Endotoxins: found only in gram-negative bacteria and Listeria (gram positive) • Exotoxins: gram-positive and gram-negative bacteria (Continues) 2-26

  27. Bacterial Disease • Signs and symptoms • High fever • Swelling • Pain • Tachycardia (rapid pulse) • Tachypnea (rapid breathing) • Abnormal, foul-smelling drainage from site • Treatment: antibiotics (kill prokaryotic bacteria without harming eukaryotic cells) 2-27

  28. Antibiotic Classification • Classified as • Bacteriostatic agents • Bactericidal agents • Broad-spectrum • Narrow-spectrum • Aerobic • Anaerobic • Super-bacteria 2-28

  29. Summary • Numerous specialties in the field of microbiology • Organisms have two names • Genus • Species • Bacteria have three basic shapes • Cocci • Bacilli • Spirella(Continues) 2-29

  30. Summary • Extreme care needed when obtaining specimens for culture • Microbiology laboratory processes specimen • Stains the collected material • Identifies bacteria • Detects bacteria susceptibility • Determination of antibiotic therapy 2-30

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