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CHAPTER 2 Medical Microbiology
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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
  careassociated infections (HAIs) through
  methods such as proper hand washing by health
  care providers and patients

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History of Microbiology

• Antonie van Leeuwenhoek (16001670s)
• Developed the microscope able to view the
  motility of wee beasties kept much of the
  knowledge to himself
• Present day
• Numerous classifications of microbes
• Numerous classifications of antibiotics
• Numerous vaccines against disease

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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

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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

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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

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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)

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Bacterial Structure and Morphology

• Three basic shapes
• Cocci (round or spherical)
• Bacilli (rod-shaped)
• Spirella (spiral)

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Cocci

• Grouped by formation
• Mono (bacteria in single formation)
• Diplo (paired bacteria)
• Strepto (chain-like formation)
• Staphylo (clustered formation)

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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

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Spirella

• Spirochetes
• Gram negative
• Spiral-shaped
• For example, syphilis, Lyme disease

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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)

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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

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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)

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Gram Stain Technique

• Place specimen on slide
• Stain with crystal violet resulting in purple hue
  of organisms
• Wash slide with water
• Flood with Grams iodine aiding adherence of
  stain
• Apply alcohol decolorizing rinse
• (Continues)

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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)

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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

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Growing and Testing Bacteria

• Culture and Sensitivity Test (CS)
• 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

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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)

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Culturing

• Primary (first) culture usually available after
  2448 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)

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Culturing

• Pathogens identified by
• Appearance
• Growth requirements
• Biochemical tests
• DNA
• These identifications may require several days

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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

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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

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Empiric Antibiotic Therapy

• Treatment begins before CS results
• Determination of prescribed antibiotic
• Type or location of suspected infection
• Usual bacteria noted with this type of infection
• Local bacterial resistance patterns
• After CS results, antibiotic therapy may need
  modification

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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)

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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)

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Antibiotic Classification

• Classified as
• Bacteriostatic agents
• Bactericidal agents
• Broad-spectrum
• Narrow-spectrum
• Aerobic
• Anaerobic
• Super-bacteria

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Summary

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

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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

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