week 7

• Gram staining


  Used to differentiate between gram-positive (purple) and gram-negative (pink) bacteria
• Why we should stain bacteria

  • To make the cells and their internal structures more visible under the light microscope
• Stain


  A substance that adheres to a cell, giving the cell color
• Purpose of staining


  To differentiate different types of organisms or to view specific parts of organisms
• Staining techniques


  1. Staining

  2. Fixation

  3. Simple staining

  4. Differential staining

  5. Gram staining
• Staining


  • Auxiliary technique used in microscopy to enhance contrast in the microscopic image
  • Stains and dyes are used to highlight structures in biological tissues for viewing with the aid of different microscopes
• Fixation

  • Aims to preserve the shape of the cells or tissue
  • Sometimes heat fixation is used to kill, adhere, and alter the specimen so it will accept stain
• Simple staining


  • Can be poured drop by drop on the slide
  • Observes morphological structure of the cell
  • Simple, easy to use
  • Staining agents used are basic and acid dyes
  • Provide the color contrast but impart the same color to all the organisms in a smear
• Differential staining


  • Uses two or more stains and allows the cells to be categorized into various groups or types
  • Provides more information about the characteristics of the cell wall (thickness)
• Bacterial conjunctivitis


  Also known as "pink eye conjunctivitis", involves irritation, reddening of conjunctiva; edema of eyelids, mucopurulent discharge; sensitivity to light
• Gram staining


  • Named after Hans Christian Gram
  • Used to differentiate between gram-positive (purple) and gram-negative (pink) bacteria
  • Used to identify certain pathogens
• Gram staining principles


  1. Uses crystal violet to stain cell walls

  2. Iodine as a mordant and fuchsin/safranin as a counterstain to mark all bacteria

  3. Gram-positive bacteria stain dark blue or violet and are rich with peptidoglycan

  4. Gram-negative bacteria are rich in lipopolysaccharide
• Gram staining steps


  1. Crystal violet (primary stain)

  2. Gram's iodine (mordant)

  3. Decolorizer (removes primary stain)

  4. Safranin (counterstain for gram-negative bacteria)
• Pathogens


  • Common are Haemophilus influenzae and Streptococcus pneumoniae, but there are other bacteria as well
• Patient care


  Standard precaution
• Reservoir and mode of transmission

  • Human to human transmission via contact with eye and respiratory discharges
  • Contaminated fingers
  • Fomites
• Haemophilus influenzae biogroup egyptius

  Also known as the Koch-Weeks bacillus, gram -, rod-shape (coccobacillus), causative agent of acute and often purulent conjunctivitis, caused worldwide seasonal epidemics (summer)
• Haemophilus influenzae biogroup egyptius virulence

  • Pili
• Streptococcus pneumonia


  • Gram +, facultatively anaerobic pathogen, in pairs, encapsulated, lancet shaped
• Streptococcus pneumonia hemolysis


  • Aerobic - alpha hemolytic
  • Anaerobic - beta hemolytic
• Streptococcus pneumonia virulence


  • Adhesin, capsule, toxin pneumolysin and IgA
• Chlamydia trachomatis


  Gram - bacterium and obligate intracellular pathogen, cell with high lipid, susceptible to sulfonamides
• Chlamydia trachomatis conjunctivitis


  Also called "swimming pool conjunctivitis", there is mucopurulent discharge
• Chlamydia trachomatis conjunctivitis transmission


  • Non/poor chlorinated swimming pool
  • In adults, occur with non-gonococcal urethritis or cervicitis (genital to eyes transfer)
• Inclusion conjunctivitis (chlamydial conjunctivitis, para trachoma)


  Caused by serotypes D to K, in adults associated with genital infection, in newborns acquired upon passage in birth canal, swelling of eyelids with mucopurulent discharge, keratitis, corneal infiltrates, and corneal vascularization
• Trachoma (Chlamydia keratoconjunctivitis)


  Also called "chronic keratoconjunctivitis", caused by serotypes A,B, and C, transmission via eye to eye by droplets and fomites, follicular conjunctivitis with diffuse inflammation involving entire conjunctiva, frequent cause of blindness
• Neisseria gonorrhoeae


  Kidney bean shaped, gram -, called "gonococcus" and common cause of STD, "ophthalmia neonatorum" - acquired upon passage in birth canal, in adults acquired through finger to eye contact, redness, swelling of conjunctiva with purulent eye discharge
• If untreated, Neisseria gonorrhoeae leads to corneal ulceration, perforation and blindness
• Prevention of Neisseria gonorrhoeae ophthalmia neonatorum

  • Neonate - 1% silver nitrate (Crede's prophylaxis) after birth
  • 1% tetracycline eye ointments
  • 0.5% erythromycin eye ointments
• Foodborne diseases may lead to

  • Gastritis - stomach
  • Enteritis - small intestine
  • Colitis - large intestine/colon
  • Gastroenteritis - stomach and small intestine
  • Hepatitis - liver
  • Dysentery - bloody diarrhea
• Establishment of infectious disease in digestive system

  • Pharmacologic action
  • Local inflammation
  • Deep tissue invasion
  • Perforation
• Bacterial enterocolitis (food poisoning)


  Illness caused by the consumption of food contaminated with bacteria or bacterial toxins, inflamed small intestine and colon/large intestine
• Mechanisms of food poisoning

  • Ingestion of performed toxin - present in contaminated food, symptoms developed hours consisting of explosive diarrhea, abdominal pain, causes are S. aureus, vibrio, clostridium
  • Infection by toxigenic organisms - involves secretory enterotoxin, dysentery
  • Infection by entero invasive organisms - proliferate, invade, destroy epithelial cells, dysentery
• Types of dysentery

  • Melena - black tarry stool
  • Hematochezia - fresh blood stool
• Gastroenteritis


  Diarrhea, inflammation of the lining of the intestines
• Dental caries (tooth decay)


  Streptococcus mutans
• Periodontal disease


  Inflammation of structures that support teeth
• Gingivitis


  Inflammation of the gingivae or gums, characterized by bleeding of the gums while brushing the teeth
• Periodontitis


  Chronic gum disease can cause bone destruction and tooth loss
• Acute necrotizing ulcerative gingivitis or Vincent's disease or "TRENCH MOUTH"


  Characterized by pain that prevents normal chewing and may be accompanied by bad breath or halitosis