Microbiology 101 Quiz

Gram Stain List

• Gram-Positive Cocci (GPC) are bacteria ending in "-coccus"
  • Streptococcus
  • Staphylococcus
  • Enterococcus
• Gram-Negative Cocci (GNC) are
  • Neisseria
  • Moraxella
  • (Few species)
• Gram-Positive Bacilli (GPR): Other bacteria
• No gram-negative bacilli on Exam 1

Characteristics of Bacteria (Prokaryotes and Eukaryotes)

• Prokaryotes: No true nucleus
  • Nucleoid is a single chromosome of double-stranded DNA
  • DNA is in a circular chromosome without a surrounding nuclear membrane
  • No nuclear membrane
  • Cell wall; protein and peptidoglycan; rigid
  • Asexual division
• Eukaryotes: True nucleus
  • Nucleus contains double-stranded DNA
  • Nuclear bound membrane
  • Most do not have cell walls
  • Sexual and asexual reproduction

Characteristics of Bacteria (Taxonomy)

• Domain → Bacteria
• Phylum → Firmicutes
• Class → Bacilli
• Order → Bacillales
• Family → Staphylococcaceae
• Genus → Staphylococcus
• Species → aureus.
• Genus is capitalized, underlined/italicized
• Species is lowercase, underlined/italicized
• Strain is not italicized / underlined

Characteristics of Bacteria (Gram Stain Procedure)

• Gram stain is the most commonly used stain in clinical microbiology
• Classified into Gram Positive and Gram Negative based on the colour they stain
• Different wall structures lead to different staining outcomes
  • Gram-positive bacteria have a thick peptidoglycan layer
  • Gram-negative bacteria have a thin peptidoglycan layer, and an outer membrane

Characteristics of Bacteria (Bacterial Replication)

• Replication is done by binary fission
• Generation time/doubling time is the time for one cell to divide into two cells

Characteristics of Bacteria (Bacterial Structure):

• Cocci = spherical
  • Coccus (round)
  • Streptococci (chain)
  • Diplococci (pair)
• Bacilli = rod-like
• Pleomorphic = varied in shape
• Spirochete = helical (spiral)
• Flagella = protein filaments for exterior motility
• Pili = hair-like protein appendages for adherence; don't provide motility
• Capsule = protective layer
• DNA in nucleoid region

Characteristics of Bacteria (Bacterial Structures Continued)

• Endospores: Dormant, highly durable dehydrated cells with thick walls; resistant to heat, drying, and chemicals
• Gram-positive bacteria form endospores
• Important in food industry; survive processing
• Lipopolysaccharides: essential component of the outer membranes of Gram-negative bacteria
• Important for virulence factors (fever, shock, attachment site, barrier)
• Capsule: Organized polysaccharide layers; shields bacteria from immune and phagocytic responses. Important virulence factor

Characteristics of Bacteria (Microbial Growth Factors)

• Temperature:
  • Psychrophiles: cold (4-15°C)
  • Mesophiles: moderate (30-35°C)
  • Thermophiles: hot (50-60°C+)
• Osmotic Pressure
  • Isotonic: equal solute concentration inside and outside the cell
  • Hypotonic: lower solute concentration outside the cell compared to inside
  • Hypertonic: higher solute concentration outside the cell compared to inside
• Chemical Requirements: Carbon, water, nitrogen, sulfur, phosphorus, trace elements (iron, copper, zinc, etc.)
• Hydrogen Ion Concentration (pH): medically important bacteria prefer pH 6.0-8.0 (body pH is ~7).
• Atmosphere:
  • Obligate Aerobes: require oxygen
  • Obligate Anaerobes: don't grow in the presence of oxygen
  • Facultative anaerobes: grow with or without oxygen
  • Capnophilic: grows better with increased CO2

Host-Parasite Interactions and Terms

• Host: organism being infected
• Parasite: any invader or agent
• Pathogen: microorganism that causes infection
• Primary pathogen: regularly cause infections
• Opportunistic pathogen: cause disease only when defenses are weakened
• Host barriers:
  • Microbiome
  • Anatomical barriers (skin)
  • Stomach acid
  • White blood cells
  • Antibodies

Host-Parasite Interactions and Terms (Continued)

• Host factors → disease: behavior, occupation, age, sex, race
• Organism factors → disease: Evasion of immune response, ability to attach, exotoxins/endotxins, enterotoxins
• Bacteremia: bacteria multiplying in the bloodstream
• Virulence: ability of an organism to cause disease
• Pyogenic: pus producing
• Disease Transmission:
  • Endogenous (infected with own bacteria)
  • Exogenous (outside bacteria)
    • Contact, droplets/aerosol

Hospital Epidemiology

• HAI: Healthcare-associated infections acquired during treatment
• Colonization: presence of microorganisms on a body surface without disease
• Infection: organisms invading body tissues
• Nosocomial infection: acquired by a patient after admission to a hospital
• Steps in an outbreak:
  • Identify the etiologic agent and conditions
  • Eliminate the reservoir
  • Prevent transmission
  • Prevent future outbreaks

Sterilization & Disinfection

• Approaches to control: body's defense mechanisms, chemotherapeutic agents, public health measures, sterilization & disinfection
• Antiseptic: Inhibits microorganism growth (e.g., alcohol, hydrogen peroxide) applied to skin;reduces number of normal flora organisms
• Aseptic: used to kill microorganisms (e.g., povidone-iodine) used in procedures such as surgery
• Cide/Cidal: to kill
• Static/Stasis: to prevent multiplication without necessarily killing (e.g., preventing bacterial reproduction within a culture)
• Disinfectant : stronger agents used for surfaces and equipment, possibly too strong for skin

Sterilization & Disinfection (Hospital/Laboratory control)

• Hospital:
  • Surgery (cleaning patient's skin, instruments)
  • Medical waste
  • Handwashing
  • PPE
  • Needle stick injury procedures (back bleed, wash wounds)
• Laboratory:
  • Universal/standard precautions
  • Lab specimens handled as infectious
  • No pipetting by mouth
  • Proper specimen handling

Sterilization & Disinfection (Methods)

• Heat: Moist or dry heat, autoclave, pasteurization, flame
• Filters: Membrane filter, HEPA
• Radiation: UV light (lab hoods), ionization radiation
• Soap: removing organic matter/loose skin cells; harbor infectious bacteria

Sterilization & Disinfection (PPE)

• PPE for controlling transmission of highly contagious diseases: gloves, lab coat, surgical mask, N95 respirator
• PPE to prevent transmission of airborne pathogens-N95 respirator, gown, gloves
• Removal protocol

Bacteria (Specific)

• Staphylococcus
  • Gram-positive cocci in grape-like clusters
  • Normal flora of skin, mucous membranes, feces
  • Catalase positive
  • Coagulase: enzyme that binds plasma fibrinogen to form a clot
  • Staph aureus is coagulase positive
  • Other Staph species are negative

Bacteria (Specific, continued)

• Staphylococcus aureus
  • Golden colored colony on agar
  • Often found on skin, nose, armpits, and groin
  • Most virulent
  • Virulence factors: coagulase and protein A (prevent phagocytosis), enterotoxins, lipase, hyaluronidase, hemolysins.

Bacteria (Specific, continued)

• Staph aureus Disease Associations
  • Skin Infections (impetigo, furuncles, carbuncles, pyogenic abscess)
  • Scalded skin syndrome (blisters/erythema)
  • Food Poisoning (meat and milk products, toxin-mediated)
  • Toxic Shock Syndrome (associated with menstruating females and tampon use)
  • Causes: bacteremia, endocarditis, pneumonia, empyema, osteomyelitis, septic arthritis, gastroenteritis

Bacteria (Specific, continued)

• Methicillin Resistant S. aureus (MRSA)
  • Antibiotic resistance
  • Related to acquisition of mec A or mec C gene
  • Resistant to B-lactams
  • Vancomycin, Daptomycin, Tigecycline/ Linezolid alternatives

Bacteria (Specific, continued)

• Streptococcus
  • Gram-positive cocci in chains.
  • Normal flora of upper and lower respiratory & intestinal tracts
  • Catalase negative

Bacteria (Specific, continued)

• Enterococcus
  • Gram-positive cocci
  • "Streptococci of fecal origin"
  • Normal intestinal flora
  • Relatively low virulence
  • Causes UTIs, endocarditis, wound infections

Bacteria (Specific, continued)

• Classification by Hemolysis:
  • Streptococcus are classified by how they breakdown red blood cells (hemolysis)
    • Alpha (partially lysed)
    • Beta (completely lysed)
    • Gamma (not lysed)
• Streptococcal Diseases:
  • S. pyogenes (Group A): Pharyngitis, scarlet fever, impetigo, sequelae → Rheumatic fever, glomerulonephritis, cellulitis
  • S. agalactiae (Group B): Neonatal Infections (meningitis, septicemia, pneumonia), normal flora in woman's lower genital tract (UTI, bacteremia, in elderly and immunocompromised)
  • S. pneumonia, Viridans strep, strep group D - can cause various other illnesses

Bacteria (Specific, continued)

• Antibiotic Treatment of Strep and Enterococcus:
  • Streptococcus: Penicillin=drug of choice, but alternatives include Vancomycin or 3rd-generation cephalosporins
  • Enterococcus: Resistant to penicillins, Cephalosporins, and other B lactams. Requires a combination therapy with penicillins and aminoglycosides, and alternatives such as Vancomycin, Synercid, or Linezolid.

Bacteria (Specific, continued)

• Gram-Positive Bacilli
  • Spore-formers:
    • Bacillus spp.: low virulence saprophytes in soil, water, dust, animals; common lab contaminants; large box-car rods
    • Clostridium spp.: inhabit soil, water, vegetation, and the large bowel of humans and other animals; anaerobes; large box-car GPRs
  • Opportunistic Pathogens:
    • Corynebacterium spp.: normal flora of skin/mucous membranes of respiratory and urogenital tract
    • Gardnerella vaginalis
    • Gardnerella vaginalis,
  • Strict Pathogens:
    • Listeria monocytogenes: Stillbirths & meningitis, infect neonates, pregnant women with foodborne illness
    • Corynebacterium diphtheriae: Diphtheria (throat infection)
    • Nocardia spp
    • Bacillus anthracis
    • Clostridium botulinum

Bacteria (Specific, continued)

• Non-Spore-Forming GPRs - Characteristics:
  • Corynebacterium spp.: Found in the environment/flora of humans & animals
    • Normal on skin, oral cavity, and genitourinary tract
    • Pleomorphic rods.
  • Nocardia spp.: found in environment but NOT normal flora
    • Partially acid-fast
    • Affects lungs, brain, and skin

Bacteria (Specific, continued)

• Gram-Positive Bacilli - Common Diseases:
  • Bacillus anthracis, Bacillus cereus, Clostridium perfringens, Clostridium difficile, Clostridium tetani, Clostridium botulinum

Bacteria (Specific, continued)

• Neisseria
  • Two primary pathogens
    • N. gonorrhoeae: Gram-negative diplococci, pili for attachment to epithelial cells, Normal in nasopharynx but can cause gonorrhea.
    • N. meningitidis: Gram-negative diplococci, pili for attachment to epithelial cells, lives in upper respiratory tract but can cause life threatening infections like meningitis and other diseases

Bacteria (Specific, continued)

• Moraxella catarrhalis:
  • Gram-negative diplococci
  • Normal flora of upper respiratory tract
  • Not fastidious
  • Otitis media, sinusitis pneumonia, bronchitis