Microbiology Bacterial Growth Quiz

Gram Stain List

• Gram-Positive Cocci (GPC) are bacteria ending in "-coccus"
  • Examples: Streptococcus, Staphylococcus, Enterococcus
• Gram-Negative Cocci (GNC)
  • Examples: Neisseria, Moraxella (only 2 species)
• Gram-Positive Bacilli (GPR) are everything else
• No gram-negative bacilli on Exam 1

Characteristics of Bacteria

• Prokaryotes
  • No true nucleus (bacteria)
  • Nucleoid: single chromosome of double-stranded DNA in a circular loop without a surrounding nuclear membrane.
  • No nuclear membrane
  • Rigid cell wall: protein and peptidoglycan
  • Asexual division
• Eukaryotes
  • True nucleus - Animal cells, plant cells, fungi
  • Contains double-stranded DNA
  • Nuclear membrane is bound
  • Most do not have a cell wall
  • Sexual and asexual reproduction

Characteristics of Bacteria (Taxonomy)

• Domain: Bacteria
• Phylum: Firmicutes (example: cocci and bacilli)
• Class: Bacilli
• Order: Bacillales
• Family: Staphylococcaceae
• Genus: Staphylococcus
• Species: aureus
• Strain: a genetic variant or subtype (example: Methicillin-resistant S. aureus)
• Genus name is capitalized, species name not capitalized (example: Staphylococcus aureus) and written in italics or underlined
• Species name comes second

Characteristics of Bacteria (Gram Stain)

• Gram stain is a grouping method used in clinical microbiology to differentiate medically important bacteria based on their wall structures.
• Gram-positive bacteria have a thick peptidoglycan layer and stain purple.
• Gram-negative bacteria have a thin peptidoglycan layer and stain pink/red.
• This difference is due to varying wall structure composed of differents layers in each bacteria type.

Characteristics of Bacteria (Reagents)

• Crystal Violet (CV): Attracted to negatively charged bacterial cells, penetrates the cell wall and stains both GP and GN cells.
• Iodine: Mordant interacts with CV to fix the dye to the cells.
• Alcohol: Decolorizes thin peptidoglycan layer in Gram-negative cells. Gram-positive cells retain the purple stain ( thick layer).
• Safranin: Counter stain. Gives color to Gram-negative cells that appear colorless after alcohol decolorization

Characteristics of Bacteria (Factors Affecting Microbial Growth)

• Temperature:
  • Psychrophiles: cold-loving (4-15°C)
  • Mesophiles: moderate temperature-loving (30-35°C)
  • Thermophiles: heat-loving (50-60°C+)
• Osmotic Pressure:
  • Isotonic: Similar internal and external solute concentration.
  • Hypotonic: lower solute concentration outside the cell; cells swell and may rupture.
  • Hypertonic: higher solute concentration outside the cell; cells shrink
• Chemical Requirements: Carbon, water, nitrogen, sulfur, phosphorus, trace elements (iron, copper, zinc). Hydrogen ion concentration (pH): medically important bacteria prefer pH 6.0-8.0 (body pH ~7).
• Atmosphere:
  • Obligate aerobes: require oxygen (facultative aerobes can survive with or without it)
  • Obligate anaerobes: do not use oxygen; prefer oxygen-free environments)
  • Facultative anaerobes: can grow with or without oxygen.
  • Capnophiles: require increased CO2.

Characteristics of Bacteria (Growth Patterns)

• Replication is by binary fission (cell division).
• Generation time/doubling time is the time required for one cell to divide into two cells.
• Growth patterns can be depicted in a cell growth curve with phases such as Lag, Log, Stationary, and Death.

Characteristics of Bacteria (Defining Terms)

• Cocci: Spherical bacteria (example: diplococci, streptococci)
• Bacilli: Rod-shaped bacteria
• Pleomorphic: vary in shape
• Spirochete: Helical bacteria
• Flagella: exterior protein filaments for motility and movement.
• Pili: hair-like appendages for adherence.

Characteristics of Bacteria (Other Terms)

• Endospores: highly durable dehydrated cells, resistant to heat, drying, chemicals, not all gram-positive bacteria forms them (example: C. botulinum).
• Lipopolysaccharide (LPS): outer membrane component in Gram-negative bacteria; may function as virulence factors (fever, shock, attachment).
• Capsules: Organized polysaccharide layers that shield bacteria from immune and phagocytic responses. This is also a virulence factor.

Characteristics of Bacteria (Host-Parasite Interactions)

• Host: organism being infected by a pathogen
• Parasite: any invader or agent causing disease
• Pathogen: microorganism capable of causing disease
• Primary pathogen: regularly causes infection and disease in a healthy host
• Opportunistic pathogen: usually does not cause disease in a healthy host but may cause disease in an immunocompromised host
• Host barriers:
  • Microbiome (normal flora)
  • Anatomic barriers (skin)
  • Stomach acid
  • White blood cells (neutrophils)
  • Antibodies
• Organism factors leading to disease:
  • Evasion of the immune response (capsule)
  • Ability to attach to host cells (pili)
  • Exotoxins or enterotoxins

Characteristics of Bacteria (Hospital Epidemiology)

• HAI (healthcare associated infection): infection acquired during a hospital stay/treatment
• Colonization: presence of organisms on a body surface without disease
• Infection: when organisms invade tissues causing clinical signs and symptoms
• Nosocomial infection: infection acquired by a patient after admission to the hospital
• Steps in Outbreak Investigation:

1. Identify etiologic agent, reservoir, and mode of transmission
2. Eliminate the reservoir
3. Prevent transmission
4. Prevent future outbreaks

• Chain of infection: source, mode of transmission, susceptible host

Characteristics of Bacteria (Sterilization & Disinfection)

• Approaches to control microorganism growth:
• Body's own defense mechanisms
• Chemotherapeutic agents
• Public health measures
• Sterilization & Disinfection
• Antiseptic: inhibits microorganism growth (isopropyl alcohol, hydrogen peroxide)
• Aseptic: used to sterilize (kill) (povidone iodine) - example: surgery, phlebotomy
• Cide/Cidal: to kill
• Stasis/Static: to prevent multiplication without necessarily killing
• Disinfectant: kills equipment and surfaces (e.g., 10% bleach solution)

Characteristics of Bacteria (Staphylococcus)

• Gram-positive cocci in grape-like clusters .- Found in skin, mucous membranes, and feces.
• Catalase-positive (enzyme breaks down 3% H₂O₂).
• Staphylococcus aureus is coagulase-positive. -Other Staph species are coagulase-negative.
• S. aureus is commonly found in noses, armpits, skin, and groins; and survives in the environment
• Common virulence factors: . Coagulase . Protein A (prevents phagocytosis) . Enterotoxins . Lipase . Hyaluronidase . Hemolysins (damage red blood cells)
• Notable disease associations: . Skin infections . Food poisoning (e.g., staphylococcal food poisoning; scalded skin syndrome) . Toxic shock syndrome

Characteristics of Bacteria (Methicillin-Resistant Staphylococcus aureus - MRSA)

• MRSA emerges when S. aureus develops resistance to methicillin.
• Related to the acquisition of the mecA or mecC gene
• Antibiotic treatment: vancomycin or alternatives like daptomycin, tigecycline, or others like linezolid.
• #1 cause of community acquired skin and soft tissue infections
• Can cause pneumonia, bacteremia, endocarditis, joint, and surgical site infections

Characteristics of Bacteria (Coagulase-negative Staphylococcus species)

• Staphylococcus epidermidis: Colonizes the skin of most people, low virulence. Liking to form biofilms . Can cause infections of prosthetic devices, surgical wounds, etc, with its preferred method of attachment to devices, prosthetic heart valves.
• Staphylococcus saprophyticus: Has affinity for binding to the epithelial cells of the urethra or bladder.
• Can cause urinary tract infections (UTIs), especially in sexually active young women.

Characteristics of Bacteria (Streptococcus)

• Gram-positive cocci in chains
• Normal flora of the upper respiratory and intestinal tracts
• Catalase-negative
• Compare to Staphylococcus (positive)

Characteristics of Bacteria (Enterococcus)

• Gram-positive cocci
• Commonly found in normal intestinal flora
• Relatively low virulence
• Can cause UTIs, endocarditis, wound infections

Characteristics of Bacteria (Classification by Hemolysis)

• Alpha (α): partially lysed RBCs
• Beta (β): completely lysed RBCs
• Gamma (γ): no hemolysis

Characteristics of Bacteria (Streptococcal Diseases)

• S. pyogenes (Group A): Pharyngitis, scarlet fever, rheumatic fever, acute glomerulonephritis, impetigo, cellulitis.
• S. agalactiae (Group B): Neonatal infections (meningitis, septicemia, pneumonia).
• S. pneumoniae: Pneumonia, otitis media, meningitis
• Viridans Strep: normal flora(subacute bacterial endocarditis
• Group D. Strep: Normal flora
• There are vaccines available for some of these diseases

Characteristics of Bacteria (Antibiotic Treatment of Strep and Enterococcus)

• Streptococcus: Penicillin is often the drug of choice. In cases of penicillin-resistant S. pneumoniae, vancomycin or 3rd gen cephalosporins may be used.
• Enterococcus: Intrinsically resistant to penicillins or cephalosporins, so a combination of a penicillin and an aminoglycoside is often required. In cases of resistance to drug combo (eg, vancomycin-resistant enterococcus), alternatives include synercid, linezolid, or daptomycin

Characteristics of Bacteria (Gram-Positive Bacilli)

• Spore-forming:
  • Bacillus spp.: low virulence, in soil, water, dust, animal products. Common lab contaminants. Spores survive in soil for years; can stain gram variable
  • Clostridium spp.: Anaerobic, in soil, water, vegetation, and the large bowel of humans and other animals. Large box like rods; can stain gram variable.

Characteristics of Bacteria (Non-Spore Forming GPRs)

• Corynebacterium spp.: Found in environment & human flora; normal flora(mouth, skin, respiratory/genitourinary tracts)
• Nocardia spp.: Found in soil and water; NOT part of normal human flora; partially acid-fast.

Characteristics of Bacteria (Gram-Positive Bacilli - Common Diseases)

• Listeria monocytogenes: stillbirths, meningitis, neonates, pregnant women. Foodborne illness/infection.
• Corynebacterium diphtheriae: severe pharyngitis often with a thick, leathery gray membrane. Affects myocardium and peripheral nervous systems (neurotoxin).
• Corynebacterium jeikeium: opportunistic infection of prosthetic heart valves, septicemia and skin
• Gardnerella vaginalis: bacterial vaginosis is characterized by the foul smelling discharge

Characteristics of Bacteria (Gram-Positive Bacilli-Common Diseases-Spore forming)

• Bacillus anthracis: Anthrax
• Bacillus cereus: Food poisoning
• perfringens: Food poisoning, gas gangrene
• difficile: Pseudomembranous colitis
• botulinum: Food poisoning from improperly canned food

Characteristics of Bacteria (Neisseria)

• Many species part of the normal flora of respiratory and urogenital tracts.
• N. gonorrhoeae: Obligate human pathogen, causes gonorrhea (PID, etc,), sexually transmitted infection..
• N. meningitidis: Causes meningitis (inflammation of the meninges, the membranes surrounding the brain and spinal cord -life threatening condition)..

Characteristics of Bacteria (Moraxella catarrhalis)

• Gram-negative diplococci. Normal flora of upper respiratory tract
• NOT fastidious(no special growth requirements/medium).
• Causes otitis media and sinusitis in children and pneumonia and bronchitis in immunocompromised adults,
• Common respiratory infection; susceptible to many antibiotics; known resistance to penicillin for most isolates; decongestants important to reduce inflammation.