Microbiology Exam Study Guide: Diagnostic Methods, Viral Characteristics, Microbial Growth, and Infectious Diseases

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 15: Diagnostic Methods in Microbiology

Portals of Entry for Infection

Microorganisms enter the human body through specific portals, which are critical for understanding disease transmission and specimen collection.

Common Portals: Skin, respiratory tract, gastrointestinal tract, genitourinary tract, conjunctiva.
Specimen Selection: Choose specimens based on the site of infection (e.g., sputum for respiratory, urine for urinary tract).
Example: For meningitis, cerebrospinal fluid is the best specimen.

Methods of Microbial Identification

Microbial identification relies on phenotypic, genotypic, and immunologic methods, each with distinct principles and applications.

Phenotypic Methods: Based on observable traits (morphology, staining, biochemical reactions).
Genotypic Methods: Detect genetic material (DNA/RNA) using molecular techniques.
Immunologic Methods: Use antibodies to detect antigens or immune responses.
Direct Testing vs. Cultivation: Direct testing analyzes specimens without culturing; cultivation involves growing organisms before testing.

Diagnostic Techniques

Various laboratory methods are used to identify and characterize microbes.

Biochemical Testing: Assesses metabolic capabilities (e.g., carbohydrate fermentation, catalase, oxidase tests).
AST (Antimicrobial Susceptibility Testing): Determines sensitivity to antibiotics.
PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences for detection.
PFGE (Pulsed-Field Gel Electrophoresis): Separates large DNA fragments for strain typing.
DNA Sequencing: Determines nucleotide sequence for precise identification.
ELISA (Enzyme-Linked Immunosorbent Assay): Detects antigens or antibodies using enzyme-linked reactions.
Fluorescent Antibody Staining: Uses fluorescent-labeled antibodies to visualize antigens.
Agglutination/Precipitation: Antibody-antigen reactions cause visible clumping or precipitation.
MS (MALDI-TOF): Mass spectrometry identifies proteins for rapid microbial identification.

Biochemical Tests

Biochemical tests are essential for differentiating microbial species.

Carbohydrate Fermentation: Detects acid/gas production from sugar metabolism.
Catalase Test: Identifies catalase enzyme by bubble formation with hydrogen peroxide.
Oxidase Test: Detects cytochrome oxidase enzyme by color change.

Dichotomous Key

A dichotomous key is a tool for systematic identification based on sequential choices.

Function: Guides users through a series of yes/no questions to identify organisms.
Example: "Is the organism Gram-positive?" If yes, proceed to next question; if no, follow alternate path.

Chapter 16: Skin and Eye Infections

Etiologic Agents and Disease Syndromes

Skin and eye infections are caused by diverse pathogens, each with unique characteristics.

Leishmaniasis: Leishmania species; transmitted by sandflies; causes skin ulcers.
Cutaneous Anthrax: Bacillus anthracis; contact with infected animals; black eschar lesion.
Measles: Measles virus; airborne; fever, rash, Koplik spots.
Rubella: Rubella virus; airborne; mild rash, congenital defects.
Chickenpox: Varicella-zoster virus; airborne; vesicular rash.
Smallpox: Variola virus; airborne; pustular rash, eradicated.
Acne: Propionibacterium acnes; skin flora; inflamed follicles.
Impetigo: Staphylococcus aureus, Streptococcus pyogenes; contact; honey-colored crusts.
Abscesses: Often S. aureus; pus-filled lesions.
Necrotizing Fasciitis: S. pyogenes; rapid tissue destruction.
Ringworm/Cutaneous Mycoses: Dermatophytes; contact; ring-shaped lesions.
Warts: Human papillomavirus; contact; benign skin growths.
Conjunctivitis: Bacterial/viral; pink eye.
Keratitis: Herpes simplex virus; corneal inflammation.
Ophthalmia Neonatorum: Neisseria gonorrhoeae, Chlamydia trachomatis; newborns; eye infection.
River Blindness: Onchocerca volvulus; blackfly; vision loss.

Disease	Etiologic Agent	Transmission	Reservoir	Distinguishing Features
Leishmaniasis	Leishmania spp.	Sandfly bite	Wild mammals	Skin ulcers
Cutaneous Anthrax	Bacillus anthracis	Contact	Livestock	Black eschar
Measles	Measles virus	Airborne	Humans	Koplik spots
Impetigo	S. aureus, S. pyogenes	Contact	Humans	Honey-colored crusts
River Blindness	Onchocerca volvulus	Blackfly	Humans	Vision loss
Additional info: Table includes representative diseases; full list in original notes.

Chapter 17: Nervous System Infections

Major Diseases and Their Characteristics

Nervous system infections are caused by bacteria, viruses, fungi, and prions, each with unique transmission and clinical features.

Creutzfeldt-Jakob Disease (CJD): Prion; contaminated instruments; brain tissue; rapid dementia.
Encephalitis (WNV, SLE): West Nile virus, St. Louis encephalitis virus; mosquito-borne; birds; fever, confusion.
Meningitis:
- Neisseria meningitidis: Droplet; humans; rapid onset.
- Streptococcus pneumoniae: Droplet; humans; common in adults.
- Cryptococcus neoformans: Inhalation; pigeons; chronic in immunocompromised.
- Herpes virus: Vertical/latent; humans; rare.
Neonatal Meningitis: Group B Streptococcus; vertical transmission; mothers; newborns.
Zika Syndrome: Zika virus; mosquito; humans; microcephaly in infants.
Listeriosis: Listeria monocytogenes; foodborne; animals; meningitis in neonates/elderly.
Rabies: Rabies virus; animal bite; mammals; long incubation period.
Polio: Poliovirus; fecal-oral; humans; paralysis.
Tetanus: Clostridium tetani; wound; soil; muscle spasms.
Botulism: Clostridium botulinum; foodborne; soil; flaccid paralysis.
Naegleria: Naegleria fowleri; water; environment; fatal meningoencephalitis.

Disease	Agent	Transmission	Reservoir	Syndrome
CJD	Prion	Contaminated tissue	Humans	Rapid dementia
Encephalitis (WNV)	Virus	Mosquito	Birds	Fever, confusion
Meningitis (N. meningitidis)	Bacteria	Droplet	Humans	Rapid onset
Rabies	Virus	Animal bite	Mammals	Long incubation
Polio	Virus	Fecal-oral	Humans	Paralysis
Additional info: Table includes representative diseases; full list in original notes.

Unique Features and Definitions

Rabies Incubation: Unusually long, weeks to months, allows for post-exposure prophylaxis.
Arbovirus: Viruses transmitted by arthropods (e.g., mosquitoes).
Zoonosis: Disease transmitted from animals to humans.
Prion: Infectious protein causing neurodegenerative disease.

Chapter 5: Viruses

General Characteristics of Viruses

Viruses are acellular infectious agents with unique structural and functional properties.

Virion: Complete virus particle.
Capsid: Protein shell enclosing genetic material.
Envelope: Lipid membrane surrounding some viruses.
Cytopathic Effect (CPE): Structural changes in host cells due to viral infection.
Phage: Virus infecting bacteria.
Plaque: Clear area on bacterial lawn due to phage lysis.
Latency: Dormant viral state within host.
Proto/Oncogene: Genes involved in cell growth; can be altered by viruses.
Benign/Malignant: Non-cancerous vs. cancerous growths.
Viroid: Infectious RNA molecule (plants).
Prion: Infectious protein (animals).

Lytic vs. Lysogenic Phage Life Cycles

Lytic Cycle: Virus replicates and lyses host cell.
Lysogenic Cycle: Viral genome integrates into host DNA, replicates with cell.

Steps in Viral Infection and Replication

Attachment
Penetration
Uncoating
Replication
Assembly
Release

Types of RNA Viruses

+ Sense RNA: Acts as mRNA; directly translated.
- Sense RNA: Complementary to mRNA; must be transcribed.
Retroviral RNA: Reverse transcribed to DNA (e.g., HIV).

Growing Animal Viruses

Cell cultures
Embryonated eggs
Live animals

Major Virus Families and Examples

Herpesviridae: HSV2; causes genital herpes.
Picornaviridae: Poliovirus; causes polio.
Orthomyxoviridae: Influenza virus; causes flu.
Retroviridae: HIV; causes AIDS.

Chapter 6: Microbial Growth

Key Terms and Definitions

Binary Fission: Asexual reproduction in bacteria.
Mean Generation Time: Average time for population to double.
Heterotroph: Requires organic carbon.
Autotroph: Uses CO2 as carbon source.
Chemotroph: Energy from chemicals.
Phototroph: Energy from light.
Halophile: Salt-loving organism.
Thermophile: Heat-loving organism.
Mesophile: Moderate temperature.
Psychrophile: Cold-loving organism.
Acidophile: Acid-loving organism.
Alkalophile: Alkaline-loving organism.
Obligate: Requires specific condition.
Facultative: Can adapt to different conditions.
Aerobe: Requires oxygen.
Anaerobe: Grows without oxygen.
Microaerophile: Requires low oxygen.

Essential Nutritional Elements

Carbon
Nitrogen
Phosphorus
Sulfur
Potassium
Magnesium
Calcium
Iron

Transport Mechanisms

Passive Diffusion: Movement down concentration gradient; no energy.
Facilitated Diffusion: Uses carrier proteins; no energy.
Active Transport: Uses energy (ATP); moves against gradient.
Osmosis: Water movement across membrane.
Examples of Active Transport: Sodium-potassium pump, proton pumps.

Microbial Growth Curve

Bacterial populations follow a characteristic growth curve with four stages:

Lag Phase: Adaptation, no growth.
Log Phase: Exponential growth.
Stationary Phase: Growth equals death rate.
Death Phase: Decline in population.

Methods for Enumerating Bacteria

Direct Microscopic Count: Cells counted under microscope.
Plate Counts: Colonies counted after incubation.
Membrane Filtration: Cells trapped on filter, then cultured.
Spectrophotometer (Optical Density): Measures turbidity to estimate cell concentration.

Formula for Exponential Growth

The number of bacteria after n generations:

Where is the initial number of cells, and is the number of generations.