Biomed 3

Eukaryotes (examples)

Fungi, protozoa, and helminths.

Eukaryote features

True nucleus, mitosis, organelles, and a semi-permeable membrane.

Viruses

Noncellular agents containing DNA or RNA that rely on host cells for replication.

Bacteria

DNA in cytoplasm (no nuclear membrane), binary fission replication, rigid peptidoglycan cell wall.

Bacterial cell wall

External to membrane, made of peptidoglycan, and rigid.

Gram-positive cell wall

Thick, alternating layers of NAG and NAM, crossed by peptide bridges; contains teichoic acid.

Gram-negative cell wall

Thin peptidoglycan, contains lipopolysaccharides (LPS/endotoxins), and has an outer membrane envelope.

Gram stain colors

Gram-positive = purple; Gram-negative = pink.

Crystal Violet

First step in Gram stain; dyes cells purple.

Iodine

Second step in Gram stain; acts as a mordant.

Alcohol (Gram stain)

Organic solvent step; washes out crystal violet from Gram-negative cells.

Safranin

Last step in Gram stain; counterstains Gram-negative cells pink.

Cytoplasmic membrane (bacteria)

Inside peptidoglycan wall, phospholipid bilayer containing various proteins.

Cytoplasm (bacteria)

Amorphous matrix containing 70S ribosomes (50S and 30S subunits) and plasmids.

Plasmids

Extrachromosomal DNA replicating independently; carry traits like resistance and exotoxins.

Inner nucleoid region

Bacterial region containing DNA, usually a single, circular DNA molecule.

Flagella

Long, whip-like structures made of flagellin; propel bacteria via chemotaxis.

Pili

Hairlike structures made of pilin used for attachment; found in Gram-negatives.

Bacterial spores

Metabolically inactive structures with thick keratin coats formed during nutrient depletion.

Normal flora

Organisms living symbiotically with humans (the microbiome).

Skin commensals

Staph and diphtheroids.

Oropharynx normal flora

Strep and anaerobes.

Large intestine normal flora

Enterococci and enteric bacilli.

Vagina normal flora

Lactobacilli.

Colonization

Presence of bacteria on a surface without causing disease; not an infection.

Pathogenicity

The potential to cause disease ("can it start a fire").

Virulence

Characteristics that enhance pathogenicity ("how big is the fire").

Infection

Presence of bacteria in the body, with or without disease.

Disease

Symptomatic and contagious state caused by a pathogen.

Carrier states

Microbe is present and transmissible, but host is asymptomatic.

Infectious dose

Number of organisms required to cause infection.

How bacteria cause disease

Via toxins (exotoxins/endotoxins) and invasion/inflammation.

Toxins (bacterial)

Exotoxins (secreted proteins) and endotoxins (LPS); cause systemic effects.

Invasion and inflammation

Bacteria grow locally, causing local tissue inflammation.

Communicable infection

Contagious; easily spreads from person to person.

Noncommunicable infection

Not easily transmissible between hosts.

Endemic

Present constantly at a low level (e.g., malaria in Africa).

Epidemic

Frequency of disease greater than expected in a region (e.g., measles in Texas).

Pandemic

An epidemic spreading across multiple countries.

Subclinical infection

Infection is present, but causes no symptoms (e.g., hepatitis).

Latent infection

Dormant infection that can reactivate later (e.g., tuberculosis).

Incubation period

Time between acquiring the organism and symptom onset.

Prodrome period

Phase of nonspecific symptoms, such as fever and malaise.

Specific disease period

Phase showing characteristic, diagnostic symptoms of the disease.

Recovery (convalescence)

Return to baseline health; immune system protects against future infection.

Staphylococcus

Grape-like clusters, gram +

S. aureus

Most common cause of serious disease, produces coagulase, humans are reservoirs; pyogenic or toxigenic.

MRSA treatment

Vancomycin

S. epidermis

Infection when artificial materials (valves) are present; almost always acquired in hospital.

S. saprophyticus

Genital tract

Staph lab diagnosis

Coagulase test (+ for catalase)

Streptococcus spp.

Chains or pairs, gram +, classified by hemolysis on blood agar.

Alpha hemolytic

Incomplete lysis, turns green; includes S. pneumoniae and viridans.

Beta hemolytic

Complete lysis, clear zone; includes group A and B.

Gamma hemolytic

Non-hemolytic, no change; includes Enterococcus and group D.

S. pyogenes

Group A, bacitracin sensitive; causes pharyngitis, Scarlet fever, necrotizing fasciitis, rheumatic fever.

S. agalactiae

Group B, bacitracin resistant, female genital tract; vertical transmission causes neonatal sepsis.

S. pneumoniae

Lancet-shaped cocci in pairs; causes pneumonia and otitis media.

Neisseria meningitidis

Droplet transmission, spreads to meninges, causes meningococcemia with purpuric lesions; gram - cocci.

Neisseria gonorrhoeae

Sexually transmitted, adheres via pili, milky discharge, can lead to PID; diagnosed with NAAT.

Bacillus anthracis

Gram + rods with square ends, large chains, soil-dwelling; edema/lethal factors, wool sorters disease, spores.

Bacillus cereus

Spores on reheated rice; causes food poisoning with short (4 hr) or long (18 hr) incubation.

Clostridium tetani

Spores in soil; causes spastic paralysis, lockjaw, back arching, and shows tennis racket spores.

Clostridium botulinum

Spores in soil/honey; blocks ACh causing descending weakness; risk in infants under 1.

Clostridium perfringens

Spores in soil; causes gas gangrene (necrosis, crepitus); large gram-positive rods.

Clostridioides difficile

Spore forming; clindamycin wipes out flora causing pseudomembranous colitis; diagnosed by ELISA.

Corynebacterium diphtheriae

Club-shaped gram + rods; causes pseudomembrane over tonsils or throat; droplet transmission.

Listeria monocytogenes

Small gram + rods in V/L shape; transmitted via placenta, delivery, or unpasteurized milk.

Gardnerella vaginalis

Bacterial vaginosis; gram variable, replaces lactobacilli, white/grey discharge, clue cells, pH >4.5.

Escherichia coli

Gram - rods; ferments lactose; causes UTI, meningitis, traveler's diarrhea, and HUS (O157:H7).

Salmonella

Non-lactose fermenting; typhoidal and nontyphoidal species; transmitted by poultry, reptiles, or humans.

Non-typhoidal salmonella

Causes enterocolitis, bacteremia, and osteomyelitis.

Typhoidal salmonella

Invades Peyer's patches, liver, gallbladder, and spleen; causes typhoid fever (rose spots).

Shigella

Non-lactose fermenting gram -; fecal-oral; causes local inflammation, ulceration, and bloody mucus diarrhea.

Vibrio cholerae

Curved, comma-shaped gram - rods; cholera toxin causes voluminous rice water stool.

Campylobacter jejuni

S-shaped, microaerophilic gram - rods; causes bloody diarrhea and Guillain-Barré syndrome.

Helicobacter pylori

Curved gram - rods; urease positive; attaches to gastric mucosa causing gastritis/peptic ulcers.

Klebsiella pneumoniae

Large capsule, mucoid; ferments lactose; causes UTI and pneumonia with currant jelly sputum.

Serratia marcescens

Healthcare-associated UTI/pneumonia; forms biofilms; produces red pigment (prodigiosin) at room temperature.

Proteus mirabilis

Highly motile, swarming gram - rod; urease positive; causes alkaline urine and struvite stones.

Pseudomonas aeruginosa

Strict aerobe; causes burn infections (blue/green pus); produces pyocyanin and pyoverdine.

Providencia spp.

Gram - rods; peritrichous flagella; forms biofilms; causes catheter-associated UTIs.

Morganella morganii

Gram - rod; peritrichous flagella; urease producer; causes catheter-associated UTIs.

Bordetella pertussis

Encapsulated gram - coccobacillus; pertussis toxin damages cilia; causes whooping cough.

Bartonella henselae

Gram - rod; cat scratch fever; infects endothelial cells/macrophages; granulomatous lymphadenopathy.

Legionella

Intracellular gram - rod; environmental water (AC); causes Legionnaire disease (atypical pneumonia, hyponatremia) and Pontiac fever.

Mycoplasma pneumoniae

No cell wall; transmitted via droplets; causes atypical pneumonia in ages 5-15.

Chlamydia pneumoniae

Obligate intracellular; elementary body enters, reticulate body replicates; causes walking pneumonia.

Chlamydia trachomatis

Obligate intracellular; sexually transmitted; causes urethritis, cervicitis, epididymitis, trachoma; diagnosed with NAAT.

Chlamydia psittaci

Obligate intracellular; transmitted via bird droppings; causes atypical pneumonia.

Chlamydia treatment

Doxycycline.

Treponema pallidum

Spirochete with corkscrew motility; sexually/transplacentally transmitted; causes syphilis (diagnosed by RPR).

Syphilis stages

Primary: painless chancre. Secondary: rash on palms/soles. Tertiary: Gummas, neurosyphilis.

Rickettsia rickettsii

Obligate intracellular; tick-borne; causes Rocky Mountain spotted fever (rash on wrists/ankles moving to trunk).

Borrelia burgdorferi

Spirochete; transmitted by deer tick (Ixodes); causes Lyme disease with erythema migrans.

Mycobacterium tuberculosis

Acid-fast bacillus; survives in macrophages; causes lung granuloma and hemoptysis.

Viruses (general characteristics)

Acellular, obligate intracellular parasites; cannot make own proteins/energy or be seen under light microscope.

Components of all viruses

Inner core (DNA or RNA) covered by a capsid.

Components of some viruses

Envelope (makes them fragile), surface spikes, and matrix protein.

Virus shapes

Precise geometric symmetry, determined by repeating subunits.