unit3.2

Staphylococcus aureus

Disease: Skin and soft tissue infection (SSTI) , acne, boils, bacteremia/septicemia. Transmission: Direct skin-to-skin contact. Virulence Factors: Produces coagulase (forms a fibrin capsule to wall off infection) , hemolysins , leukocidins , and some strains produce superantigens (like Toxic Shock Syndrome Toxin). Facts: Is Gram-positive and grows in grape-like clusters. Methicillin-Resistant S. aureus (MRSA) is a major threat.

Neisseria gonorrhoeae (Gonorrhea)

Disease: Gonorrhea, Pelvic Inflammatory Disease (PID) in women. Transmission: Sexual transmission. Virulence Factors: Antigenic variation, high mutation rates of major antigens, and horizontal gene transfer aid in evading host immunity. Facts: Gram-negative diplococcus. Can be asymptomatic in women. Antibiotic resistance is an urgent threat.

Treponema pallidum (Syphilis)

Disease: Syphilis (complex disease with three stages). Transmission: Sexual transmission ; entry through breaks in the epithelium. Virulence Factors: N/A (Focus is on its complex disease stages). Facts: A spirochete bacterium. Stages are: 1. Primary (Chancre). 2. Secondary/Disseminated (Rash). 3. Tertiary (Gumma, nervous system lesions, blindness). Readily treated with antibiotics.

Streptococcus pyogenes (Group A Strep, GAS)

Disease: Streptococcal pharyngitis (strep throat). Sequelae (Secondary Diseases): Scarlet fever , Rheumatic fever (autoimmune disease attacking heart/joints) , Necrotizing fasciitis. Transmission: Airborne/aerosols. Virulence Factors: M protein (acts as a superantigen in invasive infections) , Exotoxins (erythrogenic/pyrogenic toxins causing scarlet fever rash) , Hyaluronic capsule , and hemolysins (β-hemolysis). Facts: Gram-positive cocci, usually grow in long chains. Untreated strep throat can lead to sequelae.

Streptococcus pneumoniae

Disease: Main cause of community acquired pneumonia and meningitis. Transmission: Airborne; normally found in the nose and throat of healthy individuals. Virulence Factors: Polysaccharide capsule (vaccination targets this) , and the toxin pneumolysin (a hemolysin). Facts: Lacks the Lancefield antigen. Can cause multiple diseases by infecting different sites.

Bordetella pertussis (Pertussis/Whooping Cough)

Disease: Pertussis (Whooping cough). Transmission: Airborne. Virulence Factors: Pertussis toxin (AB toxin, kills host cells) , Filamentous Hemagglutinin (FHA) (adhesion) , Pertactin (adhesion) , and fimbriae (adhesion). Facts: Prevented by the Diphtheria, Tetanus, Pertussis combined vaccine (DTP); the current vaccine contains 5 antigens. Post-exposure prophylaxis with antibiotics is recommended.

Mycobacterium tuberculosis (TB)

Disease: Tuberculosis (TB). Transmission: Airborne. Virulence Factors: Its unique cell wall (high lipid content, diagnosed by acid-fast stain) and its ability to live as an intracellular parasite inside macrophage cells. Facts: Bacteria are phagocytosed by macrophages. Forms tubercles (granulomas) in the lungs from a hypersensitivity immune response. Often leads to Latent TB (containment). Antibiotic Resistant Forms: Multidrug resistant (MDR-TB) and Extensively Drug Resistant (XDR-TB).

Salmonella enterica

Disease: Salmonellosis, commonly enterocolitis. Transmission: Foodborne infection. Found in the digestive tracts of humans/animals. Virulence Factors: Combination of enterotoxins and endotoxin (LPS) cause damage and kill host cells. Facts: Subspecies are divided into many serotypes which are usually named according to the location of an outbreak (e.g., S. enterica serotype Saintpaul).

Shiga Toxin-Producing E. coli (STEC)

Disease: Bloody diarrhea; rarely, kidney failure. Transmission: Foodborne infection (e.g., contaminated ground beef, leafy greens). Virulence Factors: Produces the Shiga toxin (an AB toxin). Mechanism: Shiga toxin inhibits protein translation in host cells. Facts: The most common STEC serotype is E.coli O157:H7. Serotyped using the O antigen (LPS) and H antigen (flagella protein).

Vibrio cholerae (Cholera)

Disease: Cholera (severe diarrhea). Transmission: Waterborne (fecal-contaminated water). Virulence Factors: Produces the Cholera Toxin (an AB enterotoxin). Mechanism: The A subunit stimulates cAMP formation, blocking Na+ movement and causing net Cl− movement to the intestinal lumen. This results in massive water loss by osmosis. Facts: Mortality up to 50% unless fluid/electrolyte replacement is used.

Legionella pneumophila (Legionnaires')

Disease: Legionnaires' disease (pneumonia-like symptoms). Transmission: Waterborne; spread by aerosols (breathing mist) from contaminated hot water tanks, hot tubs, and cooling towers. Facts: A Gram-negative bacterium found in fresh water. Not spread person-to-person. It is an intracellular pathogen, living inside amoebas and APCs.

Rickettsia rickettsii

Disease: Rocky Mountain Spotted Fever. Transmission: Vector-borne (via a tick bite). Virulence Factors: Obligate intracellular parasite. Mechanism: Direct injection into the bloodstream allows for rapid simultaneous dispersal to many organs (lungs, heart, kidneys). Facts: Zoonotic disease; humans are accidental hosts.

Borrelia burgdorferi

Disease: Lyme disease (has three stages). Transmission: Vector-borne (via the deer tick bite). Virulence Factors: N/A (Focus is on its three disease stages). Facts: A spirochete bacterium. Stages include: 1. Expanding red ring rash. 2. Neurological/heart problems. 3. Demyelination of neurons years later.

Yersinia pestis (Plague)

Disease: Plague (Bubonic, Pneumonic, Septicemic). Transmission: Vector-borne (via flea bite from a wild rodent reservoir). Pneumonic plague is airborne (human-to-human). Virulence Factors: N/A. Facts: Natural disease of rodents; rats are the main reservoir. Bubonic (lymph nodes) , Pneumonic (lungs) , and Septicemic (bloodstream) are the three forms.

Clostridium tetani (Tetanus)

Disease: Tetanus (spastic paralysis). Transmission: Spore-former living in soil reservoir. Infection begins in the anoxic conditions of deep puncture wounds. Virulence Factors: Produces Tetanus Toxin (an AB toxin). Mechanism: Toxin binds to inhibitory interneurons, preventing the release of neurotransmitters, causing muscles to be constantly stimulated. Facts: Preventable using a toxoid vaccine.

Human Papilloma Virus (HPV)

Disease: Warts (abnormal growth of epithelial cells) , almost all cervical cancers. Transmission: Close contact, usually needs an abrasion. Virulence Factors: Early proteins E6 (degrades p53) and E7 (binds Rb) cause cell proliferation. Facts: Naked dsDNA virus. Infects basal epithelial cells. Prevented by vaccination and condoms.

Influenza Virus

Disease: Influenza (flu). Transmission: Highly contagious; spread by aerosols (coughing). Virulence Factors: Hemagglutinin (HA) (for attachment) , Neuraminidase (NA) (for release). Facts: Segmented ss (−) RNA genome. Subject to Antigenic Shift (reassortment in animals like pigs) and Antigenic Drift (random mutation). New vaccines required yearly.

Human Immunodeficiency Virus (HIV)

Disease: HIV infection/AIDS. Transmission: Sexual contact, blood/fluids. Virulence Factors: gp120 (binds CD4 to initiate entry). Facts: Retrovirus with an enveloped ss (+) RNA genome. Carries Reverse Transcriptase. Integrates into the host genome, leading to latency (no virion production). Infects CD4+T cells, macrophages, and dendritic cells, causing immune deficiency.

SARS-CoV-2 (Coronavirus)

Disease: COVID-19. Transmission: Airborne/aerosols. Virulence Factors: Spike glycoprotein (S) binds the ACE2 receptor on target cells. Mutations in S (e.g., N501Y) led to increased infectivity and pandemic initiation. Facts: Enveloped ss (+) RNA genome. Virion RNA is directly translated. Replication involves RNA-dependent RNA pol. Virion assembly occurs in the ER, and the envelope is derived from the ER.