CL

Microbio Lecture 4

Gram Positive Cocci

  • Size: 10 µm

Staphylococcus aureus

  • Name Origin: "Staphule" means grape in Greek.

  • Exotoxins produced by staph aureus (a single one wont produce all):

    • Cytotoxins

    • Hemolysins

    • Enterotoxins (A-E, G-I)

      • an exotoxin that binds or affects the intestinal tract.

    • Exfoliative toxins (ETA, ETB)

    • Toxic shock syndrome toxin 1

Enzymes

  • Coagulase

    • Causes coagulation of fibrin.

    • Found in almost all pathogenic staphylococci.

    • Used in lab tests to differentiate from S. epidermidis, S. capitis, and S. saprophyticus.

  • Beta-lactamase (penicillinase)

    • Destroys penicillin.

Epidemiology and Infection

  • Carried in ~15% of the normal population.

  • Common carriage sites: anterior nares, axilla, perineum, and hands.

  • Problems:

    • 85-90% of hospital strains are penicillin resistant.

    • Causes localized purulent infections (pustules, boils, styes, conjunctivitis, otitis, etc.).

    • Associated with pneumonia, osteomyelitis, septicaemia, endocarditis, food poisoning, toxic shock syndrome, and scalded skin syndrome.

    • Impetigo is caused by sta3ph aureus

Nosocomial Infections

  • Major cause of hospital-acquired infections from stitch abscesses, infected wounds.

  • Prevention:

    • Aseptic technique in ER and OR.

    • Education of health personnel.

    • Handwashing.

Staphylococcus epidermidis

  • Part of normal skin/mucous membrane flora.

  • Generally non-pathogenic; can cause infections in compromised patients, including:

    • Post-operative infections (brain, open heart, endocarditis, shunt infections).

  • Opportunistic pathogen.

Streptococci

  • Arranged in pairs or chains; "streptos" means twisted in Greek.

  • Subdivided into groups based on:

    • Hemolytic properties (alpha, beta).

    • Carbohydrate C antigen (Lancefield classification).

    • M-protein classification.

    • gamma hemolytic: do nothing to red blood cells

    • beta-hemolytic: completely destroy red blodd cells, leading to a clear zone around the colony on blood agar.

    • alpha-hemolytic: partially lyse red blood cells, resulting in a greenish discoloration around the colony on blood agar.

Streptococcus pyogenes

  • Group A, beta-hemolytic.

  • Causes:

    • Acute tonsillitis (strep throat), potentially leading to rheumatic heart disease.

    • Skin infections (impetigo, cellulitis).

    • Fever and septicemia.

Toxins

  • Streptolysins (O and S) that affect neutrophils and macrophages.

  • Streptococcal pyrogenic exotoxins (SPEs) involved in scarlet fever rash.

Enzymes

  • Hyaluronidase aids in bacterial spreading.

  • Virtually all strains are penicillin G sensitive.

  • Prevention:

    • Education of health personnel.

    • Aseptic obstetric procedures.

    • Early detection and treatment.

Flesh-eating disease (Necrotizing fasciitis)

  • Caused by Streptococcus pyogenes.

  • Mechanism:

    • Toxins hijack plasminogen, activate proteases to aid spreading.

    • Bacteriophage enables escape from neutrophil attacks.

Streptococcus agalactiae

  • Group B, commonly found in the vagina of healthy women.

  • Can cause neonatal infections:

    • Early septicemia (respiratory distress/shock at birth) with high fatality rates.

    • Delayed meningitic form (1-12 weeks post-partum).

Streptococcus faecalis (Enterococcus)

  • Group D, part of normal GI-tract flora.

  • Opportunistic infections in compromised individuals.

Viridens streptococci

  • Found in the oral cavity.

  • Can cause endocarditis in patients with damaged heart valves.

Streptococcus pneumoniae

  • Known as pneumococcus.

  • Features:

    • Polysaccharide capsule has antiphagocytic properties (90 distinct serotypes).

    • Found in the naso-pharynx of healthy individuals.

  • Can cause:

    • Lobar pneumonia

    • Meningitis

  • Prevention strategies:

    • Target groups include the elderly, alcoholics, and those in crowded living conditions.

    • Vaccination is recommended.

Neisseria meningitidis

  • Gram-negative diplococci.

  • Laboratory isolation:

    • Grown on chocolate agar at 5-10% CO2, 37°C.

    • Selective media (Thayer-Martin) when isolating from the nasopharynx.

  • Frequently found in healthy individuals.

  • Antiphagocytic polysaccharide capsule with 13 serogroups (A, B, C, X, Y, W135 most prevalent).

Transmission and Infection

  • Carriers can develop infection or spread to non-immune individuals.

  • Infects only humans; commonly in children or those in crowded settings.

  • Results in:

    • Meningitis

    • Septicemia

    • Waterhouse-Friderichsen syndrome (severe septicemia complication).

Meningitis Symptoms in Infants

  • Signs include:

    • Bulging soft spot, high temperature, extreme sleepiness, vomiting, irritability.

    • Fast breathing, changing skin color.

  • Recognize purple bruises or rash as urgent signs.

Historical Background

  • First described by Arthur Francis Voelcker in 1894.

  • Comprehensive review by Carl Friderichsen in 1918 led to the syndrome's naming.

Prevention and Treatment of Meningitis

  • Primary treatment involves penicillin.

  • Vaccination recommended for specific age groups (11-12 years, college students).

    • Conjugated vaccine for serogroups A, C, Y, and W135.

    • Vaccine for infants against serogroup C.

Neisseria gonorrhoeae

  • Gram-negative diplococci (0.6-1 µm).

  • Grown on Thayer-Martin plates in CO2.

  • Second highest reported STD in the US after chlamydia (~350,000 cases/year).

Clinical Manifestations

  • MEN:

    • Acute urethritis (90-95% cases).

  • WOMEN:

    • 50% are asymptomatic; cervicitis.

    • Potential complications include PID (pelvic inflammatory disease) and sterility.

  • Neonatal infections can lead to gonococcal ophthalmia neonatorum (conjunctivitis).

Spread and Diagnosis

  • Can enter bloodstream leading to disseminated infections (meningitis, endocarditis).

  • Diagnosis:

    • MEN: microscopy of urethral discharge.

    • WOMEN: culture from endocervical and anal swabs.

Treatment and Resistance

  • Increasing penicillin resistance in certain regions.

  • Recommend ceftriaxone, cefixime, and combined treatments.

  • Simultaneous treatment of partners is essential; no vaccine available.