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.