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Questions and Answers
Which surface antigen of S. pyogenes helps in resisting phagocytosis?
What type of toxin produced by S. pyogenes induces fever and a red rash?
What is the primary means of transmission for S. pyogenes infections?
Which of the following describes a typical characteristic of Impetigo caused by S. pyogenes?
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Which enzyme produced by S. pyogenes is responsible for digesting fibrin clots?
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What component in sebum is known for its antimicrobial properties?
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Which bacteria are primarily responsible for normal skin microbiota?
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What type of acne is characterized by few scattered pustules with no inflammation?
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What treatment is commonly prescribed for moderate acne?
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What is the most common resident bacterium of the skin associated with acne?
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What type of skin lesion is considered severe and includes high risk of scarring?
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Which characteristic is typical for Staphylococcus aureus?
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Which agent is known to loosen clogged follicles in the treatment of moderate acne?
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What function does penicillinase serve in Staphylococcus aureus?
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Which toxin produced by Staphylococcus aureus is responsible for inducing systemic organ damage?
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What is a common predisposing factor for Staphylococcus aureus infections?
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Which condition is characterized by an abscess forming inside the bone due to Staphylococcus aureus?
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What type of infection manifests as bubble-like swellings that break and peel away, most commonly in newborns?
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What role does hyaluronidase play in the virulence of Staphylococcus aureus?
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How does food intoxication occur in relation to Staphylococcus aureus?
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Which localized staphylococcal infection is a more severe form characterized by clusters of furuncles?
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What is a characteristic feature of cutaneous anthrax lesions?
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Which of the following is not a virulence factor associated with Bacillus anthracis?
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What type of infection is scarlet fever primarily associated with?
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Which of the following describes a common characteristic of the genus Bacillus?
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What is the role of rapid diagnostic tests in the identification of streptococcal skin infections?
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What is the mortality rate associated with gastrointestinal anthrax?
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Which type of anthrax infection has a mortality rate of 100%?
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What is a common treatment for gas gangrene caused by Clostridium perfringens?
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Which virulence factor of Clostridium perfringens is associated with tissue destruction?
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What is the incubation period for leprosy?
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What type of lesions are characterized as shallow and asymmetrical in leprosy?
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Which method is commonly used for the diagnosis of leprosy?
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Which of the following statements about human papillomavirus (HPV) is true?
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Which treatment method is NOT commonly used for removing warts caused by HPV?
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How is chickenpox primarily transmitted?
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What is the primary prevention method for shingles?
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What is the most effective prevention strategy for leprosy?
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Which of these fungal organisms causes ringworm?
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Study Notes
Skin Defenses
- Sebum, salt from perspiration, and lysozyme fight microbial growth
- Skin has a normal microbiota: gram-positive, salt-tolerant bacteria
- Staphylococci, Micrococci, and Diphtheroids are common skin residents
Acne
- Cutibacterium acnes (formerly known as Propionibacterium acnes) is the most common cause
- It is a gram-positive, aerotolerant-to-anaerobic, nontoxigenic rod
- C. acnes resides in pilosebaceous glands
- Sebum can block channels with skin cells leading to acne
- Mild acne has few scattered pustules, no inflammation, and no scarring
- Treatment for mild acne: topical agents and salicylic acid preparations
- Inflammatory/moderate acne has many pustules, slight inflammation, and can spread beyond the face
- Treatment includes oral accutane (isotretinoin), topical antibiotics, benzoyl peroxide, and visible blue light
- Nodular cystic/severe acne has hard, painful lesions and a high risk of scarring
- Treatment includes isotretinoin and oral antibiotics
Staphylococcus
- S. aureus is a common inhabitant of the skin and mucous membranes
- S. aureus are spherical cells in irregular clusters
- S. aureus are gram-positive, lack spores and flagella, and may have capsules
- S. aureus grow in large, round, golden-yellow colonies on agar
- S. aureus is a facultative anaerobe and can withstand high salt, extreme pH, and high temperatures
- S. aureus produces many virulence factors
Staphylococcus aureus Virulence Factors
- Enzymes: Coagulase, Hyaluronidase, Staphylokinase, Penicillinase
- Toxins: Hemolysins, Leukocidins, Enterotoxin, Exfoliative toxin, Toxic shock syndrome toxin (TSST)
Staphylococcus aureus Epidemiology
- Present in most environments frequented by humans
- Can be isolated from objects or materials that carry infection (fomites)
- Most commonly found in the anterior nares, skin, and nasopharynx
- Predisposition to infection includes poor hygiene, poor nutrition, tissue injury, and immunodeficiency
Staphylococcus Infections
- Localized Infections: Folliculitis, Furuncle, Carbuncle, Impetigo
- Systemic Infections: Osteomyelitis, Bacteremia
Streptococcus pyogenes
- Group A Streptococcus
- Gram-positive, spherical, arranged in chains
- Facultative anaerobe
- Produces hemolysis on blood agar
- Expresses surface antigens including C substance, fimbriae, M protein, and capsule
Streptococcus pyogenes Virulence Factors
- Extracellular Toxins: Streptolysins (cell and tissue injury), Erythrogenic toxin (fever and rash), Superantigens (strong monocyte and lymphocyte stimulants)
- Extracellular Enzymes: Streptokinase (digests fibrin clots), Hyaluronidase (breaks down connective tissue)
Streptococcus pyogenes Epidemiology and Pathogenesis
- Humans are the only reservoir
- Asymptomatic carriers exist
- Transmission: direct contact, droplets, food, and fomites
- Portal of entry: skin and respiratory system
- Children are predominantly affected for cutaneous and throat infections
- Systemic infection and sequelae possible without treatment
Streptococcus Clinical Disease
- Skin Infections: Impetigo and Erysipelas
- Scarlet Fever: Caused by erythrogenic toxin of group A Streptococcus
Bacillus
- Gram-positive rods
- Endospore-forming, motile
- Mostly saprobic
- Aerobic and catalase positive
- Digest complex macromolecules
- Source of antibiotics
- Primary habitat is soil
Medically Important Bacillus Species
- Bacillus anthracis
- Bacillus cereus
Bacillus anthracis
- Large, block-shaped rod
- Produces central spores under extreme conditions
- Virulence factors: polypeptide capsule and exotoxins
- Causative agent of anthrax
Types of Anthrax
- Cutaneous Anthrax: A lesion that begins as a bump, develops into a blister, then an ulcer with a black center
- Gastrointestinal Anthrax: Caused by ingestion of contaminated food, mortality rate of 50%
- Inhalational Anthrax: Caused by inhaling endospores, mortality rate of 100%
Anthrax Control and Treatment
- Anthrax occurs naturally in cattle, sheep, goats, camels, and antelopes
- Cattle are routinely vaccinated
- Vaccines for high-risk occupations and military personnel use toxoids with 6 doses and annual boosters
- Treatment includes ciprofloxacin or doxycycline
Gangrene
- Caused by loss of blood supply to tissue (ischemia) leading to death of tissue (necrosis)
- Clostridium perfringens causes gas gangrene (rapidly progressing gangrene with foul-smelling gas)
Gas Gangrene
- Predisposing factors include surgical incisions, compound fractures, diabetic ulcers, septic abortions, puncture wounds, and gunshot wounds
- Clostridium perfringens is a gram-positive, endospore-forming anaerobic rod that grows in necrotic tissue
Clostridium perfringens Virulence Factors
- Toxins: Alpha toxin (RBC rupture, edema, tissue destruction)
- Enzymes: Collagenase, Hyaluronidase
Clostridium perfringens Pathology
- C. perfringens requires damaged and dead tissue with anaerobic conditions for growth
- C. perfringens spores germinate and release exotoxins and destructive enzymes
- Fermentation of carbohydrates in muscle cells produces gas and further tissue destruction
Treatment and Prevention of Gangrene
- Immediate cleansing of wounds, deep wounds, compound fractures, and infected incisions
- Removal of damaged tissue
- Large doses of cephalosporin or penicillin
- Hyperbaric oxygen therapy
- No vaccines available
Mycobacteria: Acid-Fast Bacilli
- Gram-neutral, irregular bacilli
- Acid-fast staining due to mycolic acids in the cell wall
- Strict aerobe, catalase positive
- Do not form capsules, flagella, or spores
- Slow-growing
Medically Important Mycobacteria Species
- Mycobacterium tuberculosis
- Mycobacterium leprae
Mycobacterium leprae: Leprosy Bacillus
- Strict parasite that feeds from host carbon sources
- Cannot be grown on artificial media or tissue culture
- Slowest growing Mycobacterium species
- Multiplies inside host cells in globi (large packets)
- Causes leprosy (Hansen’s disease), a chronic disease starting on the skin and mucous membranes then progressing to nerves
Epidemiology and Transmission of Leprosy
- Not highly virulent
- Risk factors include poor health and crowded living conditions
- Transmission: droplets
- Infection requires prolonged direct skin-to-skin contact with an infected person (months)
- Rare but still exists today
- Endemic in Asia and Africa
Course of Infection and Disease
- M. leprae lives in nasal membranes and skin
- Macrophages ingest bacilli but M. leprae survives phagocytosis
- Incubation period is 2-5 years
- If untreated, bacilli grow in the skin and then migrate to peripheral nerves
Leprosy Lesions
- Tuberculoid: Asymmetrical, shallow lesions that damage the nerves resulting in loss of pain sensation
- Lepromatous: Deep, nodular lesions causing severe disfigurement of the face and extremities
Leprosy Diagnosis
- Combination of symptomology, microscopic examination of lesions, and patient’s medical history
- Symptoms: numbness in hands and feet, loss of sensitivity, muscle weakness, thickened earlobes, and persistent stuffy nose
- Feather test: detects M. leprae
- Acid-fast bacilli in skin lesions and nasal discharges
Leprosy Treatment and Prevention
- Treatment involves long-term therapy with steroids and antibiotics
- Prevention includes surveillance of high-risk populations and a currently in-development vaccine
Human Papillomavirus (HPV)
- Cause papillomas (warts) - squamous epithelial growth
- Over 100 HPV strains exist
- Transmission: direct contact with lesions or contaminated fomites
- Incubation period is 2 weeks to a year
- Common warts: small, painless, elevated, rough growth on fingers
- Plantar warts: deep, painful warts on the soles of feet
- Genital warts: most common STD in the US, ranges from tiny bumps to cauliflower-like masses
Treatment and Prevention of HPV
- Removal of warts: Cryotherapy, electrodesiccation, and salicylic acid
- Topical drugs: imiquimod and Bleomycin
- Vaccination against HPV strains
Herpes Simplex Virus (HSV)
- Belongs to the Herpesviridae family
- All strains show prolonged latency and cause recurrent infections
- Complications occur in older adults, chemotherapy patients, and immunocompromised individuals
- Common in AIDS patients.
- Source of many diseases: chickenpox, shingles, mononucleosis, cold sores, and genital herpes
- HSV infection is prevalent in the population
Chickenpox
- Caused by varicella-zoster virus (Herpesvirus 3)
- Transmission: respiratory route (droplets) and direct contact with rash
- Pus-filled papules develop on the skin
- Virus may remain dormant in dorsal root ganglia (spinal nerves)
- Prevention: live attenuated vaccine
Shingles
- Caused by reactivation of latent Herpesvirus 3
- Virus is released from peripheral nerves back to the skin
- Rash usually appears on the chest, abdomen, or back but can also develop on the face and genitals
- Postherpetic neuralgia: burning pain on the skin after rash disappears
- Prevention: live attenuated vaccine
- Treatment: acyclovir (antiviral drug) may lessen symptoms
Rubeola (Measles)
- Caused by Measles virus
- Transmission: respiratory route
- Virus lives in the nose and throat
- Macular rash on skin and Koplik's spots in the throat and mouth
- Symptoms last up to 10 days
- Prevention: vaccination
- No treatment, it goes away on its own
Rubella (German Measles)
- Caused by Rubella virus
- Macular rash on skin and fever
- Rash resolves in 5 days
- In pregnant women, Rubella virus can cause congenital rubella syndrome, leading to severe fetal damage
- Prevention: vaccination
- No treatment
Fungal Infections on Skin: Dermatomycosis
- Ringworm: caused by Trichophyton, Microsporum, and Epidermophyton (dermatophytes), which produce enzymes that digest keratin
- Creates a rash on various body parts
Locations of Ringworm Infection
- Tinea corporis: body
- Tinea pedis: athlete's foot
- Tinea capitis: scalp
- Tinea barbae: beard
- Tinea unguium: nails
- Tinea cruris: groin
Dermatomycosis Treatment
- Topical antifungals (e.g., tolnaftate)
Scabies
- Caused by the mite Sarcoptes scabiei
- Mite burrows into skin and lays eggs, causing a rash with intense itching
- Transmission: direct contact with rash or fomites
- Treatment: topical insecticides
Pediculosis
- Caused by lice (head louse)
- Affects scalp and skin
- Lice feed on host blood and lay eggs on hair
- Transmission: direct contact or sharing belongings
- Treatment: topical insecticides
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Description
Explore the mechanisms of skin defenses against microbial growth and the common causes of acne. This quiz covers the role of different bacteria, the types of acne, their characteristics, and treatment options. Discover effective strategies for managing acne at various severity levels.
