Study guide Ch 19 skin and wounds microbial diseases
Chapter 19: Microbial Disease of Skin and Wounds
1. Skin Inhospitality to Microbes
Inhospitable Environment:
High salt concentration from sweat evaporation.
Sebum (oily lipid from sebaceous glands) has antimicrobial properties.
Antimicrobial chemicals in sweat and sebum inhibit microorganism growth.
The epidermis consists of dry, dead, keratinized cells covered in salt and oil that prevent microbial invasion.
Skin sloughs off attached microbes.
Normal Skin Microbiota:
Competes with potential pathogens for nutrients and space.
Can survive in harsh conditions created by skin environment.
2. Dendritic Cells in Epidermis
Function to phagocytize microbes.
Deliver microbial antigens to lymphocytes, facilitating immune response.
3. Normal Microbiota of Skin
Lipophilic Yeast:
Malassezia: Digest sebum, rarely pathogenic, may cause Malassezia rashes.
Aerobic Gram-Positive Bacteria:
Genera: Staphylococcus, Micrococcus, tolerating 5-10% salt.
Example: Staphylococcus epidermidis: competes and secretes enzymes that inhibit pathogenic growth.
Diphtheroids:
Pleomorphic gram-positive bacteria such as Propionibacterium acnes which causes acne and lowers skin pH via propionic acid production.
4. Skin Infecting Bacteria
Notable pathogens: Staphylococcus, Streptococcus, Propionibacterium, Bartonella, Pseudomonas, Rickettsia.
5. Buruli Ulcer
Pathogen: Mycobacterium ulcerans.
Toxin: Mycolactone - destroys fat & muscle cells.
Transmission: Through insect bites (water bugs/beetles) that carry the pathogen.
Symptoms: Starts as painless nodule, followed by swelling, pain, and foul-smelling fluid.
Treatment:
Debridement, skin grafts, and antibiotics (Rifampicin & Streptomycin).
6. Staphylococcal Skin Infections
Types of Infections: Pimples, boils (furuncles), carbuncles, sty.
Folliculitis: Inflammation of hair follicle, becomes pus-filled (often a pimple).
Furuncles: Larger, painful nodular swellings from folliculitis.
Carbuncles: Multiple furuncles with combined inflammation and pus.
Caused primarily by Staphylococcus species, which are salt-tolerant and facultative anaerobes.
7. Common Species of Staphylococci
Staphylococcus epidermidis: Normal microbiota; opportunistic infections but lacks virulence factors.
Staphylococcus aureus: Transient pathogen with virulence factors including enzymes (e.g., coagulase, lipases), and toxins (e.g., cytolytic toxins).
8. Staphylococcal Scalded Skin Syndrome (SSSS)
Symptoms: Redness, blistering starting near the mouth and spreading.
Causative Agent: Some strains of Staphylococcus aureus producing exfoliative toxins.
Diagnosis: Characteristic skin sloughing, no organism culture.
Treatment: Intravenous antimicrobial drugs like cloxacillin.
9. Impetigo and Erysipelas
Impetigo: Characterized by honey-colored crusted lesions, primarily caused by S. aureus and Streptococcus pyogenes.
Features: Pus-filled vesicles on red bases.
Erysipelas: Spreads to lymph nodes causing intense pain and inflammation.
Symptoms: Distinct red areas with clear margins and swollen lymph nodes.
10. Necrotizing Fasciitis
Causes: Primarily by Streptococcus pyogenes, can involve Staphylococcus aureus and Clostridium.
Symptoms: Intense pain, rapidly spreading redness and swelling; skin becomes distended.
Treatment: Surgical removal of dead tissue and intravenous antibiotics (clindamycin, penicillin).
11. Acne
Causative Agent: Propionibacterium acnes, causing inflammation due to excessive oil production.
Treatment: Antimicrobials (e.g., Benzoyl peroxide), retinoids (e.g., Accutane).
Diagnosis: Visual examination of skin.
12. Cat Scratch Disease
Causative Agent: Bartonella henselae.
Symptoms: Fever, malaise, and lymphadenopathy at the scratch site.
Diagnosis: Serological testing; treatment involves antimicrobials.
13. Pseudomonas Infections
Pathogen: Pseudomonas aeruginosa, an opportunistic pathogen.
Characteristics: Produces blue-green pigment; virulence factors include fimbriae, exotoxins, and biofilms.
Disease Association: Common in burn victims, otitis externa (swimmer's ear).
14. RMSF (Rocky Mountain Spotted Fever)
Causative Agent: Rickettsia rickettsii.
Vector: Infected ticks (Dermacentor species).
Symptoms: Rash, fever, and cardiovascular issues due to damage to blood vessels.
Diagnosis: Serological testing; treatment involves doxycycline.
15. Cutaneous Anthrax
Causative Agent: Bacillus anthracis.
Symptoms: Painless ulcerated lesion (eschar) at wound site.
Treatment: Ciprofloxacin; vaccination for high-risk individuals.
16. Gas Gangrene
Causative Agents: Various Clostridium species, primarily C. perfringens.
Symptoms: Necrosis of tissues, gas production, intense pain.
Treatment: Wound debridement and antibiotics.
17. Smallpox
Causative Agent: Variola virus.
Diagnosis: Unique pox lesions, characterized progression through macules, papules, and pustules.
Prevention: Vaccination.
18. Herpes Infections
Causative Agents: Human herpesviruses 1 and 2, causing lesions on skin and mucous membranes.
Symptoms: Painful skin lesions, recurrent occurrences due to virus latency.
19. Warts
Causative Agent: Papillomavirus causing benign epithelial growths.
Treatment: Various removal techniques available (laser, freezing).
20. Chicken Pox and Shingles
Causative Agent: Varicella-zoster virus (VZV).
Symptoms: Rash progresses through distinct stages; shingles reactivates from latent virus with painful rash.
21. Measles
Causative Agent: Measles virus (single-stranded RNA).
Symptoms: Flu-like symptoms followed by rash, Koplik's spots in the mouth.
22. Rubella
Causative Agent: Rubella virus (single-stranded RNA).
Symptoms: Mild rash; congenital infections can cause severe birth defects.
Prevention: Vaccination.
23. Fungal Infections
Causes: Cutaneous mycoses caused by dermatophytes.
Symptoms: Ringworm, athlete's foot, jock itch.
Treatment: Topical antifungals.
24. Leishmaniasis (Kala-azar)
Pathogen: Leishmania (protozoan parasite).
Vector: Female sandfly.
Forms: Cutaneous, mucocutaneous, and visceral leishmaniasis.
25. Scabies
Causative Agent: Sarcoptes scabiei (itch mite).
Symptoms: Intense nocturnal itching, rash localized to burrowing areas.
Treatment: Miticidal lotions and cleaning contaminated items.
26. Emerging Diseases and Case Studies
Buruli Ulcer and other case studies highlighting the virulence factors, infections, and potential treatments.
Chapter 19: Microbial Disease of Skin and Wounds
1. Skin Inhospitality to Microbes
Inhospitable Environment:
The skin provides a high salt concentration due to the evaporation of sweat, limiting the growth of many microorganisms.
Sebum, an oily lipid produced by sebaceous glands, possesses intrinsic antimicrobial properties that act against various pathogens.
Additionally, sweat contains antimicrobial chemicals, such as dermcidin, that inhibit the proliferation of microorganisms on the skin's surface.
The epidermis is composed of dry, dead, keratinized cells that are continually sloughed off, which helps remove attached microbes and prevents invasion.
Normal Skin Microbiota:
The normal microbiota of the skin plays a crucial role in competing with potential pathogens for nutrients and space, thereby lowering the risk of infections.
This microbiota has evolved to survive in the harsh conditions created by skin characteristics, such as low moisture availability and varying pH levels.
2. Dendritic Cells in Epidermis
Dendritic cells serve an essential role in the skin by phagocytizing invading microbes.
After ingestion, they deliver microbial antigens to lymphocytes (a type of white blood cell), facilitating an adaptive immune response and promoting defense against subsequent infections.
3. Normal Microbiota of Skin
Lipophilic Yeast:
Malassezia: These yeasts are known to digest sebum, rendering them relatively non-pathogenic under normal circumstances; however, they can cause Malassezia rashes, particularly in immunocompromised individuals or during certain stress conditions.
Aerobic Gram-Positive Bacteria:
Genera: Staphylococcus and Micrococcus, both of which can tolerate high salt concentrations of 5-10%.
Example: Staphylococcus epidermidis is part of the skin's normal flora and helps inhibit the growth of pathogenic organisms by competing for resources and secreting inhibitory enzymes.
Diphtheroids:
These are pleomorphic gram-positive bacilli, such as Propionibacterium acnes, contributing to acne development by metabolizing skin oils and producing propionic acid, which lowers skin pH, thereby inhibiting the growth of transient pathogens.
4. Skin Infecting Bacteria
Key pathogens include Staphylococcus, Streptococcus species, Propionibacterium, Bartonella, Pseudomonas, and Rickettsia, all of which can cause a range of infections depending on their characteristics and the body’s immune status.
5. Buruli Ulcer
Pathogen: Mycobacterium ulcerans.
Toxin: Mycolactone is the primary toxin produced, leading to the destruction of fat and muscle cells.
Transmission: The pathogen is primarily transmitted through insect bites from water bugs or beetles that are vectors for the bacterium.
Symptoms: This disease often begins as a painless nodule that progresses to swelling, pain, and the discharge of foul-smelling fluid, which can lead to significant disfigurement if untreated.
Treatment: Standard treatment includes surgical debridement of necrotic tissue, skin grafts, and antibiotic therapy with Rifampicin combined with Streptomycin.
6. Staphylococcal Skin Infections
Types of Infections: These include different forms such as pimples, boils (furuncles), carbuncles, and sty.
Folliculitis: Represents inflammation of hair follicles, typically leading to pus accumulation and localized discomfort.
Furuncles: Develop from folliculitis as larger, painful swellings filled with pus.
Carbuncles: Form when multiple furuncles coalesce, leading to extensive inflammation and pus accumulation.
These infections are primarily caused by various Staphylococcus species, notable for their salt tolerance and ability to thrive as facultative anaerobes.
7. Common Species of Staphylococci
Staphylococcus epidermidis: A component of normal skin flora but can lead to opportunistic infections, particularly in immunocompromised patients due to its lack of virulence factors.
Staphylococcus aureus: Identified as a transient pathogen characterized by notable virulence factors, including enzymes like coagulase and lipases, as well as toxins including cytolytic toxins that exacerbate disease severity.
8. Staphylococcal Scalded Skin Syndrome (SSSS)
Symptoms: The disease manifests with redness and blistering, typically initiating near facial regions (like the mouth) and spreading throughout the body.
Causative Agent: Certain strains of Staphylococcus aureus produce exfoliative toxins, resulting in severe skin sloughing.
Diagnosis: The clinical presentation is highly characteristic, and traditional culture of the organism may not be required due to the evident symptoms.
Treatment: Administration of intravenous antimicrobial agents such as cloxacillin is common to counteract the infectious strain.
9. Impetigo and Erysipelas
Impetigo: Notably characterized by honey-colored, crusted lesions that arise from the infection of the skin, primarily caused by Staphylococcus aureus or Streptococcus pyogenes.
Features: The skin lesions typically present as pus-filled vesicles atop red bases, representing an infection that is common in children.
Erysipelas: An infection that can spread to lymph nodes, resulting in intense pain and marked inflammation.
Symptoms: Patients often exhibit distinct red areas with clear, demarcated margins and associated swollen lymph nodes, indicating extensive infection.
10. Necrotizing Fasciitis
Causes: Primarily instigated by Streptococcus pyogenes, though it can involve Staphylococcus aureus and Clostridium species.
Symptoms: Characterized by intense pain, rapid spreading redness and swelling, and the appearance of skin becoming distended and discolored.
Treatment: Urgent surgical intervention is necessary to remove necrotic tissue along with intravenous antibiotic therapy, commonly with clindamycin and penicillin.
11. Acne
Causative Agent: Propionibacterium acnes is primarily responsible for inflammatory lesions associated with acne, as it thrives in high oil conditions.
Treatment: Commonly involves the use of topical and systemic antimicrobials like Benzoyl peroxide and retinoids (e.g., Accutane).
Diagnosis: Diagnosis is primarily based on a visual examination and assessment of the skin’s lesions.
12. Cat Scratch Disease
Causative Agent: Bartonella henselae is responsible for this zoonotic infection transmitted through cat scratches.
Symptoms: Patients often experience fever, malaise, and marked lymphadenopathy at the site of the scratch, leading to swollen lymph nodes.
Diagnosis: Serological testing for Bartonella antibodies is typically utilized for confirmation; treatment generally involves the use of antimicrobials.
13. Pseudomonas Infections
Pathogen: Pseudomonas aeruginosa, is an opportunistic pathogen widely recognized for its virulence in immunocompromised hosts.
Characteristics: This bacterium is known for producing a distinct blue-green pigment. Its virulence factors encompass fimbriae that enable adhesion, exotoxins that damage host cells, and the formation of biofilms that protect it from immune response and antibiotic treatment.
Disease Association: Pseudomonas infections are particularly prevalent among burn victims and can lead to conditions such as otitis externa (commonly referred to as swimmer's ear).
14. RMSF (Rocky Mountain Spotted Fever)
Causative Agent: The disease is caused by Rickettsia rickettsii, transmitted through bites from infected ticks, particularly the Dermacentor species.
Symptoms: Characteristically presents with a rash, fever, and cardiovascular complications due to damage incited upon blood vessels.
Diagnosis: Diagnosis is achieved through serological testing; initial treatment may include doxycycline to manage the infection promptly.
15. Cutaneous Anthrax
Causative Agent: Bacillus anthracis, the bacterium responsible for anthrax, can cause cutaneous forms with significant public health implications.
Symptoms: Patients develop a painless, ulcerated lesion (eschar) at the wound entry site where the spores of the bacterium enter.
Treatment: Treatment protocols include the use of ciprofloxacin, especially among those with potential occupational exposures, complemented with vaccinations for individuals at high risk.
16. Gas Gangrene
Causative Agents: Various species of Clostridium, primarily C. perfringens, are responsible for gas gangrene infections.
Symptoms: This infection is characterized by rapid necrosis of tissues, the formation of gas (often palpable in tissues), and intense pain in the affected area.
Treatment: Management involves surgical debridement to remove necrotic tissues combined with antibiotic therapy tailored against Clostridial infections.
17. Smallpox
Causative Agent: The variola virus is the causative agent of smallpox.
Diagnosis: Clinically diagnosed by the presence of unique pox lesions, with disease progression typified by macules (flat lesions), papules (raised lesions), and pustules (filled with fluid).
Prevention: The most effective prevention strategy has historically involved vaccination, which has led to the global eradication of smallpox.
18. Herpes Infections
Causative Agents: Human herpesviruses type 1 and type 2 are responsible for the lesions observed on the skin and mucous membranes.
Symptoms: Patients experience painful vesicular lesions that can recur due to the virus's ability to establish latency in the host.
19. Warts
Causative Agent: Human papillomavirus (HPV) is implicated in causing benign epithelial growths, commonly known as warts.
Treatment: Various techniques for wart removal include laser treatments and cryotherapy (freezing).
20. Chicken Pox and Shingles
Causative Agent: The varicella-zoster virus (VZV) causes both chickenpox (primary infection) and shingles (reactivation).
Symptoms: Initially manifests with a rash that progresses through distinct stages; shingles manifestation occurs when the virus reactivates, resulting in a painful, localized rash.
21. Measles
Causative Agent: The measles virus, a single-stranded RNA virus, is responsible for causing measles.
Symptoms: Patients often present with flu-like symptoms before developing a characteristic rash and Koplik's spots (small white lesions) inside the mouth, leading to severe complications if untreated.
22. Rubella
Causative Agent: The rubella virus (single-stranded RNA) causes rubella, also known as German measles.
Symptoms: Often involves a mild rash; however, congenital rubella syndrome can lead to severe birth defects if infections occur during pregnancy.
Prevention: Vaccination is the key strategy for prevention against rubella, particularly for women of childbearing age.
23. Fungal Infections
Causes: Cutaneous mycoses are mainly instigated by dermatophyte fungi.
Symptoms: Common manifestations include ringworm, athlete's foot, and jock itch, representing superficial fungal infections.
Treatment: Treatment typically consists of topical antifungals, emphasizing patient education on hygiene practices to prevent recurrence.
24. Leishmaniasis (Kala-azar)
Pathogen: Caused by the protozoan parasite Leishmania, transmitted by the bites of infected female sandflies.
Forms: It presents in various forms: cutaneous, mucocutaneous, and visceral leishmaniasis, each varying in severity and signs.
25. Scabies
Causative Agent: Sarcoptes scabiei, the itch mite, is responsible for scabies.
Symptoms: Patients commonly report symptoms such as intense nocturnal itching and localized rashes at burrowing sites.
Treatment: The condition can be effectively treated with topical miticidal lotions along with thorough cleaning of contaminated items to prevent reinfestation.
26. Emerging Diseases and Case Studies
Investigate recent case studies such as Buruli ulcer, examining the virulence factors, infection mechanisms, and potential treatment protocols, highlighting the importance of continued research and awareness in combating emerging infectious diseases.