Please enable JavaScript.
Coggle requires JavaScript to display documents.
Case 1: Medical Microbiology - Coggle Diagram
Case 1: Medical Microbiology
Describe the Structure of the Skin
The skin has 3 layers:
Epidermis
Epidermis makes cells
Contains Melanin which gives skin its colour
Dermis
Dermis has Sebaceous Glands that make oils to protect the skin
Sweat Glands that take part in Thermoregulation and assist in cooling the body through the production of sweat
Nerve endings in Dermis help you feel heat, cold, and pain
Subcutaneous Fat
Subcutaneous fat attaches skin to muscles and bones, helps control your temperature
What are the most important functions of Skin ?
Skin protects the tissues from external microbial invasion.
List the Skin Infections that occur in the Skin Layers
Infection of the Skin Layers:
Keratinized skin layers
Impetigo
Erysipelas
Cellulitis
Necrotizing fasciitis
Skin Ulcers and Granulomatous Infections
Infections of the Hair follicles, Sweat glands and Sebaceous Glands
Describe the Classifications of Wound Infections
Wound Infections can be classifies as follows:
Class 1 - Clean
Class 2 - Clean Contaminated
Class 3 - Contaminated
Class 4 - Dirty-Infected
Skin Infections
What is the Pathogenesis of Skin Infections ?
Skin Infections can occur due to the following:
Microbial invasion from an external source
Caused by organisms/toxins reaching the skin through the bloodstream as part of the systemic disease.
Infection in the Hair Follicles, Sebaceous Glands and Sweat Glands
List the Infections of the Hair Follicles, Sebaceous Glands and Sweat Glands
Folliculitis
Furuncles
What is Folliculitis ?
Folliculitis is a minor infection of the Hair Follicles
It is caused by Staphylococcus Aureus
It commonly affects areas of friction with sweat glands such as:
Neck
Axillae
Buttocks
Blockage of ducts with inspissated (thick) sebum, as in acne vulgaris, predisposes to the condition
Name the other causes of Folliculitis besides Staph. aureus
Folliculitis is also caused by Pseudomonas aeruginosa, especially associated with jacuzzi use.
In acne Vulgaris, which involves inflammation of hair follicles and associated sebaceous glands, the comedo of acne results from the multiplication of Cutibacterium acnes
Furuncles
What are Furuncles ?
Furuncles are small abscesses that develop in the region of a hair follicle.
Furuncles are caused by Staphylococcus aureus
Spread of Furuncles to the Dermis and Subcutaneous Tissues can result in a more extensive, multi-located abscess - Carbuncle
Furuncles can occur singly or in multiples resulting in troublesome and re-occurring disease
List the Treatment of Folliculitis and Furuncles
Drain pus, antibiotics not usually necessary
If Cellulitis develops - Cloxacillin or Cefuroxime may be used
Infections of the Skin Layers
List the Infections of the Skin Layers
Infection of Keratinized Layers
Dermatophyte Fungi
B. Impetigo
Erysipelas
Cellulitis
Necrotizing Fasciitis
Infection of the keratinized Layers: Dermatophyte Fungi
Dermatophyte Fungi
What are the Dermatophyte Fungi ?
Dermatophyte Fungi are the ONLY organisms that can use Keratin on cells, hair and nails
Dermatophyte Fungi are particularly adapted to these sites , cannot grow at 37-degrees Celsius.
And therefore, fail to invade deeper layers.
*Candida species are another type of fungus that can also infect superficial layers of the skin
What is Dermatophytosis
Dermatophytosis is also known as ringworm
List the species of fungi responsible for Dermatophytosis
Trichophyton
Microsporum
Epidermophyton
What parts of the body is the Infection found in ?
Feet: Tinea Pedis
Red, swollen, peeling, itchy skin between toes
-Severe cases: blisters on feet
Groin: Tinea Cruris
Scalp: Tinea Capitis
Scaly, itchy, red circular bald spots with broken hair or hair loss
General Body area: Tinea Corporis
Red, scaly, annular border with raised edges
Nails: Onychomycosis
Nail is thickened and eroded, pigmented, friable
List the types of Treatment for Dermatophyte Infections
Oral Terbinafine, Fluconazole, Itraconazole, Griseofulvin
For mild infections use Tropical Preparations
For more extensive infections use Oral Anti-Fungals
For Nail infections we use Long Treatment Duration
How do we do a Diagnosis for Dermatophyte Infections ?
Skin scapings sent to the lab
KOH preparation
Hyphae or Spores detected
Culture
PCR (Polymerase Chain Reaction)
B. Impetigo
What is B. Impetigo ?
B. Impetigo is the most common bacterial infection in kids.
B. Impetigo is very contagious
What is B. Impetigo caused by ?
Streptococcus Pyogenes are the main cause of B. Impetigo, followed by Staphylococcus aureus
Secondary skin infections of existing lesions may occur.
List the types of B. Impetigo
Non-Bullous Impetigo
Bullous Impetigo
List the Signs and Symptoms of Non-Bullous Impetigo
Non-Bullous Impetigo is caused by Strep. Pyogenes
Non-Bullous Impetigo causes multiple coalescing lesions on the face (perioral and perinasal regions) and extremities or in areas with a break in the natural skin defense barrier
Initial lesions are small vesicles or pustules that rupture and become honey-coloured crust
With a moist Erythematous Base
Non-Bullous Impetigo is usually a self-limited process that resolves within 2 weeks
List the Signs and Symptoms of Bullous Impetigo
Bullous Impetigo is caused by strains of Staphylococcus aureus
It is less contagious than Non-Bullous Impetigo
Bullous Impetigo occurs on the face, extremities, axillae, and perianal region of neonates
Bullous Impetigo can also affect older children and adults
Bullous Impetigo causes large serum-filled blister (bullae) within the skin layers at the site of infection
Once Bullae rupture, they leave behind a rim of scale around an erythematous, moist base BUT no crust
Followed by a brown scalded-skin appearnce
Rarely infant may present with pneumonia, septic arthritis or osteomyelitis
How do we diagnose B. Impetigo ?
B. Impetigo diagnosis is based on history and clinical findings
Bacterial culture and sensitivity are recommended
Why ?
To identify possible methicillin-resistant Staphylococcus aureus (MRSA)
To identify if an Impetigo outbreak has occurred
To identify if post-streptococcal glomerulonephritis is present
What are the Treatment Options for B. Impetigo ?
Tropical Antibiotic Therapy
Mupirocin
If complicated, systemic manifestations or part of outbreak - treat with Cloxacillin, Amoxicillin - Cefuroxime
Erysipelas
What is Erysipelas ?
Erysipelas is a rapidly, spreading infection of the deeper layers of the Dermis
Erysipelas is caused by Streptococcus Pyogenes
What are the clinical Symptoms of Erysipelas ?
Erythema (Red)
Pain
Fever
Lymphadenopathy
Butterfly wing rash if face is involved
What are the complications of Erysipelas ?
Complications:
Septicaemia
Local skin necrosis
What are the treatment options for Erysipelas ?
Erysipelas requires immediate treatment with Penicillin or Erythromycin
Cellulitis
What is Cellulitis ?
Cellulitis can develop by extension from a skin or wound infection
What causes Cellulitis ?
Cellulitis is commonly caused by Staphylococcus aureus and Streptococcus pyogenes
BUT enteric GNB, clostridia and anaerobes are also implicated
What are the Symptoms of Cellulitis ?
Cellulitis:
Present with Acute Inflammation and Erythema
Swelling
Pain plus constitutional symptoms
What are the treatment options for Cellulitis ?
Oral antibiotics: Penicillin, Erythromycin
IV antibiotics: Penicillin G
Elevate infected leg
Necrotizing Fasciitis
What is Necrotizing Fasciitis ?
Necrotizing Fasciitis is a serious infection with a high mortality rate.
There are 3 subtypes of necrotizing soft tissue infection (NSTI):
Type 1
Type 2
Type 3
Type 1
Results from a Polymicrobial Infection
It caused by Group A Streptococci ( Streptococci Pyogenes), Mixed Aerobes and Anaerobes
Organisms typically extend to subcutaneous tissue from Contagious Ulcer or Infection or after trauma
Streptococci can arrive from remote site to site of infection via the bloodstream
Type 1 NSTI often result in Gas Gangrene
Diabetic patients are at risk of getting Type 1 NSTI
Type 2
Results from a Monomicrobial Infection
It is caused by Streptococcus pyogenes, Staphylococcus aureus
Usually occurs in younger patients
Who are usually healthy, but may have a history of IV drug use, trauma
Type 3
Type NSTI is associated with aquatic injuries
Caused by Vibrio Vulnificus
What is the Pathogenesis for Necrotizing Soft Tissue Infection ?
Occlusion of blood vessels which results in Necrosis and Infarction
Which facilitates the growth for obligate anaerobes (Bacteroides)
What are the Symptoms of NSTI ?
Symptoms:
Intense pain, area is red, hot and swollen
Bullae, Crepitus (from soft tissue gas) and Gangrene may develop
Spread to adjacent tissues
Acutely ill, High fever, tachycardia, Confusion and Hypertension
May develop Streptococci toxic shock syndrome
How do we diagnose NSTI ?
Diagnosis involves:
History and clinical exam
Raised white blood cell count, Increased CRP
Soft tissue gas on X-ray indicates Gas Gangrene
Positive Blood or tissue cultures (Group Streptococci)
What is the treatment for NSTI ?
Surgical debridement (removal of necrotic tissue to promote wound healing) and antibiotics
Skin Ulcers and Granulomatous Lesions
List the types of Skin Ulcers and Granulomatous Lesions
Hepatic Ulcers
Syphilis Ulcers
Mycobacterium marinum
Hepatic Ulcers
What are Hepatic Ulcers ?
Hepatic Ulcers are caused by HSV (Herpes Simplex Virus) by direct infection
HSV invades through the skin to produce a local, vesicular lesion followed by Ulceration
Syphilis Ulcers
What is Syphilis ?
Syphilis Ulcers are a bacterial infection caused by: Spirochete Treponema Pallidum
Syphilis is usually transmitted through Sexual Contact
The Bacteria enters through a break in the skin
Syphilis causes a Chancre or multiple Chancres
A chancre is a painless ulcer
Mycobacterium marinum
What is Mycobacterium marinum ?
Mycobacterium marinum is called "fish tank Granuloma"
Organism enters through superficial abrasions from rocks or pool walls
It is a self-limiting granuloma
Fungal Mycetoma (Eumycetoma)
What is Fungal Mycetoma ?
Fungal Mycetoma is a Chronic, progressive skin disease
Usually involves the foot, or lower extremities
What are the Clinical (Symptoms/signs) of Fungal Mycetoma ?
Localized tissue swelling
Sinus tracts
Production of grains
Who are most affected by Fungal Mycetoma ?
-Farmers or Farm workers
Outdoor people
What microorganism causes Fungal Mycetoma ?
Common fungi:
-Madurella species
-Scedosorium apiospernum
What is the treatment for Fungal Mycetoma ?
Treatment:
Anti-fungals
Itraconozole
Bacterial Mycetoma
What causes Bacterial Mycetoma ?
Bacterial Mycetoma is caused by a Gram positive bacteria usually Actinomycetes group
The presentation of Bacterial Mycetoma is similar to that of Fungal Mycetoma
Identification of the Pathogen is necessary to direct treatment
What is the treatment for Bacterial Mycetoma (Actinomyces) ?
Penicillin
Surgery
Cervico-facial abscess from actinomycetes group - Sulphur granules and branching bacteria
Wound Infections
What is a wound ?
A wound is damage to the integrity of biological tissue, including skin, mucous membranes, and organ tissue.
The criteria for recognizing infected wounds:
The presence of abscess, cellulitis
The presence of secretions
It is critical that wounds are cleaned, and dressed appropriately to limit the spread of infection and further injury.
CDC Classification of Wounds
List the Wound Classes and their description
Class 1 - Clean
Class 2 - Clean Contaminated
Class 3 - Contaminated
Class 4 - Dirty Infected
Class 1
Class 1 wounds are clean wounds
Wound is NOT infected and inflammation is NOT present.
Wound is primarily closed
If draining of the wound is required, a closed draining method is necessary
Additionally, these wounds do not enter the Respiratory, Alimentary, Genital, or Urinary Tracts
Wounds have a less than 2% Infective Risk
Class 2
Class 2 Wounds are Clean-Contaminated Wounds
Wounds lack unusual contamination
Class 2 Wounds enter the Respiratory, Alimentary, Genital and Urinary Tracts
However, the wounds have entered these tracts under controlled conditions. Eg: Appendectomy
Class 2 wounds have a less than 10% Infective Risk
Class 3
Class 3 Wounds are Contaminated Wounds
These are fresh, open wounds that can result from insult to sterile techniques or leakage from the Gastrointestinal Tract into the wound
Additionally, Incisions made that can result in Acute or Lack of Purulent inflammation are considered Class 3 Wounds
Class 3 wounds have a 20% Infective Risk
Class 4
Class 4 Wounds are Dirty-Infected Wounds
Class 4 wounds typically result from improperly cared for traumatic wounds
Class 4 wounds demonstrate devitalized tissue
And most commonly result from microorganisms present in perforated viscera or the operative field
Class 4 wounds have about 40% Infective Risk
List the Risk Factors for Infected Wounds
Microbial Factors
-- Bacterial inoculation, Virulence
Systemic Factors
-- Age
-- Malnutrition
-- Poor Tissue Perfusion
-- Hypovolemia
-- Immunosuppressants
Wound Characteristics
-- Non-viable tissue in wound
-- Hematoma
-- Presence of Foreign material
-- Pre-existent Sepsis
Operative Characteristics
-- Poor Surgical Techniques
-- Lengthy Operation
-- Intraoperative Contamination
-- Hypothermia
-- Prolonged Pre-Operative stay in Hospital
Aetiology for type of cause of Wound
Trauma: clostridium perfringens
Surgical:
Staphylococcus aureus
Group A Streptococci, Streptococcus Pyogenes
Surgical (Dirty):
S. aureus
Burns:
S. aureus
Candida sp.
Animal Bites:
Pasturella
Describe the Lab Diagnosis for infected Wounds
Tissue sample or Pus aspirate or Deep Swab from infected wound is sent to the lab
Gram Stain for Infected organisms is done.
Staining for Fungal Elements
Most laboratories routinely will culture for both aerobic, and anaerobic organisms
Fungal cultures can be requested
Isolation of single colonies allows further growth and identification of the specific organism
Sensitivity testing then follows mainly for aerobic organisms
Other techniques include the following:
Tests for antigen from the organisms through Enzyme-linked Immunoassay (ELISA) or Radioimmunoassay
Detection of antibody response to organisms in host sera
PCR (Polymerase Chain Reaction) to detect small amounts of Microbial DNA
1 more item...