-
4 normal defense mechanism of the skin
- normal skin flora
- skin integrity
- rapid cell turnover
- antimicrobial effect of the lipid layer (pH 5.5)
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4 most common resident skin flora
- SCMP
- Staphylococcus
- Corynebacterium
- Micrococcus
- Propionibacterium acnes
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4 ways of pathogenesis of skin and soft tissue infections
- breach of normal skin integrity
- alteration of normal skin flora
- change in local environment of the tissues
- introduction of exogenous/endogenous microbial flora
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3 microorganisms causing Dermatophytosis
- MET
- microsporum spp.
- epidermophyton floccosum
- trichophyton spp.
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Causative agent of Dermatomycosis
non-dermophytic fungi e.g. candida albicans
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typical presentation of dernatophytosis
ringworm
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how to make diagnosis of dermatophytosis?
- KOH wet mount
- fungal culture
-
treatment for dermatophytosis
topical/ systemic antifungal agent
-
what is dermatophytosis?
superficial infection of keratinized tissue by dermatophytes
-
what is Paronychia?
superficial infection of the nail fold
-
what are causative agents of paronychia?
- acute: S. aureus
- chronic: Candida spp. esp. Candida albicans
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what is Impetigo?
superficial intra-epidermal unilocular veicopustule
-
2 common pathogens leading to impetigo
- Streptococcus pyogenes
- Staphylococcus aureus
-
Impetigo most common in which age group?
children
-
Epidemiology of impetigo
highly communicable
-
what are the presentations of impetigo?
- vesicles -> pustule -> golden-yellow crust in exposed areas e.g. forearm, face
- heals without scarring
-
Laboratory diagnosis of impetigo
culture of exudate beneath crust
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what is folliculitis?
abscess formation around hair follicles
-
what is the most common causative agent of folliculitis?
S. aureus
-
what is furnacles?
subcutaneous abscess
-
what is cellulitis?
acute spreading infection of the skin involving the subcutaneous tissues
-
what are the causative agents of cellulitis?
- Streptococcus pyogenes
- Staphylococcus aureus
- Vibrionaceae
- Enterobacteriaceae
-
Predisposing factors of cellulitis
- trauma
- underlying skin lesions
-
What is the clinical presentation of cellulitis?
- local signs of inflammation
- ill-defined margin of inflammation
- local abscess
- fever
- chills
- bacteraemia
-
how to make diagnosis of cellulitis?
clinical diagnosis
-
What is erysipeals?
superficial, dermarcated infection involving lymphatics, epidermis
-
What causes erysipeals?
group A streptococcus
-
who is more prone to erysipeals?
e.g. DM patients
-
what are the common sites of erysipeals?
- face (swollen regions with distinct borders)
- lower limb
-
what are the clinical presentations of erysipeals?
- painful red lesions with distinct border spreading rapidly
- marked subepidermal oedema with heavy infiltration of PMNs
-
Treatment of pyoderma
beta lactam antibiotics
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treatment of cellulitis
beta lactum antibiotics
-
treatment of erysipeals
beta lactam antibiotics
-
treatment for MSSA
- cloxacillin
- beta-lactam-beta-lactamase inhibitor
-
treatment of MRSA
- vancomycin
- non-beta-lactam antibiotics
-
treatment for beta haemolytic antiboitics
penicillin
-
what will increase the risk of HA-MRSA infection?
- use of antibiotics
- frequent hospitalisation
-
Clinical presentations of CA-MRSA infection
- soft tissue abscess e.g. furuncles
- fulminant and rapidly fatal pneumonia (necrotising pneumonia)
-
treatment for CA-MRSA
- resistant to beta-lactam antibiotics
- susceptible to other agents like clindamycin
-
Characteristics of CA-MRSA
- different antibiogram from HA-MRSA
- special genetic elements
- Panton-Valentine leukocidin
-
3 Features of necrotising soft tissue infections
- multiple tissue levels involvement
- thromobosis of BV perforating hte dascial envelope
- extension of necrosis under the skin
-
Aetiology of Type I necrotizing fasciitis
anaerobes e.g. bacteriodes and clostridium + facultative anaerobes e.g. streptococci, enterobacteriaceae
-
predisposing factor of Type I necrotising fasciitis
after intra-abdominal or pelvic surgery before the days of peri-operative antibiotic prophylaxis
-
Aetiology of type II necrotising fasciitis
- Streptococcus pyogenes
- Staphylococcus aureus may be involved
-
Aetiology of type III necrotising fasciitis
vibrio spp. esp. vibrio vulnificus
-
predisposing factor of Type III necrotising fasciitis
- exposure to water
- consumption of seafood containing the pathogens
-
Clinical presentation of Necrotising fasciitis
- fever
- pain
- oedema
- skin become cyanotic and finally dusky and black (full thickness necrosis of skin)
- septic shock
-
appearance of lesion
- tender esp. at the spreading edge
- central part become anasthetic
-
Management of necrotising fasciitis
- surgical emergency
- supportive treatment for sepsis
- early and aggresive surgical debridement
- antibiotics
-
Microbiology of Clostridial myonecrosis (gas gangrene)
- Clostriduim perfringens (85-90%)
- other clostridium spp.
- can be mixed with other facultative anaerobes
-
Pathogenesis of Gas gangrene
muscle injury and contamination with soil or other foreign material containing spores of Clostridium perfringenes -> coagulative necrosis of muscle fibers
-
4 Clinical features of gas gangrene
- local tense oedema
- serosanguineous discharge
- foul odor of wound
- crepitus
-
Lab diagnosis of gas gangrene
- Gram smear of wound discharge (numerous bacteria but few leukocytes)
- aerobic and anaerobic culture
-
Difference between surgical wound and surgical site
- surgical wound: skin incision
- surgical site: organ space deep to the skin and soft tissue e.g. peritoneum and bone
-
4 indications of wound infection
- pus from the incision
- pain, tenderness, localized swelling, redness, dehiscence of wound and sometimes with fever
- organisms isolated from an aseptically obtained culture of tissue or fluid from the wound
- Gram smear of the soft tissue/ fluid/ swab may reveal numerous leukocytes and bacteria
-
4 wound classes
- clean
- clean contaminated
- contaminated
- dirty
-
Aetiology of surgical wound infection
depending on the type of operation
-
what is Osteomyelitis?
an infectious process involving the various components of bone, i.e. periosteoum, medullary cavity and cortical bone
-
3 types of osteomyelitis
- acute osteomyelitis
- chronic osteomyelitis
- prosthesis-related infection
-
route of infection of acute osteomyelitis
- haematogenous osteomyelitis (monomicrobial)
- contiguous focus osteomyelitis (polymicrobial)
-
route of infection of chronic osteomyelitis
untreated or inadequately treated acute osteomyelitis
-
route of infection of prosthesis-related infection
- pathogens are usually introduced during operation or from post-operative wound infection
- haematogenous spread
-
pathology of osteomyelitis
- acute inflammation -> obliteration of vascular channels -> ischaemia and necrosis
- subperiosteal extension of infection -> lifting of periosteum away from bone -> bone formation
- ischaemic segments of bone separated to form the sequestrum
-
Causative agent of acute haematogenous osteomyelitis in infants
- S. aureus
- S. agalactiae
- E. coli
-
Causative agent of acute haematogenous osteomyelitis in children > 1 y.o.
- S. aureus
- S. pyogenes
- Haemophilus influenzae (uncommon after 4 y.o.)
-
Causative agent of acute haematogenous osteomyelitis in adults
S. aureus
-
route of infection of vertebral osteomyelitis
haematogenous
-
Involvement of vertebral osteomyelitis
- usu 2 adjacent IV disc
- as segmental arteries supplying vertebrae and the IV disk
-
4 Predisposing factors of contiguous focus osteomyelitis
- trauma
- surgical operations of bone
- open fractures
- chronic soft tissue infections
-
Pathogenesis of contiguous focus osteomyelitis
vascular insufficiency
-
Causative agent of contiguous focus osteomyelitis
- Polymicrobial
- S. aureus
- Gram -ve bacilli
- strep
- enterococci
- anaerobes
-
Commonest causative agent of skeletal mycobacterial infection
Mycobacterium tuberculosis
-
route of infection of skeletal mycobacterial infection
- haematogenous spread during primary infection
- contiguous lymphadenitis
-
Pathological changes of chronic osteomyelitis
- a nidus of infected, ishaemic, dead bone (sequestrum)
- local infection -> local bone loss, persistent drainage, local abscess or adjacent soft tissue inflammation, sinus tract formation
-
Clinical features of acute osteomyelitis
- fever
- chills
- leukocytosis
- pain
- local swelling
- (signs may be non-specific/ minimal)
-
Clinical features of chronic osteomyelitis
- chronic pain and drainage
- low grade fever
- (could be mild)
-
clinical diagnosis of osteomyelitis
- Radiological: Plain X-ray (change lags at least 2 weeks), CT, MRI
- Radionuclide imaging (bone scan)
-
Microbiological diagnosis of osteomyelitis
- blood culture
- operative biopsy of bone lesion for culture
- (in case of chronic osteomyelitis, culture of sinus tract is not reliable for predicting the organisms causing osteomyelitis)
-
Treatment for osteomyelitis
- prolonged course of treatment
- surgical debridement (removal of dead bone essential in chronic osteomyelitis)
-
route of infection of infective arthritis
- haematogenous seeding
- direct inoculation
-
pathology of infective arthritis
- synovium is highly vascular and lacks a basement membrane -> susceptible to bacterial seeding
- intra-articular inflammation -> destruction of articular cartilage
-
Clinical features of infective arthritis
- pain and decreased ROM
- fever, swollen joint, leukocytosis
- usu. large joints but all joints will be affected
-
infective causes of polyarthritis
- virus
- Neisseria gonorrhoeae
-
Causative agents in acute infective arthritis in infants <1 month
- S. agalactiae
- S. aureus
- aerobic Gram -ve bacilli e.g. E. Coli
-
Causative agents in acute infective arthritis in children <2 y.o.
H. influenzae B
-
Causative agents in acute infective arthritis in children >2 y.o. and adults
S. aureus
-
Causative agents in acute infective arthritis in young sexually active adults
Neisseria gonorrhoeae: part of gonococcal infection and usually polyarticular
-
Causative agents in acute infective arthritis in IV drug addicts
- S. aureus
- Pseudomonas aeruginosa
-
Diagnosis of infective arthritis
- blood culture
- diagnostic synovial fluid aspirate: leukocyte count, crytals, Gram stain, culture
- synovial biopsy
-
treatment of infective arthritis
- antibiotics
- surgical drainage
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