Transcript DERMAL AND MUSCULOSKELETAL INFECTIONS

DERMAL AND MUSCULAR
INFECTIONS
MSC TID 1
28TH APRIL 2010
Nyakundi BM
DERMAL AND MUSCULAR
INFECTIONS
Infections of the skin can be primary eg primary
pyodermas or secondary eg to burns or surgical
wounds.Primary pyodermas include;impetigo,furuncles,carbuncles,chancriform
lesions,cellulitis.There are many possible pathogens that can
be found in abcesses ,burns, wounds and draining sinuses.
PATHOGENS
• Bacterial-Gram positive• Staphylococcus aureus,Streptococcus
pyogenes,Enterococcus species,Anaerobic
Streptococcus,Clostridium perfringens,Actinomyces
Israeli
• Bcterial Gram Negative• Proteus species,Pseudomonas aeruginosa,Escherichia
coli,Bacteroides,Klebsiella and Pasteurella species.
• Also Mycobacterium leprae,ulcerans,tuberculosis and
marinum.
Dermal Infections
• These can be primary
• Or secondary infections eg on
burns,wounds.
• Also secondary infections can occur as a
result of bacteraemia eg in staph
aureus,Group A streptococci and
Neisseria meningitidis
Sumary of predisposing factors
• Minor injuries,insect bites,friction
blisters,superficial fungal
infections,burns,use of indwelling
catheters in children and minor surgical
procedures.
Overview of the various Bacterial
Pathogens
• Staph aureus is the commonest pathogen isolated from
subcutaneus abscesses and skin wounds.Penicillin and
methicillin resistant strains are common causes of
hospital acquired wound infections.
• P.aeruginosa is associated with infected burns and
hospital acquired infections.
• Chronic leg ulceration is common in those with sickle cell
disease.The commonest patogens isolated-S aureus,P
aeruginosa,S pyogenes and bacteriodes speceies.
• Mycobacterium tuberculosis is associated with “cold”
abcsesses
Overview of the various bacterial
pathogens
• Yersinia pestis causes plague.It is called
bubonic plague when the organisms infects a
lymph gland and produces a painful swelling
called a bubo.The organism can be found in the
fluid aspirated from the bubo
• Bacillus anthracis causes anthrax with the
cutaneous form of the disease producing a
pustule on the hand or arm with highly
contagious fluid.
Overview of the various bacterial
pathogens
• E coli,Proteus species,P aeruginosa and
Bacteroides species are the pathogens most
frequently isolated from abdominal abscesses
and wounds.
• C perfringens is found mainly in deep wounds
where anaerobic conditions exist.
• A Israeli and other species of Actinomyces
cause Actinomycosis-small yellow granules can
be found in pus from a draining sinus.
Overview of the various bacterial
pathogens
• M leprae can be found in skin smears of
lepromatous leprosy and occassionally in
borderline forms of the disease.
• T carateum causes pinta-central
america,colombia,T pertenue causes yaws esp
in west africa
• Vincents organisms (Borrelia vincenti with gram
neg anaerobic fusiform organisms) are
associated with tropical ulcers. Esp in
malnourished childrens legs.Staphylococci and
streptococci are secondary invaders.
SKELETAL MUSCLE INFECTIONS
• Classification of infectious myositis;
• This can be by the type of process
involved ;
• 1.Pyogenic and predominantly localized(spreading by contiguity)
• 2.Non pyogenic and predominantly
generalized
Pyogenic,localized infections
• Bacteria invade muscle either from
contigous sites ( eg skin and
subcutaneous abscesses,penetrating
wounds, decubitus ulcers,osteomyelitis) or
by haematogenous spread from a distant
focus.
• Clinical pattern includes pyomyositis,gas
gangrene,non clostridial
(crepitant)myositis,psoas abscess.
Clinical patterns and principal
aetiological agents
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1.Pyomyositis- staph aureus
2.Gas gangrene- clostridium perfringens
3.Non clostridial (crepitant) myositis;
a)anaerobic streptococcal gangrene-caused by
peptostreptococcus,group A streptococci/S aureus
b)Group A streptococcal necrotizing myositis
c)synergistic non clostridial anaerobic myonecrosiscaused by mixed infections-Bacteroides and other
anaerobic gram neg non spore forming bacilli ;
peptostreptococci and various streptococci;E
coli,klebsiella,Enterobacter.
d)Infected vascular gangrene-same as (c) above.
e)Aeromonas hydrophila myonecrosis
Clinical patterns cont.
• 4. Psoas abscess- caused by Gramnegative bacilli;staph aureus,M.
tuberculosis
Clinical patterns
• Non pyogenic and predominantly
generalized
• 1.Myalgias-caused by bacteraemia eg
meningococcaemia,rickettsioses eg rocky
mountain spotted fever.
• 2.pleurodynia-coxsakie B
• 3.myalgias with eosinophiliatrichinosis,cysticercosis
• 4.myalgia secondary to other viruses
Laboratory diagnosis
• Collection and transport of pus,ulcer
material and skin specimens;
• Pus from an abscess is best collected at
the time when the abscess is incised and
drained,or after it has ruptured naturally.
• Avoid contamination of the specimen with
commensal organisms from the skin.
• A specimen from a wound should be taken
before and antiseptic dressing is applied.
Laboratory diagnosis cont.
• When mycetoma is suspected;
• Obtain a specimen from a draining sinus tract
using a sterile hypodermic needle to lift up the
crusty surface over the sinus opening.This
ensures that the pus obtained is free from
secondary organisms and the draining granules
can be seen clearly and removed for
microscopic examination.
• Transfer the pus to a sterile container.
Lab diagnosis-specimens
• When tuberculosis is suspected,aspirate a
sample of the pus and transfer it to a sterile
container
• When the tissue is deeply ulcerated and
necrotic,aspirate a sample from the side wall of
the ulcer using a sterile needle and
syringe,transfer to sterile container.
• Fluid from pustules ,buboes,blisters-use sterile
needle and syringe for aspiration and transfer to
sterile container
Lab diagnosis
• Serous fluid from skin ulcers may contain
treponemes;collect a drop of exudate onto
a clean cover glass and invert it onto glass
slide then for dark ground microscopy.
• Skin smears for mycobacterium leprae.
• Specimens from patients with suspected
plague/anthrax are highly infectious- sould
be labelled HIGH RISK and handled with
care
Specimen description
• 1.Gross examination-If patient is suspected to
have mycetoma or actinomycosis, report the
apperance of the specimen/granules.
• 2.Microscopic examination-Gram stain,ziehlnielsen stain;also Giemsa stain is bubonic
plague is suspected and polychrome loefflers
methylene blue when anthrax is suspected.Also
dark field microscopy when yaws, pinta
suspected.
Lab diagnosis-culture
• 3.Culture of specimen;
• A)Innoculation done on blood agar to isolate
staph aureus and streptococci,add a bacitracin
disc if streptococci are seen in gram smear.incubate aerobically-candle extinction jar-,35-37
C in CO2
• B)on mac conkey agar to isolate gram negative
rods-incubate aerobically
• C)Into cooked meat medium or thioglycollate
broth.Cooked meat should be 35-37 C for up to
72 hrs.Subculture at 24 hrs and if need be 48
and 72 hrs
Anaerobic culture
• When anaerobic infection is suspected( specimen foul
smelling or gram smear shows mixed anaerobic flora,a
second blood agar plate is innoculated and incubated
anaerobically for upto 48 hrs
• The anaerobic blood agar may be made selective by
adding neomycin-this inhibits majority of anaerobic
facultative gram negative rods.
• To aid detection of anaerobes, a metronidazole disc can
be added to the anerobic blood plates;aerobes will grow
to the disc,and many anaerobes will show a zone of
inhibition.
Anaerobic culture results
• Anaerobic blood agar and cooked meat culture;
• Clostridium perfrigens( hydrogen sulfide gas
production,reddening but no decomposition of meat –
saccharyolytic reation), on anaerobic blood agar- double
zone haemolysis
• B fragilis-on cooked meat –decomposition,blackening of
the meat- foul smelling proteolytic reaction;on anaerobic
blood agar-non haemolytic grey colonies
• Peptostreptococcus- on cooked meat produces
hydrogen sulphide gas; on anaerobic blood agar small
non hemolytic colonies produced;gm positive cocci and
resistant to metronidazole disc.
Other tests
• For mycobaterium tuberculosis and
ulcerans- culture
• Yersinia pestis- blood or bubo aspirate
culture.when plague is suspected, initial
smear report should indicate if bipolar
organisms were seen.
treatment
• Most anaerobic infections are caused by
penicillin susceptible bacteria with the exception
of infections originating from the intestinal tract
or vagina.
• Such infections contain B fragilis, which
produces Beta lactamase and is resistant to
penicillins ampicillin and most cephalosporins.
• Treatment is by
clindamycin,metronidazole,chloramphenicol.