Transcript wounds

Wound Infection
Dr. Kiarash Ghazvini
Department for bacteriology and virology,
Mashhad University of medical Sciences
WOUNDS AND ABSCESS
• Infections of soft tissues are associated with
production of pus and said pyogenic.
• A wide variety aerobic and anaerobic species
participate singly or in combination in
infectious of wounds.
WOUNDS AND ABSCESS
• The commonest pyogenic bacteria are S.aureus, S
.pyogenes ,P. aeruginosa, coliforms bacilli.,
anaerobic organisem :particularly Clostridium perfringens
, bacteroides spp ,anaerobic cocci..
• In many cases there is a mixed infection with
more than one bacterial spp.
wounds
Wound infections may be endogenous or
exogenous.
–Endogenous infections are caused by organisms
that are in commensal in the patient .
–Exogenous infections the source is out of the body
cross-infection is a particular example.the causal
organism is spread from person to person. infection
may occur after accidental or intentional trauma of
the skin or tissue. (Surgical postoperative sepsis. )
• Wounds are liable to contamination with a
multiplicity of organisms from the body
surfaces and environment.
• Infection of a wound is difficult to define , and
no clear rules can be given to distinguish it
from colonization and contamination.
Contamination
• The contaminating organisms are present in
small numbers
Colonization
• In the case of commensal or low grade
pathogenes it can be described
colonization.
Infection
• Infection occurs when they evades the
host defences.replicates in large numbers
and attacks the host tissue.
Wounds:Classification
Acute
Chronic
• Caused by external damage
to intact skin
• Precipitated by predisposing
conditions that lead to
compromise
of
dermal/epidermal tissue
• Types
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Surgical
Bites
Burns
Minor cuts
Abrasions
Severe traumatic
• Types
• Impaired venous drainage
• Impaired arterial supply
• Metabolic diseases eg.
diabetes
Wound infections: Etiology
• Surgical wounds
– Aerobes: S. aureus, coagulase negative staphylococci, Enterococcus
spp. E. coli, P. aeruginosa, Enterobacter spp.
– Anaerobes: Bacteroides spp., Peptostreptococcus, Closthdium spp.
• Acute soft tissue infections
– Staph aureus only organism in 30%
– 30-50% mixed aerobes/anaerobes
– 20-30% other eg. Group A streptococci, Clostridium spp.
• Bite wounds
– Special pathogens: Pasteurella muftocida, Capnocytophaga
canimorsus, Bartonella henselae, Eikenelfa corrodens
– Other mixed aerobes and anaerobes
Wound infections: Etiology
• Burn wounds
– Primarily aerobic organisms: P. aeruginosa,
Staphylococcus aureus, E. coli, Klebsiella spp.
Enterococcus spp. and Candida spp.
• Diabetic foot ulcers
– Aerobes: Staph aureus, Streptococcus spp. P. aeruginosa,
Enterococcus spp., enterics
– Anaerobes: Peptostreptococcus, Bacteroides spp.,
Prevotella spp.
• Decubitus ulcers
– Mixed aerobic and anaerobic bacteria
SAMPLING
•
Biopsy
●
Aspirate from depth of the wound
– if possible pus or exudate should be submitted in a small screwcapped bottle, a firmly stoppered tube or sterile syringe and needle.
SAMPLING
• Swabs are inefficient sampling and
are strongly discouraged.
• If it is decided to send swabs tow swab is
necessary , one for microscopy ,one for
culture.
SAMPLING
• Delay in the transit of specimen to the
laboratory must be avoided.especially
swabs where the exudate may dry.
CONTINUE…
• If the swab is dry, moisture it well with a little
sterile broth or saline .
• the examination of material on swabs for
mycobacteria is always unsatisfactory.
• Physicians should be instructed that when a special
investigation is required ,they usually should state on
the request form.
SAMPLING
● Clean
the wound margins with 70%
ethyl alcohol.
Wound Cultures
• For closed Wounds
– Prepared site as described for obtaining Blood Culture
– Aspirate as much purulant material as possible
– Transport in aerobic /anaerobic transport media
Laboratory examination
• Special methods of examination should be
applied to particular specimens.
• the basic procedures usually include
– Naked eye examination, (for macroscopy criteria
,such as color , odor consistency,..)
– The microscopical examination,
– Culture on aerobic and anaerobic blood agar
plates, on MacConkey agar and in cooked –meat
broth .
Microscopy
• Much useful information may be obtained from
smear by Gram-staining. We should notice
– presence and relative numbers of PMNs , SEC and bacteria
– morphology of Gram – positive or Gram – negative
bacteria.
– Examination of a wet film for fungi or motile bacteria.
– A smear stained by the Ziehl- Neelsen method should be
examined when the clinical circumstances suggest the
tubercle bacillus., another mycobacterium or a nocardia
may be present
Wound Cultures
• Culture for aerobic and anaerobic bacteria if
appropriately collected
– Gram stain results suggest adequate collection or
presence of inflammation
– Tissues or aspirates vs. swabs
– Primary plating media: 5% SBA, Choc agar,
MacConkey agar; anaerobic plates and thio if
appropriately collected
• Identify anaerobes to Genus level only
• Perform susceptibility testing of predominant
organisms only
CULTURE
• the specimen should be inoculated on two
plates of blood agar (SBA 5%),
– the one for incubation at 37c, 5-10% CO2.,for 1824h.
– The other for incubation anaerobically .
• It should also be plated on Mac Conkey or
CLED agar, for identification of coliforms , staphylococci ,
enterococci, also be inoculated into a tube of cooked –meat
broth for the enrichment of exacting aerobes and anaerobes.
CULTURE
• Colonies should be noted and more tests for
identification and antibiotic susceptibility tests
done.
• If there is no growth after 24h ,all plates should
be reincubated for another 24h
• for
slow-growing
pathogen
such
as
Actinomyces israeli or some species of
bacteroides it should be incubated longer for
about 7 days.
CULTURE
• if at 24 h or 48 h there is growth on cookedmeat broth , but no growth on the plates , the
broth should be filmed and subcultured.
• if tuberculous or fungal infection is suspected ,
the specimen should be cultured by the
appropriate methods on special media.
Wound Cultures: Extent of Workup
Possible approaches
• Use Gram stain result
– Work up organisms seen on stain only
– List others
• Work up any potential pathogens to maximum
of three, list others present by morphology
• Work up any quantity S. aureus, P. aeruginosa,
beta hemolytic streptococci, enterics and gramnegative anaerobes
Wound Specimens: Algorithms
• Three approaches
– PMN predominance
– Q-Score
– Q-2-3-4 system
Wound Cultures: Examples
• Gram stain results: (Acceptable)
– Many neutrophils, no epithelial cells, Many gram positive
cocci in clusters, Many gram negative bacilli, Few
morphotypes resembling skin flora
• Work up (identify and perform susceptibility testing):
Gram positive cocci in clusters and gram neg bacilli
• Culture report: Many S. aureus, many Klebsiella
pneumoniae, light aerobic bacteria resembling skin
flora
Workup of Wound Cultures
• Q-Score System
– Good quality specimen (Q3)
• Up to 3 organisms can be considered as potential
pathogens and worked up (ID/AST)
– Lower quality specimen (Q2, Q1)
• More SEC
• Fewer organisms are worked up
Workup of Wound Cultures
• Q-Score System
– If the Q-score is greater than or equals the PP in culture
• Workup all potential pathogens
– If Q-Score is less than the PP in culture
• Look at the Gram stain
Workup all PP that are seen on GS
Morphologically ID others
If all PP present on GS then only Morph ID all
Wound Cultures: Examples
• Gram stain: many neutrophils, few epithelial
cells, Gram positive cocci in clusters, Gram
positive cocci in chains,
• Culture grows: many S. aureus, many Group
A streptococci, few enteric bacilli
• Work up: S. aureus, Group A streptococcus:
limited ID and no susceptibility on enteric
bacilli susceptibility testing on Group A strep
not required
Wound Cultures: Example
• Gram stain: many neutrophils, few
epithelial cells, Gram positive cocci in
clusters, Gram positive cocci in chains,
• Culture grows: many S. aureus, many
Group A streptococci, few enteric bacilli
Workup of Wound Cultures
• Q/2-3-4 System
– Culture workup is based on the # of PP present
• 2PP-ID/AST
• 3PP
– Look at the Gram stain
» " Workup two PP if they are seen on GS
» " If all 3 present on GS then Morph ID
• 4PP
– Morph ID only
Wound Cultures: Example
• Q score = 2 [PMN (+3), few epi (-1)]
• Q/2-3-4 = 3 PP
• look at gram stain
– Work up: S. aureus, Group A streptococcus,
Morph ID and no susceptibility on enteric bacilli
Interpretation and reporting
• A pure growth of a recognized pathogen
obtained from a wound or closed abscess is
easily interpreted as significant and will be
reported to the physician as being so.
• Mixed cultures grown from superficial lesions
are the basic difficulty.
Interpretation and reporting
• Scanty growths of skin commensals such as staph or
diphteheroid bacilli are usually disregarded and not
reported. and a few colonies of E.coli grown from a
perineal . But clostridium perfringens is important.
• In superficial lesions such as varicose ulcers , present
of mixed commensal is not important.
• The result is reported: Many mixed fecal and skin
bacteria present. without giving identities or antibiotic
sensivities.
• But a pure growth of a commensal from an
aspirated deep wound is not contamination
and should be reported with AST
performance.
• In general, a numerous or predominant organism
is likely to have pathogenic significance.
• But the relative numbers of the colonies of the different
organisms on a culture plate may not reflect the relative
numbers of the organisms in the lesion .for they are
subject to many variations such as the relative speed of
growth of different species., antibiotic interactions
between different species and the greater tendency of
the more delicate pathogenes to die during transport of
specimens.
• For such reason a causal pathogen may be cultured in
smaller numbers than a contaminating commensal.
Wound Cultures: Examples
• Gram stain: Many neutrophils, few epithelial cells,
multiple morphotypes
• Culture grows: more than 3 potential pathogens
• Consider source
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Tissue or aspirate ?
Contamination likely ?
Type of patient
May need to consult with clinician or Infectious Diseases
service