wounds

1
(No Transcript)
2
Wound Infection

• Dr. Kiarash Ghazvini
• Department for bacteriology and virology,
• Mashhad University of medical Sciences

3
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.

4
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.

5
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. )

6

• 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.

7
Contamination

• The contaminating organisms are present in small
  numbers

8
Colonization

• In the case of commensal or low grade pathogenes
  it can be described colonization.

9
Infection

• Infection occurs when they evades the host
  defences.replicates in large numbers and attacks
  the host tissue.

10
WoundsClassification

• Acute
• Caused by external damage to intact skin
• Types
• Surgical
• Bites
• Burns
• Minor cuts
• Abrasions
• Severe traumatic

• Chronic
• Precipitated by predisposing conditions that lead
  to compromise of dermal/epidermal tissue
• Types
• Impaired venous drainage
• Impaired arterial supply
• Metabolic diseases eg. diabetes

11
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

12
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

13
SAMPLING

• Biopsy
• ? Aspirate from depth of the wound
• if possible pus or exudate should be submitted in
  a small screw-capped bottle, a firmly stoppered
  tube or sterile syringe and needle.

14
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.

15
SAMPLING

• Delay in the transit of specimen to the
  laboratory must be avoided.especially swabs where
  the exudate may dry.

16
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.

17
SAMPLING

• ? Clean the wound margins with 70 ethyl alcohol.
  

18
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

19
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 .

20
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

21
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

22
CULTURE

• the specimen should be inoculated on two plates
  of blood agar (SBA 5),
• the one for incubation at 37c, 5-10 CO2.,for
  18-24h.
• 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.

23
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.

24
CULTURE

• if at 24 h or 48 h there is growth on cooked-meat
  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.

25
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
  gram-negative anaerobes

26
Wound Specimens Algorithms

• Three approaches
• PMN predominance
• Q-Score
• Q-2-3-4 system

27
(No Transcript)
28
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

29
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

30
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 stainWorkup all PP that are
  seen on GSMorphologically ID othersIf all PP
  present on GS then only Morph ID all

31
(No Transcript)
32
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

33
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

34
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

35
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

36
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.

37
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.

38

• 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.

39

• 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.

40
Wound Cultures Examples

• Gram stain Many neutrophils, few epithelial
  cells, multiple morphotypes
• Culture grows more than 3 potential pathogens
• Consider source
• Tissue or aspirate ?
• Contamination likely ?
• Type of patient
• May need to consult with clinician or Infectious
  Diseases service

41
(No Transcript)