Download wounds and abscess

Microorganisms infecting the skin
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.
• Wound infection and abscesses
occur as complication of surgery,
trauma or disease that may interrupt
a mucosal or skin surface.
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. )
Lab procedure
• Firstly. In order to
identify the different
microorganism that
cause wound
infection, we should
collect a proper
specimen from the
area of the wound.
1- Aspiration Technique
This method considered to be the perfect and the
most used method for specimen collection from
an abscess or deep wound area.
a. Disinfect the area by using 70% alcohol.
b. Local anesthetic by using pethedin.
c. Insert sterile needle deeply inside the abscess
of the wound and aspirate the largest amount
of specimen.
2- Swab procedure
• Swabs are inefficient sampling and are strongly discouraged. It
is not common as the aspiration because it holds less volume
and more subjected to contamination.
A. Disinfect using 70 % alcohol.
B. Local anesthetic by using pethedin.
C. Open the abscess with a sterile knife and drain the puss and
purulent material that gets out.
• D. put the sterile cotton swab in the area of
the draining and rotate it to get the largest
volume possible and then place the swab in its
special container.
• E. clean the area of the wound and remove
the pus.
Transportation
• Transport the specimen to
the lab as soon as possible.
In case ……
• Aspirated specimen: put it
in to anaerobic containers,
in which oxygen is excluded
or filled with Co2. (Keep at
Moist conditions & Room
temperature).
• Swab specimens: the cotton
should be put in transport
media called stiurts media.
to preserve the specimen
from drying and prevent the
over growth of rapidly
growing microorganism.
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
Microscopy
• Much useful information may be obtained from
smear by Gram-staining. We should notice
– presence and relative numbers of PMNs 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
Specimen processing
inoculation
• Aspirated specimen: if it is thick we should
emulsify in normal saline or thioglycolate
media in order to make suspension. And we
do the culture by streaking method.
• Colonies of Streptococcus
pyogenes on sheep blood
agar.
• Notice: * Presence of b
hemolysis
around
colonies
• * Enhanced hemolysis
around stabbing sites
• * Sensitivity to bacitracin
(Disk A)
Streptococcus pyogenes
• Pin point colony:
(white or gray)
• Gram stain: G+ve, cocci,
single chain.
• Catalase enzyme:
differentiate between
Streptococcus –ve
Staphylococcus +ve
Staphylococcus aureus
Identification Process
Microscopic morphology
• Gram Positive Cocci in clusters
IDENTIFICATION PROCESS
Biochemical Tests
• Catalase
• Coagulase
• Mannitol salt Agar growth
1.
Catalase Test
• Place a drop of 3% H2O2 on glass slide.
• Select colonies to be tested
• Mix colonies in drop of H2O2 (Hydrogen Peroxide)
• H2O2
catalase
H2O + O2
Catalase Test
Bubbles = positive
catalase present
No bubbles = negative
no catalase present
•All Staphylococcus species are catalase positive
Catalase +ve
Catalase -ve
2. COAGULASE TEST:
3. Coagulase converts fibrinogen to fibrin
• Pathogenic strains coat themselves in fibrin to evade immune
system
3.
Growth on Salt Mannitol agar
• streak plate with organism
• if mannitol is fermented - acid is produced
• Phenol red (indicator) turns yellow in presence of acid
• incubate 18-24 hrs at 37o C
Coagulase-negative Staphylococi
Growth seen, but no color change
• Staphylococcus aureus
Growth AND color change
Pseudomonas aeruginosa
• Greenish discoloration
of media due to
production of
pyocyanin by
Pseudomonas
aeruginosa
Pseudomonas aeruginosa
• Results of oxidase
test
CLOSTRIDIUM SPECIES
• Genus Clostridium consists of
Gram positive, anaerobic, spore
forming bacilli.
Common Species
• Clostridium perfringens – Gas
gangrene
• Clostridium botulinum –
Botulism
• Clostridium tetani
– Tetanus
Microscopic morphology
• Clostridium perfringens
• Gram Positive bacilli
Clostridium tetani
Gram positive bacilli
with drum stick appearance
Anaerobic Jar & Gas Pack
Leishmaniasis
• Obligatory intracellular belong to genus
Leishmania
• It is transmitted by sandflies.
Morphological stages of the Leshmania spp. affecting
humans
Leishmania species
Amastigote
Promastigote
Intracellular in
macrophages in
humans
In midgut, then proboscis
of sandfly ( infective stage
to human) and in culture
Amastigotes of Leishmania
Promastigotes of Leishmania
Mode of infection
• Bite of female
sand flies
• Phlebotomine
(in Old World)
• promastigotes
(infective stage)
Life cycle
Depending on the
species of
parasite
amastigotes may
cutaneous leishmaniasis
Diagnosis:
• Smear: Giemsa stain – microscopy for LD
bodies (amastigotes)
• Biopsy: microscopy for LD bodies or culture in
NNN medium for promastigotes
NNN medium
• agar slant overlaid with
defibrinated rabbit
blood used to detect
the presence of
Leishmania.
Schistosomiasis
• Females are slender and delicate, whereas
males are much bigger and have a spiny
trough or groove into which the female fits
and locks in.
• The male consumes blood and feeds the
female most of it, which she turns into eggs,
which pass out of the host and can begin the
life cycle again.
Blood fluke is a special kind of flukes because of
following characters:
(1) The adult worms look like nematodes, elongated cylindrical in
shape.
(2) Two sexes are separate.
(3) egg without operculum, but with a terminal spine.
(4) only one intermediate host required.
(5) The infective stage is cercaria.
(6) The infective route is by skin.
(7) The eggs are main pathogenic stage.
Paired male and female adult worms. The female is the darker, curled
worm within the male's gynacophoric canal.
Mature egg is oval in shape, slight yellow in color, shell is thin
without an operculum but with a terminal spine. The content is a
miracidium.
Cercaria is infective stage. It is composed of the body and forked
tail (including tail stem and fork) and has 5 pairs of penetrating
glands in the body.
oval in shape, slight
yellow in color, shell
is thin without an
operculum but with a
terminal spine.
A Comparison of Schistosome Eggs
S. mansoni
Lateral spine
S. haematobium
Terminal spine
S. japonicum
No spine
Cutaneous Fungal Infections
oDermatophytosis - "ringworm" disease of the
nails, hair, and the skin caused by fungi called
dermatophytes.
oDermatomycosis - more general name for any
skin disease caused by a fungus.
Diagnosis
• Note the symptoms.
• Microscopic
examination of slides of
skin scrapings, nail
scrapings, and
hair. Often tissue
suspended in 10 % KOH
solution to help clear
tissue.