Wound infections

Wound infection and abscesses occur as complication of surgery, trauma or disease that may interrupt a mucosal or skin surface.

There are a number of ways in which micro-organisms can gain access to a wound Direct contact: eg transfer from equipment or the hands of careers Airborne dispersal: micro-organisms deposited from the surrounding air Self-contamination: physical migration from the patient's skin or gastrointestinal tract

Lab procedure Firstly. In order to identify the different microorganisms that cause wound infection, we should collect a proper specimen from the area of the wound.

1- Aspiration Technique This method is considered to be the perfect and the most used method for specimen collection from an abscess or deep wound area.

Disinfect the area by using 70% alcohol. Local anesthetic by using pethedin. Insert sterile needle deeply inside the abscess of the wound and aspirate the largest amount of specimen.

NOTE: it’s very important here to empty the needle from air after you take the specimen in order to preserve the viability of anaerobic microorganism

2- Swap procedure Disinfect using 70 % alcohol. It is not common as the aspiration because it holds less volume and more subjected to contamination. Disinfect using 70 % alcohol. Local anesthetic by using pethedin. Open the abscess with a sterile knife and drain the puss and purulent material that gets out.

D. put the sterile cotton swap in the area of the draining and rotate it to get the largest volume possible and then place the swap in its special container. E. clean the area of the wound and remove the puss.

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). Swap 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.

Media used for Isolation Blood Media: most commonly used. Chocolate agar : Thioglycolate media: (enriched) MacConkey agar: Enterobacteria.

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.

Swap method take the swap under sterile condition, rotate it on the first quadrant of blood agar plate and replace it in a thioglycolate broth.

Colonies of Streptococcus pyogenes on sheep blood agar. Notice: * Presence of β 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: differentiates between Streptococcus –ve Staphylococcus +ve

Staphylococcus aureus G-positive cocci in clusters, typical of Staphylococcus aureus Catalase test used to differentiate Staphylococci from Streptococci

Coagulase test used to differentiate S Coagulase test used to differentiate S. aureus from other Staphylococcus spp.

Mannitol salt agar: selective and differential for Staphylococcus spp. (Staphylococcus aureus  manitol fermenteryellow)

Pseudomonas aeruginosa Greenish discoloration of media due to production of pyocyanin by Pseudomonas aeruginosa

Pseudomonas aeruginosa Results of oxidase test

Clostridium spp. Different locations of endospores within bacteria

Bacterial endospores positively stained, with the use of malachite green

Clostridium tetani Clostridium tetani, which typically infects the body through a deep wound. An acute, often fatal infectious disease caused by the bacterium Clostridium tetani, which usually enters the body through a wound and produces a toxin that affects nerve conduction. Tetanus is characterized by painful, spasmodic contractions of voluntary muscles, especially of the jaw.

E. coli G-negative bacilli, typical of E. coli Colonies of E. coli on MacConkey agar (Pink color indicates lactose fermentation)

IMViC reaction of E. coli: + + - - KIA A/A

Leishmania spp

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