Pyogenic Infections

(Wounds, Abscesses, Burns, Sinuses)

Possible Pathogens

@ Gram negative bacteria:

# Pseudomonas aeruginosa, Proteus spp. Escherichia coli, Bacteroides spp, Klebsiella spp., Pasteurella spp.

@ Gram positive bacteria:

# Staphylococcus aureus, Streptococcus pyogenes, Enterococci, Anaerobic streptococci, other streptococci, Clostridium tetani, Cl. perfringens, Actinomycetes, Myco. tuberculosis.

@ Fungi:

# Mycetoma spp, Histoplasma, Blastomyces, C. albicans, Cryptococcus neoformans.

Association with Pyogenic Infections:

@ S. aureus causes abscesses and skin infection

@ P. aeruginosa is associated with burns and hospital cross infections.

@ E. coli, Proteus spp, P. aeruginosa, and Bacteroides spp. are pathogens isolated from abdominal abscesses.

@ C. perfringens is found in deep wounds and gas gangrene.

@ C. tetani causes umbilical neonatal infection.

@ Bacteroides spp. cause infections of respiratory tract and female genital tract.

@ M. tuberculosis causes cold abscesses without inflammation

Commensals

@ Commensal organisms found in pus is due to specimen contamination while collection.

@ Sources of contamination are: the skin, clothes, soil, or air

@ Commensal skin organisms may cause acne vulgaris

Lab. Diagnosis of Pyogenic Infections

Collection and Transport:

@ Collect 5 ml of pus in sterile container

@ If pus is absent, use a swab and put in Amies transport medium.

@ If mycetoma is suspected, collect from a sinus by a needle.

@ If tuberculosis is suspected, aspirate pus and put in a container.

Macroscopy:

@ Look and report: # Colour of pus # Colour of granules: white, yellow, brown, red, or black. # Shape, size, and consistency of granules. # A magnifying lens is to identify granules of mycetoma. # Colour of amoebic abscess pus: red brown, grey, yellow

Microscopy

Gram smear:

@ Examine a stained smear for: # Gram positive cocci (S. aureus, streptococci, enterococci). # Gram negative rods (Proteus, E. coli P. aeruginosa, Bacteroides) . # Gram positive rods (C. perfringens).

Ziehl-Neelsen smear:

@ Examine for acid fast bacilli.

Potassium hydroxide preparation: @ Specimen without granules:

# Look for: Budding of Candida and C. neoformans. Look for branching of Nocardia.

@ Crush granules on a slide, mix with potassium hydroxide, and look for mycetoma granules and Actinomyces yellow granules.

Culture:

@ Inoculate one blood agar plate and Mac Conkey agar plate and incubate aerobically at 37°C overnight.

@ Inoculate a neomycin plate & a second blood agar plate and incubate at 37°C anaerobically for up to 48 hours.

@ Inoculate a cooked meat medium and incubate at 37°C for up to 72 hours.

@ For TB, decontaminate the specimen by immersing in 4% sodium hydroxide solution for 10 minutes, and inoculate an LJ slope and incubate for 8 weeks

@ For fungi, inoculate a Sabouraud agar

Examination of Cultures

@ In LJ slope: Look for M. tuberculosis producing raised, dry, creamy colonies. 

@ In blood, neomycin, Mac Conkey agar: Look for colonies of S.aureus, E. coli, ß-haemolytic Strep, Cl. perfringens, Pseudomonas, Proteus, Enterococcus, Bacteroides spp, and anaerobic cocci

@ In cooked meat medium: Look for turbidity, reddening of the meat, gas bubbles (Cl. Perfringens), decomposition & blackening of meat (Bacteroides)

@ Subculture the cooked meat medium if the anaerobic plates were sterile.