Post on 05-Jan-2016
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.