(Wounds, Abscesses, Burns, Sinuses) 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.