Pus, Ulcer Material, Skin Specimens are common samples for microbiological examination in a tertiary care center set up like gram stain, culture, and sensitivity.
Abscess
Container: Aerobic swab moistened with Stuart’s or Amie’s medium
Patient preparation: Wipe the area with sterile saline or 70% alcohol. Swab along the leading edge of the wound.
Transport to the laboratory: Within 24 hours at room temperature.
Attention
Pus from an abscess is best collected at the time the abscess is incised and drained, or after it has ruptured naturally. When collecting pus from abscesses, wounds, or other sites, special care should be taken to avoid contaminating the specimen with commensal organisms from the skin. As far as possible, a specimen from a wound should be collected before an antiseptic dressing is applied.
For additional investigations
Look for granules: When mycetoma or actinomycosis is
suspected
Blood agar
Incubate aerobically
MacConkey agar
Incubate aerobically
Cooked meat medium
For anaerobic bacteria
Subculture at 24 hours, 48 hours, and 72 hours as indicated
Optional
Neomycin blood agar when
anaerobic infection is suspected
Incubate anaerobically up to 48 h
Culture for M. tuberculosis or M. ulcerans
Requires facilities of a
Tuberculosis Reference Laboratory
Examine Microscopically of Pus, Ulcer Material, Skin Specimens
Gram smear
For pus cells and bacteria
Optional steps
Ziehl-Neelsen smear: When tuberculosis or M. ulcerans disease is suspected
KOH preparation:
When a fungal or actinomycete infection is suspected
Giemsa or Wayson’s smear:
When bubonic plague is suspected
Polychrome methylene blue:
When cutaneous anthrax is
suspected
Dark-field microscopy:
To detect treponemes when
yaws or pinta is suspected
Day 2 and Onwards
Examine and Report Cultures of Pus, Ulcer Material, Skin Specimens
Blood agar and MacConkey agar cultures
Look particularly for:
S. aureus
S. pyogenes
P. aeruginosa
Proteus species
E. coli
Enterococcus species
Klebsiella species
Anaerobes:
C. perfringens
Bacteroides fragilis group
Peptostreptococcus species
Depending on the nature of organisms
Antimicrobial sensitivity pattern also depends on the nature of organism involvement
Organism isolated
Antimicrobial sensitivity pattern
Sensitive (S)
Resistant (R)
Intermediate (I)
Bacteria
Gram-positive
Staphylococcus aureus
Streptococcus pyogenes
Enterococcus species
Anaerobic streptococci
Other streptococci
Clostridium perfringens
and other clostridia
Actinomycetes
Actinomyces israeli
Also Mycobacterium tuberculosis
Gram-negative
Pseudonomas aeruginosa
Proteus species
Escherichia coli
Bacteroides species
Klebsiella species
Pasteurella species
Fungi
Histoplasma
Candida albicans,
mycetoma causing fungi
Parasites
Entamoeba histolytica
(in pus aspirated from an amoebic liver abscess)
Commensals
Any commensal organisms found in pus are usually those that have contaminated the specimen from skin, clothing, soil, or from the air if an open wound.
Ulcer Material and Skin Specimens
Possible pathogens
Bacteria
Gram-positive
Staphylococcus aureus
Streptococcus pyogenes
Enterococcus species
Anaerobic streptococci
Erysipelothrix rhusiopathiae
Bacillus anthracis
Gram-negative
Escherichia coli
Proteus
Pseudomonas aeruginosa
Yersinia pestis
Vincent’s organisms
Mycobacterium leprae
Mycobacterium ulcerans,
Treponema carateum,
Treponema pertenue.
Viruses
Poxviruses
herpes viruses
Fungi
Dermatophytes (ringworm fungi)
Malassezia furfur
Fungi that cause chromoblastomycosis
Candida albicans
Parasites
Leishmania species
Onchocerca volvulus
Dracunculus medinensis
Commensals
Commensal organisms that may be found on the
skin include:
Gram-positive
Staphylococci
Micrococci
Anaerobic cocci
Viridans streptococci
Enterococci
Diphtheroids
Propionibacterium acnes
Gram-negative
Escherichia coli
and other coliforms