A wide variety of microbes can be isolated in pus, which are related to the large number of sites and the nature of the biological products. The samples can be divided into three classes:
Class 1: These come from closed deep areas that are normally sterile (serous, pleural, joint, pericardial, and synovial fluid; brain abscess, etc.). These samples are obtained during a surgical procedure using a needled syringe. In cases of infection, they are usually monomicrobial and are not contaminated (microorganisms from the skin are eliminated by asepsis before the surgical procedure). A foul odor and a “chocolate” color should prompt an investigation for anaerobic organisms and the use of an adequate means of transport.
Class 2: These come from deep areas that are in communication with surfaces with commensal flora (fistulated abscess).
– Disinfect the outer orifice with a bactericidal solution.
– Using a needled syringe, try to take the sample from as deep an area as possible. A catheter can also be used. The quantity of fluid sampled should be sufficient for the investigation of anaerobic microorganisms.
Class 3: Suppurated fluid collections coming from superficial areas with their own commensal flora (eschar, burns).
– Remove the cellular and tissue debris by lavage with normal saline.
– Several techniques are then possible:
- aspiration by sterile pipette
- skin biopsy
- sample per syringe
- swab (technique to be avoided since not specific).
NB: In each of these cases, the clinical information is essential for orienting the bacteriological research and differentiating the contaminants from infectious organisms. If the patient is receiving antibiotic therapy, the drug(s) should be noted. The samples should be taken quickly to the laboratory.
For the safety of the laboratory employees and those who transport the samples, needled syringes are not accepted.
7.1.1 Ear pus
– The sample is taken by swabbing in cases of otitis externa.
– For otitis media, the sample is done by the specialist (ENT) during myringotomy: the pus is aspirated using a suction machine.
7.1.2 Ophthalmic pus
The sample is taken with a swab from the medial angle of the eye, in the lacrimal sac.
In newborns, take a second swab sample to investigate for Chlamydia.