Dependence of Specimen on Infection Site
To ensure that bacteriological test results are as accurate as possible, clinical material must be collected directly from the site of the infectious process. Depending on the pathology, the types of biological material studied may include pus, various necrotic masses, or body fluids.
The choice of a specific substrate is strictly tied to the localization of the inflammatory process:
| Disease (Process) | Clinical Material |
|---|---|
| Pneumonia | Sputum |
| Cystitis | Urine |
| Meningitis | Cerebrospinal fluid (CSF) |
| Colitis | Feces |
| Abscesses and phlegmon | Pus from the lesion |
Proper selection ensures that the laboratory receives the medium where the concentration of the target pathogen is maximal.
General Collection Principles (Asepsis and Timing)
The pre-analytical phase requires strict adherence to a number of rules. Any error at this stage makes further laboratory work meaningless.
- Timing of collection relative to treatment: Clinical material must be obtained strictly before starting targeted therapy (administration of antibiotics or antifungals). If medications have already been initiated, the bacteriological culture is highly likely to yield a false-negative result.
- Strict asepsis: Only sterile containers are used for specimen collection. The main task of the physician and nurse is to completely eliminate contamination—the introduction of environmental microflora from the patient's own skin or medical personnel's hands. For example, the slightest breach in technique during blood collection introduces skin saprophytes into the sample. They will grow in the laboratory, leading to a misdiagnosis.
- Labeling: Each sample must be carefully labeled. The patient's full name, date of birth, and type of submitted material must be indicated. It is critically important to record the exact time of sample collection, as this determines the assessment of specimen suitability for analysis.
Transportation and the Time Factor
Delivery of material at the initial stage of testing must be carried out promptly. Strict time regulations require that the interval from collection to inoculation on nutrient media does not exceed 1–2 hours.
There are several reasons for such strict limitations:
- Death of fastidious microorganisms: many pathogens do not survive long outside the host organism.
- Distortion of quantitative analysis: rapidly growing microflora can multiply within hours to such an extent that they suppress the growth of the true pathogen.
- Sample degradation: putrefactive and fermentative processes begin rapidly in the material.
Sealed containers, tubes, or specialized transport systems containing supporting nutrient media are used for delivery to maintain bacterial viability.
Special requirements for anaerobes: Non-spore-forming anaerobes are extremely sensitive to atmospheric oxygen and die rapidly upon contact with it. To preserve them, highly specialized methods that completely exclude aeration are used: specialized transport media or vessels filled with inert gas.
Collection Methods in Special Cases
The technique for obtaining a clinical sample varies depending on the procedure. Specific methods include:
- Duodenal intubation: bile collection is performed fractionally. Material is collected in portions (A, B, and C), with each placed in a separate, strictly sterile tube.
- Intraoperative collection: during surgical interventions, material (such as pus or exudate) is obtained via syringe aspiration. Maximum aseptic rules are observed, and the material is collected into a single tube.
In both cases, the rule for delivery time remains unchanged—no later than 1–2 hours after sample collection.