What is the correct standard method for the short-term storage of microbiological specimens such as urine, st… - KGMU 2023

KGMU 2023

Applied Microbiology & Infection control

Easy

Appeared in: KGMU 2023

Explanation

The standard method for short-term preservation of common microbiological specimens (urine, stool, swabs) is refrigeration at 2-8°C, with 4°C being a common set point.
Refrigeration slows down the metabolic rate of bacteria, which prevents the rapid overgrowth of commensal (normal flora) organisms.
This preservation method ensures that the viability of potential pathogens is maintained without altering the original microbial balance in the sample, leading to more accurate diagnostic culture results.
Specimens like urine can be stored for up to 24 hours at 4°C, and stool for up to 72 hours at 4°C, if immediate processing is not possible.

Option A: Freezing at -80°C is a method for long-term preservation (archiving) of pure bacterial isolates or viruses, not for short-term storage of clinical specimens. The process of freezing and thawing can damage or kill many types of bacterial cells, leading to a false-negative culture.
Option C: Storing specimens at room temperature (around 25°C) allows for the rapid and uncontrolled multiplication of bacteria. This can cause commensal organisms to overgrow the actual pathogens, making isolation and identification difficult or impossible.
Option D: An incubator at 37°C is used to actively grow bacteria on culture plates in the laboratory. Placing a raw specimen directly in an incubator would promote rapid, non-selective growth of all bacteria present, spoiling the sample for diagnostic purposes.

Visual 1: Infographic - A chart showing different types of specimens (urine, stool, blood, CSF) and their correct short-term storage temperatures (refrigerator, incubator) and maximum holding times. This visually reinforces the correct procedures for each specimen type.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Short-term storage of microbiological specimens as background academic context rather than a clinical decision trigger.
Proper specimen handling is a critical nursing responsibility that directly impacts diagnostic accuracy and patient treatment. An incorrect storage method can lead to a missed diagnosis or inappropriate antibiotic therapy.
Nurses must ensure that specimens are labeled correctly and transported to the lab promptly. If a delay is unavoidable, the nurse is responsible for storing the specimen at the correct temperature.
What if? If a urine sample for culture is left at room temperature for 4 hours before being sent to the lab, the bacterial count could be falsely elevated due to the multiplication of contaminants, potentially leading to a misdiagnosis of a urinary tract infection and unnecessary antibiotic treatment.

How to Approach the Question

First, identify the core question: It asks for the 'standard method' for 'short-term storage' of common microbiological samples (urine, stool, swabs).
Think about the goal of short-term storage: to preserve the sample as it is, without letting bacteria die or multiply.
Evaluate the temperature options based on this goal:
-80°C (freezer): This is extreme cold, likely for long-term preservation, and might kill bacteria.
37°C (incubator): This is body temperature, ideal for growing bacteria, not preserving a sample.
25°C (room temp): This is warm enough for many bacteria to multiply, which would alter the sample.

Concept Tested & Keywords

Concept Tested: Short-term storage of microbiological specimens
Stem keywords: short-term storage, microbiological specimens, urine, stool, swabs
Lead-in keywords: correct standard method
Negative lead-in flag: false

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