A rapid grower among the following is:

ESIC Nursing Officer -2019 (Shift -1)

Applied Microbiology & Infection control

Easy

Appeared in: ESIC Nursing Officer -2019 (Shift -1)

Explanation

Mycobacteria are classified as rapid or slow growers based on their growth rate on solid culture media, with a 7-day cutoff.
Rapid growers are defined as those that form visible colonies in less than 7 days.
Mycobacterium abscessus is a well-known nontuberculous mycobacterium (NTM) that fits this definition, making it a rapid grower.
This rapid growth is a key characteristic used for its preliminary identification in a clinical microbiology laboratory.

Option A: Mycobacterium gordonae is a slow-growing mycobacterium. It is known as the "tap water bacillus" and is classified as a scotochromogen (Runyon Group II), meaning it produces pigment in both light and dark, but its growth takes longer than 7 days.
Option C: Mycobacterium avium is a classic example of a slow-growing mycobacterium. It is part of the Mycobacterium avium complex (MAC) and is a significant cause of pulmonary disease, but it requires several weeks to grow in culture.
Option D: Mycobacterium bovis is a member of the Mycobacterium tuberculosis complex, the group of bacteria that causes tuberculosis. All members of this complex are characteristically slow growers, taking 4-8 weeks to show visible growth on Löwenstein–Jensen medium.

Visual 1: Diagram: Runyon classification of nontuberculous mycobacteria. This chart visually organizes NTM into four groups based on growth rate and pigment production, clearly showing rapid growers (Group IV) as a distinct category.
Visual 2: Image: Comparative culture plates. A side-by-side view of a culture plate with M. abscessus showing visible colonies after 5 days, next to a plate with M. avium showing no visible growth at the same time point, effectively illustrates the concept of rapid vs. slow growth.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of Mycobacteria based on growth rate as background academic context rather than a clinical decision trigger.
The distinction between rapid and slow growers is clinically crucial. A lab report of a 'rapid-growing acid-fast bacillus' alerts the clinician to a potential NTM like M. abscessus, which requires a different antibiotic regimen than tuberculosis.
Rapid growers like M. abscessus are notorious for causing skin, soft tissue, and post-surgical wound infections. They are often highly resistant to standard antibiotics, making treatment challenging.
Nurses may be involved in collecting specimens (e.g., sputum, wound swabs) for culture. Understanding that different mycobacteria have different growth rates helps in managing expectations for lab turnaround times and appreciating the importance of preliminary reports.

How to Approach the Question

First, identify the core concept being tested in the question, which is the classification of mycobacteria.
Focus on the keyword 'rapid grower'. Recall the definition that distinguishes rapid from slow growers, which is the ability to form colonies in less than 7 days.
Systematically evaluate each option based on this definition.
Recall or deduce that M. abscessus is a classic example of a rapid grower.
Eliminate the other options by identifying them as slow growers: M. gordonae (scotochromogen), M. avium (MAC), and M. bovis (TB complex).
Confirm your choice by selecting the only option that fits the 'rapid grower' category.

Concept Tested & Keywords

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