Microbiology for Chiropractic Students: Mycobacterium 101

While the Part I microbiology section may see like a bore, as a chiropractic student, understanding the various pathogens that can affect human health is crucial for a well-rounded approach to patient care. One of the most significant bacterial pathogens you'll encounter in your studies is Mycobacterium, the genus responsible for diseases such as tuberculosis. In this guide, we’ll explore the characteristics of Mycobacterium, the importance of Lowenstein-Jensen medium in its identification, and why this knowledge is essential for your chiropractic practice.

Understanding Mycobacterium

Mycobacterium is a genus of bacteria known for its slow growth, unique cell wall structure, and ability to cause chronic infections. The most notable species in this genus are Mycobacterium tuberculosis (causing tuberculosis) and Mycobacterium leprae (causing leprosy).

Key Characteristics

1. Cell Wall Structure
   • Mycobacterium has a thick, waxy cell wall rich in mycolic acids. This unique structure makes it resistant to many common antibiotics and disinfectants, contributing to its persistence in the environment and within host organisms.
2. Acid-Fast Staining
   • Due to its waxy cell wall, Mycobacterium does not stain well with traditional Gram stains. Instead, it is identified using an acid-fast stain, such as the Ziehl-Neelsen stain, which highlights the bacteria’s resistance to decolorization.
3. Slow Growth
   • Mycobacterium species grow very slowly, with M. tuberculosis taking up to six weeks to form visible colonies. This slow growth rate is a significant factor in the challenges associated with diagnosing and treating infections caused by these bacteria.

Lowenstein-Jensen Medium: A Critical Tool for Culturing Mycobacterium

Given the slow-growing nature of Mycobacterium, specialized culture media are required to support its growth and isolation. The Lowenstein-Jensen (LJ) medium is the most widely used medium for this purpose.

Composition of Lowenstein-Jensen Medium

1. Egg-Based Medium
   • LJ medium is primarily composed of whole eggs, which provide the necessary nutrients for Mycobacteriumto grow. The medium also contains malachite green, which inhibits the growth of contaminating bacteria and fungi, allowing Mycobacterium to thrive.
2. Glycerol and Asparagine
   • Glycerol serves as a carbon source, while asparagine is included as a nitrogen source, both essential for the growth of Mycobacterium species.
3. Antibiotics
   • In some formulations, antibiotics such as penicillin and nalidixic acid are added to the LJ medium to further suppress the growth of non-Mycobacterium contaminants.

Function and Application in Diagnosis

Lowenstein-Jensen medium is indispensable in the clinical microbiology lab for the following reasons:

1. Culturing Mycobacterium Species
   • LJ medium is used to culture clinical specimens suspected of containing Mycobacterium, such as sputum samples from patients with tuberculosis. The medium supports the growth of Mycobacterium tuberculosis, allowing it to form characteristic rough, buff-colored colonies.
2. Identification and Diagnosis
   • The colonies grown on LJ medium can be further tested to confirm the presence of Mycobacterium tuberculosis through biochemical tests and molecular techniques like PCR. This process is crucial for diagnosing tuberculosis and initiating appropriate treatment.
3. Antimicrobial Susceptibility Testing
   • LJ medium can also be used in susceptibility testing, where different antibiotics are added to the medium to determine the most effective treatment options for a given strain of Mycobacterium.

Mycobacterium and the Lowenstein-Jensen medium are key topics in the Microbiology domain of your NBCE Part I exam. There are a loads more of other pathogens to learn and studying and remembering which one is Gram negative versus a spirochete versus which was is transmitted from snails can be overwhelming. This is why our CAL board reviews have mnemonics, colorful drawings and charts to help you remember everything you need to know about microbiology. Want to check out our review courses? Go here!

We hope this blog post reminded you of some important facts about mycobacterium!

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