*Mycoplasma pneumoniae* is a prokaryotic pathogen that causes atypical pneumonia. Unlike most other bacteria, it lacks a peptidoglycan cell wall, rendering it naturally resistant to cell wall-targeting antibiotics such as amoxicillin. However, it can be successfully treated with antibiotics like azithromycin that target bacterial ribosomes.

Mycoplasma pneumoniae

The genus *Mycoplasma* consists of more than $${}100$$ species of bacteria that lack a cell wall and are classified as low G+C gram-positive bacteria, despite not staining with Gram-stain reagents. These bacteria are extremely small, with some diameters around $${}0.2$$ μm, which is smaller than certain large viruses. Due to the absence of a cell wall, *Mycoplasma* cells are pleomorphic, meaning they lack a fixed shape, can assume diverse forms, and may resemble tiny animal cells, making them challenging to identify.

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Individual cells of a specific prokaryotic organism typically exhibit a characteristic shape, known as cell morphology. While thousands of prokaryotic organisms exist, only a handful of morphologies are commonly seen microscopically. These standard shapes include spherical (coccus), rod-shaped (bacillus), curved comma-shaped (vibrio), short oval-like rods (coccobacillus), long rigid corkscrews (spirillum), and loose, flexible helical spirals (spirochete).

Cell Morphologies

Low G+C gram-positive bacteria are a diverse group of microorganisms characterized by having less than 50% guanine and cytosine nucleotides in their DNA. This category contains multiple classes and genera of bacteria, including several significant pathogens.

Low G+C gram positive bacteria

Al-mohanna, Moshtaq & H., quine. (2016). MORPHOLOGY AND CLASSIFICATION OF BACTERIA. 

Morphology and Classification of Bacteria

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Mycoplasmas

Pathogenic bacteria are bacteria that can cause infectious disease.

Pathogenic Bacteria

Which of the following bacterial morphologies is characterized by a spiral shape?

Which bacterial morphology is described as rod-shaped?

Which bacterial morphology is described as spherical in shape?

Which bacterial morphology is described as comma-shaped?

The term coccus (plural: cocci) is used to describe prokaryotic cells that possess a round, spherical shape.

Coccus

The term vibrio (plural: vibrios) is used to describe prokaryotic cells that are shaped like curved rods, closely resembling a long comma.

Vibrio

The term coccobacillus (plural: coccobacilli) refers to prokaryotic cells that appear as short rods, closely resembling ovals.

Coccobacillus

The term spirillum (plural: spirilla) describes prokaryotic cells that possess a long, spiral shape, visually resembling a corkscrew.

Spirillum

Spirochetes are gram-negative bacteria characterized by long, spiral-shaped bodies that can reach lengths up to $${}250$$ μm. Due to their extreme thinness, they are difficult to view under conventional brightfield microscopes, typically requiring darkfield fluorescent microscopy instead, and are highly difficult or impossible to culture in a laboratory.

Spirochete

Pleomorphism is the biological characteristic of certain cells or microorganisms, such as *Mycoplasma* species, that allows them to assume a variety of shapes rather than having a single characteristic morphology.

Pleomorphism

The term bacillus (plural: bacilli) refers to rod-shaped prokaryotic cells. In taxonomy, Bacillus is also a genus of low G+C gram-positive bacteria, many of which can form resilient endospores.

Bacillus

Clostridia are a group of low G+C gram-positive bacteria that are typically obligate anaerobes and capable of producing endospores.

Clostridia

Mycoplasmas are gram positive bacteria even though they lack a cell wall. They were identified by being gram positive because of their low G+C content genome. 

Mycoplasmas 

Bacilli is a class of low G+C gram-positive bacteria that includes both rod-shaped and spherical (coccus-shaped) species, such as the genera Bacillus and Staphylococcus.

Bacilli

Lactobacillales is an order of low G+C gram-positive bacteria that includes the genera Enterococcus, Lactobacillus, Leuconostoc, and Streptococcus.

Lactobacillales

The term staphylococcus (plural: staphylococci) describes a cellular arrangement where spherical cells (cocci) form grape-like clusters. Taxonomically, Staphylococcus is a genus of low G+C gram-positive bacteria.

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