[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › Gram-positive rods [Microbiology](https://durgical.com/en/microbiology/) · [Bacteria](https://durgical.com/en/microbiology/#d-bacteria) # Gram-positive rods - Bacteria Gram-positive rods: spore-forming clostridia and bacilli, corynebacteria, Listeria and the branching Nocardia and Actinomyces. Updated 2026-11-01 ## What they are This group gathers very different Gram-positive rods. The spore formers are Clostridium and Clostridioides (anaerobes) and Bacillus (aerobic); many cause disease through powerful toxins. Non-spore formers include Corynebacterium and Listeria, plus the branching filaments Nocardia (aerobic, weakly acid-fast) and Actinomyces (anaerobic). ## What they share - Spores: Clostridium, Clostridioides and Bacillus - Exotoxins drive the disease: tetanus, botulism, diphtheria, anthrax - Listeria: intracellular, grows in the fridge - Branching: Nocardia (aerobic) and Actinomyces (anaerobic) ## Key points - Tetanospasmin: blocks GABA and glycine release from inhibitory interneurons; spastic paralysis. - Botulinum toxin: blocks acetylcholine release; descending flaccid paralysis. - Diphtheria toxin: ADP-ribosylates elongation factor 2 and halts protein synthesis. - C. difficile: spores survive alcohol; wash with soap and water. - Nocardia: sulfonamides; Actinomyces: penicillin. ## Microorganisms in this group - [**Clostridium tetani** A soil bacterium whose spores enter through wounds and make a toxin that causes severe muscle spasms; vaccination prevents it. Exam priority: high](https://durgical.com/en/microbiology/clostridium-tetani/) - [**Clostridioides difficile** A bacterium that causes diarrhoea and colitis, mostly after antibiotics; its spores resist alcohol and are removed by washing with soap and water. Exam priority: high](https://durgical.com/en/microbiology/clostridioides-difficile/) - [**Clostridium botulinum** A soil bacterium whose toxin, the most potent known, causes a flaccid paralysis that can stop breathing. Exam priority: medium](https://durgical.com/en/microbiology/clostridium-botulinum/) - [**Clostridium perfringens** A bacterium that causes gas gangrene in deep wounds and a common food poisoning from reheated meat and gravy. Exam priority: medium](https://durgical.com/en/microbiology/clostridium-perfringens/) - [**Corynebacterium diphtheriae** A bacterium whose toxin can form a grey membrane in the throat and damage the heart and nerves; vaccination prevents it. Exam priority: medium](https://durgical.com/en/microbiology/corynebacterium-diphtheriae/) - [**Listeria monocytogenes** A bacterium of chilled foods that can cause miscarriage, newborn sepsis and meningitis in pregnant women, newborns, older and immunosuppressed people. Exam priority: medium](https://durgical.com/en/microbiology/listeria-monocytogenes/) - [**Bacillus anthracis** A spore-forming bacterium of soil and livestock that causes skin, lung or gut anthrax; it does not spread between people. For completeness](https://durgical.com/en/microbiology/bacillus-anthracis/) - [**Bacillus cereus** A spore-forming bacterium that causes food poisoning from reheated rice (fast vomiting) or from other foods (diarrhoea). For completeness](https://durgical.com/en/microbiology/bacillus-cereus/) - [**Nocardia** A filamentous soil bacterium that causes lung infection and brain abscess in immunosuppressed people, and skin infection after wounds. For completeness](https://durgical.com/en/microbiology/nocardia/) - [**Actinomyces israelii** A normal mouth bacterium that, after an injury, causes chronic abscesses with sinus tracts draining yellow grains, mostly in the jaw and neck. For completeness](https://durgical.com/en/microbiology/actinomyces-israelii/) ## Test yourself Think of the answer, then tap the question to see it. ## Which Gram-positive rods form spores? Clostridium, Clostridioides (anaerobes) and Bacillus (aerobic or facultative). ## How does the paralysis of tetanus differ from that of botulism? Tetanus causes spastic paralysis (it blocks inhibitory neurons); botulism causes flaccid paralysis (it blocks acetylcholine at the neuromuscular junction). ## Which Gram-positive rod grows at fridge temperature and crosses the placenta? Listeria monocytogenes. ## How are Nocardia and Actinomyces told apart? Nocardia is aerobic and weakly acid-fast; Actinomyces is anaerobic, not acid-fast and forms sulfur granules. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/groups/gram-positive-rods/) [← All of microbiology](https://durgical.com/en/microbiology/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Tetanus](https://www.who.int/news-room/fact-sheets/detail/tetanus) (WHO, 2026); [Botulism](https://www.who.int/news-room/fact-sheets/detail/botulism) (WHO, 2023); [Diphtheria](https://www.who.int/news-room/fact-sheets/detail/diphtheria) (WHO, 2025); [C. diff: Facts for Clinicians](https://www.cdc.gov/c-diff/hcp/clinical-overview/index.html) (CDC, 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/groups/gram-positive-rods/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/groups/gram-positive-rods/