[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › Other clinically important bacteria [Microbiology](https://durgical.com/en/microbiology/) · [Bacteria](https://durgical.com/en/microbiology/#d-bacteria) # Other clinically important bacteria - Bacteria Eight bacteria outside the big groups that still show up in exams: anaerobes, bites, seafood, the hospital, Whipple and the non-venereal treponemes. Updated 2026-11-01 ## What they are A practical group, not a taxonomic one: bacteria a student meets in one very specific clinical setting. Each has a classic clue (foul-smelling abscess, painful genital ulcer, cat bite, raw oysters, cystic fibrosis, ICU resistance, PAS-positive macrophages or skin lesions in tropical children). ## What they share - Most are Gram-negative; Tropheryma whipplei is Gram-positive and treponemes do not show well on Gram stain - Almost all are recognised by context: a bite, seawater, the hospital, cystic fibrosis or rural poverty - Several carry intrinsic resistance that changes the antibiotic choice (AmpC in Enterobacter, Burkholderia against aminoglycosides and polymyxins) - None has a vaccine for human use ## Key points - Intra-abdominal abscess with foul pus and gas: think Bacteroides fragilis and cover anaerobes. - Painful genital ulcer with a suppurative bubo: chancroid (H. ducreyi); syphilis gives a painless ulcer. - Cellulitis within hours of a cat or dog bite: Pasteurella multocida. - Patient with cirrhosis who ate raw oysters and develops sepsis with skin bullae: Vibrio vulnificus. - Enterobacter and Serratia in the ICU: AmpC and carbapenemases narrow the treatment options. ## Microorganisms in this group - [**Bacteroides fragilis** An anaerobe of the colon that, once it escapes through a perforation or surgery, forms foul-smelling abdominal and pelvic abscesses. Exam priority: medium](https://durgical.com/en/microbiology/bacteroides-fragilis/) - [**Haemophilus ducreyi** A sexually transmitted bacterium that causes chancroid: painful genital ulcers with inguinal lymph nodes that suppurate. For completeness](https://durgical.com/en/microbiology/haemophilus-ducreyi/) - [**Pasteurella multocida** A bacterium from the mouths of dogs and cats that infects bites and scratches: the skin turns red, swollen and painful within hours. For completeness](https://durgical.com/en/microbiology/pasteurella-multocida/) - [**Burkholderia cepacia complex and Burkholderia pseudomallei** Soil and water bacteria: B. cepacia infects the lungs in cystic fibrosis; B. pseudomallei causes tropical melioidosis. For completeness](https://durgical.com/en/microbiology/burkholderia-cepacia-complex-and-burkholderia-pseudomallei/) - [**Vibrio vulnificus and Vibrio parahaemolyticus** Seawater vibrios: diarrhoea from raw shellfish and wound infections that can kill people with liver disease. For completeness](https://durgical.com/en/microbiology/vibrio-vulnificus-and-vibrio-parahaemolyticus/) - [**Enterobacter, Serratia and Citrobacter** Hospital Enterobacterales that infect patients with urinary catheters, lines or ventilators and pile up antibiotic resistance. For completeness](https://durgical.com/en/microbiology/enterobacter-serratia-and-citrobacter/) - [**Tropheryma whipplei** A rare bacterium that causes Whipple disease: joint pain, diarrhoea with malabsorption and weight loss; untreated, it is fatal. For completeness](https://durgical.com/en/microbiology/tropheryma-whipplei/) - [**Non-venereal treponemes (yaws, bejel and pinta)** Relatives of the syphilis agent spread by skin contact among children in poor tropical areas: yaws, bejel and pinta. For completeness](https://durgical.com/en/microbiology/non-venereal-treponemes/) ## Test yourself Think of the answer, then tap the question to see it. ## Which bacterium of this group is the Gram-negative anaerobe most often isolated from abdominal abscesses? Bacteroides fragilis, part of the normal colonic flora. ## How is chancroid told apart clinically from primary syphilis? Chancroid gives a painful, ragged ulcer with tender inguinal nodes; the syphilitic chancre is painless with a clean base. ## In which patients does Burkholderia cepacia complex cause severe respiratory infection? People with cystic fibrosis or other chronic lung disease and immunocompromised hospital patients. ## What do yaws, bejel and pinta share with syphilis? They are caused by treponemes that cannot be told apart from Treponema pallidum by morphology or by syphilis serology. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/groups/other-clinically-important-bacteria/) [← 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: [Mixed Anaerobic Infections - Infectious Disease - MSD Manual Professional Edition](https://www.msdmanuals.com/professional/infectious-diseases/anaerobic-bacteria/mixed-anaerobic-infections) (MSD Manual Professional Edition, 2025); [About Carbapenem-resistant Enterobacterales (CRE) | CRE | CDC](https://www.cdc.gov/cre/about/index.html) (CDC, 2025); [Chancroid - STI Treatment Guidelines](https://www.cdc.gov/std/treatment-guidelines/chancroid.htm) (CDC, 2021). ## **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/other-clinically-important-bacteria/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/