Intracellular and atypical bacteria, mycobacteria and spirochaetes
Why intracellular, wall-deficient, acid-fast and spiral bacteria escape routine Gram stain and culture, need antibiotics that reach inside cells, and are diagnosed by serology, antigen tests or PCR.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- These organisms share three problems: routine Gram stain and culture miss them, beta-lactams often fail, and diagnosis relies on serology, antigen detection or PCR.
- Obligate intracellular: Chlamydia, Coxiella burnetii (Q fever), Rickettsia, Orientia (scrub typhus). Facultative intracellular: Legionella, Listeria, Salmonella Typhi, Brucella, Mycobacterium tuberculosis.
- Wall-deficient: Mycoplasma has no cell wall, so it is beta-lactam resistant by design.
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Sources
- Mandell, Douglas, and Bennett's Principles and Practice of Infectious DiseasesElsevier, 9th edition, 2020
- Therapeutic Guidelines: Antibiotic (2025 update)AU/NZTherapeutic Guidelines Limited, 2025
- Australian STI Management Guidelines for Use in Primary Care: SyphilisAU/NZAustralasian Society for HIV, Viral Hepatitis and Sexual Health Medicine (ASHM), Accessed November 2026
- Australian Immunisation Handbook: Q feverAU/NZAustralian Technical Advisory Group on Immunisation (ATAGI), Digital edition, accessed November 2026
- CDC Yellow Book 2026: Typhoid and paratyphoid feverCenters for Disease Control and Prevention, 2026
- Last updated
- 14 November 2026
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