Medical Microbiology and Pathogenic Microorganisms
Domain 7 links pathogens to syndromes, transmission, vectors and laboratory diagnosis. Learn the pairings and one diagnostic clue for each.
Bacterial diseases
Tuberculosis is caused by Mycobacterium tuberculosis, spreads by air and is diagnosed by acid-fast staining and the Mantoux test. Typhoid is caused by Salmonella Typhi, spreads faecally-orally and is investigated by blood culture and the Widal test. Cholera is caused by Vibrio cholerae, gives rice-water stools and is toxin-driven. Tetanus is caused by Clostridium tetani and causes spastic paralysis. Diphtheria is caused by Corynebacterium diphtheriae with a pseudomembrane. Leprosy is caused by Mycobacterium leprae and affects skin and nerves. Anthrax is caused by Bacillus anthracis; plague by Yersinia pestis with a flea vector. Staphylococci and streptococci cause pus-forming and toxin-mediated infections.
Viral, fungal and protozoan diseases
Polio spreads faecally-orally; rabies follows an animal bite and shows Negri bodies; HIV is blood- and sexually transmitted and depletes CD4 cells; dengue is transmitted by Aedes aegypti. Hepatitis B, influenza and measles are also viral. Fungal diseases include candidiasis, aspergillosis and dermatophytosis. Protozoan diseases include malaria (Plasmodium, female Anopheles), amoebiasis (Entamoeba histolytica), giardiasis, leishmaniasis and trypanosomiasis. Helminths include Ascaris and Wuchereria.
Worked example
A patient has fever, cough and acid-fast red rods in sputum. Reasoning: red bacilli after Ziehl–Neelsen staining are mycobacteria; the clinical picture and acid-fast smear point to pulmonary tuberculosis. Culture on Lowenstein–Jensen medium confirms.
Traps
HIV is not transmitted by mosquitoes. Malaria is caused by a protozoan, not a virus. Cholera disease is mainly toxin-mediated, not invasion. The dengue vector is Aedes, not Anopheles. Widal is not definitive for typhoid. Negri bodies are cytoplasmic inclusions in rabies.