Rickettsiae and Rickettsial Diseases: One Family, Many Fevers
The rickettsiae explained: obligate intracellular bacteria spread by arthropods that infect blood vessels and cause typhus, spotted fever, scrub typhus, and Q fever, with how the d...
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Gram-Negative Cocci and Coccobacilli
Neisseria, Moraxella, Haemophilus and related gram-negative coccal organisms
About Gram-Negative Cocci and Coccobacilli
Gram Negative Cocci
Neisseria gonorrhoeae, Neisseria meningitides, Moraxella catarrhalis, and other Neisseria spp. are clinically relevant gram-negative cocci.
N. gonorrhoeae is the leading cause of sexually transmitted disease whereas N. meningitides is a leading cause of fatal bacterial meningitis.
Scrub Typhus (Orientia tsutsugamushi): The Eschar, Diagnosis, and Treatment
How Orientia tsutsugamushi causes scrub typhus, why the eschar at the chigger bite is the key clinical clue, how it is diagnosed (IFA, ELISA, Weil-Felix OX-K), and why treatment is...
Moraxella catarrhalis: Identification, How to Tell It from Neisseria, and Disease
How Moraxella catarrhalis causes otitis media, sinusitis, and respiratory infection, and how the laboratory tells it apart from Neisseria, since the two look identical on Gram stai...
Neisseria meningitidis: Properties, Pathogenesis, Virulence Factors, and Lab Diagnosis
Neisseria meningitidis causes life-threatening bacterial meningitis and meningococcaemia. Learn its serogroups (A, B, C, W, X, Y), virulence factors (capsule, LOS, fimbriae, IgA pr...
Acinetobacter baumannii: A Drug-Resistant ICU Pathogen and How It Is Identified
Why Acinetobacter baumannii is one of the most drug-resistant hospital pathogens, how it survives on surfaces to cause ICU outbreaks, and how the laboratory identifies it as a non-...
Thayer-Martin Agar (Modified): Composition, Principle, Uses, and Colony Characteristics of Neisseria
Modified Thayer-Martin (MTM) agar is the standard selective medium for isolating Neisseria gonorrhoeae from genital specimens. Learn its VCNT antibiotic selectivity, GC agar base c...
Gram-Negative Cocci and Coccobacilli of Medical Significance: List, Diseases, and Lab Identification
The medically important Gram-negative cocci include Neisseria gonorrhoeae (gonorrhoea, ophthalmia neonatorum), N. meningitidis (meningitis), and Moraxella catarrhalis (otitis media...
Differences between Neisseria gonorrhoeae and Neisseria meningitidis: A Complete Comparison
N. gonorrhoeae and N. meningitidis are both Gram-negative diplococci but differ fundamentally in capsule, diseases, transmission, maltose fermentation, serogroups, vaccine availabi...
New York City (NYC) Medium: Composition, Principle, Uses, and Colony Characteristics
New York City (NYC) medium is a selective medium for Neisseria gonorrhoeae that uniquely supports genital Mycoplasma and Ureaplasma alongside Neisseria. Learn its principle, horse...
Brucellosis (Brucella): The Intracellular Cause of Undulant Fever, and How It Is Diagnosed
How Brucella causes brucellosis (undulant fever), why hiding inside macrophages makes it a chronic, relapsing infection that is slow to culture and a laboratory biohazard, and how...
Typhus Fever: Epidemic and Endemic Typhus, and How They Differ from Typhoid
The two typhus-group rickettsial diseases explained: epidemic (louse-borne) typhus caused by Rickettsia prowazekii and endemic (murine, flea-borne) typhus caused by Rickettsia typh...
Neisseria gonorrhoeae: Properties, Pathogenesis, Virulence Factors, and Lab Diagnosis
Neisseria gonorrhoeae causes gonorrhoea: the second most common STI globally. Learn its Gram-negative diplococcus properties, virulence factors (pili, Opa proteins, IgA protease, L...
FTA-ABS Test: Interpretation, When It Confirms Syphilis, and FTA-ABS vs TPPA
How to interpret an FTA-ABS result: what reactive-plus-reactive-RPR confirms, why FTA-ABS stays positive for life, why it cannot monitor treatment, and how it now compares to TPPA...