Diseases caused by Gram-negative Cocci, Curved and Spiral Bacteria

Major Pathogens

1. Neisseria
   • Gram-negative diplococci, often seen inside PMNs
   • Selective culture on Thayer-Martin agar; oxidase-positive
   • Clinical Diseases
     • N. gonorrhoeae - gonorrhea (STD) 
     • N. meningitidis - meningitis
2. Moraxella catarrhalis
   • Gram-negative diplococci; oxidase-positive
   • Bronchitis, bronchopneumonia, otitis, sinusitis
   • Endogenous microbiota
3. Vibrio
   • Curved rods; usually oxidase-positive, motile
   • Found in fresh & salt water; contaminated shellfish
   • Produce exotoxins
   • Clinical diseases
     • V. cholerae: Cholera - severe diarrhea + dehydration; epidemic
     • V. parahaemolyticus:  Gastroenteritis - milder symptoms
     • V. vulnificus: wound infections + tissue necrosis (seawater & shellfish)
4. Helicobacter pylori
   • Curved rods with thickened flagella
   • Urease-positive microaerophiles
   • Clinical Disease
     • Peptic ulcer disease
5. Campylobacter jejuni
   • Curved rods; motile, microaerophile
   • Zoonotic; farm & domestic animals
   • transmission via contaminated food, water
   • Most common cause of bacterial gastroenteritis
6. Borrelia
   • Spirochaetes, hard to culture
   • Microaerophiles
   • Transmission by vectors
   • Microscopy used for diagnosing relapsing fever - spirochaetes in blood
   • ELISA or IF used for Lyme Disease
   • Clinical Diseases
     • Lyme disease
     • Endemic relapsing fever
     • Epidemic relapsing fever
7. Treponema pallidum
   • Spirochaetes; difficult to culture
   • Dark-filed microscopy useful for identification
   • Rapid DFA tests available
   • Clincal Diseases
     • Syphilis
     • Yaws, pinta, bejel
8. Leptospira
   • Spirochaetes; aerobic, bent, 2 flagella
   • Can penetrate membranes and into CNS
   • Clinical Diseases
     • Leptospirosis
     • Weil's disease

Major Diseases

1. Campylobacteriosis
2. Cholera
3. Gastroenteritis
4. Gonorrhea
5. Leptospirosis
6. Lyme disease
7. Meningitis
8. Peptic ulcer disease
9. Relapsing fever
10. Syphilis
11. Weil's disease
12. Yaws