Biological Properties and Morphology
The causative agent of gonorrhea was discovered by Albert Neisser in 1879. These are typical Gram-negative, kidney-shaped bacteria that occur in pairs as diplococci. They do not form spores but possess pili on their surface. A characteristic feature upon microscopy of purulent discharge is the intracellular localization of bacteria within leukocytes (the phenomenon of incomplete phagocytosis), although extracellular forms are also found.
Biochemically, Neisseria gonorrhoeae is relatively inactive, fermenting (oxidizing) only glucose. They are aerobic chemoorganotrophs with extremely fastidious nutritional requirements. Gonococci do not grow on simple media: cultivation requires native proteins (serum, blood, ascitic fluid) or the amino acid arginine. Optimal conditions include a temperature of 36–37 °C, pH 7.3–7.4, and an elevated carbon dioxide concentration.
Virulence Factors
The virulence of the pathogen is determined by the structure of the outer cell wall membrane and pili. The main feature of the gonococcus is its ability to evade the immune response due to the high variability of the pilin protein amino acid sequence (both between different strains and within a single strain).
Key virulence factors:
- Pili: Responsible for initial adhesion to the epithelium, inhibit neutrophil phagocytosis, and participate in genetic exchange.
- Por proteins (Protein I): Prevent phagosome-lysosome fusion, allowing bacteria to survive inside phagocytes.
- Opa proteins (Protein II): Provide tight adherence to host cells.
- Protein III: Protects the bacterium against complement by blocking the bactericidal action of blood serum.
- Lipooligosaccharide (LOS): An analog of Gram-negative LPS, acting as an endotoxin that causes cell damage and an inflammatory response.
- IgA proteases: Enzymes that cleave secretory immunoglobulins, facilitating mucosal colonization.
Clinical Presentation and Epidemiology
The sole reservoir and source of infection is humans (strict anthroponosis). The disease is transmitted primarily sexually (gonorrhea) and affects mucous membranes lined with columnar epithelium: the urogenital tract, rectum, and oropharynx. Vertical (contact) transmission to the conjunctiva during passage through infected birth canals can occur in newborns, leading to acute purulent conjunctivitis known as blennorrhea.
Pathogenesis stages include adhesion, invasion into the submucosa (within 24–48 hours) with LOS release, and neutrophil migration to the focus. This results in epithelial shedding and purulent exudate formation. In men, the typical presentation is urethritis with dysuria and purulent discharge, frequently complicated by prostatitis. In women, 70% of cases are asymptomatic, though chronic inflammation can lead to infertility.
Immunity following infection is non-sterile and short-lived, failing to establish protective mechanisms, which allows for frequent reinfections.
Diagnosis and Treatment
The pathogen is extremely fragile in the external environment: sensitive to drying, sunlight (UV), and disinfectants. This requires special conditions during collection and transport of biological specimens (preventing drying and cooling of purulent discharge).
Diagnostic Methods:
- Bacterioscopy: Gram staining of smears. Detection of intracellular Gram-negative diplococci is the primary criterion. However, in women, the method has low specificity due to commensal diplococci in the normal flora.
- Bacteriological ("Gold Standard"): Culture on specialized media supplemented with amino acids. Necessary for differential diagnosis from non-gonococcal urethritis.
- Additional: PCR, direct fluorescent antibody (DFA) testing, and co-agglutination (for antigen detection). Serology is rarely used (primarily for chronic forms).
Treatment Principles: Cephalosporins and fluoroquinolones are utilized. Due to rapid resistance evolution (emergence of penicillinase-producing strains, resistance to tetracyclines and ciprofloxacin), performing antibiotic susceptibility testing prior to treatment is highly recommended. For chronic forms, immunotherapy (killed gonococcal vaccine) is applied.