Pathogenic Bacteria: Structure, Symptoms and Diagnosis
Bacterial Structure and Protective Layers
Capsule
The capsule is a structure composed of viscous carbohydrate substances. It plays a protective role against phagocytosis and the attack of antibodies.
Bacterial Cell Wall
The bacterial cell wall is formed by peptidoglycan and other substances. It is a rigid wrapper that supports the strong osmotic pressure to which bacteria are subjected.
Pathogenic Neisseria Species
Gonococcus (Neisseria gonorrhoeae)
Clinical manifestations:
- Men: Urethritis with thick, yellowish pus, painful urination, and dysuria.
- Women: Pelvic inflammatory disease (PID), salpingitis, endocervicitis, and secretions characterized by yellow mutism.
Pathogenesis
Bacteria with daughter cells are virulent. They affect the mucosa of the genitourinary tract (TGU), eyes, rectum, and pharynx. This leads to tissue invasion, inflammation, and fibrosis.
Meningococcus (Neisseria meningitidis)
Clinical manifestations: Thrombosis of blood vessels, headache, vomiting, and a rigid neck developing within a few hours.
Pathogenesis
The bacteria colonize the nasopharynx, utilizing adhesion to epithelial cells to reach the circulation. They cross the blood-brain barrier, resulting in bacteremia, meningococcemia, and meningoencephalitis.
Surface Proteins and Antigens
Pili (Hair-like structures)
Pili facilitate adherence to host cells and provide resistance to phagocytosis. They are formed by proteins called pilins, which act as different antigens.
POR (P1): Porin Proteins
The POR (P1) protein extends through the cell membrane of the gonococcus and is presented as a trimer to form pores. These pores allow the passage of nutrients into the cell. They are used for serological typing and agglutination corrections resulting from monoclonal antibodies (variants: 18Xa, 28xb).
OPA (P2): Opacity Proteins
OPA (P2) functions in adherence within colonies and within the host cell. Gonococci may have 1, 2, or 3 types of OPA. These are only found in opaque colonies and are absent in transparent colonies.
RMP (P3): Reduction-Modifiable Proteins
RMP (P3) are reduction-modified proteins relating to the formation of pores on the surface of cells.
Lipooligosaccharides (LOS)
Unlike Gram-negative bacilli (BG-) which have LPS, gonococcal LOS lack the long-chain antigen. Gonococcal infections are mainly attributed to these structures.
Other Pathogenic Bacteria
Bartonella Species
- Bartonella bacilliformis: Causes Oroya fever and Peruvian verruga.
- Bartonella quintana: Causes Trench fever (noted in World War I).
- Bartonella henselae: Causes Cat scratch fever.
Streptobacillus moniliformis
This bacterium is the causative agent of rat-bite fever.
Inflammatory Responses and Transmission
Exudative Type
An acute inflammatory reaction characterized by liquid edema, polymorphonuclear leukocytes (PMN), and mononuclear cells (MN) that surround the tubercle bacillus.
Productive Type
Characterized by a chronic granuloma with three zones: the central zone, the media, and the peripheral zone.
Transmission Mechanisms
Transmission occurs via the air, skin lesions, and the gastrointestinal tract.
Diagnostic Serologic Tests
Non-Treponemal Tests
- VDRL (Venereal Disease Research Laboratory)
- RPR (Rapid Plasma Reagin)
Treponemal Tests
- FTA-ABS (Fluorescent Treponemal Antibody Absorption)
- TPHA-MH (Treponema Pallidum Hemagglutination Assay)
- TPI (Treponema Pallidum Immobilization)