Bacterial Pathogens and Associated Diseases

Enterohemorrhagic Escherichia coli (EHEC, strain O157:H7)

Enterohemorrhagic E. coli is a major pathogenic strain responsible for severe gastrointestinal illness. It is notable for its virulence factors and potential to cause outbreaks.

• Etiology:

  • Aerobic or facultatively anaerobic

  • Gram negative

  • Rod shaped (bacillus)

• Virulence Factors:

  • Has virulence plasmids

  • Genes for fimbriae, adhesins, and exotoxins

  • Colonizes intestinal tract of humans and animals

• Clinical Features:

  • Diarrhea

  • Cramps

  • Nausea and vomiting

  • O157:H7 causes:

    • Hemorrhagic colitis: inflammation of the colon causing bloody diarrhea

    • Hemolytic uremic syndrome: damage to small blood vessels, leading to clot formation and possible kidney failure

• Transmission: Commonly found in soil, plants, decaying vegetation, and water; indicates improper water and sewage systems.

Urinary Tract Infections (UTIs): Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Pseudomonas spp., Staphylococcus spp.

UTIs are among the most common bacterial infections, often caused by enteric bacteria from the intestinal flora.

• Etiology:

  • E. coli – most common, 70%

  • Proteus mirabilis – 10%

  • Klebsiella pneumoniae – 10%

  • Non-enteric bacteria (e.g., Pseudomonas, Staphylococcus) cause some UTIs

• Virulence Factors:

  • Invasion: Flagella for swimming and attachment (used by E. coli, P. mirabilis, Pseudomonas aeruginosa)

  • Attachment: Fimbriae for tight binding to urinary tract epithelial cells

• Clinical Features:

  • Dysuria: painful, burning urination

  • Urinary urgency: strong, sudden urge to urinate

  • Frequency: urination 8+ times a day or 2+ times at night

  • Cloudiness of urine: >100,000 bacteria/mL indicates UTI

  • Hematuria: blood-tinged urine due to inflammation

  • Bacteremia: spread of bacteria from urinary system to blood

• Transmission: Bacteria from skin or rectum can travel up the urethra and into the bladder.

• Groups at Risk:

  1. Elderly men with bladder issues

  2. Patients with catheters

  3. Diabetics

  4. Women using diaphragms as birth control

  5. Young girls being potty trained

• Diagnosis and Testing:

  • Urinalysis: testing for leukocytes (WBCs), erythrocytes (RBCs), and causative bacteria

• Treatment and Prevention:

  • Most infections resolve without antibiotics

  • Antibiotics prevent spread to kidneys and blood

  • Prevention: proper hygiene, urinating after intercourse, cranberry juice (may help prevent E. coli attachment)

• Epidemiology: 8 million cases of UTIs diagnosed annually in the U.S.

Syphilis – Treponema pallidum

Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum. It progresses through distinct clinical stages.

• Etiology:

  • Gram negative spirochete (tightly coiled, helical shape, axial filaments)

• Virulence Factors:

  • Hooked tip for attachment to epithelial cells

  • Hyaluronidase for spreading between cells

  • Glycocalyx for protection from phagocytosis

• Clinical Features:

  1. Primary stage: Chancre (firm, painless ulcer), lasts 3-6 weeks

  2. Secondary stage: Skin rash, fever, swollen lymph glands, patchy hair loss

  3. Latent stage: Clinically inactive, can last for years

  4. Tertiary stage: Internal organ involvement, gummas (soft, non-cancerous growths), neurological and cardiovascular symptoms

• Transmission: Sexual contact; sometimes mother to child

• Diagnosis and Testing: Serological tests (antibody tests)

• Treatment and Prevention:

  • Penicillin is preferred treatment

  • Antibiotic treatment for all sexual contacts

  • Practice abstinence, monogamy, and condom use

• Epidemiology: Fewer than 10,000 reported cases per year in the U.S.; most common in sex workers and drug users

Lymphogranuloma venereum/Trachoma (ocular) – Chlamydia trachomatis

Chlamydia trachomatis is a unique bacterium responsible for genital and ocular infections, including the leading cause of nontraumatic blindness worldwide.

• Etiology:

  • No cell wall; two membranes without peptidoglycan

  • Grows and multiplies within vesicles of host cells

  • Unique developmental cycle: elementary bodies (EB, infectious) and reticulate bodies (RB, replicative)

• Virulence Factors:

  • Invasion: Enters through abrasions, infects cells with specific receptors

  • Evasion: Avoids immune detection

• Transmission:

  • Eye to eye via droplets

  • Hands

  • Contaminated fomites

  • Fecal contamination

  • Respiratory droplets

  • Infants during birth

• Diagnosis and Testing: Demonstration of bacteria inside cells from site of infection

• Treatment and Prevention:

  • Antibiotics for genital and ocular infections

  • Surgical correction for trachoma-related deformities

• Epidemiology: Most common reportable STD in the U.S.; major cause of eye infections worldwide

• Diseases:

  • Lymphogranuloma venereum: Initial genital lesion, formation of buboes, possible pelvic inflammatory disease

  • Non-gonococcal urethritis: Urethral inflammation not caused by Neisseria gonorrhoeae

  • Proctitis: Inflammation of anus and rectum lining

  • Trachoma-ocular disease: Scarring of conjunctiva, leading to blindness; often occurs during childbirth

Summary Table: Key Bacterial Pathogens and Features

Key Equations and Definitions

• Incidence Rate:

• Prevalence:

• Virulence: The degree of pathogenicity of a microorganism, often determined by its ability to invade host tissues and produce toxins.

• Fimbriae: Hair-like appendages on bacteria that facilitate attachment to host cells.

• Hemolytic Uremic Syndrome (HUS): A condition characterized by the destruction of red blood cells and kidney failure, often associated with EHEC infection.

Additional info: Academic context and definitions have been expanded for clarity and completeness.