Infectious Diseases of the Genitourinary System: Microbiology Study Notes

Genitourinary System: Structure and Function

Overview

The genitourinary system comprises the urinary and reproductive systems, both of which are susceptible to various infectious diseases. Understanding their anatomy and natural defenses is essential for studying their microbiology.

• Urinary System: Includes kidneys, bladder, ureters, and urethra.

• Reproductive System: Includes male and female reproductive organs.

Urinary System Anatomy

• Kidneys: Filter blood, remove waste, balance fluids, and produce urine.

• Bladder: Balloon-shaped organ that stores urine.

• Ureters: Thin tubes carrying urine from kidneys to bladder.

• Urethra: Tube allowing urine to exit the body.

Male Reproductive System

• Testes: Produce sperm and testosterone; housed in the scrotum for temperature regulation.

• Epididymis: Site for sperm maturation and storage.

• Vas deferens: Duct transporting sperm during ejaculation.

• Accessory glands: (Seminal vesicle, prostate, bulbourethral gland) add fluid to semen, nourish sperm, and neutralize vaginal acidity.

• Urethra and penis: Pathway for urine and semen expulsion.

Female Reproductive System

• Ovaries: Release eggs and secrete hormones (progesterone, estrogens).

• Fallopian tubes: Transport eggs; site of fertilization.

• Uterus: Supports fetal growth and development.

• Cervix: Narrow opening of the uterus; contains antimicrobial mucus.

• Vagina: Acidic canal supporting sperm entry, childbirth, and housing resident microbiota.

Natural Defenses of the Genitourinary Tract

Urinary Tract Defenses

• Mechanical: Flushing action of urine removes microbes.

• Chemical: Acidic pH of urine inhibits microbial growth.

• Enzymatic: Lysozymes and lactoferrin degrade bacterial cell walls and sequester iron.

• Immunological: Secretory IgA antibodies neutralize pathogens.

• Desquamation: Shedding of epithelial cells lining the tract removes attached microbes.

Female Reproductive Tract Defenses

• Low pH: Maintained by Lactobacillus dominance, especially after adolescence.

• Cervical mucus: Thickens to form a protective plug during certain menstrual phases.

• Mucosal immunity: Secretory IgA antibodies neutralize pathogens.

Normal Microbiota of the Genitourinary Tract

Key Microbial Species

• Urinary tract: Streptococcus, Corynebacterium, Lactobacillus, Prevotella, Veillonella, Gardnerella

• Female genital tract: Lactobacillus (childbearing years), Streptococcus, Prevotella, Snethia, Gardnerella, Candida albicans

• Male genital tract: Similar to urinary tract; outer surface of penis: Pseudomonas, Staphylococcus; anaerobic gram-negatives.

Note: Microbial composition can shift with hormonal changes, menstrual cycle, and pregnancy.

Table: Genitourinary Tract Defenses and Normal Microbiota

Tract	Defenses	Normal Biota
Urinary Tract (Both Genders)	Flushing action of urine, shedding of epithelial cells, lysozyme, lactoferrin, secretory IgA	Streptococcus, Staphylococcus, Corynebacterium, Lactobacillus, Prevotella, Veillonella, Gardnerella
Female Genital Tract (Childhood/Postmenopausal)	Mucus secretions, secretory IgA	Same as urinary tract
Female Genital Tract (Childbearing Years)	Acidic pH, mucus, secretions, secretory IgA	Often Lactobacillus, variable others including Streptococcus, Prevotella, Snethia, Gardnerella, Candida albicans
Male Genital Tract	Same as urinary tract	Urethra: same as urinary tract; outer surface: Pseudomonas, Staphylococcus; anaerobic gram-negatives

Major Infectious Diseases of the Urinary Tract

Urinary Tract Infections (UTIs)

UTIs are the most common bacterial infections in adults, primarily caused by uropathogenic Escherichia coli (UPEC).

• Cystitis: Infection of the bladder. Symptoms: pain in the pubic area, frequent urination, pain during urination, cloudy or bloody urine.

• Pyelonephritis: Infection of the kidneys. Symptoms: back pain, high fever, can cause permanent kidney damage.

• Urethritis: Infection of the urethra.

Key facts: 400 million people affected worldwide; women are more susceptible; recurrent infections are common.

Table: UTI Causative Organisms and Features

Causative Organism(s)	Virulence Factors	Treatment	Epidemiological Features
Escherichia coli	Adhesins, motility	Usually nitrofurantoin	Causes 90% of community UTIs, 50-70% of CA-UTIs
Staphylococcus saprophyticus	N/A	Usually nitrofurantoin	Small percentage of community UTIs, lower percentage of CA-UTIs
Enterococcus	N/A	Based on susceptibility; vancomycin-resistant Enterococcus is a serious threat	Frequent cause of CA-UTIs

Additional info: CA-UTI = catheter-associated UTI; prevention includes hygiene and limiting catheter use.

Leptospirosis

Leptospirosis is a zoonotic disease caused by Leptospira interrogans, transmitted via contact with urine or fluids from infected animals, or contaminated water/soil.

• Symptoms: Sudden flu-like symptoms, high fever, headache, muscle aches, conjunctivitis, vomiting. Severe cases (Weil's syndrome) involve kidney and liver damage, jaundice, anemia, and neurological disturbances.

• Virulence factors: Adhesins and invasion proteins.

• Diagnosis: Slide agglutination test for antibodies; CDC can culture specimens.

• Treatment: Doxycycline, penicillin G, or ceftriaxone.

• Prevention: Avoiding contaminated water/soil.

Table: Leptospirosis Disease Summary

Causative Organism(s)	Transmission	Virulence Factors	Diagnosis	Prevention	Treatment	Epidemiology
Leptospira interrogans	Contaminated soil/water	Adhesins, invasion proteins	Serology, culture	Avoid contaminated vehicles	Doxycycline, penicillin G, ceftriaxone	100-200 US cases/year; 80% seropositive in tropical areas

Urinary Schistosomiasis

Caused by the helminth Schistosoma haematobium, which lodges in bladder blood vessels. Endemic to Africa and the Middle East.

• Symptoms: Itchiness at entry, fever, chills, diarrhea, cough, later urinary symptoms, chronic infection possible.

• Pathogenesis: Invades intact skin, attaches to endothelium, antigenic cloaking, eggs in urine.

• Diagnosis: Identification of eggs in urine, PCR methods.

• Treatment: Praziquantel.

• Prevention: Avoiding contaminated water.

Table: Urinary Schistosomiasis Disease Summary

Causative Organism(s)	Transmission	Virulence Factors	Diagnosis	Prevention	Treatment	Epidemiology
Schistosoma haematobium	Contaminated water	Antigenic cloaking, granulomatous response	Eggs in urine, PCR	Avoid contaminated water	Praziquantel	120 million infected in sub-Saharan Africa

Infectious Diseases of the Female Reproductive Tract

Vaginitis

Vaginitis is inflammation of the vagina, usually due to infection.

• Causative agents: Candida albicans (yeast), Trichomonas vaginalis (protozoa), Gardnerella species (bacteria).

Candidiasis

• Dimorphic fungus and normal biota in many humans.

• Opportunistic infection, often after disruption of normal flora.

• Detectable by wet prep or Gram stain; grows in thick, curd-like colonies.

• Treated with topical/oral azole drugs.

Trichomoniasis

• Caused by Trichomonas vaginalis, the most common non-viral STD.

• Often asymptomatic; in females, causes white to green frothy discharge.

• Infection during pregnancy increases risk of premature labor and low-birth-weight infants.

• Treated with metronidazole.

Table: Vaginitis Disease Summary

Causative Organism(s)	Transmission	Virulence Factors	Diagnosis	Prevention	Treatment	Distinctive Features	Epidemiology
Candida albicans	Opportunism	Hypha-specific toxin, candidalysin	Wet prep, Gram stain	N/A	Topical/oral azoles	White, curd-like discharge	75% of women report at least one episode
Trichomonas vaginalis	Direct contact (STI)	TV lipoglycans (TvLG)	Pap smear, Gram stain	Barrier use	Metronidazole, tinidazole	Discharge may be greenish	7-8 million women infected/year

Bacterial Vaginosis

• Common in women of childbearing age; not always sexually transmitted.

• Produces fishy odor, discharge, and itching; does not induce inflammation.

• Associated with reduction of Lactobacillus and mixed infection by Gardnerella vaginalis, Atopobium, Mobiluncus.

• Can lead to pelvic inflammatory disease (PID), infertility, and ectopic pregnancies.

• Treated with metronidazole or clindamycin.

Table: Bacterial Vaginosis Summary

Causative Organism(s)	Transmission	Diagnosis	Treatment	Distinctive Features	Epidemiology
Mixed infection	Opportunism or STI	Visual exam, Pap smear	Metronidazole, clindamycin	Fishy-smelling discharge	7.4 million new US cases/year; prevalence 20-51% worldwide

Other Major Genitourinary Infections

Gonorrhea

• Caused by Neisseria gonorrhoeae; infects only humans.

• Transmitted through all forms of sexual contact.

• Uses fimbriae to attach to mucosal epithelial cells.

• Many isolates are antibiotic-resistant.

Syphilis

• Caused by spirochete Treponema pallidum.

• Transmitted sexually and vertically (mother to fetus).

• Primary stage: chancre at entry site; secondary: rash, fever, sore throat; tertiary: gummatous, cardiovascular, or neurological disease.

• Barrier protection (condoms) reduces risk.

Genital Herpes

• Caused by HSV-1 and HSV-2; DNA viruses with glycoprotein spikes.

• Become latent in nerve ganglia; reactivation causes recurrent lesions.

• Transmission via direct exposure to secretions.

• Treated with acyclovir and derivatives (reduce symptoms, not curative).

• Neonatal herpes: high mortality if CNS is involved; cesarean section recommended if outbreak at delivery.

Human Papillomaviruses (HPV)

• Over 200 related viruses; some cause genital warts, others cause cancer (notably HPV-16, HPV-18).

• Vaccination (9-valent Gardasil) protects against most cancer-causing and wart-causing strains.

• HPV can cause cancers in both males and females.

Group B Streptococcus Colonization

• Beta-hemolytic Streptococcus in group B colonizes 10-40% of US women.

• Infants can be colonized during birth, risking life-threatening infections.

• CDC recommends screening pregnant women and treating with penicillin/ampicillin if positive.

Table: Group B Streptococcus Colonization

Causative Organism(s)	Transmission	Diagnosis	Prevention/Treatment	Epidemiology
Group B Streptococcus	Vertical(mother to infant)	Culture of mother's genital tract	Penicillin/ampicillin	US: 15-45% carriage; 1.8-3.2/1000 live births; international: 12-27% carriage