Urinary and Reproductive System Infections: Microbiology Study Notes

Urinary and Reproductive System Infections

Overview of the Urinary System

The human urinary system is responsible for filtering blood, removing waste, and regulating fluid balance. It consists of two kidneys, two ureters, a bladder, and a urethra. The anatomical differences between male and female urethras influence susceptibility to infection.

• Female urethra: Short and straight, increasing risk of infection.

• Male urethra: Longer and curved, offering more protection against ascending infections.

The Genitourinary System Microbiome

The genitourinary tract harbors a diverse microbiome that varies with age, sex, and health status. The composition differs by anatomical site and physiological state.

• Common genera: Lactobacillus and Streptococcus are predominant.

• Other microbes: Staphylococcus, Corynebacterium, Candida albicans, etc.

• Lactobacillus species produce lactic acid, lowering vaginal pH (3.5–4.5) and inhibiting pathogen growth.

• The female reproductive tract microbiome changes with life stages: adolescence, childbearing, and postmenopausal periods.

Natural Defenses of the Genitourinary Tract

The urinary and reproductive tracts possess several innate defenses to prevent infection:

• Flushing action of urine

• Shedding of epithelial cells

• Acidity of urine and vagina

• Antibacterial agents: lysozyme, lactoferrin, antimicrobial peptides

• Normal flora: competitive exclusion of pathogens

• Secretory IgA in mucus

Pathogens That Cross the Placenta (TORCH Agents)

Some pathogens can be transmitted from mother to fetus (vertical transmission), leading to serious complications. These are collectively referred to as TORCH agents:

• Toxoplasma gondii

• Other infections: HIV, syphilis, varicella-zoster virus, enteroviruses

• Rubella virus

• Cytomegalovirus

• Herpes simplex viruses

Complications include stillbirth, congenital defects, and spontaneous abortion.

Urinary Tract Infections (UTIs)

Classification and Pathogenesis

UTIs are classified by the site of infection:

• Lower UTIs: Urethritis (urethra), cystitis (bladder)

• Upper UTIs: Ureteritis (ureters), pyelonephritis (kidneys)

Bacteria are the leading cause of UTIs, often due to proximity of the urethra to the anus and genitalia. Women are at greater risk due to a shorter urethra and its anatomical position.

• Transmission: Endogenous transfer from GI tract, environmental sources, or hospital-acquired (catheters)

Etiology, Symptoms, and Treatment

• Most common cause: Escherichia coli (80% of cases)

• Virulence factors: Adhesins, motility, siderophores

• Symptoms: Urgency to urinate, dysuria (painful urination), pyuria (pus in urine)

• Treatment: Nitrofurantoin, TMP-SMX

Reproductive System Viral Infections

Herpes Simplex Viruses (HSV-2)

HSV-2 is a DNA virus causing genital herpes. It can establish latency in nerve cells and reactivate under certain conditions.

• Transmission: Sexual contact, oral sex, vertical transmission during birth (neonatal herpes)

• Symptoms: Often asymptomatic; may cause mild flu-like illness and recurrent lesions

• Treatment: Acyclovir and derivatives reduce symptoms but do not cure

• Reactivation triggers: Stress, UV radiation, injury, menstruation, other infections

Human Papillomavirus (HPV)

HPV is a nonenveloped DNA virus causing genital warts and is associated with certain cancers.

• Virulence: Immune evasion

• Transmission: Sexual contact, autoinoculation

• Symptoms: Most infections are asymptomatic; warts on genitals

• Complications: Cervical and genitourinary cancers (HPV-16, HPV-18)

• Treatment: Removal of warts (laser, freezing, chemicals)

• Prevention: Vaccination

Reproductive System Bacterial Infections

Neisseria gonorrhoeae

Neisseria gonorrhoeae is a gram-negative diplococcus causing gonorrhea and ophthalmia neonatorum.

• Virulence factors: Fimbriae, IgA proteases

• Transmission: Sexual contact, childbirth

• Symptoms: Males: urethritis, painful urination, yellowish discharge (often asymptomatic); Females: mucopurulent/bloody discharge, painful urination

• Complications: Pelvic inflammatory disease (PID), ophthalmia neonatorum (blindness in newborns)

• Prevention: Prophylactic erythromycin for newborns

Chlamydia trachomatis

Chlamydia trachomatis is a gram-negative, obligate intracellular parasite causing chlamydia and lymphogranuloma venereum.

• Virulence factor: Prevents phagosome-lysosome fusion

• Transmission: Sexual contact, childbirth

• Symptoms: Males: discharge, painful urination; Females: cervicitis, discharge, PID; up to 75% asymptomatic

• Lymphogranuloma venereum: Invasion of lymphatic tissues, swollen lymph nodes (buboes), fever

• Treatment: Azithromycin or doxycycline

Treponema pallidum (Syphilis)

Treponema pallidum is a gram-negative spirochete causing syphilis, which progresses through several stages if untreated.

• Virulence factors: Hooked tip for attachment, membrane lipoproteins trigger inflammation

• Transmission: Sexual contact, transplacental

• Treatment: Penicillin G (especially effective in early stages)

Stages of Syphilis

• Primary syphilis: Chancre at site of entry (genitalia, oral cavity, nipples, anus)

• Secondary syphilis: Fever, headache, sore throat, red/brown rash, hair loss; occurs ~3 months after infection

• Latency: No visible symptoms, can last years

• Tertiary syphilis: Gummas (lesions) in liver, skin, bone; neurosyphilis (headaches, convulsions, blindness, dementia)

Congenital Syphilis

• Transmission: Mother-to-fetus during pregnancy

• Complications: Fetal abnormalities, nasal/tooth/palate deformations, blindness, deafness, miscarriage, stillbirth

Reproductive System Eukaryotic Infections

Candida albicans

Candida albicans is a dimorphic fungus and part of the normal microbiota. It can cause vulvovaginal candidiasis under conditions of dysbiosis.

• Virulence factors: Dimorphism (yeast to hyphal form)

• Transmission: Endogenous (overgrowth due to antibiotics, hormonal changes, etc.)

• Symptoms: Vaginal itching, thick curd-like discharge

• Treatment: Azole antifungals (clotrimazole, miconazole)

Trichomonas vaginalis

Trichomonas vaginalis is a flagellated protozoan causing trichomoniasis, a common sexually transmitted infection.

• Virulence factors: Flagella for motility, glycocalyx for adherence

• Transmission: Sexual contact

• Symptoms: Many cases asymptomatic; females: white/green frothy discharge, dysuria, itchiness; males: dysuria, urethritis, discharge

• Treatment: Metronidazole