Urinary tract infections (UTIs) are a common bacterial menace. From E. coli to Klebsiella, various microbes can invade our plumbing system, causing symptoms like painful urination and fever. Understanding these culprits is key to effective treatment and prevention.

Beyond the usual suspects, some sneaky bacteria like Leptospira and Chlamydia can also wreak havoc on our urinary system. These infections often require special diagnostic techniques and treatment approaches. Knowing their unique characteristics helps in tackling these less common but potentially serious threats.

Bacterial Pathogens and Infections of the Urinary System

Common bacterial pathogens in UTIs

• Escherichia coli (E. coli)
  • Most frequently encountered cause of urinary tract infections (UTIs) accounting for a significant proportion of cases
  • Commensal bacteria that typically resides in the gastrointestinal tract without causing disease
  • Certain strains possess unique virulence factors enabling them to colonize and infect the urinary system
    • Express adhesion molecules called P fimbriae that facilitate attachment to the uroepithelial cells lining the urinary tract (bladder, ureters)
    • Secrete toxins such as hemolysin which lyse red blood cells and damage the host tissue
    • Can form biofilms, contributing to antibiotic resistance and persistent infections
• Klebsiella pneumoniae
  • Gram-negative rod-shaped bacteria that ranks as the second leading bacterial cause of UTIs after E. coli
  • Possesses a prominent polysaccharide capsule contributing to its pathogenicity and antibiotic resistance
  • Frequently implicated in hospital-acquired UTIs especially in catheterized patients or those with prolonged hospital stays (catheter-associated UTI or CAUTI)
• Proteus mirabilis
  • Motile gram-negative rod exhibiting characteristic swarming motility on agar plates
  • Elaborates the enzyme urease which hydrolyzes urea into carbon dioxide and ammonia
    • Ammonia production raises urinary pH leading to precipitation of magnesium and calcium phosphate crystals (struvite stones)
• Staphylococcus saprophyticus
  • Coagulase-negative staphylococcal species that does not produce the enzyme coagulase unlike S. aureus
  • Major cause of uncomplicated UTIs in young women of reproductive age often following sexual intercourse
• Enterococcus faecalis
  • Gram-positive cocci that normally inhabit the gastrointestinal tract as part of the commensal flora
  • Displays intrinsic resistance to several antibiotics (cephalosporins) and can acquire resistance to vancomycin
  • Frequently causes UTIs in patients with indwelling urinary catheters or other urologic instrumentation

Symptoms and diagnosis of urinary infections

• Cystitis (infection of the urinary bladder)
  • Patients experience:
    • Dysuria manifesting as a burning sensation during urination due to inflammation of the urethra and bladder
    • Increased frequency and urgency of urination as the inflamed bladder becomes irritable and less distensible
    • Discomfort or pain in the lower abdominal area (suprapubic region) where the bladder is located
    • Presence of visible blood in the urine (gross hematuria) or microscopic hematuria detectable on urinalysis
  • Diagnostic evaluation involves:
    • Urinalysis to detect the presence of white blood cells (leukocytes), nitrites produced by certain bacteria, and bacteria on microscopy
    • Urine culture to isolate and identify the causative bacterial pathogen and determine its antibiotic susceptibility profile
• Pyelonephritis (infection of the kidney parenchyma)
  • Patients manifest:
    • High-grade fever often accompanied by chills and rigors due to the systemic inflammatory response
    • Severe, unilateral flank pain overlying the affected kidney due to stretching of the renal capsule
    • Gastrointestinal symptoms such as nausea and vomiting resulting from the inflammatory process
    • Lower urinary tract symptoms of cystitis may also be present concurrently
  • Diagnostic workup entails:
    • Urinalysis and urine culture to confirm the presence of infection and identify the etiologic agent
    • Blood cultures to assess for concomitant bloodstream invasion (bacteremia) by the urinary pathogen
    • Radiologic imaging such as CT scan or ultrasound to evaluate for renal abscesses, obstruction, or other complications

Leptospira and Chlamydia in urinary system

• Leptospira
  • Thin, coiled, highly motile spirochete bacteria that infect both humans and animals (zoonosis)
  • Acquired through contact with soil or water contaminated by the urine of infected animals (rodents, dogs, livestock) or through direct exposure to animal urine
  • Penetrates intact mucous membranes or abraded skin and disseminates hematogenously to various organs
    • In the kidneys, invades and multiplies within the renal tubular epithelial cells causing tubulointerstitial nephritis
    • Severe cases progress to acute renal failure characterized by oliguria, azotemia, and electrolyte imbalances
  • Diagnosis relies on serologic tests (microscopic agglutination test) to detect antibodies and PCR to identify Leptospira DNA in clinical samples
• Chlamydia trachomatis
  • Obligate intracellular bacteria that exclusively replicate within host cells and cannot be cultured on artificial media
  • Most commonly transmitted through sexual contact making it one of the most prevalent sexually transmitted infections worldwide
  • Primarily infects the genital tract (urethra, cervix) but can ascend to the upper genital and urinary tract
    • In males, causes urethritis (urethral inflammation) and epididymitis (inflammation of the epididymis)
    • In females, can lead to pelvic inflammatory disease (PID) involving the uterus, fallopian tubes, and ovaries
  • Nucleic acid amplification tests (NAATs) performed on urine samples or genital swabs are the diagnostic gold standard for detecting Chlamydia

Special considerations in urinary tract infections

• Asymptomatic bacteriuria: Presence of bacteria in the urine without clinical symptoms, often requiring no treatment except in specific populations (e.g., pregnant women)
• Antibiotic resistance: Increasing prevalence of multidrug-resistant uropathogens, necessitating careful antibiotic selection based on local resistance patterns and susceptibility testing
• Recurrent UTIs: Some patients experience frequent infections due to factors like antibiotic resistance, biofilm formation, or anatomical abnormalities