Lactobacillus in Urine: No Treatment Indicated
Lactobacillus species at 100,000 CFU/mL in urine represents normal urogenital flora contamination, not a urinary tract infection, and should not be treated with antibiotics. 1
Why Lactobacillus is Not a Uropathogen
- Lactobacillus species are explicitly excluded as clinically relevant urine isolates in otherwise healthy individuals according to established diagnostic criteria 1
- These organisms are part of the normal vaginal and periurethral flora and commonly contaminate urine specimens during collection 1
- The presence of Lactobacillus does not meet the microbiological definition of a UTI, regardless of colony count 1
Addressing the Vague Back Pain
The back pain requires evaluation independent of the urine culture results:
- Consider alternative diagnoses such as musculoskeletal pain, nephrolithiasis, or other non-infectious causes since the urine culture does not support UTI 1
- If clinical suspicion for pyelonephritis remains high despite the Lactobacillus result, obtain a repeat urine culture with careful midstream collection technique to avoid contamination 1
- Perform imaging (ultrasound initially) if symptoms persist to evaluate for structural abnormalities, stones, or obstruction 1
When to Suspect True UTI vs. Contamination
True uropathogens that would warrant treatment include 1, 2:
- E. coli (most common, ~75% of cases)
- Klebsiella species
- Proteus species
- Pseudomonas species
- Enterococcus species
Common pitfall: Treating asymptomatic bacteriuria or contaminated specimens leads to unnecessary antibiotic exposure, promotes resistance, and may eliminate protective commensal flora 1
Clinical Context Matters
- In asymptomatic patients, even true bacteriuria (>10⁵ CFU/mL of uropathogens) should not be treated except before urological procedures breaching the mucosa or in pregnant women 1
- The 2024 European Association of Urology guidelines strongly recommend against screening or treating asymptomatic bacteriuria in women without risk factors, patients with diabetes, postmenopausal women, and elderly patients 1
Recommended Action Plan
- Do not prescribe antibiotics for the Lactobacillus growth 1
- Evaluate the back pain clinically with focused history (onset, character, radiation, associated symptoms) and physical examination (costovertebral angle tenderness, fever) 1
- If UTI remains suspected clinically, obtain a properly collected repeat urine culture with urinalysis looking for pyuria (WBCs) and true uropathogens 1
- Consider imaging if symptoms persist or if patient has risk factors for complicated UTI (diabetes, immunosuppression, known urological abnormalities) 1