Should I continue cefdinir for my urinary tract infection now that the urine culture grew Lactobacillus?

Discontinue Cefdinir – Lactobacillus is Not a Pathogen in UTI

You should stop cefdinir immediately because Lactobacillus species are not clinically relevant urine isolates and are considered normal vaginal/urethral flora contaminants, not uropathogens requiring treatment. 1

Why Lactobacillus Does Not Require Treatment

• Lactobacillus species (including L. delbrueckii) are explicitly excluded as clinically relevant urine isolates in otherwise healthy patients according to the American Academy of Pediatrics guidelines, which classify organisms such as Lactobacillus spp., coagulase-negative staphylococci, and Corynebacterium spp. as contaminants rather than pathogens. 1

• Lactobacilli are normal commensals of the vaginal and urethral flora and are typically considered contaminants when cultured from urine specimens, particularly in female patients. 2

• The presence of Lactobacillus in urine culture does not meet the threshold for significant bacteriuria requiring antimicrobial therapy, as these organisms do not cause the typical inflammatory response associated with true urinary tract infection. 1

Clinical Decision-Making Algorithm

If the patient is asymptomatic or symptoms have resolved:

• Stop cefdinir immediately
• No further antimicrobial therapy is needed
• Reassure the patient that Lactobacillus represents normal flora, not infection 1, 2

If the patient has persistent urinary symptoms (dysuria, frequency, urgency, suprapubic pain):

• Obtain a repeat urine culture with proper collection technique (midstream clean-catch or catheterized specimen) to rule out contamination 1
• Look for a true uropathogen (E. coli, Klebsiella, Proteus, Enterococcus, Staphylococcus saprophyticus) with colony counts ≥50,000 CFU/mL 1
• If repeat culture shows only Lactobacillus again, consider non-infectious causes of urinary symptoms (interstitial cystitis, urethral syndrome, vaginitis, sexually transmitted infections) 1

Rare Exception: True Lactobacillus UTI

• Lactobacillus as a true pathogen is extraordinarily rare and has been documented in only isolated case reports, typically in patients with significant urological abnormalities (chronic urinary retention, indwelling catheters, benign prostatic hyperplasia) or immunosuppression. 2, 3

• Even in these rare documented cases, Lactobacillus UTI presented with chronic pyuria (white blood cells in urine) and persistent symptoms despite multiple antibiotic courses, not as an incidental culture finding. 2, 3

• If you suspect true Lactobacillus UTI (which would be highly unusual), you would need:

  • Persistent symptoms despite treatment
  • Pyuria on urinalysis (≥10 WBC/hpf)
  • Pure growth of Lactobacillus on multiple properly collected cultures (not just one)
  • Exclusion of other causes of symptoms 2, 3

Critical Pitfall to Avoid

• Do not continue antibiotics based solely on a positive culture for Lactobacillus, as this represents overtreatment of asymptomatic bacteriuria or contamination and contributes to antimicrobial resistance without clinical benefit. 1

• Treating asymptomatic bacteriuria is harmful and leads to unnecessary antimicrobial exposure, selection of resistant organisms, and adverse drug effects without improving outcomes. 1

Additional Concern About Cefdinir for UTI

• Cefdinir has poor urinary penetration and low bioavailability, making it a suboptimal choice for UTI treatment even when a true uropathogen is present. 4

• Recent evidence shows cefdinir has nearly twice the treatment failure rate (23.4% vs 12.5%, p=0.006) compared to cephalexin for uncomplicated UTI, with higher rates of subsequent cephalosporin-resistant organisms on repeat culture. 4

• Cefdinir is not FDA-approved for UTI treatment and is indicated only for respiratory tract infections, pharyngitis/tonsillitis, and skin infections—not urinary tract infections. 5