Background: Diabetes mellitus is a chronic metabolic disorder strongly associated with an increased susceptibility to urinary tract infections (UTIs). Diabetic patients are particularly predisposed to recurrent and complicated UTIs due to impaired immune defenses, autonomic neuropathy, glycosuria, and repeated antibiotic exposure, which collectively accelerate the emergence of multidrug-resistant (MDR) uropathogens. This study aimed to screen and evaluate the preliminary in vitro inhibitory activity of a combined Lactobacillus consortium against representative multidrug-resistant Gram-negative uropathogens isolated from diabetic patients in Baghdad. Methods: A total of 100 midstream urine specimens were collected from diabetic patients presenting with suspected UTIs across Baghdad hospitals between April 2025 and November 2025. Bacterial isolates were identified using conventional microbiological methods and confirmed using the automated VITEK-2 Compact system. Following antimicrobial susceptibility testing, representative MDR isolates of Escherichia coli, Klebsiella pneumoniae, and Proteus spp. were selected. The in vitro inhibitory potential of a multi-strain probiotic consortium comprising five species (Lactobacillus acidophilus, L. plantarum, L. rhamnosus, L. reuteri, and L. casei) was assessed using the agar-well diffusion method on Mueller–Hinton agar at four concentrations (125, 250, 500, and 1000 mg/mL). Results: Among the confirmed Gram-negative isolates, high rates of multidrug resistance were recorded. The probiotic diffusion assay revealed no detectable zone of inhibition (0 mm) against Escherichia coli or Proteus spp. across all evaluated concentrations (125–1000 mg/mL). In contrast, a limited, concentration-dependent inhibitory response was observed against Klebsiella pneumoniae, producing a measurable zone of inhibition of 15 mm exclusively at the highest concentration of 1000 mg/mL, with no measurable inhibition at lower concentrations. Conclusion: The tested Lactobacillus consortium demonstrated selective, threshold-dependent in vitro inhibition against Klebsiella pneumoniae only at the maximum concentration, while failing to elicit measurable inhibition against the local MDR isolates of E. coli and Proteus spp. under the current assay conditions. These preliminary findings indicate that probiotic inhibitory capacity against uropathogens is not universal, but strictly strain-, species-, and concentration-dependent. Probiotics cannot replace conventional antibiotic therapy. Rather, they may serve only as potential supportive adjuncts, and extensive further investigations including the evaluation of cell-free supernatants, specific postbiotics, molecular determinants of resistance, and synergy testing are required before any clinical adjunctive utility can be established.
