Slow-growing and fastidious uropathogens in hospitalized patients: an up-to-date review

Urinary tract infections (UTIs) are among the most common bacterial infections and a major cause of healthcare-associated infections. Although Escherichia coli remains the most common uropathogen, an increasing number of slow-growing Gram-positive bacteria are now recognized as important causes of UTIs. These include Aerococcus spp. Actinotignum (formerly Actinobaculum) schaalii, Lactobacillus delbrueckii, Alloscardovia omnicolens, Corynebacterium urealyticum and Gardnerella vaginalis. Historically underdiagnosed or misidentified, these organisms are now better detected due to advances in diagnostic microbiology. They predominantly affect elderly patients with significant comorbidities, urinary tract abnormalities or instrumentation, and may cause severe and invasive infections, including bacteremia and infective endocarditis. Diagnosis is challenging due to fastidious growth requirements, nitrite-negative urine dipstick results, and misidentification by conventional methods. MALDI-TOF mass spectrometry and optimized culture conditions are therefore essential for accurate detection. Antimicrobial management is complicated by variable or intrinsic resistance to commonly used antibiotics, including fluoroquinolones, fosfomycin, trimethoprim-sulfamethoxazole, and mecillinam, and by limited susceptibility testing recommendations. Empirical UTI treatment regimens are therefore often inadequate, and targeted antimicrobial susceptibility testing is strongly recommended in severe, recurrent, or refractory infection. This review summarizes the microbiological characteristics, epidemiology, and antimicrobial susceptibility profiles of these slow-growing and fastidious uropathogens, highlighting diagnostic and therapeutic challenges and future perspectives.