A 9-year-old girl complains of fever up to 38.5°C, headache, inertness, weakness, loss of appetite, stomachache, and frequent painful urination. Provisional diagnosis of acute pyelonephritis is made. Clinical urine analysis: specific gravity – 1016, no protein, leukocytes – 10-15 in the vision field. What investigation method can verify the diagnosis of urinary tract infection?