My Mother Went To Her PCP Yesterday, She Has Bronchitis

My mother went to her PCP yesterday, she has bronchitis & a positive urine culture that initially in 48 hrs showed gram negative organism. Today he made me call to ck if the antibiotic prescribed was correct: Cipro, when the C&S got ready for the urine test, he changed antibiotic for Nitrofurantoin. What organism he found? I am confused