A 34-year-old woman comes lo the office due to dysuria. The pa | USMLE Biochemistry Videos & Books

A 34-year-old woman comes lo the office due to dysuria. The patient has a history of recurrent urinary tract infections. A urine sample is collected and sent for culture. Gram-negative bacteria isolated from the urine are found to form pink colonies on lactose-containing MacConkey agar. Several days later, bacterial isolates from a second urine sample are found to form white colonies when plated on the same type of medium. Genetic analysis shows that the more recent isolates have a single nucleotide deletion within the lac operon DNA sequence.