Susceptibility of Pseudomonas aeruginosa of various pyocin types to the newly synthesized ampicillin derivative, N-(6,7-difluoroquinolonyl)ampicillin.

Six hundred and thirty-two isolates of Pseudomonas aeruginosa of 17 pyocin types were collected in 1993 in Taiwan. Types 1, 10, 3, 35 and 12 were the most common pyocin types identified in Taiwan with isolation frequencies of 47.3%, 24.4%, 7.6%, 3.6% and 2.2%, respectively. Several pyocin subtypes were determined. All pyocin types (one isolate of each tested) were resistant to ampicillin and nalidixic acid, but sensitive to fluoroquinolone antibiotics, such as norfloxacin and enoxacin, indicating that cross-resistance to quinolone antibiotics of nalidixic acid and fluoroquinolone derivatives has not developed. A new ampicillin derivative of 6,7-difluoroquinolonic acid, N-(6,7-difluoroquinolonyl)-ampicillin (AU-1), was synthesized by coupling ampicillin with 6,7-difluoroquinolonic acid (FP-3). Compound AU-1 was much more active than either ampicillin or FP-3 alone against all pyocin types of P. aeruginosa and induced filamentation in most growing cells.