الملخص

Abstract Four isolates of P.mirabilis previuosly identified from urine were obtained from the laboratory of microbiology in the college of education. The isolates were tested for their resistance to the antibiotics Ampicillin (Amp), Tettracycline (Tc), Chloramphenicol (Cm), Gentamycin(Gm) and Ciprofloxacin(Cip). There were differences in the antibiotic pattern of the isolates.These isolates were mutagenized by nitrous acid (0.05M) for 5 and 10 minutes.It was found that the percentage of removing the antibiotic resistance at 5 minutes was (0-76) but the 10 minutes treatment caused death to all cells. The bacterial isolates showed variation in losing their ability to hydrolize urea.Swarmming phenomenon was not affected by the process of mutagenesis and retained in the all mutagenized colonies of the isolates.