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AmpC beta lactamase producing Gram-negative bacteria have emerged worldwide. It is important to distinguish plasmid mediated AmpC β lactamases from chromosomally mediated enzymes for surveillance, epidemiology and hospital infection control as plasmid mediated genes can spread to other organisms. Occurrence of blaCMY-1 AmpC β-lactamase, a plasmid mediated cephamycinase was studied in 100 consecutive isolates of Escherichia coli from cases of complicated urinary tract infection (UTI). Screening for AmpC production was done by modified Hodge test, three dimensional test and AmpC disk test. All isolates showing a positive result by 2 out of 3 tests were then tested for blaCMY-1 gene by PCR. Fifty nine isolates were positive for AmpC β lactamase production, 56.6 per cent were positive by PCR. Eight out of 13 isolates which were negative by EDTA disk method were positive by PCR, whereas none of the isolates negative by 3D and modified Hodge test was positive by PCR. Among admitted patients urinary catheterisation was the major risk factor followed by obstructive uropathy, three patients developed urosepsis. High occurrence of blaCMY-1 AmpC β-lactamase warrants health care workers to endorse good hospital practices.