prevalence of ampc β-lactamase in clinical isolates of <i>escherichia coli</i>, <i>klebsiella </i>spp<i>.</i>, and <i>proteus mirabilis</i> in a tertiary hospital in tehran, iran

Background]<i>ampc</i> βlactamase confers resistance to a variety of βlactam agents, and all plasmidmediated <i>ampc</i> genes are considered clinically significant. the transfer of the <i>ampc</i> gene to plasmid has resulted in dissemination among the <i>enterobacteriaceae</i> family, including <i>escherichia coli</i>, <i>klebsiella </i>spp<i>.</i>, and <i>proteusmirabilis</i>.[objectives]the prevalence of plasmidmediated <i>ampc</i> genes was determined in isolates of <i>e. coli</i>, <i>klebsiella </i>spp<i>.</i>, and <i>p. mirabilis</i> with reduced susceptibility to cefoxitin or extendedspectrum cephalosporins by the multiplex pcr method.[methods]a total of 310 consecutive nonduplicate isolates of <i>e. coli</i>, <i>klebsiella </i>spp<i>.</i>, and <i>p. mirabilis</i> were obtained from various clinical specimens. isolates with positive screening test results were subjected to further molecular evaluation.[results]fifty isolates were positive on the screening test. among them, positive pcr reactions were identified in 35/221 and 12/77 isolates of <i>e. coli</i> and <i>klebsiella </i>spp<i>.</i>, respectively, including 16 (34.0%) for <i>cit</i> only, 7 (14.8%) for <i>dha</i> only, and 24 (51.0%) for both <i>dha</i> and <i>cit</i>. no isolate was positive for <i>fox</i> or <i>mox</i>. no <i>proteus</i> organism was positive for <i>ampc</i> genes.[conclusions]currently, phenotypic tests are unable to accurately and reliably recognize plasmidmediated <i>ampc</i> βlactamaseproducing organisms. although not possible for routine testing, clinical laboratories, especially in referral centers, should employ molecular testing for surveillance studies.