ABSTRACT
AmpC beta-lactamases, enzymes produced by a range of Gram-negative bacteria and able to hydrolyse penicillins, monobactams, cephalosporins and cephamycins, are not inhibited by beta-lactamase inhibitors. They are spread via plasmids and pose a huge epidemiological and diagnostic problem. The production of AmpC B-lactamases was tested in various Gram-negative bacteria. Of strains isolated from urine of patients diagnosed with urinary tract infection, we selected those that were resistant to third generation cephalosporins and did not produce extended-spectrum beta-lactamases (ESBL). The production of inducible AmpC was assayed by modified DDST (double disk synergy test) and that of constitutive AmpC was tested on agar containing oxacillin as an AmpC inhibitor. All constitutive AmpC producers were also tested for susceptibility to amikacin, piperacillin/tazobactam, cefoperazon/sulbactam, imipenem, meropenem and colistin by the disk diffusion method on MH-agar. Altoghether 119 strains (68 strains of Klebsiella pneumoniae, 20 strains of Escherichia coli and 12 strains of Enterobacter aerogenes) were tested. We detected 38 constitutive AmpC producers, including primarily K. pneumoniae (17 strains), E. coli (10 strains) and E. aerogenes (4 strains). Thirty-two strains were inducible AmpC producers (21 K pneumoniae strains, 6 Morganella morganii strains and 3 E. aerogenes strains). Two K. pneumoniae strains were ESBL/AmpC coproducers. The constitutive AmpC producers showed relatively good susceptibility to cefepim (84.2%) and carbapenems.
