AmpC beta lactamases among ESBL producing Escherichia coli and Klebsiella pneumoniae - If you don't look, you won't find

Amp C beta lactamases confer resistance to a wide variety of beta lactams and pose both diagnostic and therapeutic challenges, as their presence goes undetected in the presence of ESBLs. We evaluated 52 ESBL positive clinical isolates of E.coli (n=41) and K.pneumoniae (n=11) for AmpC production by a phenyl boronic acid disc (PBA) and the 3 dimensional enzyme test (3DET). The PBA method detected 24 (58.5%) and 9 (82%) E.coli and K.pneumoniae isolates as AmpC positive, while detection by the 3DET increased the numbers to 29 (70.7%) and 10 (91%) isolates, respectively. We conclude that a large number (75%) of ESBL producers are also found to produce AmpC and that the PBA disc method is a very useful and reliable method for routine use in laboratories.