Source: Fisher MA, Stamper PD, Hujer KM, Love Z, Croft A, Cohen S, Bonomo RA, Carroll KC, Petti CA. Performance of the Phoenix bacterial identification system compared with disc diffusion methods for identifying extended-spectrum beta-lactamase, AmpC and KPC producers. J Med Microbiol. 2009 Jun;58(Pt 6):774-8.
Beta-lactamases are enzymes produced by some bacteria and are responsible for their resistance to beta-lactam antibiotics e.g., pencillins, cephamycins and carbapenems. Extended-spectrum beta-lactamases (ESBLs), AmpC and KPC beta-lactamases are some of the common beta-lactamases produced by the members of Enterobacteriaceae. Accurate detection of beta-lactam producers is critical for decision making in therapeutic and infection control. There are many methods of ESBL detection, some of them are automated while others are manual. Recently, Phoenix Automated Microbiology System has been designed by BD diagnostics.
In the present study, the authors (1) compared the disc diffusion (DD) method of Clinical and Laboratory Standard Institute (CLSI) with Phoenix method for identifying ESBL+ isolates of K. pneumoniae and E.coli, (2) sssessed the value of an extended phenotypic method [cefpodoxime and aztreonam±clavulanic acid (CA)] for enhancing ESBL detection, (3) evaluated boronic acid (BA) with cefotetan or ceftazidime±CA to identify AmpC producers that could mimic or mask ESBL production, and (4) assessed these phenotypic tests with KPC-positive clinical isolates.
Conclusions:
Of 100 isolates identified as ESBL- by Phoenix system, 4 were false negative as determined by DD testing. OF the 10 isolates identified as ESBL+ by Phoenix system, 46 were false positive.
Half of the KPC+ isolates were reported as carpenem –susceptible by Phoenix system.
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