Reports of the production of multiple β-lactamases in a single gram-negative pathogen are increasing (1, 2, 6). Isolates of Klebsiella species producing KPC-2, SHV extended-spectrum β-lactamases (ESBLs), and inhibitor-resistant TEM-30 β-lactamases have been reported as endemic in New York City (1). The present report identifies a Klebsiella pneumoniae isolate from New York City which produced up to 10 different β-lactamases, including a FOX-like plasmid-mediated AmpC, in addition to the previously reported KPC, SHV ESBL, and IRT β-lactamases (1). The K. pneumoniae isolate was obtained from the sputum of a patient with a mesothelioma. No carbapenem antibiotics were given to the patient prior to the isolation of the K. pneumoniae isolate. CLSI (formerly NCCLS) disk diffusion and broth microdilution assays (4) revealed that the K. pneumoniae isolate lacked susceptibility to levofloxacin (>16 μg/ml), amikacin (32 μg/ml), piperacillin-tazobactam (>128 μg/ml), ceftazidime (128 μg/ml), cefotaxime (64 μg/ml), aztreonam (>128 μg/ml), and cefoxitin (>64 μg/ml) but was susceptible by microbroth tests to tigecycline (0.5 μg/ml), minocycline (4 μg/ml), polymyxin B (1 μg/ml), cefepime, and imipenem. However, when broth microdilution tests were performed with an inoculum of 107 CFU/ml instead of 105 CFU/ml, the MICs of both imipenem and cefepime increased (4 μg/ml to 32 μg/ml and 8 μg/ml to >128 μg/ml, respectively). The MICs of tigecycline, minocycline, and polymyxin B were not affected when a higher inoculum was used. The presence of an ESBL was indicated by the CLSI ESBL confirmatory disk tests but not by the CLSI ESBL broth microdilution confirmatory tests (4). Isoelectric focusing (IEF) indicated that this isolate produced up to 10 different β-lactamases. Characterization of these enzymes was performed, as previously described, using IEF, inhibitor profiles, cefotaxime gel hydrolysis assays, and PCR (5-7, 8, 9). Using these techniques, 8 of 10 β-lactamases were identified. Three of these enzymes hydrolyzed cefotaxime. The pI and inhibitor profiles of these enzymes suggested the production of an SHV-12-like ESBL, a KPC-like carbapenem-hydrolyzing enzyme, a FOX-like AmpC, a PSE-1-like β-lactamase, and an OXA β-lactamase. In addition, TEM-1-like, TEM-30-like, and SHV-1-like enzymes were also identified (Table (Table1).1). PCR amplification using family-specific primers substantiated the presence of these genes within the K. pneumoniae isolate and identified the OXA β-lactamase as an OXA-9-like β-lactamase. Sequence data generated using the same primers that amplified the blaOXA product also suggested that the gene was blaOXA-9. TABLE 1. Identification of the β-lactamases produced by the K. pneumoniae isolate Accurate β-lactam susceptibility testing can be expected to become increasingly difficult over the next few years due to an increase in isolates producing multiple β-lactamases. The numbers and types of β-lactamases produced by the K. pneumoniae isolate from New York described in this report are a cause for concern, especially with respect to detecting ESBL, AmpC, and KPC-type enzymes. The CLSI microbroth ESBL confirmatory tests were unable to detect the presence of the SHV ESBL in this isolate, and these tests also suggested imipenem susceptibility, even though the isolate produced a KPC-type enzyme. As the number of pathogens producing multiple β-lactamases continues to rise, the difficulties in identifying the mechanisms responsible for β-lactam MICs will increase (1, 2, 6, 10). Clinical laboratories need the option of molecular testing in addition to phenotypic testing for the identification of resistance mechanisms that may be masked by the production of multiple enzymes. Additional testing options for these highly resistant pathogens may help avert future outbreaks like the ones reported for KPC-producing K. pneumoniae isolates in New York (1-3).
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Jun 30, 2022
Aishwarya Naira + 6
