536. Challenges in Using MALDI-TOF Technology to Assess for KPC Resistance in Klebsiella pneumoniae isolates in America.

Background The emergence of Klebsiella pneumoniae Carbapenemase-producing Enterobacteriaceae (KPC-E) has created a major public health concern. In clinical practice, rapid identification of KPC-KP has important implications for clinical management and infection control. In some settings matrix-assisted laser desorption ionization time of flight (MALDI-TOF) software has been used for rapid detection of KPC producing K. pneumoniae with high sensitivity and specificity. Genomic sequencing has determined that the 11.09 m/z peak is related to protein expression from the P109 gene found mostly in Tna4401a isoform among KPC-E. In our study, we evaluated the use of MALDI-TOF automated detection software to evaluate for KPC detection among a diverse group of KPC-E isolates. Methods We tested 52 KPC-E isolates from various hospitals in Connecticut and the Centers for Disease Control and Prevention (CDC) Antibiotic Resistance (AR) Bank. All specimens were verified as KPC-producing strains by detection of the blaKPCgene through polymerase chain reaction. Protein extraction using the standard extraction method was performed on sub-cultured isolates. Each isolate was tested three times on MALDI-TOF MS with the incorporated bio-subtype KPC module. An organism confidence or log score value of 2 or higher was considered valid. Results Among 52 tested KPC- K. pneumoniae isolates, 44 (85%) were from various hospitals in Connecticut, eight (15%) came from the AR Bank. Only 15 (25.1%) of the isolates were detected as KPC-producing using the MALDI-TOF KPC module. Further investigation by peak analysis confirmed all 15 isolates detected positive demonstrated a peak at 11.09 m/z. The 11.09 m/z peak was not found in the 37 specimens that were not detected. Conclusion The results from our study suggest low sensitivity using this software and contradicts results seen in previous European studies. The Tna4401a isoform is often seen in KPC-2 strains, which may be less prevalent in our sample of isolates, explaining the poor sensitivity of MALDI-TOF. Further study is needed to explore this finding and potential opportunities for MALDI-TOF for rapid identification of KPC-KP. Disclosures All authors: No reported disclosures. [ABSTRACT FROM AUTHOR]