Methods: Serratia marcescens isolates demonstrating in vitro carbapenem resistance were recovered over a 12-month period from six distinct patients. Antibiotic resistance was determined by standard methods. Real-time PCR for bla(KPC), mcr gene, bla(NDM-1), bla(VIM), and bla(OXA-48) was performed. Patient comorbidities, source of culture, location in the hospital, and co-infection with other CR organisms were investigated.
Results: Fourteen Serratia marcescens isolates demonstrating in vitro carbapenem resistance were recovered from six individual patients. All six patients had a history of chronic respiratory failure with tracheostomy and at least partial ventilator dependence. Five of the patients were located on the pulmonary intermediate care unit, and one in the pediatric intensive care unit. Twelve of the 14 isolates were tracheal or sputum cultures. Five of the sputum cultures from two patients were co-infected with CR Pseudomonas, and one sputum culture was simultaneously positive for CR Klebsiella pneumoniae and Enterobacter Cloacae. Nine out of 14 isolates were positive for blaKPC-3, two were blaKPC-2 positive, and three were blaKPC-negative, with no mechanism of carbapenem resistance determined yet. None of the other genes were detected.
Conclusion: Most carbapenem resistant Serratia isolates were derived from respiratory tract and were found to be positive for blaKPC-3. This suggests that plasmid encoded carbapenemases are emerging among Serratia in the US, which is already being reported in China. Genomic sequencing may establish whether this represents a clonal expansion and whether the blaKPC plasmid was transferred from Klebsiella or Enterobacter to Serratia in one of the patients.
O. Kaplun, None
E. Sin, None
B. C. Fries, None
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