P.Y.HON1, C. YANG2, C.M.Z. KANG1, N.M. THEVASAGAYAM1, D.P. PRATIM3, M.Y. ABDAD1, K. MARIMUTHU1, O.T. NG1, S.VASOO1
National Centre for Infectious Diseases1, Nanyang Technological University2, Tan Tock Seng Hospital3
The recently discovered plasmid-encoded genes causing polymyxin resistance (mcr), and less common carbapenemases and are not routinely screened for. This study aims to study the prevalence of mcr and uncommon carbapenemase-producing(CP) genes in a collection of gram negative bacilli(GNB) bacteria.
150 GNB (50 CPGNB, 60 ESBL-producers and 40 non-ESBL and non-CPGNB) were subject to a mutilplex conventional PCR for mcr detection. In addition 15 GNB isolates, positive for modified carbapenemase-inactivation method (mCIM or eCIM), but negative for blaKPC, blaNDM, blaOXA-48-type, blaVIM, blaIMP and blaIMI by PCR were subject to a panel of miscellaneous PCRs. Whole genome sequencing (WGS) was performed on mcr positive and a subset of isolates positive with a positive CIM test but negative to our PCR targets.
Of the 150 isolates screened, 1 Escherichia coli carrying the mcr-1 gene was found, also confirmed by WGS which identified it as ST131, and carrying a variety of other antibiotic resistance genes. Of the 15 GNB isolates with a positive CIM test, miscellaneous PCR revealed OXA-23 (n=2), OXA-24 (n=1) in 3 Acinetobacter baumanii isolates, and OXA-23 in one Proteus mirabilis isolate. WGS was performed on a Klebsiella pneumoniae and Enterobacter cloacae isolate and found them to belong to ST1922 and ST702, and harboring plasmid AmpCs.
Plasmid-mediated colistin resistance (mcr) was uncommon in our collection of GNB; blaOXA-23, usually confined to Acinetobacter, was unexpectedly found in a Proteus mirabilis isolate. Suspected CPGNB with no-defineable carbapenemases by extensive carbapenemase-gene PCR screening may be due to AmpC production, alongside other beta-lactamases.