PSEUDOMONAS AERUGINOSA – A HIDDEN RESERVOIR OF CARBAPENEMASE-PRODUCING (CP) GENES

Abstract

Intro: Patients who are at risk of carriage of carbapenem-producing Gram negative bacteria(CPGNB) are screened upon hospitalization as part of infection control and prevention (IPC) strategy. However, non-fermenters such as Pseudomonas aeruginosa harboring carbapenemases may be missed if they are not systematically evaluated. Non-fermenters may serve as a potential reservoir of carbapenemase genes circulating in the hospital environment. As part of an on-going CPGNB surveillance programme, we evaluated Pseudomonas isolates suspected of being CPGNB (positive surveillance sample PCR) with the modified CIM, and the CARBA-5 test . Methods: 270 Pseudomonas aeruginosa and 1 Pseudomonas putida were isolated from rectal swab/stool samples from April 2019 – May 2022 that were positive by Carba-R Xpert for carbapenemase gene(s) (IMP1(n=47), VIM(n=38), NDM(n=149), KPC(n=2), OXA-48(n=20), IMP1&NDM(n=2), IMP1&OXA-48(n=2), NDM&OXA-48(n=10), VIM&NDM(n=1)). These isolates were subjected to the mCIM and CARBA-5 assays. Findings: 234 isolates were positive for IMP, NDM and VIM on CARBA-5, and 36 isolates were CARBA-5 negative. Notably, the agreement between Carba-R Xpert surveillance specimen result and a positive CARBA-5 was 87.2%, 95.9%, 97.3% for IMP, NDM and VIM is found. For the mCIM test this was 82.9%, 93.2%, 23.6%, respectively. Of the 12 samples positive for CARBA-5 that had a companion OXA- 48 genotype as detected in Xpert Carba-R, 11 samples yield >=1 OXA-48 positive Enterobacterales that is co-detected during the screening, and 2 samples with KPC had these detected in other Enterobacterales from the surveillance specimen. The sensitivity of the mCIM to detect CARBA-5 positive IMP and NDM isolates was 95.1% and 93.2% respectively. The mCIM only had a sensitivity of 24.3% for CARBA-5 VIM positive Pseudomonas. Conclusion: Presence of CP genes in P. aeruginosa is unsurprising however maybe missed if laboratories do not systematically evaluate for this. CP genes that are not detected by CARBA-5 could possibly reside on other companion species from the same sample.