Molecular surveillance of carbapenemase-producing Pseudomonas aeruginosa at three medical centres in Cologne, Germany

Abstract

Background: Pseudomonas aeruginosa is a common pathogen causing hospital-acquired infections. Carbapenem resistance in P. aeruginosa is either mediated via a combination of efflux pumps, AmpC overexpression, and porin loss, or through an acquired carbapenemase. Carbapenemase-producing P. aeruginosa (CPPA) strains are known to cause outbreaks and harbour a reservoir of mobile antibiotic resistance genes, however, few molecular surveillance data is available. The aim of this study was to analyse the prevalence and epidemiology of CPPA in three German medical centres from 2015 to 2017.

Methods: Identification and susceptibility testing were performed with VITEK 2 system. P. aeruginosa non-susceptible to piperacillin, ceftazidime, cefepime, imipenem, meropenem and ciprofloxacin (4MRGN according to the German classification guideline) isolated from 2015 to 2017 were analysed. A two-step algorithm to detect carbapenemases was performed: phenotypic tests (EDTA- and cloxacillin-combined disk tests) followed by PCR, Sanger sequencing, and eventually whole genome sequencing. CPPA isolates were further genotyped by RAPD and PFGE. In-hospital transmission was investigated using conventional epidemiology.

Results: Sixty two P. aeruginosa isolates were available for further analysis, of which 21 were CPPA as follows: bla_VIM-1 (n = 2), bla_VIM-2 (n = 17), bla_NDM-1/bla_GES-5 (n = 1) and the newly described bla_IMP-82 (n = 1). CPPA were mostly hospital-acquired (71.4%) and isolated on intensive care units (66.7%). All (except one) were from the tertiary care centre. PFGE typing revealed one large cluster of VIM-2-producing CPPA containing 13 isolates. However, using conventional epidemiology, we were only able to confirm three patient-to-patient transmissions, and one room-to-patient transmission, on several intensive care units.

Conclusions: These data give insight into the epidemiology of CPPA in three centres in Germany over a period of 3 years. Carbapenemases are a relevant resistance mechanism in 4MRGN-P. aeruginosa, illustrated by genetically related VIM-2-producing strains that seem to be endemic in this region. Our data suggest that infection control measures should especially focus on controlling transmission on the ICU and support the need for a local molecular surveillance system.

Keywords: Carbapenemase; Pseudomonas aeruginosa; Surveillance; VIM-2.

Fig. 1

Overview of new cases with CPPA from 2015 to 2017 (Q = quarter year)

Fig. 2

Epidemiological timeline and transmission route of PFGE type A VIM-2-producing P. aeruginosa. Each node represents one patient at time of first isolation. Arrow indicates genetically and epidemiological confirmed transmission events (dashed line = room-to-patient; continuous line = patient-to-patient). Encircled nodes indicate ward of transmission. Positions of the nodes on the y-axis were randomly chosen