Decreased susceptibility to didecyldimethylammonium chloride among clinical strains of Pseudomonas aeruginosa, a ten years retrospective study, at the University Hospital of Caen, France.

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Pottier, Marine | Gravey, François | Castagnet, Sophie | Auzou, Michel | Guillaume, Leduc | Demuynck, Marion | Léon, Albertine | Le Hello, Simon

Edité par CCSD -

International audience. Background Didecyldimethylammonium chloride (DDAC) is a quaternary ammonium compounds (QACs) used in several disinfection process in hospital and veterinary environments. Throughout 2018, numerous strains of Pseudomonas aeruginosa (PSAE) isolated in the University Hospital (UH) of Caen presented a decreased susceptibility to DDAC according to the NFEN-13727+A2 referential. Mechanisms involved are incompletely understood, but first studies suggest MexAB-OprM implication. Decreased susceptibility to disinfectant agents is a major concern to public health as it allows pathogens to persist in their environment. The purpose of this study was to assess the emergence of DDAC decreased susceptibility among clinical strains of PSAE isolated in a French UH over the last decade.Methods Ten strains per year were randomly and retrospectively selected between 2011 and 2020 (table I). Minimum inhibitory concentrations (MICs) of DDAC was assessed using broth microdilution method, on concentrations ranging from 8 to 512 mg.L-1, in triplicate per strain. The threshold of decreased susceptibility was set at MIC>62,9 mg.L-1 corresponding to the concentration of DDAC in a disinfectant solution according to the manufacturer instructions.Results Clinical strains were mainly isolated from respiratory, urinary and blood culture/catheter samples, respectively 25%, 21%, 15% (Table.I). At least one strain with decreased susceptibility phenotype was found, for each type of sample and for each year studied. Their MIC were always of 64mg.L-1 or 128mg.L-1. Respiratory, surgical pus, urinary and digestive samples were those with the highest rate of decreased susceptibility, respectively 32%, 31%, 29% and 29% (Figure.I). Regardless the sample origin, the average decreased susceptibility rate was 27%. The lower rate (10%) was found for 2015, 2017 and 2020 while the higher rate (60%) occurred in 2014 (Figure.II). This rate doesn’t seem increase over time with an annual average of 28%.Conclusions Decreased susceptibility to DDAC is not a new phenomenon, but a spread out one. This could explain why PSAE is a resident bacteria in hospital. Studies are ongoing to test PSAE strains isolated from environment samples and from animals. It will be interesting to monitor the evolution of this decreased susceptibility in massive use of disinfection products linked to SARS-CoV pandemic and to continue to explore mechanisms involved.

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