High prevalence and moderate diversity of Pseudomonas aeruginosa in the U-bends of high-risk units in hospital.

The presence of P. aeruginosa in water supply is clearly identified as a risk factor for P. aeruginosa infection in critical care units, even if routes of transmission are often unclear and remain a matter of debate. We determined here the frequency of U-bends contaminated with P. aeruginosa in high-risk units and described the population structure of this opportunistic pathogen in a non-outbreak situation. Eighty-seven U-bends from sinks of rooms in five wards were sampled 3 times and P. aeruginosa was detected in 121 of the 261 (46.4%) U-bend samples. We genotyped 123 P. aeruginosa isolates with pulsed-field gel electrophoresis and multilocus sequence typing and found 41 pulsotypes distributed in 21 Sequence Types (STs). Seven major ST (ST111, CC235, CC253, ST520, ST539, ST1216, and ST1725) were overrepresented in the collection, including the high-risk clones ST111, CC253, and CC235. The distribution of the 21 STs in the cladogram of the species was uneven with most major STs clustering into 2 clades. The major STs were found in different units and buildings and could be represented by a high diversity of pulsotypes. Altogether, this suggests a long term presence of P. aeruginosa in the hospital water network, possibly contaminated by the distribution water or by plumbing fittings before putting into service. Analysis of resistance rates showed that the deficiency of porin OprD was very frequent in U-bends isolates that may benefit from this resistance mechanism in hospital water fittings. In conclusion, our study demonstrates that U-bends of high-risk units are very frequently contaminated with P. aeruginosa with a moderate genomic diversity and with an over-representation of adapted clones.