Implementation and evaluation of methods for the optimal detection of carbapenem-resistant and colistin-resistant Pseudomonas aeruginosa and Acinetobacter baumannii from stools.

Carbapenem-resistant Acinetobacter baumannii (CRAB) and Pseudomonas aeruginosa (CRPA), as well as polymyxin-resistant A. baumannii (PMR-AB) and P. aeruginosa (PMR-PA), were used to test different enrichment strategies from spiked stools. Three procedures were compared, namely, direct inoculation on selective plates and plating after a 24-h enrichment step in tryptic soy broth with or without antibiotics. Selective agar plates were used including CHROMagar-Pseudomonas supplemented with meropenem (2 mg/L), and CHROMagar-MDR-Acinetobacter agar and CHROMagar COL-APSE plates. Use of enrichment broths significantly enhanced the recovery of CRAB, CRPA, PMR-AB, and PMR-PA. However, supplementing or not the pre-enrichment broth with antibiotics had no impact. The proposed strategy for screening multidrug-resistant nonfermenters is of low cost, is easy to implement, and might be useful for outbreak containment.