Optimizing a culture-based approach to detect intestinal carriage of carbapenem-resistant Pseudomonas aeruginosa in humans.

INTRODUCTION AND

OBJECTIVE

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) causes severe and potentially life-threatening infections in hospitalized patients with mortality rates exceeding 40%. To detect intestinal CRPA carriage in humans for surveillance purposes or to prevent spread and outbreaks in hospitals, a highly-sensitive culture method is needed. We aimed to develop such a highly-sensitive method, that would be feasible in laboratories with limited resources as well.

METHODS

This study used seven well-defined CRPA strains belonging to high-risk clones, including six strains with a carbapenemase gene and one OprD-deficient strain. We applied a stepwise approach that included four enrichment broths and eight Pseudomonas aeruginosa-selective culture media. Spiking experiments were performed to further evaluate the combination of the most sensitive enrichment broths and selective agar plates using human stools.

RESULTS

The two most sensitive enrichment broths were tryptic soy broth (TSB) with 2 mg/L vancomycin and TSB with 2 mg/L vancomycin and 2 mg/L imipenem and the most sensitive selective agar plates were Pseudomonas isolation agar (PIA; Becton Dickinson), PIA (Sigma-Aldrich), and M-PA-C (Becton Dickinson). After the spiking experiment, the best method for detecting CRPA based on sensitivity and selectivity was the combination of TSB with 2 mg/L vancomycin and 2 mg/L imipenem as an enrichment broth for overnight incubation, followed by subculturing the broth on M-PA-C agar plate.

CONCLUSION

We have thus developed a highly-sensitive selective method to detect intestinal CRPA carriage in humans that can be applied in limited-resource laboratories. This may contribute to overall efforts to control CRPA.