Accelerating diagnosis: Direct detection of carbapenem resistance in positive blood culture broth

Background: The aims of this study was to compare the phenotypic and genotypic methods for detecting carbapenem resistance genes, assess the effectiveness of direct detection of these genes in blood culture broth versus clinically significant culture isolates, and identify the risk factors, antibiotic treatments, and outcomes associated with infections caused by carbapenem-resistant Gram-negative bacteria. Methods: A laboratory-based prospective time-bound study was conducted which included samples of blood cultures with growth of carbapenem-resistant Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter species. Phenotypic detection method for carbapenem resistance was done followed by conventional polymerase chain reaction (PCR) for the detection of 5 common carbapenemases (New Delhi metallo-beta-lactamase, oxacillinase 48, IMP, Verona integron–encoded metallo-beta-lactamase, and Klebsiella pneumoniae carbapenemase) from colonies and directly from the blood culture bottle. Results: Phenotypic method showed a sensitivity of 95%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 92.5%. PCR from blood culture broth showed a sensitivity of 91.3%, specificity of 83%, accuracy of 88.6%, and Cohen's Kappa value of 0.84. Significant risk factors were male sex, ≥55 years of age with comorbidities—diabetes mellitus—history of antibiotic use, and intensive care unit admission >three days with an indwelling device. Conclusion: PCR, being more definitive, showed good sensitivity and high specificity when used directly on positive blood culture broths, reducing false positives. This method decreased turnaround time by 48 hours, enabling timely, appropriate empirical treatment and potentially reducing mortality, morbidity, and healthcare costs.