ABSTRACT
BACKGROUND: Colistin has become a last-resort antibiotic for the management of multidrug-resistant gram-negative bacteria. The disk diffusion test is cheap and easy to perform but may be unreliable for colistin susceptibility testing due to poor diffusion of the large colistin molecule. An improved agar diffusion test would increase the reliability of colistin susceptibility testing. This study aimed to modify Muller-Hinton agar (MHA) to improve colistin diffusion in agar.METHODS: MHA was modified by reducing the agar concentration from 100% to 30% and supplementing with protamine. We tested 60 gram-negative clinical isolates of Pseudomonas aeruginosa (N=27) and Acinetobacter calcoaceticus-baumannii complex (N=33). Disk diffusion test results were interpreted based on minimum inhibitory concentrations determined by broth microdilution.RESULTS: The modified MHA yielded the best performance metrics, including 94.7% sensitivity, 100% specificity, and an area under the curve of 0.995 (95% confidence interval, 0.982–1.000), P<0.001, at a cut-off point of 13 mm.CONCLUSIONS: A reduction of the agar concentration from 100% to 30% and the addition of protamine improved colistin diffusion in agar and allowed routine colistin susceptibility testing in a clinical microbiology laboratory, but should be handled with caution.
ABSTRACT
BACKGROUND: Respiratory tract infections are major public health threats, and the identification of their causative microbes helps clinicians to initiate timely and appropriate antimicrobial therapy and prevent the secondary spread of infection. The main goal of this study was to compare two multiplex real-time polymerase chain reaction (PCR) assays used to detect respiratory viral pathogens in nasopharyngeal swab specimens. METHODS: Between September and October 2017, a total of 84 nasopharyngeal specimens were obtained consecutively from patients in a tertiary hospital using a flocked swab with 3 mL universal transport medium (COPAN Diagnostics, USA). A total of 64 positive and 20 negative sample results from the LG AdvanSure RV real-time RT-PCR kit (LG Life Sciences, Korea) were further retested using a new AdvanSure RV-plus a real-time RT-PCR kit to compare their performance. RESULTS: Statistical analysis of positive and negative agreement between the two different kits was conducted between the newly introduced AdvanSure RV-plus real-time RT-PCR kit and the AdvanSure RV real-time RT-PCR. The overall agreement was 96.4%, with positive agreement of 98.4% and negative agreement of 90%. The evaluated sensitivity and specificity of AdvanSure RV-plus real-time RT-PCR were 96.9% and 94.7%, respectively, with a kappa value of 0.9 (P<0.001). CONCLUSION: The performances of LG AdvanSure RV real-time RT-PCR and the new AdvanSure RV-plus real-time RT-PCR kit showed strong overall agreement. AdvanSure RV-plus real-time RT-PCR had a better detection rate and could detect coronavirus 229E and enterovirus, especially with a high detection rate in coinfection. AdvanSure RV-plus real-time RT-PCR can be considered a useful tool for respiratory virus diagnosis in clinical laboratories.