Evaluation of EDTA and Dipicolinic Acid in Broth Microdilution with Polymyxin B as a Phenotypic Test to Detect the mcr-1 Gene

Evaluation of Early Reading of Broth Microdilution Technique for Polymyxin B

Delay in the results of standard phenotypic susceptibility tests is the main obstacle to adequate antibiotic treatment. For this reason, the European Committee for Antimicrobial Susceptibility Testing has proposed the Rapid Antimicrobial Susceptibility Testing for the disk diffusion method directly from blood culture. However, to date, there are no studies evaluating early readings of polymyxin B broth microdilution (BMD), the only standardized methodology for assessing susceptibility to polymyxins. This study aimed to evaluate modifications in the BMD technique for polymyxin B using fewer antibiotic dilutions and reading after an incubation time of 8-9 hr (early reading) in comparison to 16-20 hr of incubation (standard reading) for isolates of Enterobacterales, Acinetobacter baumannii complex, and Pseudomonas aeruginosa. A total of 192 isolates of gram-negative bacteria were evaluated and the minimum inhibitory concentrations were read after early and standard incubations. The early reading presented 93.2% of essential agreement and 97.9% of categorical agreement with the standard reading of BMD. Only three isolates (2.2%) presented major errors and only one (1.7%) presented a very major error. These results indicate a high agreement between the early and the standard reading times of BMD of polymyxin B.

Detection of mcr-1-mediated resistance to polymyxins in Enterobacterales using colistin disk chelator application

Objective. To evaluate the possibility of using the colistin disk chelator application (CDCA) method as simple and available screening tool for detection of mcr-1-mediated resistance to polymyxins in Enterobacterales. Materials and Methods. A total of 47 colistin-resistant Enterobacterales isolates obtained in 2014–2020 within multicenter MARATHON study were included in the experiment. Colistin susceptibility testing was performed using Mueller–Hinton broth microdilution method according to ISO 20776-1:2006. Interpretation of the results was performed according to EUCAST v.12.0 clinical breakpoints. MCR-genes were detected by multiplex real-time PCR. Phenotypic screening for mcr-expression was performed on Mueller–Hinton agar by application of dipicolinic acid in concentration of 1,000 mcg/disk in 10 µL volume per disk and 0.5 M solution of EDTA in 5 µL volume per disk. Chelating effect was registered by differences in zone of growth inhibition around colistin disks with and without chelator. Measurements were performed with the help of caliper in millimeters. Statistical data processing was carried out in accordance with guidelines for statistical analysis in medical researches using MS-Excel tool. Results. In 25 of 47 included in the experiment enterobacteria isolates mcr-genes were detected by molecular method. MCR-detection by CDCA method identified the average difference value of the zones of growth inhibition for colistin and its combination with EDTA and DPA as 4.1 mm and 3.7 mm respectively for mcr-positive isolates and 1.7 mm and 1.2 mm respectively for mcr-negative isolates. Statistical analysis estimated that a difference of ≥ 3 mm in zone of growth inhibition for combination of colistin with one of the chelating agents when compared to colistin only allows us to conclude that a studied isolated carries mcr-1-mediated resistance to polymyxins. In addition, sensitivity of the test was 96% and specificity was 91% if DPA is used, while EDTA showed only 88% sensitivity and 77% specificity. Conclusions. Proposed method appears as available technique for phenotypic screening of the Enterobacterales order for mcr-1-mediated resistance to polymyxins for practical laboratories in present conditions. The use of DPA is preferred because of better specificity and sensitivity rates.

The Characteristic of Virulence, Biofilm and Antibiotic Resistance of Klebsiella pneumoniae

Klebsiella pneumoniae is an important gram-negative opportunistic pathogen that causes a variety of infectious diseases, including urinary tract infections, bacteremia, pneumonia, and liver abscesses. With the emergence of multidrug-resistant (MDR) and hypervirulent K. pneumoniae (hvKP) strains, the rapid spread of these clinical strains in geography is particularly worrying. However, the detailed mechanisms of virulence and antibiotic resistance in K. pneumoniae are still not very clear. Therefore, studying and elucidating the pathogenic mechanisms and drug resistance mechanism of K. pneumoniae infection are important parts of current medical research. In this paper, we systematically summarized the virulence, biofilm, and antibiotic tolerance mechanisms of K. pneumoniae, and explored the application of whole genome sequencing and global proteomics, which will provide new clues for clinical treatment of K. pneumoniae.