RESUMEN
Objective:To construct a recombinant bioluminescent bacteriophage (HT7) targeting Escherichia coli, and evaluate its ability to identify Escherichia coli. Methods:Initially, pCRISPR-sg (1-10) and PFN-1000 plasmid strains were constructed by genetic engineering, and the most efficient small guild RNA (sgRNA) were screened by bilayer plate. By the gene editing technique, which comprised homologous recombination and clustered regularly interspaced short palin dromic repeats (CRISPR)-Cas system, the Nanoluc luciferase gene was integrated into the downstream non-coding region of 10A gene of T7 phage, to constructe the bioluminescent phage HT7 successfully. The difference of biological characteristics between HT7 phage and T7 phage was evaluated by plaque assay and liquid amplification assay. In addition, 51 strains of Escherichia coli, 20 strains of Klebsiella pneumoniae, 14 strains of Staphylococcus aureus, 6 strains of Enterococcus faecium, 5 strains of Enterococcus faecalis, 3 strains of Acinetobacter baumannii and 1 strain of Pseudomonas aeruginosa were collected and isolated to evaluate the limit of detection and specificity of HT7 phage. Results:Among the 10 CRISPR-targeted cleavage systems constructed, sgRNA8 exhibited the highest cleavage efficiency, with a cleavage rate of 0.18. After three rounds of recombination screening using the pCas9/pCRISPR/PFN-1000 triple-plasmid system, PCR validation yielded recombinant phage bands at 2 798 bp, indicating the successful construction of the HT7 phage. The recombinant phage showed significant differences in biological characteristics in terms of lysis efficiency ( P<0.001), one-step growth curve ( P=0.001), and infection multiplicity ( P=0.031). Both lysis burst time and log growth node were extended by 10 min, with the optimal infection multiplicity being 0.1. Clinical sample testing identified lysis of 6 strains of Escherichia coli within 4.5 h, while other strains remained unaffected, with detection of pathogenic bacteria below 10 CFU/ml. Conclusions:The developed pCas9/pCRISPR/PFN-1000 triple-plasmid editing system efficiently edits the bacteriophage genome. The constructed HT7 fluorescent bacteriophage enables the detection of Escherichia coli below 10 CFU/ml within 4.5 hours, demonstrating low detection limits and high detection specificity.
RESUMEN
Objective:A high-throughput assay for the detection of five common clinical Candidaemia pathogens was established by combining polymerase chain reaction (PCR) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).Method:Establishment of methodology. We selected Candida albicans, Candida parapsilosis, Candida glabrata, Candida krusei, Candida tropicalis to be the target pathogens and the internal transcribed spacer (ITS) region as the target gene. Specific single base extension primers were designed to perform single base extension reaction in the same reaction system. MALDI-TOF MS was used to detect the characteristic peaks of each target pathogen. The sensitivity and specificity of the detection system were verified by using spiked blood samples. Totally 108 blood samples from proven or suspected candidaemia patients were collected from October 2021 to September 2022 in a hospital in Beijing. The results of nucleic acid mass spectrometry were compared with those of clinical blood culture. Results:The established nucleic acid mass spectrometry detection system can simultaneously detect five common clinical Candida species. Each strain can produce specific product peaks and there is no mutual interference between the strains. The detection limit of Candida albicans was 100 CFU/ml. The detection limit of Candida parapsilosis, Candida glabrata, Candida krusei and Candida tropicalis was 10 CFU/ml. For the 108 blood samples, the sensitivity, specificity, positive predictive value and negative predictive value of nucleic acid mass spectrometry were 94.74% (36/38), 97.14% (68/70), 92.31% (36/39) and 98.55% (68/69), respectively. The McNemar χ 2 test showed no significant difference between the two methods ( P>0.05), and the Kappa consistency test showed good consistency between the two methods ( Kappa=0.9, P<0.05). Conclusion:A nucleic acid mass spectrometry detection system suitable for clinical candida detection was successfully constructed, and the method validation results were consistent with the clinical blood culture.