Novel antimicrobial peptides identified in legume plant, Medicago truncatula.

One of the major issues in healthcare today is antibiotic resistance. Antimicrobial peptides (AMPs), a subclass of host defense peptides, have been suggested as a viable solution for the multidrug resistance problem. Legume plants express more than 700 nodule-specific cysteine-rich (NCR) peptides. Three NCR peptides (NCR094, NCR888, and NCR992) were predicted to have antimicrobial activity using in silico AMP prediction programs. This study focused on investigating the roles of the NCRs in antimicrobial activity and antibiofilm activity, followed by in vitro toxicity profiling. Different variants were synthesized, i.e., mutated and truncated derivatives. The effect on the growth of Klebsiella pneumoniae and methicillin-resistant Staphylococcus aureus (MRSA) was monitored post-treatment, and survived cells were counted using an in vitro and ex vivo killing assay. The antibiofilm assay was conducted using subinhibitory concentrations of the NCRs and monitoring K. pneumoniae biomass, followed by crystal violet staining. The cytotoxicity profile was evaluated using erythrocyte hemolysis and leukemia (K562) cell line toxicity assays. Out of the NCRs, NCR094 and NCR992 displayed mainly in vitro and ex vivo bactericidal activity on K. pneumoniae. NCR094 wild type (WT) and NCR992 eradicated K. pneumoniae at different potency; NCR094 and NCR992 killed K. pneumoniae completely at 25 and 50 µM, respectively. However, both peptides in the wild type showed negligible bactericidal effect on MRSA in vitro and ex vivo. NCR094 and its derivatives relatively retained the antimicrobial activity on K. pneumoniae in vitro and ex vivo. NCR992 WT lost its antimicrobial activity on K. pneumoniae ex vivo, yet the different truncated and mutated variants retained some of the antimicrobial role ex vivo. All the different variants of NCR094 had no effect on MRSA in vitro and ex vivo. Similarly, NCR992's variants had a negligible bactericidal role on MRSA in vitro, yet the truncated variants had a significantly high bactericidal effect on MRSA ex vivo. NCR094.3 (cystine replacement variant) and NCR992.1 displayed significant antibiofilm activity more than 90%. NCR992.3 and NCR992.2 displayed more than 50% of antibiofilm activity. All the NCR094 forms had no toxicity, except NCR094.1 (49.38%, SD ± 3.46) and all NCR992 forms (63%-93%), which were above the cutoff (20%). Only NCR992.2 showed low toxicity on K562 (24.8%, SD ± 3.40), yet above the 20% cutoff. This study provided preliminary antimicrobial and safety data for the potential use of these peptides for therapeutical applications.IMPORTANCEThe discovery of new antibiotics is urgently needed, given the global expansion of antibiotic-resistant bacteria and the rising mortality rate. One of the initial lines of defense against microbial infections is antimicrobial peptides (AMPs). Plants can express hundreds of such AMPs as defensins and defensin-like peptides. The nodule-specific cysteine-rich (NCR) peptides are a class of defensin-like peptides that have evolved in rhizobial-legume symbioses. This study screened the antimicrobial activity of a subset of NCR sequences using online computational AMP prediction algorithms. Two novel NCRs, NCR094 and NCR992, with different variants were identified to exhibit antimicrobial activity with various potency on two problematic pathogens, K. pneumoniae and MRSA, using in vitro and ex vivo killing assays. Yet, one variant, NCR094.3, had no toxicity toward human cells and displayed antibiofilm activity, which make it a promising lead for antimicrobial drug development.

Blood culture contamination in a tertiary care hospital of Saudi Arabia. A one-year study.

OBJECTIVES: To monitor blood culture contamination (BCC) rates in a tertiary care hospital in Saudi Arabia. Methods: Blood cultures submitted to the Microbiology Laboratory of King Fahad Hospital, Madina, Saudi Arabia between January and December 2017 were analyzed prospectively. Positive blood cultures were either designated as true bacteremia with confirmed bloodstream infection or BCC. RESULTS: Among 5,536 blood cultures from 2201 patients, 364 (6.6%) mirrored BCC. There was an upward trend in contamination rates in specific months. With respect to total blood cultures from respective units over a one-year period, medical ward contributed to the highest contamination rate (10.3%). Blood culture contamination rate in the wards ranged from 4.5-10.3%, with a higher contamination rate in elderly, aged 60-80 years. Staphylococcus epidermidis (S. epidermidis) was the most frequent contaminant (44.5%). Conclusion: The escalated contamination rates in September to October may be attributed to difficulty in sampling blood by the less competent nurses during annual pilgrimage season. High influx of patients and shortage of trained nurses may have resulted in increased incidence in December-January and March-April. The prevalence of skin-resident S. epidermidis may be due to improper aseptic conditions. Ours is the first report on evaluation of BCC rates in Madina and call for renewed efforts in this direction.