Inappropriate use of antibiotics is globally creating public health hazards associated with antibiotic resistance. Bacteria often acquire antibiotic resistance by altering their genes through mutation or acquisition of plasmid-encoding resistance genes. To treat drug-resistant strains of bacteria, the recently developed CRISPR-Cas9 system might be an alternative molecular tool to conventional antibiotics. It disables antibiotic-resistance genes (plasmids) or deactivates bacterial virulence factors and sensitizes drug-resistant bacteria through site-specific cleavage of crucial domains of their genome. This molecular tool uses phages as vehicles for CRISPR-cas9 delivery into bacteria. Since phages are species-specific and natural predators of bacteria, they are capable of easily injecting their DNA to target bacteria. The CRISPR system is packaged into phagemid vectors, in such a way that the bacteria containing the antibiotic-resistance plasmid sequence or that containing specific DNA sequences were made to be targeted. Upon CRISPR delivery, Cas9 is programmed to recognize target sequences through the guide RNA thereby causing double-strand cleavage of targeted bacterial DNA or loss of drug resistance plasmid, which results in cell death. Remarkably, the safety and efficacy of this newly developed biotechnology tool and the biocontrol product need to be further refined for its usage in clinical translation.

Background Mastitis is one of the challenges impairing the development of the dairy industry. Among mastitis-causing bacteria, S. aureus and E. coli represent the main causative agents that threaten the farmers not only due to the high incidence rate and zoonotic potential but also due to reports of multi-drug resistance. The study was conducted to assess the antimicrobial activity of selected medicinal plants against multidrug-resistant bacterial isolates from clinical bovine mastitis. Milk samples from mastitis cases were aseptically collected and S. aureus and E .coli isolates were identified, the antibiotic sensitivity test pattern of the isolate were confirmed. Four medicinal plants were collected; extracted and their in vitro effectiveness on multidrug-resistant S. aureus and E. coli isolates of bovine mastitis was validated compared to the conventionally used antimicrobial drugs. Results Crude extracts from the four plants were effective against both susceptible and resistant isolates. Extract of Crotona macrostachis at 100mg/mL MIC showed the highest mean zone of inhibition (20.2 ± 1.48) on E. coli while Prunes Africana at 50mg/mL MIC showed 12.9 ± 0.74. The highest mean zone of inhibition 13.8 ± 0.84 for Datura Stamonium at a MIC of 100mg/mL and lowest mean zone of inhibition 11.64 ± 0.86 for Crotona macrostachis at 100mg/mL MIC was observed on S. aureus. Moreover, compared to S. aureus, better efficacy was observed for all tested plant extracts against E. coli. Conclusion This study indicated that traditional medicinal plant preparations might be considered as an alternative option for the treatment of resistant isolates of clinical bovine mastitis.