In vitro antibiofilm and quorum sensing inhibition activities of selected South African plants with efficacy against bovine mastitis pathogens

Bovine mastitis is a critical pathology in global dairy herds, causing economic losses due to decreased production and increased culling. The continuous use of conventional antibiotics has led to antimicrobial resistance and treatment failures. The ability of mastitis bacteria to form biofilms is associated with resistance, while quorum sensing plays a vital role in biofilm formation. This complex interplay between quorum sensing (QS) and biofilm formation challenges mastitis management, necessitating the development of alternative therapeutics to combat this microbial threat effectively. This study aimed to investigate the biofilm forming ability (BFA) of 29 bacterial strains isolated from milk from cattle diagnosed with clinical cases of mastitis in Brain Heart Infusion broth (BHI) and Tryptic Soy broth (TSB). Of these strains, 93.10 % (27) and 68.97 % (20) demonstrated BFA in TSB and BHI, respectively. Compared to BHI, TSB appeared to enhance BFA of the bacteria except for Streptococcus (Str.) uberis strains. Four selected South African plants with known antibacterial activities were tested for their antibiofilm and antiquorum sensing activities against the biofilm-forming mastitis isolates. Searsia lancea demonstrated antibiofilm forming activity against all organisms tested. All the plants demonstrated good biofilm disruption ability (BDA) against 24 h preformed biofilms of the isolates except for Erythrina caffra, while S. lancea displayed good BDA against all the 48 hour preformed biofilms of the bacteria. Generally, the plants' antibiofilm activities appeared to improve as the biofilm matured, with few exceptions. The ethanol extracts of S. lancea demonstrated MQSIC activity at 2.50 mg/mL, and the lowest MQSIC₅₀ value (< 0.08 mg/mL), demonstrating its quorum quenching ability. The ability of these plants, especially S. lancea, to inhibit QS and biofilms at various developmental stages may play a pivotal role in managing mastitis infections and curbing the emergence of antimicrobial resistance. Nonetheless, further research is needed to elucidate the precise mechanisms underlying the inhibition of quorum signaling and biofilms, and to identify the specific compounds responsible for the observed activities.