Antibacterial activity of plant extracts against Streptococcus equi subsp. zooepidemicus isolates from guinea pigs with lymphadenitis in Ecuador

Lymphadenitis is a commonly occurring and contagious disease in guinea pigs caused by different pathogens, including Streptococcus sp., Staphylococcus sp., and Corynebacterium sp. This study aimed to characterize the bacteria isolated from pus extracted from abscessed mandibular lymph nodes of diseased guinea pigs in Ecuador in 2019 and evaluate the in vitro antibacterial activity of the total extracts of three plant species. Isolates were recovered from three diseased guinea pigs with Lymphadenitis on a farm in Imbabura, Ecuador province. The bacteria were characterized through microbiological, biochemical, and molecular tests as Streptococcus equi subsp. zooepidemicus. Furthermore, the susceptibility of S. equi subsp. zooepidemicus to three plant extracts belonging to the Asteraceae family, Acmella ciliata, Bidens andicola, and Gazania splendens collected in Ecuador, were assessed in vitro by the microdilution method. Our data indicate that all the evaluated extracts showed activity, with a Minimum Inhibitory Concentration (MIC) of 22.50 mg/mL for Acmella ciliata, 11.25 mg/mL for Bidens andicola, and 5.60 mg/mL for Gazania splendens. Bidens andicola extract showed the highest efficacy with a % inhibition of 63.90 at the highest tested concentration (45 mg/mL). This is the first report on the bioactivity of these plant species against S. equi subsp. zooepidemicus.