Phenotypic and genotypic characterization of bovine mastitis isolates of Staphylococcus aureus for biofilm formation

Staphylococcus aureus is one of the most common pathogens responsible for contagious mastitis in ruminants. The ability of S. aureus to form biofilm in vivo is considered to be a major virulence factor influencing its pathogenesis in mastitis. The objectives of the study were to examine in vitro slime production, biofilm formation, and the presence of the ica gene locus and icaA and icaD genes in S. aureus isolates from bovine mastitis. Thirty-two of the 35 isolates tested produced slime on Congo red agar, whereas only 24 of the isolates were found to produce biofilm in vitro. However, all the 35 isolates possessed the ica locus, icaA and icaD genes. This study indicates a high prevalence of the ica genes among S. aureus mastitis isolates, and their presence is not always associated with in vitro formation of slime or biofilm. A combination of phenotypic and genotypic tests is recommended for investigating biofilm formation in S. aureus.     

Inactivation of bacterial fish pathogens by medium-chain lipid molecules (caprylic acid, monocaprylin and sodium caprylate)

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of caprylic acid (CA), monocaprylin (MC, monoglyceride ester of CA) and sodium caprylate (SC) on Edwardsiella ictaluri, E. tarda, Streptococcus iniae and Yersinia ruckeri in Mueller Hinton broth (MHB) were investigated. In addition, the bactericidal kinetics of CA and MC on the aforementioned pathogens in MHB, and that of SC in water, were determined. The MIC of CA and SC on E. ictaluri, E. tarda, S. iniae and Y. ruckeri were 7.5 and 50 mM, 7.5 and 50 mM, 10 and 25 mM, and 7.5 and 25 mM respectively. For MC, the MIC was in between 2.5 and 5 mM for all the pathogens. The MBC of CA, MC and SC on E. ictaluri, E. tarda, S. iniae and Y. ruckeri were 10, 5 and 100 mM; 10, 5 and 100 mM; 15, 5 and 75 mM; and 10, 5 and 75 mM respectively. The three lipid molecules exerted a substantial antimicrobial effect on the fish pathogens studied. The results indicate that CA and its derivatives could potentially be used for treating and controlling bacterial fish diseases, but extensive validation studies in fish are needed before recommending their usage.