Antimicrobial susceptibility of cinnamon and red and common thyme essential oils and their main constituent compounds against Streptococcus suis

Abstract

Streptococcus suis is an emerging zoonotic pathogen causing different diseases, in both humans and pigs. Generally, the control of this pathogen is based on antimicrobial therapy, but the development of bacterial resistance has led one to look for new options. In this sense, the essential oils (EOs) constitute a promising alternative. The activity of cinnamon, common thyme and red thyme EOs and their main active compounds (cinnamaldehyde and thymol) against S. suis isolates from pigs (n = 50) and humans (n = 6) was determined by the broth microdilution method. MIC50–90, MBC50–90 and the bactericidal index (BI) (minimal bactericidal concentration (MBC)/minimal inhibitory concentration (MIC)) were calculated. Also, the time‐kill curve of each product against the S. suis P1/7 European reference strain was determined. No differences in the MIC or MBC values were observed between all the tested products, which suggest a homogeneous behaviour of S. suis, independently of their origin, organ of isolation or resistance profile. All the products showed a concentration‐dependent and time‐dependent killing activity and achieved the virtual eradication of S. suis at supra‐inhibitory concentrations within the first 5 min of exposure, except cinnamaldehyde that showed only bacteriostatic effect. It suggests that these products could be utilized as antimicrobials in veterinary medicine for the control of this zoonotic pathogen.

A Focused Insight into Thyme: Biological, Chemical, and Therapeutic Properties of an Indigenous Mediterranean Herb

“…Regarding the effect of thyme on Streptococcus species, data have been documented for S. mutans, that causes dental caries but might also cause infective endocarditis [ 101 ], S. pyogenes that causes sore throat or pharyngitis [ 102 ], and the zoonotic pathogen, S. suis [ 103 , 104 ]. Interestingly, a novel model of delivery of topical products for acne vulgaris, an antimicrobial, standardized, nano-emulgel was synthesized from thyme and clove essential oils, and screened in vitro and in vivo against clinical skin bacterial isolates ( Pseudomonas stutzeri , Enterococcus faecium and Bacillus thuringiensis ).…”

In Vitro Antimicrobial Activity of Medicinal Plant Extracts against Some Bacterial Pathogens Isolated from Raw and Processed Meat

“…Generally, the control of bacterial pathogens depends on antimicrobial therapy, but the development of bacterial resistance has led to the search for new options. The use of essential oils in this regard represents a promising alternative [25]. Persister cells and viable but non-culturable (VBNC) cells could survive during exposure to high doses of antibiotics.…”

“…VBNC cells establish a prime public health concern, thus, they have been reported in 51 human pathogens and they are hard to be eradicated through standard sterilization actions, such as heat, acid, ethanol, or even by antibiotic or osmotic stress [26][27][28][29][30][31][32][33]. In this sense, the use of essential oils as food preservatives constitute a promising alternative [25].…”