Background and Aim: Antimicrobial-resistant Streptococcus species causes several diseases in humans with infection recurrence in some cases. Handling of food under unhygienic conditions resulted in transmission of pathogens to food leading to risks for consumers' health. This work studies the possible role of humans in transmission of human pathogens to food products. In this study, we focused on the presence of antimicrobial resistance Streptococcus pyogenes, Streptococcus mitis, and Streptococcus pneumoniae found in respiratory patients and in some meat products. We detected the risk factors for patient's infection and examined the antibacterial effect of oregano oil nanoemulsion (ONE) at different concentrations against the multi-drug resistance strains of streptococci.

Materials and Methods: Microbiological culture and polymerase chain reaction were used to identify S. pyogenes, S. mitis, and S. pneumoniae in 120 throat swab samples and 200 meat products. The disk diffusion method was used for investigating the prevalence of resistance against 10 antimicrobials that are commonly used in the treatment of humans and animals. ONE at four concentrations (0.5%, 1.0%, 2.0%, and 3.0%) with an average particle size of 45.4 nm was identified using transmission electron microscopy. The effect of ONE on Streptococcus species isolates was examined using the well diffusion method. Risk factors for human infection were detected using statistical analysis.

Results: S. pyogenes, S. mitis, and S. pneumoniae were detected in 14 (11.7%), 9 (7.5%), and 7 (5.8%), respectively, of 120 throat swabs of patients. These bacteria were also detected in 11 (5.5%), 8 (4%), and 6 (3%), respectively, of 200 meat products samples. Beef luncheon had the highest infection rate for the three species of streptococci. The majority of these isolates showed resistance to antimicrobials such as tetracycline and amoxicillin/clavulanic acid. ONE had an inhibitory effect on the growth of S. pyogenes, S. mitis, and S. pneumoniae, and its effect was significantly increased at a high concentration (3%), with a mean inhibition zone of 36.45±0.302 mm. Very young and old patients, those with chronic diseases, and those exposed to the infection several times were most susceptible to infection.

Conclusion: ONE may be used as a therapeutic agent at safe and specific doses, and also in the food industry, to prevent the spoilage of food and protect human health.

Keywords: meat products, Oregano oil nanoemulsion, Streptococcus pneumoniae, Streptococcus mitis, Streptococcus pyogenes.