TY  - JOUR
TI  - Biotyping and antibiotic susceptibility of animal streptococci from raw/thermized milks of native Epirus sheep breeds
AU  - Samelis, John
AU  - Kakouri, Athanasia
PY  - 2026
JO  - Exploration of Foods and Foodomics
VL  - 4
SP  - 1010187
DO  - 10.37349/eff.2026.1010187
UR  - https://www.explorationpub.com/Journals/eff/Article/1010187
AB  - Aim: Animal streptococci surviving thermization of raw milk prior to traditional Greek cheese processing may include both harmless and potentially harmful strains with multiple antibiotic resistances. Therefore, the aims of this study were to biotype and evaluate the antibiotic resistance and primary technological and safety properties of wild streptococci occurring in Greek sheep milk before and after mild thermization. Methods: Sixteen Streptococcus isolates previously isolated from two raw/thermized (65oC; 30 s) counterpart milks of native Epirus sheep breeds and identified by 16S ribosomal RNA (rRNA) gene sequencing were biochemically characterized using conventional methods (phenotypic tests, sugar fermentation patterns, API 20 STREP and API ZYM profiles) and assessed for susceptibility to eight antibiotics by the disk diffusion method, and for their milk acidification capacity, bacteriocin activity, enzymatic activity profiles, and biogenic amine (BA) formation in vitro. Results: Tetracycline-resistant (57% of the total 7 isolates) Streptococcus parauberis and ciprofloxacin-resistant Streptococcus gallolyticus subsp. pasteurianus (1 isolate) and Streptococcus lutetiensis (2 isolates) strains occurring in raw milk were not recovered post-thermally. Instead, thermization selected for a tetracycline-resistant (50% of the total 6 isolates) thermophilic group previously genotyped as Streptococcus equinus, herein biotyped as Streptococcus pneumoniae. None of the Streptococcus isolates was resistant to ampicillin, chloramphenicol, erythromycin, gentamycin, penicillin, or vancomycin, or β-hemolytic, or produced histamine and tyramine. The milk acidifying activity rate (final skimmed milk pH 4.79 to 5.47 after growth at 37oC for 6 h, gradually decreasing to 22oC for a total of 48 h) of the isolates was species-dependent and increased in the order S. equinus > S. gallolyticus > S. lutetiensis > S. parauberis. Conclusions: Except for the two bacteriocin-producing and α-galactosidase-positive S. lutetiensis antilisterial strains (KFM 55 and KFM 60), which show promise, all animal streptococci derived from Epirus sheep milk should be considered a priori unsafe for inclusion in complex natural cheese starter cultures because they belong to pathogenic, mastitis-causing species or subspecies. The two promising S. lutetiensis strains require further safety evaluations for streptococcal virulence and antibiotic resistance genes, mainly to ciprofloxacin, before their commercial use as natural cheese starters.
ER  -