Identification, antibacterial and antifungal effects, antibiotic resistance of some lactic acid bacteria

Abstract A total of 74 lactic acid bacteria (LAB) isolates were obtained from yoghurt, cheese, raw milk, boza and whey. 36 strains were identified at species levels as Lactococcus lactis (15), Lc. garvieae (8) Lactobacillus plantarum (7), Enterococcus faecium (3), Leuconostoc citreum (2) and Lb.casei (1) by MALDI-TOF MS analysis. The strains were tested for antimicrobial properties using disc diffusion method against Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Cronobacter sakazakii, Bacillus cereus and Salmonella Typhimurium. 18 strains from available samples showed antimicrobial activity. Formation zones were appeared from 7 mm to 19 mm against all bacteria, except B. cereus. Additionally, antibiotic susceptibility of these 18 strains were investigated and strains related to 18 LAB were found resistant despite of 72.2% rifampicin, 53.3% tetracycline and vancomycin, 27.7% to erythromycin and nitrofurantoin. In this study, we investigated antifungal effects of the strains. LAB were screened for antifungal effects by using dual agar overlay against mycotoxigenic Aspergillus candidus, Cladosporium cladosporioides, Cladosporium sphaerospermum, Mucor hiemalis, Ulocladium chartarum, Aspergillus niger and Penicillium expansum. 18 LAB isolates showed antifungal effects. As a result, Enterococcus faecium has antimicrobial and antifungal properties, and therefore, it can be used under various experimental conditions in future studies.摘要 本研究从酸奶、奶酪、生乳、博扎（boza，传统发酵谷物饮品）和乳清中共计分离得到74株乳酸菌（lactic acid bacteria, LAB）。其中36株通过基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）分析完成种水平鉴定，分别为乳酸乳球菌（Lactococcus lactis，15株）、加氏乳球菌（Lc. garvieae，8株）、植物乳杆菌（Lactobacillus plantarum，7株）、屎肠球菌（Enterococcus faecium，3株）、柠檬明串珠菌（Leuconostoc citreum，2株）以及干酪乳杆菌（Lb. casei，1株）。研究采用纸片扩散法，针对单核细胞增生李斯特氏菌（Listeria monocytogenes）、金黄色葡萄球菌（Staphylococcus aureus）、产志贺毒素大肠杆菌O157:H7（Escherichia coli O157:H7）、阪崎克罗诺杆菌（Cronobacter sakazakii）、蜡样芽孢杆菌（Bacillus cereus）及鼠伤寒沙门氏菌（Salmonella Typhimurium）开展抗菌活性测试，结果显示18株分离株具备抗菌活性，其对除蜡样芽孢杆菌外的所有受试菌的抑菌圈直径介于7 mm至19 mm之间。此外，本研究对这18株菌株进行了抗生素敏感性检测，结果表明72.2%的受试菌株对利福平耐药，53.3%的菌株对四环素与万古霉素耐药，仅27.7%的菌株对红霉素及呋喃妥因耐药。本研究同时探究了这些菌株的抗真菌活性：采用双琼脂覆盖法，针对产毒真菌白色曲霉（Aspergillus candidus）、暗色枝孢霉（Cladosporium cladosporioides）、球孢枝孢霉（Cladosporium sphaerospermum）、潮湿毛霉（Mucor hiemalis）、图表乌洛拉霉（Ulocladium chartarum）、黑曲霉（Aspergillus niger）及扩展青霉（Penicillium expansum）开展抗真菌活性筛选，最终有18株乳酸菌分离株表现出抗真菌活性。综上，屎肠球菌（Enterococcus faecium）兼具抗菌与抗真菌活性，可在未来研究的多种实验条件下得到应用。