Heat treatment effects on the antimicrobial activity of macrolide and lincosamide antibiotics in milk

Antibiotic residues in milk can cause serious problems for consumers and the dairy industry. Heat treatment of milk may diminish the antimicrobial activity of these antibiotic residues. This study analyzed the effect of milk processing (60 °C for 30 min, 120 °C for 20 min, and 140 °C for 10 s) on the antimicrobial activity of milk samples fortified with three concentrations of three macrolides (erythromycin: 20, 40 and 80 μg/liter; spiramycin: 100, 200, and 400 μg/liter; and tylosin: 500, 1,000, and 2,000 μg/liter) and one lincosamide (lincomycin: 1,000, 2,000, and 4,000 μg/liter). To measure the loss of antimicrobial activity, a bioassay based on the growth inhibition of Micrococcus luteus was done. The data were analyzed using a multiple linear regression model. The results indicate that treatment at 120 °C for 20 min produces inactivation percentages of 93% (erythromycin), 64% (spiramycin), 51% (tylosin), and 5% (lincomycin), while treatment at 140 °C for 10 s results in generally lower percentages (30% erythromycin, 35% spiramycin, 12% tylosin, and 5% lincomycin). The lowest loss or lowest reduction of antimicrobial activity (21% erythromycin and 13% spiramycin) was obtained by treatment at 60 °C for 30 min.     

Phenotypic and molecular assessment of antimicrobial resistance in Lactobacillus paracasei strains of food origin

Antimicrobial resistance data in food-associated lactic acid bacteria (LAB) such as lactobacilli are mostly based on nonstandardized methodologies and/or have been obtained for only a limited number of strains. This susceptibility study included a diverse collection of 115 isolates mainly of food origin originally identified as Lactobacillus paracasei or Lactobacillus casei. Upon reidentification and removal of potential replicate isolates using repetitive DNA element PCR fingerprinting, 65 genotypically unique L. paracasei strains and the L. casei type strain were selected for broth microdilution and Etest assays using the LAB susceptibility test medium. In both methodologies, strains appeared uniformly susceptible to ampicillin and clindamycin but exhibited natural resistance to streptomycin and gentamicin. Three L. paracasei strains from cheese displayed acquired resistance to tetracycline (MIC > or = 32 microg/ml) and/or to erythromycin (MIC >16 microg/ml), which was linked to the presence of a tet(M) or tet(W) gene and/or an erm(B) gene, respectively. Partial sequencing revealed that the tet(M) genes found in two of these strains belonged to two tet(M) sequence homology groups previously found in enterococci. Collectively, phenotypic and genotypic data allowed us to propose tentative epidemiological cutoffs for L. paracasei and L. casei for differentiating susceptible strains from those strains harboring one or more acquired resistance factors.     

Characterization of Antibiotic Resistance Genes from Lactobacillus Isolated from Traditional Dairy Products

Lactobacilli are widely used as starter cultures or probiotics in yoghurt, cheese, beer, wine, pickles, preserved food, and silage. They are generally recognized as safe (GRAS). However, recent studies have shown that some lactic acid bacteria (LAB) strains carry antibiotic resistance genes and are resistant to antibiotics. Some of them may even transfer their intrinsic antibiotic resistance genes to other LAB or pathogens via horizontal gene transfer, thus threatening human health. A total of 33 Lactobacillus strains was isolated from fermented milk collected from different areas of China. We analyzed (1) their levels of antibiotic resistance using a standardized dilution method, (2) their antibiotic resistance gene profiles by polymerase chain reaction (PCR) using gene‐specific primers, and (3) the transferability of some of the detected resistance markers by a filter mating assay. All Lactobacillus strains were found to be resistant to vancomycin, but susceptible to gentamicin, linezolid, neomycin, erythromycin, and clindamycin. Their susceptibilities to tetracycline, kanamycin, ciprofloxacin, streptomycin, quinupristin/dalfopristin, trimethoprim, ampicillin, rifampicin, and chloramphenicol was different. Results from our PCR analysis revealed 19 vancomycin, 10 ciprofloxacin, and 1 tetracycline‐resistant bacteria that carried the van(X), van(E), gyr(A), and tet(M) genes, respectively. Finally, no transferal of the monitored antibiotic resistance genes was observed in the filter mating assay. Taken together, our study generated the antibiotic resistance profiles of some milk‐originated lactobacilli isolates and preliminarily assessed their risk of transferring antibiotic gene to other bacteria. The study may provide important data concerning the safe use of LAB.     

Antibiotic Resistance Traits and Molecular Subtyping of Staphylococcus aureus Isolated from Raw Sheep Milk Cheese

The main objective of the present research was to evaluate the antibiotic resistance profiles of Staphylococcus aureus isolated from raw sheep milk cheese. A total of 150 strains were isolated from curd cheese samples and identified as S. aureus. The survey on antibiotic resistance was carried out on 47 strains, selected among isolates showing differences in the banding pattern after Pulsed Field Gel Electrophoresis (PFGE) screening or, belonging at the same pulsotype but isolated from different cheese samples. On selected strains antimicrobial resistance against ampicillin, penicillin, cloxacillin, tetracycline, erythromycin, and vancomycin was assessed by broth microdilution method. The presence of the genes coding for antibiotic resistance and virulence factors (agr alleles, sea‐see, and tst) was also investigated by PCR. Thirty‐one isolates belonging to agrI and agrIII groups carried at least one gene coding for enterotoxins or toxic shock syndrome toxin. Approximately 60% of the selected strains were susceptible to the tested antibiotics. Twelve of 47 isolates showed multiple resistance against ampicillin and penicillin. Only 1 strain, represented by a unique PFGE profile showed simultaneous resistance to ampicillin, penicillin and cloxacillin. Single resistance against tetracycline was found in 5 isolates belonging to 2 different pulsotypes. The results of this study suggest that the recovery of S. aureus resistant strains in raw milk cheese samples is quite common but it is limited to few antibiotic classes, mainly β‐lactams and tetracyclines. None of the strains showed resistance to erythromycin and vancomycin.     

Resistance of potential probiotic lactic acid bacteria and bifidobacteria of African and European origin to antimicrobials: determination and transferability of the resistance genes to other bacteria

Probiotic bacteria and starter cultures of Lactobacillus, Weissella and Bifidobacterium of African and European origins were studied and compared for their susceptibility to antimicrobials. The study included, for all isolates, determination of MICs (Minimal Inhibitory Concentration) for 24 antimicrobials, detection of resistance genes by PCR reactions using specific primers and sequencing of positive amplicons. The ability of Lb. reuteri from Africa to transfer the erythromycin resistance gene erm(B) to closely related bacteria was investigated by conjugation. Variations were observed and high levels of intrinsic resistance were found among the tested species. Positive amplicons were obtained for resistance genes encoding aminoglycoside (aph(3')-III, aadA, aadE) and tetracycline (tet(S)) from isolates from Europe and macrolide (erm(B)) from an isolate from Africa. However, only the erm(B) gene found in Lb. reuteri L4: 12002 from Africa contained a homologous sequence to previously published sequences. This gene could be transferred in vitro to enterococci. Higher prevalence of phenotypic resistance for aminoglycoside was found in isolates from Europe.     

市售即食食品中非致病菌的耐药性及耐药基因转移的研究

目的 了解西安市即食食品中的非致病菌的耐药性分布、耐药程度及耐药基因的转移情况,分析潜在的食品安全问题.方法 对西安市的几家大型超市零售的熟肉、果盘、凉拌菜3大类即食食品样品进行食源性非致病菌的红霉素和氨苄青霉素耐药性分析、耐药基因转移、菌株16 S rRNA序列测序鉴定等.结果 42.5％的分离株具有不同程度的红霉素耐药性,47.5％的分离株具有不同程度的氨苄青霉素耐药性,21.2％的分离株同时具有2种抗生素耐药性;11.3％的红霉素耐药株耐药性高达160 mg/L,6.3％的氨苄青霉素耐药株耐药性高达500 mg/L.随机挑选的部分耐药株在无抗生素培养基中连续传代1000代以后,60％的氨苄青霉素耐药株和45％的红霉素耐药株的耐药性消失.部分耐药株的耐药基因可水平转移至非耐药株中.这些耐药株多为肠球菌、葡萄球菌、芽孢杆菌、假单胞菌等.结论 即食食品中的非致病菌有潜在的风险,耐药基因在细菌间的转移可能对人体敏感肠道菌群和致病菌有一定影响.     

Isolation and molecular characterization of antibiotic-resistant lactic acid bacteria from poultry and swine meat products

The transfer via the food chain from animals to humans of microbes that are resistant to antimicrobial agents is of increasing concern. To determine the contributions of nonpathogenic microflora to the occurrence and spread of antibiotic resistance (AR) genes in the food chain, 123 lactic acid bacteria were isolated from 29 samples of raw and processed pork and chicken meat products that had previously tested positive for one or more AR genes that encode clinically relevant ARs: tet(M), tet(O), tet(K), erm(A), erm(B), erm(C), aac (6')-Ie aph (2")-Ia, mecA, and blaZ. All of the isolates were initially tested for their AR gene profiles by PCR. The 59 isolates carrying a tet, erm, or blaZ gene were taken through molecular identification, analyzed by determination of the MIC, and subjected to genetic fingerprinting. Lactococcus garvieae was the predominant species (28 isolates), followed by Lactobacillus plantarum (11 isolates) and L. salivarius (6 isolates), whereas Lactococcus lactis subsp. lactis, Lactobacillus johnsonii, L. reuteri, L. crispatus, and L. brevis were identified at lower frequencies. The tet(M) and erm(B) genes were the most frequently detected. Assessment of multiple resistances in 18 tet positive (tet+) isolates revealed that tet(M) plus erm(B) and tet(K) plus erm(B) were the most frequent AR gene patterns. Partial sequencing of the tet(M) open reading frame of three selected strains showed high sequence similarities (> 99%) with tet(M) genes previously found in human pathogens (Listeria monocytogenes and Neisseria meningitidis). Southern hybridization with plasmid profiles revealed these strains contained tet(M)-carrying plasmids.     

鲜牛奶中耐药性细菌的分离与鉴定

目的:分离鉴定鲜牛奶中耐药性细菌的分布。方法:利用含有四环素(16μg/mL)、环丙沙星(4μg/mL)或庆大霉素(16μg/mL)的Luria-Bertani平板,分离样品中的耐药性细菌;采用K-B纸片法对分离菌株的耐药性进行确认;利用血平板测定分离菌株的溶血性;利用16S rRNA方法对分离菌株进行鉴定。结果:对30份采自河北张家口地区新鲜无菌牛奶样品的平板筛选结果显示,具有耐受1种以上抗菌素细菌的样品为23份(76.67%),具有耐受2种以上抗菌素细菌的样品为7份(23.33%),具有耐受3种以上抗菌素细菌的样品为1份(3.33%);共分离得到耐受四环素菌株37株、耐受环丙沙星8株、耐受庆大霉素菌株7株;随机挑选6株(每种抗菌素耐受细菌选取2株)进行16S rRNA鉴定,结果为黏质沙雷氏菌(Serratia marcescens)1株、铜绿假单胞菌(Pseudomonas aeruginosa)2株、琼氏不动杆菌(Acinetobacter junii)1株、阪崎肠杆菌(Cronobacter sakazakii)1株和金黄色葡萄球菌(Staphylococcus aureus)1株;6株细菌中α溶血3株,β溶血1株,γ溶血2株;纸片法验证结果显示,只有1株分离细菌对庆大霉素敏感。结论:鲜牛奶样品中普遍存在多种耐药性细菌,抗菌素平板可以用于初步分析牛奶样品的耐药性细菌。     

Antibiotic resistance and virulence traits of enterococci isolated from Baylough, an Irish artisanal cheese

Eight representative Enterococcus strains from a collection of over 600 previously isolated from an Irish artisanal cheese were subjected to phenotypic and genotypic analysis of antibiotic resistance and virulence properties. Genes encoding resistance to tetracycline (tet(M) and tet(L)) and/or erythromycin (erm(B)) were detected in five strains. In addition, all strains contained two or more of the virulence genes tested (agg, gel, cyl, esp, ace, efaAfs, and efaAfm). Further investigation into the transferability and environmental dissemination of these resistance and virulence traits will allow risk assessment and safety evaluation of artisanal cheeses.     

Assessment of antibiotic susceptibility within lactic acid bacteria strains isolated from wine

Susceptibility to 12 antibiotics was tested in 75 unrelated lactic acid bacteria strains of wine origin of the following species: 38 Lactobacillus plantarum, 3 Lactobacillus hilgardii, 2 Lactobacillus paracasei, 1 Lactobacillus sp, 21 Oenococcus oeni, 4 Pediococcus pentosaceus, 2 Pediococcus parvulus, 1 Pediococcus acidilactici, and 3 Leuconostoc mesenteroides. The Minimal Inhibitory Concentrations of the different antibiotics that inhibited 50% of the strains of the Lactobacillus, Leuconostoc and Pediococcus genera were, respectively, the following ones: penicillin (2, < or =0.5, and < or =0.5 microg/ml), erythromycin (< or =0.5 microg/ml), chloramphenicol (4 microg/ml), ciprofloxacin (64, 8, and 128 microg/ml), vancomycin (> or =128 microg/ml), tetracycline (8, 2, and 8 microg/ml), streptomycin (256, 32, and 512 microg/ml), gentamicin (64, 4, and 128 microg/ml), kanamycin (256, 64, and 512 microg/ml), sulfamethoxazole (> or =1024 microg/ml), and trimethoprim (16 microg/ml). All 21 O. oeni showed susceptibility to erythromycin, tetracycline, rifampicin and chloramphenicol, and exhibited resistance to aminoglycosides, vancomycin, sulfamethoxazole and trimethoprim, that could represent intrinsic resistance. Differences were observed among the O. oeni strains with respect to penicillin or ciprofloxacin susceptibility. Antibiotic resistance genes were studied by PCR and sequencing, and the following genes were detected: erm(B) (one P. acidilactici), tet(M) (one L. plantarum), tet(L) (one P. parvulus), aac(6')-aph(2") (four L. plantarum, one P. parvulus, one P. pentosaceus and two O. oeni), ant(6) (one L. plantarum, and two P. parvulus), and aph(3')-IIIa (one L. plantarum and one O. oeni). This is the first time, to our knowledge, that ant(6), aph(3')-IIIa and tet(L) genes are found in Lactobacillus and Pediococcus strains and antimicrobial resistance genes are reported in O. oeni strains.     

Prevalence,antimicrobial susceptibility,and antibiotic resistance gene transfer of Bacillus strains isolated from pasteurized milk

Pasteurization is carried out in dairy industries to kill harmful bacteria present in raw milk. However, endospore-forming bacteria, such as Bacillus, cannot be completely eliminated by pasteurization. In this study, a total of 114 Bacillus strains were isolated from 133 pasteurized milk samples. Antibiotic susceptibility tests showed that the percentage of Bacillus with intrinsic resistance to ampicillin and penicillin were 80 and 86%, respectively. Meanwhile, some Bacillus isolates had acquired resistance, including trimethoprim-sulfamethoxazole resistance (10 isolates), clindamycin resistance (8 isolates), erythromycin resistance (2 isolates), and tetracycline resistance (1 isolate). To further locate these acquired resistance genes, the plasmids were investigated in these 16 Bacillus strains. The plasmid profile indicated that Bacillus cereus BA008, BA117, and BA119 harbored plasmids, respectively. Subsequently, the Illumina Novaseq PE150 was applied for the genomic and plasmid DNA sequencing. Notably, the gene tetL encoding tetracycline efflux protein was found to be located on plasmid pBC46-TL of B. cereus BA117. In vitro conjugative transfer indicated that pBC46-TL can be transferred into Bacillus invictae BA142, Bacillus safensis BA143, and Bacillus licheniformis BA130. The frequencies were of 1.5 × 10^?7 to 1.7 × 10^?5 transconjugants per donor cells. Therefore, Bacillus strains with acquired antibiotic resistance may represent a potential risk for the spread of antibiotic resistance between Bacillus and other clinical pathogens via horizontal gene transfer.     

降解多种抗生素残留的乳酸菌的筛选鉴定及特性研究

为研究和筛选高效降解抗生素残留的乳酸菌,采用高效液相色谱法与微生物学方法相结合的方式进行初步筛选,从土壤中分离获得一株乳酸菌菌株P3-4,结合菌落及菌体形态、通过Biolog自动微生物鉴定系统鉴定和16S rDNA基因序列相似性分析,鉴定菌株P3-4为乳酸片球菌（Pediococcus acidilactici）。乳酸菌P3-4在MRS培养基中具有抗生素残留降解能力,对红霉素、罗红霉素与螺旋霉素的降解率分别能达到92.1%、68.9%和82.8%。为菌株P3-4的进一步开发利用提供了理论支持。     

牦牛奶酪中乳酸菌对抗生素的药敏性

分析牦牛奶酪中乳酸菌对常用抗生素的药敏性。采用纸片扩散法测定分离自牦牛奶酪的39 株乳酸菌对8 种常用抗生素的药敏性。结果表明：39 株乳酸菌都有耐药性,主要对万古霉素、新霉素、链霉素和萘啶酮酸有抗性,抗性菌株分别达到了36 株（92.3%）、32 株（82.1%）、38 株（97.4%）和39 株（100%）,菌株的耐药性有一定的种间差异,部分菌株有多重耐药性。     

液相色谱-串联质谱法测定牛奶和奶粉中6种大环内酯类药物的残留量

建立了液相色谱串联质谱测定牛奶和奶粉中6种大环内酯类药物(螺旋霉素、吡利霉素、竹桃霉素、替米卡星、红霉素和泰乐菌素)残留量的分析方法。采用乙腈提取目标物,OasisHLB固相萃取柱净化提取液,液相色谱-串联质谱测定,外标法定量。牛奶中6种大环内酯类药物的检测低限(LOQ)为1μg/kg,奶粉的LOQ为8μg/kg。6种分析物在0～100μg/L的浓度范围内呈良好线性,线性相关系数>0.992。方法在三个水平的添加回收率在81.5%～96.1%之间,相对标准偏差在3.29%～9.96%之间。方法回收率高、重现性好,适用于牛奶、奶粉等样品中大环内酯类药物残留的定量及确证检测。     

乳品生产链金黄色葡萄球菌的污染、耐药性分析及β-内酰胺类药物耐药基因的检测

为分析乳品生产链中金黄色葡萄球菌(Sa)的污染及耐药情况,从部分乳品生产企业采集乳样(生鲜牛乳、生产车间半成品牛乳、成品牛乳)523份,按照GB 4789.10-2010及PCR方法分离鉴定Sa菌株1;采用微量肉汤稀释法,测定Sa分离株对12种抗生素的药敏性,并利用多重PCR方法分析Sa对β-内酰胺类药物耐药性的产生与其耐药相关基因(mecA、blaZ)的关联性。结果显示,乳样Sa总分离率为24.9%(129株),其中生鲜牛乳、中间半成品牛乳及成品牛乳Sa污染率分别为37.5%、7.1%和0.0%;受试Sa分离株对青霉素的耐药率(97.7%)最高,其它依次是氨苄西林(95.4%)、甲氧苄啶/磺胺甲噁唑(61.9%)、阿莫西林/克拉维酸(61.7%)、红霉素(39.7%)、四环素(36.6%)、盐酸林可霉素(35.2%);所有菌株均对苯唑西林、头孢噻呋、氟苯尼考敏感;多重耐药Sa分离率为69.8%,主要对青霉素类、磺胺类、大环类脂类、林可胺类及四环素类表现出多重耐药;多重PCR检测结果显示,129株测试Sa的nuc、blaZ、mecA阳性率分别为100.0%、60.5%及0.0%;不同生产环节乳源Sa携带blaZ基因与其对β-内酰胺类药物的耐药表型有一定的对应关系。结果表明,乳品生产链Sa污染及耐药现状已不容乐观,应引起重视,避免食源性疾病的发生。     

Enterococci from Appenzeller and Schabziger raw milk cheese: antibiotic resistance, virulence factors, and persistence of particular strains in the products

Enterococci are natural residents of human and animal intestinal tracts, and grow to high numbers in a variety of cheeses. The aim of this study was to determine the diversity of enterococci in two types of artisanal raw milk cheese (Schabziger and Appenzeller) and to investigate whether particular strains with triple resistance against chloramphenicol (Chl), tetracycline (Tet), and erythromycin (Ery) persist in the production system. Of 46 cheese samples, a total of 312 Enterococcus strains were isolated over a 5-month period on selective agar plates containing Chl, Tet, or, Ery. Enterococcus faecalis was the predominant species (80.7%), followed by Enterococcus faecium (5.1%), and Enterococcus durans (11.7%). According to the phenotypic resistance patterns, a selection of 150 strains was analyzed with PCR for the presence of genes encoding resistance to Ery (ereA, ereB, mphA, ermA, ermB, ermC, mrsA/mrsB, mefA/mefE), and Tet (tetM, tetL). Because virulence factors have been linked to the pathogenicity of enterococci, the strain selection was also tested for the presence of the following virulence factors: Agg, GelE, Cyl, Esp, EfaAfs, EfaAfm, Cpd, Cob, and Ccf. All tested strains contained at least two of the nine virulence genes taken into analysis. Pulsed-field gel electrophoresis patterns of the isolates showed a limited persistence of several strains over a period of 1 to 2 months in Schabziger, and more than 2 months in Appenzeller. Finally, the enterococcal flora in the two types of cheeses seems to be rather unrelated. Within 150 strains from 25 different cheese samples (11 Appenzeller and 14 Schabziger), 41 pulsed-field gel electrophoresis patterns could be identified, and only 1 of these was found in enterococci from both types of cheese.     

Antibiotic susceptibility of Bifidobacterium thermophilum and Bifidobacterium pseudolongum isolates from animal sources

The widespread use of antimicrobial substances has led to resistant populations of microorganisms in several ecosystems. In animal husbandry, the application of antibiotics has contributed to resistance development in pathogenic and commensal bacteria. These strains or their resistance genes can be spread along several ecological routes, including the food chain. Antibiotic resistance is important in terms of the safety of industrial strains, such as probiotics for food and feed. Bifidobacterium thermophilum and Bifidobacterium pseudolongum are known to comprise the major part of the bifidobacterial microbiota in the gut and feces of cattle and pigs. In this study, the antimicrobial susceptibility in bifidobacterial isolates of these species was investigated. Isolates from the beef and pork production chain were identified and typed to strain level, and the antimicrobial susceptibility level was tested to a set of antibiotics. Isolates with low susceptibility levels were screened by PCR for already described resistance genes. Strains atypically resistant to clindamycin, erythromycin, and tetracycline were determined. The resistance genes tet(O), tet(W), and erm(X) were detected in the bifidobacterial species that were examined.     

适应性进化和改造质粒稳定性促进枯草芽孢杆菌合成N-乙酰神经氨酸

N-乙酰神经氨酸(N-acetylneuraminic acid,NeuAc)作为营养化学品和药物中间体在保健品和医药领域具有广泛的应用。为了提升重组枯草芽孢杆菌(Bacillus subtilis)合成NeuAc的产量,首先利用NeuAc生物传感器(NeuAc-Biosensor)调控抗生素抗性基因表达,在抗生素存在条件下将细胞生长与NeuAc合成相关联。进而通过增加抗生素浓度进行适应性进化,促进NeuAc合成效率提升。研究结果显示,当利用NeuAc-Biosensor分别调控壮观霉素抗性基因(spc)和红霉素抗性基因(erm)时,高产菌株能够在较高抗生素浓度条件下生长。通过在培养过程中逐步增加抗生素浓度开展适应性进化,结果表明采用壮观霉素和红霉素进行双抗性适应性进化时,进化获得的菌株中假阳性率(产量未提高的菌株比例)为46.7%,显著低于采用壮观霉素或红霉素单一抗生素进化获得的菌株中假阳性率(73.3%和66.7%)。通过适应性进化与发酵验证得到1株NeuAc产量为(3.16±0.19)g/L的菌株,产量比出发菌株提高了31.7%。为进一步解决发酵过程中重组B.subtilis质粒丢失的问题,通过将必需基因folB(编码二氢喋呤醛缩酶,dihydroneopterin aldolase)插入携带NeuAc合成途径关键酶编码基因重组质粒并且敲除基因组中的folB基因,质粒的丢失率由34.1%下降至11.8%。该研究提升了重组B.subtilis合成NeuAc的产量和稳定性,为重组B.subtilis发酵法生产NeuAc奠定了基础。     

Characterization of coagulase-positive staphylococci isolated from tank and silo ewe milk

The prevalence of coagulase-positive staphylococci (CPS) was studied among 390 samples of ewe milk. Fifty-seven (14.85%) samples of tank milk and all samples (6) of silo milk gave a positive result on Baird-Parker agar base supplemented with rabbit plasma fibrinogen, whereas amplification of the coagulase (coa) gene was successful in 6 (1.56%) samples of tank milk and in all silo samples. Phenotypic and genetic analysis of 153 isolates identified 151 (98.69%) as Staphylococcus aureus. Amplification of the coa gene was positive for 149 isolates (97.39%). The staphylococcal enterotoxin (SE) C gene was detected in 116 strains (75.82%), whereas more than one SE gene was carried in 5 strains (3.26%). None of the isolates harbored the genes for SEE or for methicillin resistance. A high prevalence of CPS carrying enterotoxin genes should be of concern because ewe milk is mainly processed into raw milk cheeses. The detection of the coa gene from milk samples could help to assess the microbiological safety of raw milk intended for direct use in the dairy industry.     

内蒙古传统发酵乳制品中乳酸菌的分离及其耐药性研究

以内蒙古通辽地区自制的奶豆腐和酸性奶油（乌日莫）为材料,采用稀释涂布法从中分离乳酸菌,通过分子生物学技术对其进行菌种鉴定,并对其耐药性进行研究。结果表明,共分离纯化得到80株乳酸菌,经鉴定,归属于13个种,分别为短乳杆菌（Lactobacillus brevis）、粪肠球菌（Enterococcus faecalis）、乳酸片球菌（Lactobacillus acidilacticii）、乳酸乳球菌（Lactococcus lactis）、瑞士乳杆菌（Lactobacillus helveticus）、屎肠球菌（Enterococcus faecium）、戊糖片球菌（Pediococcus pentosaceus）、副干酪乳杆菌（Lactobacillus paracasei）、食二酸乳杆菌（Lactobacillus digitalis）、奥塔基乳杆菌（Lactobacillus ottaki）、耐久肠球菌（Enterococcus durans）、植物乳杆菌（Lactobacillus plantarum）、开菲尔乳杆菌（Lactobacillus kefir）,表现出高的生物多样性。80株乳酸菌对萘啶酸的耐药率为100%;对链霉素、环丙沙星、万古霉素的耐药率较高,分别为95.00%、80.00%、72.50%;对利福平和四环素的耐药率中等,分别为51.25%,45.00%;对红霉素、氯霉素的耐药率较低,分别为26.25%、23.75%。此外,76株（95%）的乳酸菌还具有多重耐药性。