{"title":"The need for microscopy of “typical” colonies of escherichia coli on Endo Agar","authors":"S. Kuzminskiy, H. T. Arkhypchuk","doi":"10.33273/2663-9726-2020-52-1-77-78","DOIUrl":null,"url":null,"abstract":"Identification of coliform bacteria is carried out in almost all food products and feeds. This method is standardized in a number of regulatory documents. It is one of the most widely used in laboratory practice and well known to sanitary microbiologists. It is based on the inoculation of the product in enrichment broth, followed by preliminary identification on Endo agar. Typical coliform bacteria grow on it in the form of red colonies with metallic lustre. Such characteristic external signs, together with the controlled selectivity of the medium itself, sometimes encourage bacteriologists to conclude that coliform bacteria were detected without the necessary Gram stained microscopy. It should be noted that the current methodology for monitoring the suitability of nutrient media in Ukraine does not sufficiently consider the specifics of sanitary and microbiological studies of food products. Thus, according to the information letter of the Ministry of Healthcare of Ukraine, Endo agar selectivity can be considered acceptable if at least 108 cells of Staphylococcus aureus strain ATCC 25923 are inhibited. The reason for this condition may be the direction of the said regulatory document mainly to laboratories that carry out microbiological diagnosis of infectious diseases, including purulent-inflammatory ones, caused by S. aureus. But these bacteria are rarely found in food products. But DSTU ISO 11133-2: 2006, which relates to testing food products and feed, offers a typical representative of the intestinal micro-flora (Enterococcus faecalis ATCC 29212) as a non-target microorganism for controlling the selectivity of the medium for Escherichia coli group bacteria. Unlike regulatory documents of ministries and departments, state standards in Ukraine are not binding. At the same time, a significant part of laboratories researching food products subordinate to the Ministry of Healthcare and in their work should be guided by the above-mentioned information letter.\n\nTherefore, it is necessary to consider the reports concerning the possible growth of red colonies with a metallic lustre, which are typical for coliform bacteria and do not even belong to the family of enterobacteria, in Endo medium. So, examining pasteurized juices on Endo medium, we observed the colonies with the above-mentioned characteristics, but with further microscopy we found large, gram-positive cells of a round shape like yeast.\n\nThus, adherence to standardized techniques for compulsory microscopy of suspicious colonies, including “typical-type” ones, should be mandatory for identification of coliform bacteria. The question also arises as to the appropriateness of revising the list of test strains to control Endo agar selectivity. To spread the use of chromogenic agar for the selective detection and identification of coliform bacteria and E. coli on foods other than milk is promising. This medium makes it possible to identify the most specific and stable signs of the mentioned bacteria, namely beta-D-galactosidase and beta-D-glu-curonidase activity.","PeriodicalId":231282,"journal":{"name":"One Health and Nutrition Problems of Ukraine","volume":"14 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"2020-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"One Health and Nutrition Problems of Ukraine","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.33273/2663-9726-2020-52-1-77-78","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Identification of coliform bacteria is carried out in almost all food products and feeds. This method is standardized in a number of regulatory documents. It is one of the most widely used in laboratory practice and well known to sanitary microbiologists. It is based on the inoculation of the product in enrichment broth, followed by preliminary identification on Endo agar. Typical coliform bacteria grow on it in the form of red colonies with metallic lustre. Such characteristic external signs, together with the controlled selectivity of the medium itself, sometimes encourage bacteriologists to conclude that coliform bacteria were detected without the necessary Gram stained microscopy. It should be noted that the current methodology for monitoring the suitability of nutrient media in Ukraine does not sufficiently consider the specifics of sanitary and microbiological studies of food products. Thus, according to the information letter of the Ministry of Healthcare of Ukraine, Endo agar selectivity can be considered acceptable if at least 108 cells of Staphylococcus aureus strain ATCC 25923 are inhibited. The reason for this condition may be the direction of the said regulatory document mainly to laboratories that carry out microbiological diagnosis of infectious diseases, including purulent-inflammatory ones, caused by S. aureus. But these bacteria are rarely found in food products. But DSTU ISO 11133-2: 2006, which relates to testing food products and feed, offers a typical representative of the intestinal micro-flora (Enterococcus faecalis ATCC 29212) as a non-target microorganism for controlling the selectivity of the medium for Escherichia coli group bacteria. Unlike regulatory documents of ministries and departments, state standards in Ukraine are not binding. At the same time, a significant part of laboratories researching food products subordinate to the Ministry of Healthcare and in their work should be guided by the above-mentioned information letter.
Therefore, it is necessary to consider the reports concerning the possible growth of red colonies with a metallic lustre, which are typical for coliform bacteria and do not even belong to the family of enterobacteria, in Endo medium. So, examining pasteurized juices on Endo medium, we observed the colonies with the above-mentioned characteristics, but with further microscopy we found large, gram-positive cells of a round shape like yeast.
Thus, adherence to standardized techniques for compulsory microscopy of suspicious colonies, including “typical-type” ones, should be mandatory for identification of coliform bacteria. The question also arises as to the appropriateness of revising the list of test strains to control Endo agar selectivity. To spread the use of chromogenic agar for the selective detection and identification of coliform bacteria and E. coli on foods other than milk is promising. This medium makes it possible to identify the most specific and stable signs of the mentioned bacteria, namely beta-D-galactosidase and beta-D-glu-curonidase activity.
大肠菌群的鉴定几乎在所有食品和饲料中进行。该方法在许多规范性文件中进行了标准化。它是实验室实践中使用最广泛的一种,为卫生微生物学家所熟知。它是基于在富集肉汤中接种产品,然后在远藤琼脂上进行初步鉴定。典型的大肠菌群以红色菌落的形式生长在其上,具有金属光泽。这种特殊的外部标志,加上培养基本身的选择性控制,有时促使细菌学家得出结论,认为大肠菌群是在没有必要的革兰氏染色显微镜的情况下检测到的。应当指出,乌克兰目前监测营养介质适宜性的方法没有充分考虑到食品卫生和微生物研究的具体情况。因此,根据乌克兰卫生部的信息信,如果至少108个金黄色葡萄球菌菌株ATCC 25923细胞被抑制,则Endo琼脂选择性可被认为是可接受的。造成这种情况的原因可能是上述监管文件主要指向对金黄色葡萄球菌引起的感染性疾病(包括脓性炎症性疾病)进行微生物诊断的实验室。但这些细菌很少在食品中发现。但与食品和饲料检测相关的DSTU ISO 11133-2: 2006提供了肠道微生物菌群的典型代表(粪肠球菌ATCC 29212)作为控制培养基对大肠杆菌群细菌选择性的非靶微生物。与部委的规范性文件不同,乌克兰的国家标准没有约束力。同时,卫生部下属相当一部分食品研究实验室的工作也应以上述信息函为指导。因此,有必要考虑有关在远藤培养基中可能生长具有金属光泽的红色菌落的报道,这是大肠菌群的典型特征,甚至不属于肠杆菌科。因此,在Endo培养基上检查巴氏灭菌的果汁,我们观察到具有上述特征的菌落,但通过进一步的显微镜观察,我们发现了像酵母一样圆形的大型革兰氏阳性细胞。因此,对可疑菌落(包括“典型型”菌落)的强制性显微镜检查必须遵守标准化技术,以鉴定大肠菌群。问题也出现在适当修改列表的测试菌株控制远藤琼脂选择性。将显色琼脂用于牛奶以外的食品中大肠菌群和大肠杆菌的选择性检测和鉴定是有前景的。这种培养基使鉴定上述细菌最特异和最稳定的标志成为可能,即β - d -半乳糖苷酶和β - d -葡萄糖-curonidase活性。