Staphylococcus aureus, also known as "Staphylococcus aureus", belongs tostaphylococcusGenus, yesGram positive bacteriaIs a common foodborne pathogenic microorganism.The optimum growth temperature of the bacteria is 37 ℃, pH 7.4, high salt tolerance, and can grow in an environment with a salt concentration close to 10%.Staphylococcus aureus is often parasitized in the skin, nose, throat, stomach, carbuncle, suppurative sore of people and animals, as well as in the air, sewage and other environments.[1]
Scientists from Harvard Medical School proved for the first time that Staphylococcus aureus (a common skin bacterium) can directly act on nerve cells and cause itching. Relevant results were published in the November 22 issue of Cell.
The form of Staphylococcus aureus is spherical, and the colony characteristics in the culture medium are round, the colony surface is smooth, the color is colorless or golden, and there is no expansion growth characteristics. When the Staphylococcus aureus is cultured in the Colombian blood plate, the observation of the colony under light will find that there is a transparent hemolytic circle around.Staphylococcus aureus is arranged in a grape string under the microscope. Staphylococcus aureus has no spore, flagella, and most of them have no capsule.It is a common pathogenic bacteria causing food poisoning.It is common on the skin surface and upper respiratory tract mucosa.[7]
Staphylococcus aureus has a certain tolerance to high temperature. It can be completely killed in a high temperature environment above 80 ℃ for 30 minutes. In addition, Staphylococcus aureus can survive in a high salt environment and can tolerate up to 15% NaCl solution.Due to the structural characteristics of bacteria, 70% ethanol can quickly kill them in a few minutes.The metabolic type of Staphylococcus aureus is aerobic or facultative anaerobic, with low requirements for the environment. 37 ℃ is the optimal growth temperature, and it can survive in various harsh environments. Therefore, the bacteria can be cultured normally with ordinary nutrient agar.[2]
Staphylococcus aureus is a common foodborne pathogen, which widely exists in the natural environment.Staphylococcus aureus can produce enterotoxin under appropriate conditions, causingfood poisoning。Reports of food poisoning caused by Staphylococcus aureus emerge in endlessly. Food poisoning caused by Staphylococcus aureus accounts for about 25% of food borne microbial food poisoning events, and Staphylococcus aureus is second only toSalmonellaAnd Parahaemolyticus.[2]
epidemiology
Enterotoxin is a single chain small molecular protein with a molecular weight of about 26-29 kDa, low relative molecular weight, heat stability, and damage to human intestinal tract, resulting in vomiting, diarrhea and other symptoms.Research has found many types of enterotoxins or enterotoxins. In addition to the traditional enterotoxins A (SEA), B (SEB), C (SEC), D (SED), E (SEE), the enterotoxins such as SEG, SEH, SEI, SEJ, SEK, SEL, SEM, SEN, SEO, SEP, SEQ, SER, SEU, and SEV are also emerging.[2]
Limited standard
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The National Health and Family Planning Commission of China issued the National Standard for Food Safety - Limits of Pathogenic Bacteria in Food (GB 29921-2013) in 2013[3]In the national standard, the limit standard of Staphylococcus aureus was formulated, which stipulated that five samples were collected from the same batch of eight categories of food, including cooked meat products, cooked aquatic products, and cooked food products. The concentration of Staphylococcus aureus in each sample should not exceed 1000 CFU/g, and only one sample was allowed to be between 100 and 1000 CFU/g.
test method
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Traditional separation and identification methods
In the world, the detection of Staphylococcus aureus in food is usually carried out by means of biochemical identification, and at the initial stage, it is separated by plate scribing.At present, the detection of Staphylococcus aureus in food in China is in accordance with the national standard Food Microbiological Examination Staphylococcus aureus Examination (GB4789.10-2016)[4]Method in.The implementation of national standards includes qualitative testing and quantitative testing.Inoculate the broth under aseptic conditions for pre enrichment, and finally line the culture for inoculation, and conduct serological identification according to the biochemical identification method.The traditional biochemical identification method is the most commonly used identification method because of its simple operation, strong stability and low cost.
Immunological test method
Immunological testThe method is mainly based on immunological theory research, which is based on the design of antigen, antibody andImmune cell, detect the combination of antigen and antibody, and thecell factorThis is an experimental method to achieve the purpose of detection.The technical methods mainly include enzyme-linked immunosorbent assayImmunofluorescenceImmune colloidal gold method, etc.[2]
① Enzyme linked immunosorbent assay: its principle is to use the specific combination of antibody and antigen on the surface of the carrier to add some enzyme, which combines with antibody or antigen to form a marker that can track antibody or antigen. Because antigen or antibody reacts with the tested sample to produce antigen or antibody complexes, then add enzyme reaction chromogenic substrate,The amount of the product is positively correlated with the amount of the test substance. Analyze the color development to determine the content of the substance to be tested in the sample.Several ELISA techniques have been developed to detect Staphylococcus aureus in culture supernatants and food samples (such as cheese, potato salad, ham and milk).[2]
② Immunofluorescence: immunofluorescence technology uses fluorescent pigments to mark antibodies or antigens, and then detect target antigens or antibodies.After specific binding of antigen and antibody, qualitative and quantitative detection was carried out by examining the intensity of fluorescence signal.Compared with enzyme mediated immunoassay, fluorescence based immunoassay has greater potential to provide high-throughput analysis and sensitivity.[2]
③ Immunocolloidal gold method: this method uses the nitric acid fiber membrane as the stationary phase carrier, and the sample solution moves in the test strip through capillary action. At the same time, antigen or antibody specific to the substance to be tested is added to the test strip.Compared with ELISA technology,Immune colloidal gold technique The operation is simpler, there is no special technical requirements for the experimental personnel, and it is suitable for grass-roots units and on-site diagnosis.However, compared with ELISA, immunocolloidal gold has lower sensitivity and is not widely used, so further research is needed.In general, immune colloidal gold has strong development potential and broad application prospects.[2]
Molecular biological detection methods
This technology mainly includes polymerase chain reaction (PCR) technology, nucleic acid probe technology,Loop mediated isothermal amplificationAnd other technologies.
①polymerase chain reaction, PCR The principle of this method is that under the action of DNA polymerase, free DNA refers to the principle of base complementary pairing, takes template DNA as the main chain, and rapidly amplifies DNA by providing a primerDouble helix structure。PCR technology has strong specificity and high sensitivity, and has been widely used in medicine, biology and other fields.As a detection method for pathogenic microorganisms, PCR has strong stability and is the mainstream detection method.In the application of microbial detection, primer design and target sequence selection are the core of PCR method.At the same time, the PCR method also has some limitations. Because the method needs to enrich the sample, the food ingredients are complex, which will interfere with the experiment.Compared with other methods, the price of PCR technology instruments and equipment is high, and the cost is high. The popularization of PCR technology requires a certain amount of time and financial support.
② Nucleic acid probe technology: a method of hybridization with target DNA by using gene specific nucleotide sequences as probesNucleic acid hybridization technologyBy detecting the specific marker of this segment, we can judge whether the target microorganism is contained.Nucleic acid probe has the advantages of high sensitivity and strong specificity of molecular biology detection technology, but the experiment cycle is long and the operation is tedious. If the content of target microorganisms in the sample is too low, it is very easy to cause the target microorganisms in the sample not to be detected, resulting in false negative experimental results.
③ Loop mediated isothermal amplification technology: This technology is based on DNA amplification technology, which can rapidly amplify nucleic acids with strand replacement DNA polymerase under constant temperature conditions according to multiple pairs of primers designed.Compared with PCR method, loop mediated isothermal amplification method is faster and simpler in operation, lower in cost, and lower in instrument requirements, which can be widely used in the detection of foodborne pathogenic microorganisms.
Other methods
Kit method: The kit method usually concentrates more than ten or even dozens of culture media or ingredients in a specific micro device, analyzes the test phenomenon by observing some products or phenomena in the growth and metabolism process of microorganisms, and completes multiple tests in the traditional test at one time, reducing the detection time.This method can greatly shorten the test time, and get the results within 24 hours, even some can be shortened to 4 hours.Finished kits for detecting Staphylococcus aureus include API, MIS, etc.[5]
Test strip method: the paper film, paper piece or film attached to the relevant culture medium and specific color developing solution are used as the culture carrier of Staphylococcus aureus, and the number of Staphylococcus aureus in food is measured according to the growth and color development of Staphylococcus aureus on the carrier. This method is simple and easy, but the result precision is not high.[6]
Prevention and control measures
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1. Reasonably select food raw materials and ingredients, use safe water and food raw materials, improve the sanitation of the processing environment and the personal hygiene habits of operators, and avoid the pollution of Staphylococcus aureus on food.[1]
2. Keep in mind that the food should be stored at a safe temperature, and the raw and cooked food should be separated. It is suggested that the food should be cooked and eaten immediately.Heat treatment shall be adopted as far as possible to ensure the sterilization of bacteria, and secondary pollution shall be avoided after heat treatment.[1]
3. Food processing personnel who have been infected or carried some pathogen shall be restricted from engaging in food processing activities in accordance with relevant laws and regulations.[1]
4. Enterprises producing and processing dairy products, meat and other high-risk foods should seriously and strictly implement the relevant provisions of the national food safety standards.In the process of processing or in the market circulation, if it is found that some indicators of product inspection do not conform to the national food safety standards, it is necessary to focus on the interests of consumers, consciously control the quality of ex factory products, take the initiative to recall unqualified products, and prevent the potential risk of poisoning events.[1]
5. Relevant government departments should strengthen the risk identification and risk assessment research on the safety of Staphylococcus aureus in food in China.Pay attention to and continue to carry out publicity and education on the prevention and control of foodborne diseases, and timely remind consumers that in case of suspected staphylococcal enterotoxin poisoning, in addition to immediately sending the patient to the hospital for treatment, they should immediately stop eating and seal up the suspected food.At the same time, the hygiene knowledge of preventing foodborne diseases should be popularized for food production, processing and business personnel.[1]
research findings
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In September 2022, the team of Nanjing University of Posts and Telecommunications constructed a nano reagent (HCM) composed of hyaluronic acid, photosensitizers dihydroporphyrin (Ce6) and metronidazole (MNZ) for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) biofilm infection.Relevant achievements were published in the international academic journal Nature Communication。[8]
