Bacterial food poisoning
Overview
Bacteria poisoning and food poisoning are the most common cause of food-borne infections. They are mainly due to Listeria monocytogenes, Yersinia enterocolitica, type Salmonella, Staphylococcus aureus, Clostridium perfringens and Clostridium botulinum.
Listeriosis
Listeriosis is an infection caused by Listeria monocytogenes. Human infections caused by Listeria monocytogenes are now major concerns of doctors, epidemiologists and hygienists. The reason is the serious consequences of the disease especially among pregnant women and newborns.
Listeria monocytogenes is a Gram positive bacillus, asporulée, aero-anaerobic optional haemolytic catalase-positive, tend to be grouped into chains or fences. This is a mesophilic bacterium, but has the distinction of being psychrotrophic.
Listeria monocytogenes is a ubiquitous bacterium, widely distributed in the external environment: air, soil, waste water from slaughterhouses and sewage, vegetation, silage, etc.. The plant-soil environment appears to be a reservoir from which privileged Listeria monocytogenes can infect humans, animals and foods.
Pathogenicity and symptomatology
Listeria monocytogenes is a pathogen responsible for foodborne illness. Also, it can be transmitted to humans and animals by oral, ocular, skin, respiratory system or the urogenital tract.
The soluble hemolysin is the major toxic product of Listeria monocytogenes. This toxin is produced during the growth of bacteria, including intracellular position. However, the pathogenesis of listeriosis is linked primarily to its ability to multiply in the body.
In terms of human listeriosis, there are 3 types of people at risk: infants, pregnant women and immunocompromised persons.
In newborns, listeriosis has two anatomo-clinical forms: a form called early, the most frequent, often occurring in a premature and causing septicemia due to infection of the fetus in utero, and a late form which causes meningitis (neurolistériose) in children born at term and premature child.
In pregnant women, listeriosis can cause an abortion, if the contamination occurred during the first three months of pregnancy or premature delivery if the contamination occurred in recent months.
As against immunocompromised adults, listeriosis results in several forms, sometimes severe meningitis, meningoencephalitis, encephalitis pure sepsis very often fatal.
Ecology of Listeria monocytogenes
Listeria monocytogenes is a psychrotrophic bacterium which has an optimum temperature for growth ranging from 30 to 37 ° C. However, it can survive and even multiply at temperatures as low as 2 to 4 ° C. So, unlike other pathogens, the cold storage is not a guarantee of protection against growth of Listeria monocytogenes.
Despite the absence of spore, Listeria monocytogenes demonstrated a surprising resistance to various physical and chemical agents. Its destruction by pasteurization of milk is inconstant (72 ° C D = 1.6 to 2 s); pasteurization treatment (72 ° C/15 seconds in the case of milk) is considered sufficient to kill Listeria monocytogenes.
The water activity (aw) minimum for growth of Listeria monocytogenes is 0.92, whereas the minimum pH for growth is 5 (optimum pH: 7.2 - 7.6). It can grow at high levels of salt, up to 10%. In addition, the presence of salt (low dose) has a protective effect on Listeria monocytogenes when the pH values are low.
Responsible food
Among foodstuffs, milk and dairy products, including raw milk and cheese from raw milk, are the first food responsible for the transmission of Listeria monocytogenes to humans. Besides, there are also meat, carcasses of poultry and vegetables.
Means of prevention
All means of prevention must take account of the ubiquitous nature of Listeria monocytogenes and its ability to multiply at low temperatures.
The first measures passed by the strict rules of hygiene in production, manufacture, transport and storage of food. Particular attention should be paid to personal hygiene, cleaning and disinfection and cross-contamination.
Vegetables should never be irrigated with domestic wastewater. In addition, they must be washed and cooked before consumption. It is also recommended to wash again the products stored in the refrigerator (possible multiplication of germs).
Yersiniosis
The Yersiniosis is an infection caused by Yersinia enterocolitica which was identified as pathogenic in humans since 1939. However, it took several years (to 70 years) that yersiniosis is affirmed as a disease may be the result of a foodborne illness.
Yersinia enterocolitica is a Gram negative rod, ovoid or bacillary appearance, characterized by small colonies (less than 1 mm in diameter in 24 hours at 37 ° C), a mobility dependent on the temperature (still at 37 ° C, mobile at 25 ° C), not producing gas in glucose or with very little and most often a very active urease but not gelatinase. As Listeria monocytogenes, Yersinia enterocolitica is a mesophilic bacterium, but has the distinction of being psychrotrophic.
Yersinia enterocolitica is a bacterium that is not demanding, giving it the ability to survive in most foods and even to multiply, including refrigeration temperatures.
Pathogenicity and symptomatology
The pathogenicity of Yersinia enterocolitica is associated with the secretion of enterotoxin and a capacity for cell invasion.
The enterotoxin of Yersinia enterocolitica is characterized by its resistance to heat (121 ° C - 30 min), cold (4 ° C - 7 months) and to changes in pH (1 to 11). It may therefore persist for heat treatment of food and chilling, and in acidic foods and during gastric transit.
Since it persists in the food well, it is considered that the toxin can be produced and then ingested with it (food poisoning). But the fact that there are avirulent strains entérotoxigènes but it secures the pathogenicity of Yersinia enterocolitica primarily to its invasion of intestinal cells. The toxin is responsible only to the most benign and only during the initial phase.
The yersiniosis occurs primarily by diarrhea, liquid or paste, or purulent glaireuse sometimes, but rarely bloody smelly. The number of stools varies issued a few weeks or more per day.
Other symptoms are fickle: abdominal pain, vomiting, nausea, hyperthermia (39 ° C or higher).
Ecology of Yersinia enterocolitica
Yersinia enterocolitica can grow in temperatures ranging from 0 to 42 ° C with an optimum growth temperature of 29 ° C. Its optimum pH for growth is close to neutral, but may grow in the pH range from 4 to 10.
This bacterium can grow in the presence of salt (NaCl) up to 5%. It persists best beef or lamb vacuum than air.
Responsible food
Since Yersinia enterocolitica can grow in a wide range of temperatures and pH in addition to its low requirement for growth, one can find it on most food products.
Throughout history many foods have been condemned as the source of infections collective yersiniosis; include: pasteurized milk, chocolate milk drink, milk powder, tofu, and senile with cream.
Means of prevention
The application of strict hygiene is essential to prevent recontamination of food by the bacteria, whether by food-human contact, food or food-soil water. For this reason, it takes a lot insist on cleaning and disinfection and the observance of personal hygiene practices. Also, the quality of water in contact with food must be monitored.
Chilling food does not guarantee protection against the growth of Yersinia enterocolitica. It is therefore necessary, in the case of raw milk, to treatment thermisation before cold storage.
Salmonellosis
Salmonellosis is a poisoning caused by bacteria belonging to the genus Salmonella.
Salmonella bacteria are Gram negative, asporulée, belonging to the family Enterobacteriaceae. It is mobile and airborne anaerobic optional. Chimioorganotrophes, these bacteria have a fermentative and oxidative metabolism.
It is a ubiquitous germ widely distributed in nature. Its ecological habitat is the intestinal tract of humans, birds and mammals. It can contaminate food through several means: birds insects, rodents, pets, people and water.
Pathogenicity and symptomatology
Salmonella infection is mainly from food. However, it can be transmitted by simple contact with an infected animal or person to another.
The pathogenicity of Salmonella is due solely to its ability entero-invasive (invasion of intestinal cells). The release of endotoxin occurs during cell lysis.
The symptoms of human infection occur in 2 main aspects: the typhoid and paratyphoid fever and gastroenteritis.
Typhoid fever is the classic example of enteritis. The incubation period is 7 to 14 days. The disease is often initially by malaise, anorexia and headaches, followed by a fever that will increase to an average temperature of 40 ° C. bronchitis and cough may also develop over time .
As for gastroenteritis, this form of Salmonella has an incubation period of 12 to 24 hours. The main symptoms of gastro-intestinal infection are nausea, vomiting, abdominal pain and diarrhea which appear suddenly. This infection can be accompanied by headache and chills. Symptoms begin to regress spontaneously after 24-48 hours.
Death can occur, fortunately rarely, in immunocompromised individuals, children and the elderly (high morbidity, low mortality).
Ecology of salmonella
The Salmonella bacteria can multiply at temperatures ranging from 5 to 47 ° C with an optimum temperature for growth 35-37 ° C. Below 10 ° C, their growth is significantly delayed.
Freezing does not complete inhibition of Salmonella bacteria, however some is eliminated and the survivors can easily multiply when the weather becomes favorable. Against by a pasteurisation treatment (72 ° C/15 s) assured destruction in their milk.
The pH optimum for growth of Salmonella is usually between 6.5 and 7.5. The growth of the bacteria is inhibited below 4.5 and above 9. However, sensitivities can be observed variables and the use of citric acid, allowing growth at pH 4.05.
Below a water activity (aw) of 0.93, growth of Salmonella is stopped. It is also inhibited by the presence of a salt (NaCl) over 5.8%.
Ionizing radiations kill Salmonella that do not show radiorésistance particular. Doses below 10 kGy to ensure the sanitation of foods such as meat (mechanically separated) and frog legs.
Responsible food
The foods most frequently incriminated are meat and meat products, some meats, poultry and poultry products, egg products and products based on egg products, milk powder or liquid. But plant products can also serve as vectors for Salmonella.
Means of prevention
Preventing problems of salmonellosis is mainly based on the rules of hygiene and respect for the cold chain.
Hygiene rules on the handling, transport, processing and storage of food, cleaning and disinfection and hygiene must be applied at all levels of the food chain. The vegetables should never be irrigated with domestic wastewater not cleared. Similarly, we must prohibit the gathering of shellfish in polluted areas and without direct treatment of pollution.
With respect to the cold, fresh foods should be cooled as quickly as possible and kept at a temperature below 5 ° C until stabilization by appropriate procedures.
Intoxination staph
The staph is intoxination poisoning due to ingestion of food containing toxins produced by Staphylococcus aureus.
Staphylococcus aureus is a bacterium mesophilic Gram positive asporulée, facultative anaerobic airports belonging to the family Micrococcaceae.
Staphylococcus aureus are ubiquitous microorganisms, widely encountered in the air, water, wastewater and any object in contact with these substances or exposed to human handling. The skin surfaces of humans and animals are the main reservoirs of Staphylococcus aureus.
Pathogenicity and sympomatologie
The pathogenicity of Staphylococcus aureus is due to the production by some strains of this bacterium, of enterotoxins responsible for food intoxinations. It distinguishes 7 types of staphylococcal toxins: A, B, C1, C2, C3, D and E. The enterotoxin A and D are most frequently involved in food intoxinations then decreasing frequency, the enterotoxins C, B and E.
Enterotoxins are stable in a wide pH range (2 to 11), resist the action of proteolytic enzyme (trypsin, chymotrypsin, renin, papain, pepsin) and have high stability to heat.
The manifestation of symptoms of staph intoxination not require high levels of enterotoxins which corresponds to a high load in microorganisms (about 105-106bacteria / g food). That is why the presence of low loads of Staphylococcus aureus is not necessarily a danger.
Ingestion of these enterotoxins causes, within a short period of 2 to 4 hours on average (often the patients are still in place of meals), digestive disorders, sometimes violent. This is especially vomiting, diarrhea, abdominal pain, nausea and sometimes headaches and neurological disorders (prostration). Staphylococcal poisoning not accompanied by fever, and are often benign for adults recover within a few hours to several days. As against, they can be dangerous to infants or the elderly because of dehydration caused sudden vomiting and diarrhea.
Ecology of Staphylococcus aureus
Staphylococcus aureus is a bacterium mesophilic with a minimum temperature of growth of 6 ° C and a maximum temperature of 45-49 ° C. The minimum temperature for toxin production is 8-10 ° C. Unlike its toxins, S. aureus is a germ thermosensitive. Indeed, populations of 106germs / ml can be completely inactivated in 4-24 minutes to 54-60 ° C.
A pH of 4 is a minimum for the growth of Staphylococcus aureus.
The water activity (aw) minimum for growth of Staphylococcus aureus is 0.83, while his aw optimal growth was 0.99. However, the foods most commonly contaminated with Staphylococcus aureus are characterized by an aw below 0.95. This is because in the food or the water is higher, the growth of Staphylococcus aureus is inhibited by the presence of other bacteria (Staphylococcus aureus is not competitive).
Staphylococcus aureus is a halotolerant behavior. It is a bacterium that can be grown on media containing 5% of chloride and up to 10% for some strains.
Responsible food
The fact that Staphylococcus aureus is uncompetitive (inhibited in the presence of a significant competitive flora) is not a real danger in the raw products. For against, there is a danger in the contaminated products after heat treatment such as cooking or pasteurization. This contamination may be caused by manual handling during the packaging or by accidental contamination of pre-packaged products before pasteurization.
Several products have been reported as sources of staphylococcal intoxination: ham, turkey and chicken, roast beef, salads, meat, poultry, etc..
Means of prevention
Only the observance of good hygiene practices and manufacturing can prevent staph intoxination. Indeed, if the stabilization heat treatment can destroy the seeds of S. aureus, they are ineffective on the inactivation of their s'elles toxins are already present in the food.
Food contamination by S. aureus occurs especially after treatment of sanitation cooking. That is why cooked food must be packed as soon as possible and handle under hygienic conditions to avoid recontamination.
Clostridium perfringens
Clostridium perfringens is a Gram positive bacterium of the family Bacillaceae (sporulated bacilli and cocci), bacillary form, strictly anaerobic, sporulating and motionless. It is characterized by rapid speed of around 8 to 10 minutes under optimal conditions.
Clostridium perfringens is a ubiquitous germ widely distributed in nature. However, it has the distinction of being demanding in growth, it requires 13 to 14 amino acids and vitamins 5 to 6 for its growth. For this reason, only a few foods, including meat and less dairy products, are the cause of human poisoning caused by this germ.
Pathogenicity and symptomatology
The pathogenicity of Clostridium perfringens is due to its ability to produce enterotoxins. According to the antigenic nature of these enterotoxins, there are 5 strains of Clostridium perfringens: A, B, C, D and E. It is mainly the Clostridium perfringens A and C that cause human poisoning, others are pathogenic to animals.
When a food containing a large number of vegetative forms (approx. 108cells) from Clostridium perfringens is ingested in recent sporulate in the intestine, the enterotoxin is released, causing the appearance of mainly digestive disorders.
The poisoning caused by Clostridium perfringens type A are manifested by acute abdominal pain, diarrhea, nausea, fever and sometimes vomiting. These symptoms usually appear 8 to 12 hours after ingestion of the meal. The disease is rarely fatal, although some fatal cases have been reported in elderly and immunocompromised. In normal cases, symptoms disappear in 12 to 48 hours.
As for poisoning caused by Clostridium perfringens type C, they are manifested by sudden onset of acute abdominal pain and diarrhea (often bloody), vomiting several times, ending with signs of inflammation and necrosis small intestine.
Ecology of Clostridium perfringens
Clostridium perfringens is a bacterium thermotrophe, with an optimum temperature for growth 43-47 ° C, a temperature of 15 ° C and a maximum temperature of 52 ° C. Above 52 ° C, the growth of the bacteria stops and vegetative cells can be destroyed.
Sporulation and enterotoxin production are optimal at 37 ° C and becomes negligible from 46 ° C.
The optimal pH for growth of Clostridium perfringens is between 5.5 and 8 while its pH optimum sporulation and enterotoxin production is 6.5 to 7.3. A pH below 5 or above 9, the growth of the bacteria is inhibited.
The minimum water activity for growth of Clostridium perfringens is dependent on the solute, temperature, pH and other factors. But in general, the bacteria can not grow when the aw is less than 0.93. What is the aw a brine having a NaCl concentration of about 12%.
Responsible food
Food products that are most often the cause of a food poisoning Clostridium perfringens in meat products are often prepared in large quantities and are long kept at room temperature.
Dairy products, especially milk reconstituted, were also reported as the cause of poisoning by Clostridium perfringens.
Means of prevention
Among foodstuffs, meat products and dairy foods are the most favorable to the growth of Clostridium perfringens. In addition, sources of contamination of food by bacteria that are different (water, air, faeces, etc..), And because of its ubiquitous nature and its long resistance from the external environment.
To avoid the occurrence of foodborne illness to Clostridium perfringens, it is first important to prevent the initial contamination of meat and milk by following the correct techniques of slaughter (for meat) and treatment (in the case of milk). Then, immediate refrigeration is to be taken.
Regarding the meat cooked, they must be heated to temperatures sufficient (heart temperature of 74 ° C at least) to destroy the vegetative forms of Clostridium perfringens.
Botulism
The word botulism comes from the Latin word which means botulus sausage. Indeed, the first listed intoxinations botulinum have been associated with consumption of this product.
Botulism is a food intoxination caused by ingestion of food containing the neurotoxin produced by Clostridium botulinum. This bacteria attack both animals and humans, sometimes with fatal consequences, unfortunately.
Clostridium botulinum is a Gram positive bacillus, spore, strictly anaerobic, belonging to the family Bacillaceae.
Pathogenicity and symptomatology
The pathogenicity of Clostridium botulinum is due to its ability to produce neurotoxins. These are protein molecules, comprising up to 20 amino acids, released by vegetative cells in late logarithmic growth. The toxic dose is estimated at 1 nanogram (10-9g) per kg body weight.
According to their antigenic nature, there are 8 neurotoxins (A, B, C1, C2, D, E, F and G), the production of one or the other allows you to group strains of Clostridium botulinum in 4 groups :
- Group I: Includes strains of type A and proteolytic strains of types B and F.
- Group II: Includes non-proteolytic strains of types B and F, and all those of type E
- Group III: Includes strains of types C and D.
- Group IV: Understanding the type strains of G.
Botulism can result:
- or ingestion of food containing the neurotoxin produced by Clostridium botulinum. It is therefore a intoxination food. This is the mechanism of the oldest known and most classical
- or ingestion of toxins in the food perforated and / or bacteria or spores present in the food. These seeds will cross the gastric barrier and penetrate into the intestine where they produce their toxins. It is then in this case of food poisoning. This is obvious and frequent in humans.
Human botulism is a serious disease with high mortality, it is fortunately a rare disease (low morbidity, high mortality). Symptoms related to the disease in 2 to 24 hours after poisoning and is manifested by:
- Ocular paralysis and double vision;
- Secretory disorders (dry mouth default salivation);
- Swallowing disorders and speech ;
- Fewer signs, such as constipation by decreasing secretions, muscle paralysis and urinary retention may occur.
In mild forms, only the ocular paralysis are present, they usually appear and disappear in the first last. While in the most serious forms, can be observed paralysis of respiratory muscles, and death by suffocation due to paralysis of the lungs.
Ecology of Clostridium botulinum
All strains of Clostridium botulinum are anaerobic strict. They grow mainly in revenue potential redox low.
Strains of proteolytic Clostridium botulinum types A, B and F spores produce heat, which easily survive pasteurization. However, they are unable to grow and produce toxin at temperatures below 10 ° C. Against by the Clostridium botulinum type E and non-proteolytic types B and F are able to grow and produce toxins at temperatures as low as 3.3 ° C, but their spores are thermosensitive.
Regarding the pH values below 4.5 to inhibit the germination and Toxinogenesis Clostridium botulinum. Therefore we divide the food products weakly acidic (pH ≥ 4.5) and acidic foods (pH <4.5). The risk of botulism is zero for acidic products. The minimum water activity for growth of Clostridium botulinum is 0.94. Its growth is also inhibited by the presence of salt (10% or more of NaCl).
Responsible food
Because of the nature of anaerobic bacteria and the high heat resistance of spores, mainly canned food products packed in vacuum or modified atmosphere, the smoked and salted products which cause the disease botulism. A significant proportion of cases of botulism due to consumption of preserved and semi-preserved foods prepared at home.
Dairy products are rarely involved in botulism intoxinations. However, few cases have been reported following consumption of dairy products such as yoghurt and cheese. Contamination of these products by Clostridium botulinum is probably due to the use of ingredients contaminated by the germ.
Preventive measures
Compliance with good hygiene practices is required to minimize food contamination by Clostridium botulinum.
Freezing or refrigeration of food at temperatures below 3.3 ° C, acidification (to pH <4.5), salting (up to 10% salt) and the use of food additives such as nitrates and nitrites of sodium and potassium, are also effective measures to prevent the proliferation of Clostridium botulinum and the production of its toxins. When the latter are already present in a food, they can be inactivated by heating food to a temperature of 80 ° C for 6 to 10 minutes.
Clostridium botulinum spores are resistant to treatment by pasteurization, but inhibited by sterilization. In the latter case, treatment should be done on a scale equivalent to 121 ° C to heart for 3 minutes minimum. After sterilization, it is necessary to avoid possible recontamination.