1. Pathogens

2. Infection is the invasion and growth of an organism within a host organism Pathogens are infectious organisms that harm their host - Frank pathogens can cause disease in otherwise healthy individuals - Opportunistic pathogens can only cause disease in compromised individuals (burn victims, AIDS patients, the young or elderly, pregnant women, transplant patients) - Human pathogens include bacteria, viruses, and protozoa (amoebas, flagellates, and apicomplexans) Virulence is the degree of pathogenicity of a parasite determined in part by minimal infective dose, the number of organisms needed to cause an infection bacteria > viruses > parasites

3.  Food borne transmission  Ingestion of infectious agents in food  Main causes are poor sanitation, hygiene (faecal-oral route), Insufficiently cooked food  Examples of food borne disease are,  Botulism, E.coli diarrhoea

4.  Humans become infected by ingesting pathogenic bacteria, viruses or parasites in water polluted by human or animal faeces or urine.  Examples of water borne diseases -Cholera -Bacillus dysentery (shigellosis) -Tyhoid, Salmonellosis, E.coli diarrhoea

5.  Human become infected by being bitten by an insect vector  Examples of diseases are; -malaria -sleeping sickness -yellow fever

6.  Transmission is through inhalation of pathogens in aerosols  Aerosols created at waste water treatment plants, land application of sludge, showers  Examples -fungal infections

7.  Requires direct physical contact between host  Sexually transmitted diseases  Examples are -Gonorrhoea -HIV/AIDS

8.  Food borne disease is simply disease that results from the ingestion infectious agents of food  Microorganism are by far the most important agents of food borne disease, with bacteria causing the bulk of food outbreak.  Also viruses, protozoa and to a lesser extent fungi

9.  Bacillus cereus, Clostridium botulinum, C. Perfringens. E.coli, Salmonella spp, Staphylococcus spp  These microorganism once ingested with the food, when conditions are favourable, -they reproduce and produce toxins which cause diseases.  Conditions,  ideal temperature  pH  water activity and growth factors

10.  The organism: B. cereus is Gram positive rod, spore forming, non motile, non capsulate and produces haemolytic colonies on blood agar.  The organism is non lactose fermenting and produces pale colonies on Mac Conkey agar.  B. cereus produces beta lactamase and is resistant to penicillin and cephalosporin's antibiotics

11.  The disease, Bacillus cereus produces two distinct types of gastroenteritis  (a) Diarrhoeal type caused by strains of B. cereus that produces a heat sensitive enterotoxin. The toxin is formed during growth in the food and also in the intestines after ingestion of vegetative cells.

12.  (b) Emetic (nausea and vomiting) type caused by strains of Bacillus cereus that produces a heat stable enterotoxin formed in the food during stationary phase of growth.  Incubation period: diarrhoeal type 8- 16 hrs, emetic type 1-5hrs

13.  Symptoms, diarrhoeal type- profuse watery diarrhoea, abdominal pain, occasional nausea and vomiting; emetic type, nausea and vomiting, occasionally followed by diarrhoea  Infective dose: very large numbers of cells are required, diarrhoeal type >5E5/g, emetic type>1E3/g

14.  Bacillus cereus is widely distributed in the environment, soil, dust, milk, rice vegetables and other cereals that have been cooked and then stored in warm temperatures  Bacillus cereus is causes opportunistic infections in immunocompromised persons e.g pneumonia, bacteraemia wound infections

15.  Diarrhoeal type- meat and meat products, soups, vegetable dishes, dishes to which spices have been added late in cooking and then allowed to stand before eating.  Emetic type- cooked rice and pasta

16.  C. botulinum is a gram positive, motile, rod with oval sub terminal spores.  Basically the following type of strain exist A, B, E and F  Two types of C. botulinum exist: -proteolytic which include all of type of strain A and some of type B and F -non proteolytic all strains of type E and some strains of type B and F

17.  The disease, Botulism is caused by ingestion of a neurotoxin secreted into food during growth of the organism.  Infant botulism is caused by ingestion of spores of the organism leading to subsequent growth and toxin production of the toxin in the gut.  This happens before the establishment of natural flora.

18.  Incubation period: Normally 12-36 hours but can be between 2-hrs to 8 days.  Symptoms: although nausea and vomiting may occur, symptoms are mainly neurological- blurred or double vision, difficulty in swallowing, mouth dryness, speech difficulties and limbs and respiration becomes progressively paralysed

19.  The botulinal toxins are among the most toxic substances known.  Minimum lethal dose for mice 0.4- 2.5ng/kg of mouse tissue  Estimated 50% lethal dose for human is 1ng/kg of body

20.  Under anaerobic conditions, e.g in low acid canned foods such as tinned meat or fish (not acid fruits), the spores germinate and the bacilli multiply, producing the toxin.  C. botulinum can be found in soil, water and sewage.  C. botulinum can be isolated with Robert’s cooked meat medium

21.  Botulism has also been associated with food that has been inadequately heat treated or heat treated so that the spores survive and competition is low.  High water activity>0.93  Preservative present e.g. nitrite, salt are insufficient to prevent spore germination  Food that has been held at room temp within the growth range of the organism.

22.  E.coli is a gram negative usually motile rod.  E.coli belong to large group of gram negative rods referred to as enterobacteria  They are naturally found the intestinal tract, in soil, water.  Those that cause primary and opportunistic infections in humans belong mainly to the following genera

23.  The disease: Although E. coli is generally harmless part of the normal micro flora of the gut of humans and number of the groups of E.coli are pathogenic and have been associated with food borne disease.  These are;

24.  Strains of E. coli are recognised as causing diarrhoeal disease include;  Enterotoxigenic E. coli (ETEC)  Enteropathogenic E. coli (EPEC)  Enteroinvasive E.coli (EIEC)  Veterotoxigenic E.coli (VTEC)  Enterohaemorrhagic E.coli (EHEC)

25.  Incubation period: 3-4 days  Inflammation of the colon giving rise to diarrhoea and abdominal pain with bleeding –blood appear in stools.  Renal failure due to blood clots in the kidney tubules  Infective dose: the infective dose is thought to be low, possibly 10- 100organism.

26.  The natural habitat of E.coli 0157:H7 appears to be the intestines of dairy cattle.  Undercooked minced beef and raw milk have been implicated in food poisoning outbreaks.

27.  E.coli can be isolated with blood agar, MacConkey agar, XLD and DCA agar.  In XLD and DCA agar, yellow colonies are produced on XLD.  Growth of E. coli is usually inhibited by DCA agar

28.  Salmonellae are gram negative rods. With the exception of S. Pullorum-gallinum, all salmonellae are actively motile.  They are non sporing and with the exception of S.typhi  Salmonellae are aerobes and facultative anaerobes.  Their optimum temperature is 37 Deg C

29.  Salmonella enterocolitis  Infection is by ingesting salmonellae in food that has become contaminated from animal and human intestinal sources, directly or indirectly.  Common sources of infections are poultry, meat products, eggs and egg products  Food poisoning salmonella spp can cause bacteraemia, inflammation of the gall bladder, children sickle cell anaemia

30.  Salmonella can be isolated on blood agar (subcultures), XLD agar or DCA and MacConkey agar  Salmonellosis occurs within 12-24 hrs  The symptoms may include nausea, dairrhea, abdominal pain, fever, headache

31.  The gram negative genus Vibrio contains more than one member that is pathogenic to human.  Cholera is transmitted through the ingestion of faecal contaminated food or water  The organism produces an exotoxin- cholera toxin.

32.  Symptoms of the disease is accompanied by severe dehydration, vomiting, abdominal pains and acidosis associated with cholerae due to the action of the exotoxin.  This causes water and electrolytes to flow into the bowel lumen  In severe infections, typical rice water stools containing many vibrios are passed continuously. TREATMENT; Explain how

33.  Slender rods, 2,5-3,5um appearing mostly in pairs.  They are difficult to stain because of waxy constuents but once stained resist decolourisation with acid.  They are non motile, non capsulated, non sporing, grow very slowly and are aerobic  The microorganism is inhaled in small particles into the bronchioles

34.  In Miliary TB, the TB bacilli can be transmitted by inoculation,, inhalation and through food such as milk and milk products

35.  The pathogen is transmitted by direct contact with an infected person or a carrier.  The bacterium, C. diptheriae is transformed from a commensal to a pathogen by a virus called a bacterial phage.  The bacteria then starts to produce a powerful exotoxin which is absorbed into the blood stream.

36.  This toxin poisons heart muscle, kidneys and nerve tissue resulting in malfunctioning of these organs and death may follow.

37.  The organism, Gram positive spore forming rod  Five types designated A-E are recognised according to enterotoxin produced  C. perfringens type A causes the vast majority of food poisoning out break.

38.  The disease, The disease is caused by an enterotoxin that is released into the gut when mother cells release their spores.  The sporulating cells are produced from live vegetative ingested with food  Because live organisms are normally required to be ingested to cause the

39.  The disease, some authors consider this to be an infection.  Incubation period: 6-24 hrs after the ingestion of food.  Infective dose: large numbers of vegetative cells in a food are required to produce food poisoning, appro 8E/g>

40.  Clostridium perfringens is found in most soils and is consequently present in dust.  Many foods contain spores of the organism, particularly animal carcases that become contaminated during slaughter.

41.  Most outbreaks have been associated with meat or poultry that has been boiled, stewed and then held at room temperature or under warm conditions or in bulk refrigerators in which cooling is slow.