Foodborne Illnesses - CH 7 PDF

CH 7-Nonbacterial Foodborne Illnesses  Mycotoxins- Aflatoxins, Fumonisins, Ochratoxins, Alternaria toxins  Toxins from Cyanobacteria and Algae  Parasites Flatworms- Tapeworms and Flukes Roundworms- Trichinella spiralis Protozoa- Toxoplasma gondii , Sarcocystis, Giardia, Entamoeba,...

CH 7-Nonbacterial Foodborne Illnesses  Mycotoxins- Aflatoxins, Fumonisins, Ochratoxins, Alternaria toxins  Toxins from Cyanobacteria and Algae  Parasites Flatworms- Tapeworms and Flukes Roundworms- Trichinella spiralis Protozoa- Toxoplasma gondii , Sarcocystis, Giardia, Entamoeba, Cryprosorium  Viruses – Polio virus, Hepatitis A and E , Norovirus, Rotaviruses  Mycotoxins Mycotoxins are naturally occurring toxic secondary metabolites produced by different array of fungi. Certain Toxigenic species of molds produce Mycotoxins, which may contaminate foods or animal feeds, and that happen to be toxic to humans and livestock.  Several (More than 300) different mycotoxins have been identified; but the most common mycotoxins that present a concern in relation to food safety include:  aflatoxins, ochratoxin A, patulin,  fumonisins, zearalenone and deoxynivalenol (DON) Mycotoxins cause various health problems on human and domestic animals  gastroenteritis, immunosuppressive, neurotoxic, teratogenic, nephrotoxic, hepatotoxc, mutagenic and Carcinogenic Also cause significant economic losses especially in developing countries 2  Fungal growth and toxin production may occur during growing and in storage conditions Field fungi- Alternaria, Cladosporium, Fusarium spp Storage fungi – Aspergillus, Penicillium and Fusarium spp Habitat- widely distributed in nature, soil, dust and air Growth -They are aerobic, can grow at very low Aw (0.65),refrigerated temperature, low pH (pH 3.5). Optimum condition for mold growth and toxin production is: – temperature 25- 30 °C, moisture level 13-18 % vacuum packaging and thermal process can inhibit growth.  Most of the mycotoxin-producing mold strains belong to the three genera- Aspergillus, Fusarium and Penicillium. 3  Common naturally occurring Mycotoxins and their toxic effects Mycotoxin Toxigenic fungi Toxic effects s Aflatoxins Aspergillus flavus, A. Highly toxic, mutagenic, Parasiticus carcinogenic; Hapatitis (Acute toxicity), liver cirrhosis, hepatic carcinoma,, immunosuppression, growth retardation in children Ochratoxin A Aspergillus ochraceus, Nephrotoxic, immunosuppressive, A. westerdijkiae, A. possible carcinogen steynii, A. Carbonarius , Penicillium verrucosum, P. nordicum Fumonisins Fusarium verticillioides, possibly carcinogenic; esophageal F. proliferatum cancer, equine encephalomalacia Zearalenone F. graminearum, F. Hyperestrogenic and reproductive culmorum problems Trichothecen Alimentary toxic aleukia (Bleeding, es: F. sporotrichioides, F. vomiting, diarrhoea), T-2 poae Immunosuppressive DON F. graminearum, F. GIT problems, immunotoxicity 4 culmorum Food Association Toxigenic mold strains found in many foods:- corn, wheat, barley, rye, rice, beans, peanuts, bread, dry sausages, spices, apple cider, cereal grains, sorghum, coffee, oats, cottonseeds, animal feeds Mycotoxins can be secreted in milk and eggs if animals fed with mould contaminated feeds. Mycotoxins are chemically stable and resistant to heat. Thus, heating does not eliminate them from foods once the toxins are produced, even after the destruction of the fungi that produced them. Prevention Preventing growth of molds in food or feed can be achieved by – Heat treatment, anaerobic packaging, reducing Aw (below 0.6), freezing, and using specific preservatives against mold growth. 5  TOXIGENIC ALGAEA Planktonic algae can produce very toxic compounds which may be transported to filter-feeding shellfish such as mussels and clams, or small herbivorous fish The toxins pass along a food chain to large carnivorous fish which are caught for human consumption. Various forms of shell fish poisoning: Paralytic shellfish poisoning, Neurotoxic shellfish poisoning, Diarrhoeal shellfish poisoning, Amnesic shellfish poisoning, Ciguatera fish poisoning. Toxins implicated in the various forms of shellfish poisoning are not detectable organoleptically, and are also not affected by cooking. Dinoflagellates produce saxitoxin & gonyautoxin, which causes paralytic shellfish poisoning. Cyanobacterial Toxins- blooms in lakes & ponds, represent a major ecological and public health problem. cyanobacteria in public water supplies also cause gastroenteritis. Toxic Diatoms- amnesic shellfish poisoning (ASP) or domoic acid poisoning, following consumption of cultivated mussels. 6  Parasites Parasites include Helminths (worms), and protozoa. Protozoa are unicellular organisms. - Giardia, Entamoeba, Toxoplasma, Sarcocystis, Cryptosporidium Helminths are multicellular organisms classied into flat worms and round worms – Platyhelminths ( flat worms)- Flukes and Tapeworms – Nematodes (roundworms)- Trichnella spp., Ascaris  Platyhelminths: Liver Flukes and Tapeworms Two most important foodborne parasites: Trematoda-includes the liver fluke Fasciola hepatica, The Cestoda- the tapeworms Taenia solium associated with pork, and T. saginata associated with beef, are best known Liver flukes have complex life cycles which involves different hosts at different stages. The immature stage develops in water snail (Limnaea truncatula); but eventually the metacercaria is attached to grass. 7  Fasciola hepatica Affects Sheep and cattle, and rarely humans A trematode that causes biliary cirrhosis and liver rot Larval development stage takes place in the snails and water pants. Humans are contracted from ingesting a metacercaria attached to watercress; and for cattle a metacercaria with grasses.  Disease symptoms migration of immature fluke – abdominal pain etc Adults in biliary duct – symptoms associated with blockage  Occurence- worldwide Human infections in areas where sheep and cattle are raised, and humans consume raw watercress. Emerging – spread of snail habitat 8  Cestodes (tapeworms)  Taeniasis / Cysticercosis: T. saginata- humans infected by ingestion of meat that contains cysticerci. T. Solium - infection is potentially more dangerous – Humans infected by ingestion of cysticerci in pork, or – Autoinfection by Ingestion of eggs, leading to formation of cysticercosis in muscles, liver, eye, brain  Symptoms of Teaniasis Often asymptomatic Cysticercosis with T. Solium is most dangerous – Cerebral cysticercosis- nervous signs – Ocular, cardiac, spinal lesions  Prevention Use of latrine A cysticercus in musc Meat inspection Cysticerci can be destroyed in beef and pork by cooking to 600C, or freezing to −100C for 10–15 days. 9 PROTOZOA. Sarcocystis Sarcocystis are obligately two-host parasites, i. definitive host in which sexual reproduction of the parasite takes place. Include cats, dogs or humans ii. intermediate host such as cattle, sheep or pigs , the asexual cysts are formed in the tissues Two species can infect humans: S. hominis, from cattle, and S. suihominis from pigs. Symptoms- include intestinal with nausea, stomachache and diarrhea Associated Foods- raw or inadequately cooked Beef and pork containing sarcocysts Prevention- Beef and pork which have been adequately cooked lose their infectivity. 10 E. Giardia lambia/ G. intestinalis A flagellate protozoan that exists in environmental waters (cyst forms) Transmission - usually associated with water, or person to person by poor hygiene. Up on ingestion the trophozoites, are released in the gut Disease symptoms Acute and chronic cases, – diarrhea, abdominal pain, bloating, nausea, vomiting, fatigue In chronic giardiasis the symptoms are recurrent Associated Foods Giardia cysts have been found on vegetables such as lettuce and fruits such as strawberries, Waterborne outbreaks more common Any food can be contamined if washed with contaminated water, or handled by infected persons infected foodhandlers. Beavers and muskrats are major sources of Giardia cycts and contaminate water. Giardia cysts resistant to chlorine in water they are killed by the normal cooking procedures. 11 12 F. Entamoeba histolytica Cause amoebic dysentery, transmitted by the faecal-oral route. The organism is an aerotolerant anaerobe which survives in the environment in an encysted form. Sources of infection- contaminated water, food , and food handlers Cysts released in the stool contaminate the water, the cyst can survive in sewage.  Symptoms Abdominal pain, fever, severe bloody diarrhea with mucus, vomiting, back pain, and weight loss Chronic cases may last in some individuals for many years. 13 Waterborne parasites- Transmitted by drining water Cryptosporidium Giardia Toxoplasma Microsporidia Cyclospora Entamoeba Cystoisospora Balantidium Blastocystis Range of helminths  Prevention strategies for waterborne parasites Protection of water source from human and animal contamination Appropriate municipal water treatment Point of use water treatment – heating; sunlight; filters Monitoring and surveying of waterborne parsites Ability to detect an outbreak – effective monitoring of infections 14  Foodborne Viruses A virus particle is composed of either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) enclosed in a coat of protein. Extremely small- diameters generally in the range 25–300 nm Some viruses are enveloped by an outer lipid membrane Viruses are obligate intracellular parasites, and cannot multiply other than in a susceptible host cell Consequently, virus multiplication will not occur in foods; So that foods act only as a passive vehicle in the transmission of virus infection In recent years viruses have been increasingly recognized as an important cause of foodborne illness. There are currently more than 100 human enteric viruses recognized, and since these are spread by the faecal-oral route, food is one potential route for transmission.  Gastroenteritis Viruses- Human enteric viruses A number of viruses are implicated in gastroenteritis such as rotavirus, parvovirus, calicivirus , astrovirus Responsible for most outbreaks of foodborne viral gastroenteritis 15 Rotavirus Family Reoviridae; naked; dsRNA ; 70 nm in diameter Most common cause of hospitalization due to diarrhoea in children (age< 5); Infection is peak in winter months Infective dose to be 10-100 viral particles; (incubation 2 days)* Transmission is primarily fecal–oral route – contaminated water and utensils Self-limiting, mild to severe gastroenteritis characterized by vomiting, watery diarrhoea, and low-grade fever. infection is severe in infants and young children Astroviruses Small RNA viruses, star-shaped, 28 nm in diameter. endemic gastroenteritis usually in young children Similar disease to rotaviruses 16  Norovirus Family Caliciviridae, naked, ss RNA, 38 nm diameter Cause of acute gastroenteritis in USA and Europe- “Winter vomiting disease” Infective dose 10-100 viral particles; Incubation period 24- 48 hr acute-onset vomiting, watery diarrhea with abdominal cramps, and nausea. Shedding of virus in stool begins with the onset of symptoms, and maximum of 24-72 hours after exposure Transmitted: contaminated food or water; direct person- to-person spread.  Oyster & shellfish The virus is more resistant to destruction by chlorine Vaccine production seems hopeless; (several serologic varieties). 17  Poliovirus Family Picornaviridae, single-stranded RNA viruses Transmitted: faecal oral route (food, water); and person to person spread Cause gastrointestinal illness and poliomyelitis (polio) Initial symptoms- fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. Second stage- the virus invades the meninges causing back pain and headaches. In worst cases the virus may spread to spinal chord causing paralysis (lower limbs) the virus is shed intermittently in faces for several weeks. Vaccination- likely to be fully eradicated in the next few years. 18  Hepatitis A Virus ssRNA Virus replicates in guted and liver, virus are shed in feces transmitted by – Person to person – Contaminated drinking water and food Vegtables Seafood (shellfish the most common vehicle food.) Cause infectious hepatitis Symptoms : anorexia,, vomiting, malaise, fever, passage of dark urine and jaundice. Symtoms are severe in old age than in children Childhood Infection results lifetime immunity  HA Virus is resistant to low pH (pH 1), and relatively to free chlorine Destruction: heating to over 85 °C for 1 min; disinfecting surfaces with 1:100 solution of sodium hypochlorite 19  Hepatitis E calici-like particle, ss RNA Spread by drinking water Incubation time 15-60 days Illness resmbles hepatitis A no chronic carriers, No vaccin  Prevention methods for foodborne viruses Proper heat treatment of food: pasteurization effectively kill the viruses Disinfecting surfaces, equipments and water with hypochlorite Good personal hygiene, and keep suspected individuals away from handling food Vaccination 20  Microcopy and staining Microscopes employ lenses to magnify images of the cells. The advent of microscopes enable us to know the detail structure of microbial cells  light microscopes Light microscope uses visible light to illuminate cell structures. Modern light microscopes are known as compound microscopes; they enlarge images using more than one magnifying lens. Light microscopes have a limit of resolution about 0.2µm. Types of Compound light microscopes: – Bright- field – phase-contrast – dark- field – fluorescence  Electron microscopes Use electron beams. Magnification-100 000X; the resolution is improved to 0.2nm Two types of electron microscopes: 21 – Transmission Electron microscope (TEM)  Bright-field compound microscope – Most commonly used microscope in the laboratory Uses Two sets of lenses to form the image –Objective and ocular Total magnification = objective magnification  ocular magnification – Maximum magnification is ~1000X..... (1500X) Magnification alone will not provide detail structure of the image. So its capacity for discerning detail, known as the resolution of a microscope, affects to get sharp image. Resolution(resolving power) is the capacity of the lenses to distinguish fine detail and structure. Specifically, it refers to the ability to distinguish two adjacent points as separate and distinct – Resolution is determined by the wavelength of light used and numerical aperture of lens (NA). – Limit of resolution for light microscope is about 0.2 m d= resolution λ= the wavelength of the light source n = the refractive index of medium between the objective lens and specimen θ = the aperture angle 22   Bacterial Staining Specimens are visualized because of differences in contrast (density) between specimen and surroundings Bacterial cells are colorless and almost transparent. The light microscope does not provide enough contrast to see cells easily. So several dyes are used to color cells and improve contrast in light microscopy, so that the images can be seen easily.  Many basic dyes which bind to negatively charged components of cells such as cell wall structures are used to stain bacteria  E.g. Methylene blue, Safranin, Crystal violet Commonly used staining techniques in bacteria: a. Simple stain- one type of stain is used b. Differential staining- two dyes are used  Gram staining- The Gram stain is widely used in microbiology to distinguish between Bacteria with different cell wall structures Crystal violet (the primary dye) and Safranin (the secondary dye) is used to distinguish Gram-positive and Gram-negative bacteria 23  The Gram stain Most bacteria are classified as Gram positive or Gram negative according to their response to the Gram-staining procedure. The Gram stain depends on the ability of certain bacteria (G +ve bacteria) to retain a complex of crystal violet (a purple dye) and iodine after a brief wash with alcohol or acetone. G-ve bacteria do not retain the dye–iodine complex and become translucent, but they can then be counterstained with safranin (a red dye). Thus, gram-positive bacteria look purple under the microscope, and gram-negative bacteria look red. 24 Micrograph of gram-stained bacteria. The Purple cocci are G +ve , and the Pink rods are G-ve. The distinction between these two groups turns out to reflect fundamental differences in their cell wall structure 25  Bacterial cell structure Figure. Structure of prokaryotic cell. Note the lack of complex internal organelles. Gram-positive and Gram-negative bacteria differ in the details of their cell wall structure 26  Bacterial Cell Wall a thick, rigid structure external to the cell membrane maintains the integrity of the cell (shape, rigidity, protection) The Cell wall is Fully permeable Bacterial cell wall is Composed of Peptidoglycan , which is a polymer of two monosaccharide subunits (N-acetylmuramic acid and N- acetylglucosamine)cross-linked by polypeptides Based on the structural differences in their cell wall, There are two distinct structural types, known as Gram-positive and Gram-negative Bactria, and this is reason for the differences on gram staining reaction. a. G-positive- thick layer of pepetidoglycan (90%), and embedded teichoic acids. G-negative-thin layer of peptidoglycan (10%) and additional outer membrane; – The outer memebrane contains lipopolysaccharides (LPS) chains (antigen O). – The LPS is the endotoxin of G-negative bacteria; a virulence factor for organism. 27 28 Cell wall structure of G-positive (b1), and G-negative bacteria (b2). *(1) Pentaglycine bridges (G- positive bacteria), or direct bond between two amino acids of tetrapeptides (G-negative bacteria) 29  structures external to the cell wall Capsule & slime layer ( Glycocalyx) Flagella Pilli and fimbrae  Not all bacteria have all these surface structures a. Pili and Fimbriae - short filaments made of proteins – Fimbriae are used for attachment – Sex Pili- assist in conjugation one or few, slightly longer than fimbriae 30 b. Flagella Long hair-like appendages made of proteins (20 nm across & 20 mm long) used for locomotion in many bacteria Motility occurs due to the rhythmic movement of flagella. Bacteria often differ in their patterns of flagella. Flagella may be peritrichous (distributed over the entire cell) or polar; polar flafella may be monotrichous (a single flagellum at one pole), lophotrichous (a tuft of flagella at one pole), amphitrichous (flagella at both poles).  The proteinaceous nature of the flagellum gives rise to its antigenicity; called the H antigen.  Some bacteria that lack flagella move by gliding motion  Bacterial movement in response to chemical gradient is called chemotaxis 31 c. Capsule and slime layer ( Glycocalyx) The Glycocalyx are secreted surface layers, composed of sticky polysaccharides Capsule: organized and firmly attached to cell wall Slime layer: unorganized and loosely attached Function- Important in attachment to surfaces, formation of bacterial biofilms The Capsule also prevents form phagocytosis and desiccation. 32