Bacterial Agents of Foodborne Illness - Infection

• Foodborne bacterial agents


  • Salmonella spp.
  • E. coli O157:H7
  • Listeria monocytogenes
  • Campylobacter spp.
  • Vibrio spp.

  
• Foodborne bacterial agents


  • Salmonella
  • Shigella
  • E. coli: VTEC
  • Yersinia enterocolitica
  • Enterobacter sakazakii
  • Campylobacter jejuni
  • Aeromonas hydrophila
  • Vibrio: V. cholera, V. parahaemolyticus, V. vulnificus
  • Listeria monocytogenes

  
• Enterobacteriaceae family


  • Includes several genera of bacteria that cause primary infections of the human gastrointestinal (GI) tract
  • All rods Gram (-), Oxidase (-)
  • Facultative AnaO2 can grow in MAP, VP & package under oxygenic conditions
  • Some ferment Lactose e.g., E. coli (+); others not Shigella (-), Salmonella (-), Yersinia (-)
  • Fermentation of glucose: with gas production e.g., E. coli (+), Salmonella (+) (H2S (+) in TSIA without gas e.g., Shigella (-), Yersinia (-)

  
• Salmonella


  • Habitat: primarily in the gut of animals, found in sewage
  • Carried by wild animals, rodents, pets, birds, insects
  • Transmission: faecal-oral route

  
• Salmonella nomenclature


  • Genus, species, subspecies: in italics
  • Serovar: not in italics, Capital letter
  • Usually: Genus + Serovar
  • e.g. Salmonella Paris

  
• Salmonella species


  • S. enterica: 6 subsp. e.g., S. enterica subsp. enterica (I) contains 1454 serovars e.g., serovars Enteritidis, Paris, Typhi, Paratyphi, Typhimurium
  • S. bongori (20 serovars)

  
• Salmonella serovars


  • Distinguish two illnesses:
  • Typhoid fever by two serovars: S. Typhi & S. Paratyphi (human host)
  • Gastroenteritis or salmonellosis: by other serovars

  
• Salmonella characteristics


  • Facultative anaerobes, Growth in MAP
  • Temperature: 5° to 47°C, T°opt. 37°C
  • Survive in frozen (decline numbers) & refrigerated foods
  • Heat sensitive, Killed by pasteurization
  • D72 in milk 0.09min for the most resistant serotype S. Senftenberg
  • Heat resistant increases (↑) in a low aw: D70 11-17h in chocolate sauce for S. Typhimurium
  • pH: 4.0-9.5, but varies w/ acidulant: 4.05 (citric), 5.4 (acetic)
  • aw min 0.93, survive in dry foods (low aw)
  • Salt inhibition: 3-4% NaCl, salt tolerance ↑ w/ ↑ T

  
• Typhoid or enteric fever


  • Caused by S. Typhi and S. Paratyphi A,B,C
  • Risk of severity (ICMSF): severe
  • Life-threatening systemic disease: treated w/ antibiotics: chloramphenicol, ampicillin & amoxicillin
• Salmonellosis


  • Caused by non-typhoidal Salmonella
  • Risk of severity (ICMSF): moderate
  • Diarrhoea

  
• Typhoid fever pathogenesis


  1. Ingested organisms, which survive passage through the stomach acid

  2. Adhere to the (intestinal) epithelial cell of the ileum via fimbriae

  3. Engulfed by the cells, multiply in vacuole

  4. Released into laminar propria

  
• Typhoid fever symptoms


  • Fever, headache, constipation & rose red spots on the body
  • Bacterium reaches the gallbladder through phagocytes & multiplies in the bile; that flow re-infects the small intestine causing inflammation & ulceration
  • Fever, diarrhoea w/ large # of microbes excreted in a "pea soup"
  • Serious cases – hemorrhage, ulceration or intestinal perforation
  • 1-3% recovered patients become carriers (months & occasionally years), harboring Salmonella in their gallbladder
  • The fatality rate is 10% compared to 1% for salmonellosis

  
• Typhoid fever is rarely seen in North America
• Salmonellosis symptoms


  • Asymptomatic carriage to severe diarrhoea
  • Onset 6-48h after of ingestion (incubation of invasive microbes)
  • Diarrhoea & Abdominal pain, mild fever & chills & sometimes vomiting, headache & malaise
  • Self-limiting, lasting 2-7 d (more severe in susceptible groups)
  • Large # of Salmonella in the faeces during the illness
  • Can continue to be shed for up 3 months (symptomless carriers)
  • Treatment of uncomplicated cases: supportive therapy, e.g. fluid & electrolyte replacement
  • Antibiotics not recommended because they prologue the carrier state
  • Complications: Reactive Arthritis (2 to 15% of patients), 2-3w after infection in young children & elderly

  
• Salmonella infectious dose


  • From 1-100 to 107 CFU/mL or g of food
  • Varies with age (newborns, infants & elderly) & health of the victim (immunocompromised individuals), the food type & the virulence serotype
  • Ingestion of only a few cells can be infectious
  • A number of outbreaks → infective dose as low as 1-100 cells
  • Associated with more susceptible individuals (newborns & infants, elderly & immunocompromised individuals)
  • Fat food: cheese (milk fat), salami & hamburger (animal fat), chocolate (cocoa butter) protect cells to pass through the acidic stomach
  • Infective dose 200 → waterborne outbreak (1970s) (rapid transit through the stomach)

  
• Salmonella is a zoonotic infection, the major source of human illness is infected animals

  
• Salmonella transmission


  1. Contents of infected animal are ingested with food or water

  2. Natural habitat: Gastrointestinal tract

  3. Transmission by the faecal-oral route disseminated via faeces

  4. Soil, water, foods and feeds

  5. Animal to animal

  6. Person to person

  
• Foods associated with Salmonella outbreaks

  • Poultry, Meat, Eggs (shell & yolk) & Milk
  • Birds, Pets (dog), Rodent, Insects, Human Carriers

  
• Salmonella food contamination


  • Poor handling practices - temperature abuse or poor T control
  • Inadequately processed foods or post-processed contamination (e.g. milk)
  • Cross-contamination of processed foods from raw ingredients (contaminated kitchen equipment & utensils) & contaminated water
  • Period of T° abuse (undercooked) & inadequate or absent final heat treatment contribute to outbreaks
  • Microbes multiply on the food → infectious dose

  
• Salmonella spp. continue to be significant human pathogens in the global food supply for several reasons

  
• Reasons Salmonella is a significant human pathogen

  • Their presence in the environment
  • Intensive farming practices used in the meat, fish & shellfish industries (promotes spread among animals)
  • Poultry meat & eggs are predominant reservoir
  • Transovarian transmission of MO into the interior of the egg prior to shell deposition; shell sanitizing doesn't affect MO
  • Recycling of slaughterhouse by-products into animal feeds
  • Quickly adapt to environ. of high salinity & low pH, creating a problem to control this MO in food products
  • Epidemiologic evidence suggests a low infective dose

  
• Foods associated with Salmonella outbreaks

  • Poultry & poultry products
  • Eggs
  • Raw meat
  • Cross-contamination
  • Raw milk
  • Fish meal for animal feed
  • Shellfish harvested from polluted waters
  • Frozen precooked prawns
  • Fruit & vegetables

  
• Salmonella contamination of plant products

  • Increase in recent years as vehicles of human salmonellosis
  • Situation developed from increase global export of fresh & dehydrated fruits & vegetables from tropical countries
  • Problem: prevailing hygiene conditions during the production, harvesting & distribution in countries that do not always meet the minimum standards & facilitate product contamination
  • Use of polluted irrigation water, or human & animal manure as fertilizer are important contributory factors

  
• Salmonella contamination of sauces, salad dressing, cake mixes, cream-filled desserts, dried gelatin, peanut butter, cocoa & chocolate

  • Survive in dry-roasted cocoa beans (used to process chocolate) can lead to contamination of in-line & finished product
  • Chocolate production involves a heating stage: inactivation of Salmonella in molten chocolate is difficult (fat protection from the cocoa butter)
  • T/t required to eliminate this MO in sucrose-containing product w/ low aw result in an organoleptically unacceptable product
  • Salmonella can survive for many years in this products storage at Troom
  • Effective decontamination of raw cocoa beans & stringent in-plant control measures to prevent cross-contamination of in-line products are of great importance in this food industry
• Tolerance zero (absent) in ready-to-eat foods
• Irradiation of food to eliminate or reduce Salmonella

  
• Recall foods when possible microbial hazard are present in food products
• Temperature control measures


  • Cook foods to proper temperatures
  • Hold at or above 60°C (140°F)
  • Keep foods out of the danger zone: 4.4°C to 60°C (40°F to 140°F)
  • Refrigerate
• Salmonella


  Pathogenic bacteria that can cause foodborne illness

  
• Chocolate production involves a heating stage: inactivation of Salmonella in molten chocolate is difficult (fat protection from the cocoa butter)
• Temperatures/times required to eliminate Salmonella in sucrose-containing products with low water activity result in an organoleptically unacceptable product

  
• Salmonella can survive for many years in products stored at room temperature

  
• Effective decontamination of raw cocoa beans and stringent in-plant control measures to prevent cross-contamination of in-line products are of great importance in the chocolate industry
• Salmonella Outbreaks


  • Zero tolerance (absent) in ready-to-eat foods
  • Irradiation of food to eliminate or reduce Salmonella
  • Recall foods when possible microbial hazards are present

  
• Temperature control for Salmonella prevention

  • Cook foods to proper temperatures
  • Hold at or above 60°C (140°F)
  • Keep foods out of the danger zone: 4.4°C to 60°C (40°F to 140°F)
  • Refrigerate at or below 4.4°C (40°F)
  • Freeze at or below –18°C (0°F)

  
• Avoid cross-contamination between processed and raw materials
• Salmonella Prevention: Food safety

  • HACCP system in the food plant
  • Break faecal-oral-cycle transition
  • Good sanitation practice (GSP)
  • Good Hygiene Practice (GHP)
  • Hygienic transport and slaughter practices
  • Chlorination of water supplies
  • Sewage treatment and disposal

  
• Fields irrigation with treated effluents, washing of fruits & vegetables with disinfected water, education of local workers on hygienic handling of fresh products and greater protection of products from environmental contamination during all phases of handling would enhance the safety of fresh fruits & vegetables
• Escherichia coli (E. coli)


  Pathogenic bacteria that can cause foodborne illness

  
• E. coli was first isolated from children's faeces by Theodor Escherich