Food Microbiology &
Helen Billman-Jacobe
Foodborne diseases Infections
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Ray and Bhunia Ch 26
Intended learning outcomes
Understand the difference between a foodborne illness caused by a preformed toxin (intoxication), and by a pathogenic microorganism (infection) and by a toxigenic pathogen (toxicoinfection)
Understand the biology and characteristics of Escherichia coli, and why there are harmless and pathogenic types
Identify other bacteria and viruses that commonly cause foodborne infections
Pathogenesis of foodborne bacterial infections
Foodborne infection occurs by a number of essential steps • from ingestion of food containing pathogens, to the
expression of symptoms of the disease.
The diagram is useful to understand the steps involved
Pathogenesis of foodborne bacterial infections
Steps required to cause bacterial disease by infection 1. Live bacteria ingested with food
2. survive passage through stomach (low pH)
3. penetrate mucous layer of intestinal tract
4. attach to epithelial cells of intestine
5. establish infection in/on epithelial cells
6. multiply, produce toxins or invade cells/body -> symptoms
Toxico-infections vs infections
Generally, toxicoinfections involve
– either sporulation or
– lysis of bacterial cells and release toxins from lysed cells in gastrointestinal tract. Examples of pathogens that casue food borne toxicoinfections are
Aeromonas hydrophila
Bacillus cereus
Clostridium perfringens enterotoxigenic Escherichia coli (ETEC) Vibrio cholerae.
Toxico-infections vs infections
Foodborne infection occurs from the consumption of food (and water) contaminated with pathogenic enteric bacteria and viruses which invade the body via the GIT or colonise the
gut epithelium
Examples of bacterial pathogens that cause food borne infections are
E. coli Salmonella Campylobacter Listeria
Examples of viral pathogens that cause food borne infections are
Norovirus Hepatitis A virus Hepatitis E virus Human rotavirus
Pathogenesis of foodborne bacterial infections
How many bacteria are needed to cause an infection?
• Can be measured by the ‘50% infectious dose’, which is the number of infectious organisms that will cause disease in 50% of inoculated animals. Abbreviated as the ID50
• ID50 varies with species: 10 for EHEC, to 105 for Listeria
How long from ingestion to symptoms (incubation period)?
• Generally after 24 hours, as all the steps (above) take time
• Compare this with the 30min–2hr needed for intoxications
Local symptoms (abdominal pain, diarrhoea, vomiting)
Systemic (non-enteric) symptoms, for those bacteria that can spread through the body to other target organs, e.g. Listeria
Foodborne bacterial infections
Where disease is caused by infection by a bacterial species
Main examples: E.coli, Salmonella, Campylobacter, Listeria
Read the sections about E.coli, Salmonella, Campylobacter, Listeria in chapter 26
Escherichia coli
Gram negative rod, facultative anaerobe, ‘coliform’, family Enterobacteriaceae
Most strains are harmless commensals, commonly present in mammalian intestines. Some are pathogens Survive well in water, hence is used as an indicator of faecal contamination e.g. by sewage or animal manure No significant heat resistance (D60°C of 0.1min)
Can survive refrigerated or frozen temperatures for extended periods
Also survives when dried on the surfaces of seeds!! Then grows when seeds treated with water to germinate Optimum growth temperature ~ 37°C (mesophiles)
Growth down to 4.4 pH is possible, neutral pH preferred
Minimum Aw of 0.95
E.coli on MacConkey Agar
Isolation: easily done on selective/indicator media
e.g. MacConkey agar
Red colonies due to fermentation of lactose (Lac+).
Medium also has bile salts so both an indicator (differential) and selective medium.
Escherichia coli: pathogenic types Most, but not all, E. coli are harmless commensals.
• But some of the worst outbreaks of food-borne illness around the world have been due to pathogenic strains of E.coli.
Both the harmless, commensal E.coli and the pathogenic E.coli are members of the same species.
Pathogenic types differ by the possession of virulence genes, such as those specifying enterotoxins e.g. shiga toxin.
Escherichia coli: pathogenic types
Pathogenic E.coli are divided into 4 main groups: Enterotoxigenic E. coli (ETEC)
Enteroinvasive E. coli (EIEC)
Enteropathogenic E. coli (EPEC)
Enterohaemorrhagic E. coli (EHEC/STEC) e.g. type O157:H7
* STEC = shiga toxin producing E.coli.
These differ from each other in the virulence genes carried the serotype numbers O157 and H7 refer to serological reactions to a panel of antibodies to cell surface antigens.
• O is for cell wall structures
• H is for flagella proteins.
https://en.wikipedia.org/wiki/Escherichia_coli_O157:H7
Escherichia coli: pathogenic types
Strains are serotyped using panels of antibodies to O and H
e.g. if the O antigen reacted with O antibody 157 = O157
if the flagella reacted with H antibody 7 = H7 -> the strain = O157:H7
Enterohaemorrhagic Escherichia coli (EHEC/STEC)
Can cause major outbreaks, food-transmission, serious! Illness ranges from mild disease to life-threatening!
i.e. from non-bloody diarrhoea to haemorrhagic colitis life threatening = HUS (haemolytic uraemic syndrome) = TTP (thrombocytopaenic purpura)
Adhere to intestinal epithelial cells and then damages underlying microvilli
Produces shiga-like toxins (stx) -> blocks protein synthesis -> causes cell damage to kidney endothelial cells, etc.
CDC link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270005/
Serotype O157:H7 is common in Canada/USA
Serotype O111:H negative is more common in Australia
Escherichia coli: pathogenic types
Often a zoonosis
• Faecal contamination of water supplies and food handlers
• Cattle – good reservoirs for O157:H7 and similar EHEC strains
– Raw milk (unpasteurised), undercooked meat especially minced, insufficient cooking in general.
Mincing distributes the bacteria throughout the meat
• Salads/sprouts/fruit – contamination by sewage or cattle dung. These food items are normally eaten raw, so always a danger….
Normal pasteurisation temperatures are sufficient to eliminate E. coli species
German 2011 outbreak
Severe foodborne diarrhoea and kidney disease ~ 3800 cases
Caused by pathogenic E.coli, STEC
• STEC = shiga toxin producing E.coli
• Very unusual serotype; unusually virulent
The bacterial culprit on a plate – , May, 2011
http://www.spiegel.de/international/germany/0,1518,765777,00.html https://en.wikipedia.org/wiki/2011_Germany_E._coli_O104:H4_outbreak
E. coli scare: cases ‘likely to increase’ BBC News 31st May 20011
A deadly E. coli outbreak in Europe is expected to worsen in coming days, a German scientist has said. Fourteen people have died in Germany and one woman has now died in Sweden after a trip to Germany. It is thought cucumbers from Spain caused the outbreak.
Germany bans the import of Spanish cucumbers.
Spanish exporters complain they are losing $200m (£120m) a week because of the bans and do not accept that their produce is the source of the outbreak
Reaction to the cucumber crisis
Germany: Consumers told not to eat cucumbers, lettuces and raw tomatoes. 329 cases of E.coli confirmed; 14 deaths
Spain: The top European cucumber producer – threatens to seek compensation from the European Union for lost vegetables sales
Russia: Ban on all imports of cucumbers, tomatoes and fresh salad from Spain and Germany pending further notice
Austria: Ban on sale of cucumbers, tomatoes and aubergines imported via Germany Belgium: Reported to have banned cucumber imports from Spain
Netherlands: Halted all cucumber shipments to Germany
Ireland: Spanish cucumbers removed from shelves
Deadly germ comes from Spain!
Shiga toxin producing Escherichia coli
Causing damaging gastrointestinal and kidney disease
Rare pathogenic E. coli bacterial strain involved, called serotype O104:H4 STEC
Strain is a genetic hybrid of different types of pathogen, a mosaic of different virulence traits
A decisive tool for identifying that there was a common source of infection among many different illnesses were modern molecular methods for DNA analysis and strain DNA fingerprinting
These gave rapid highly specific detection of the rare strain and were invented rapidly in the middle of the outbreak
Bielaszewska et al. 2011
Results of genotyping
Comparison of the Spanish STEC isolate from cucumbers and the strain isolated from infected German patients showed that the two STEC strains were different!
What does this mean?
Epidemic profile of shiga-toxin-producing Escherichia coli O104:H4 outbreak in Germany – preliminary report. . J Medicine June 22, 2011 (10.1056/NEJMoa1106483)
http://www.nejm.org/doi/full/10.1056/NEJMoa1106483
Chronology of the outbreak
EFSA technical trace-back summary report
The epidemiological information currently available on this STEC outbreak in Germany suggests that STEC O104-contaminated sprouts are the vehicle of infection. This link is based on the results of a cohort study which is corroborated by analysis of trace-back and trace-forward studies carried out by the HEC Task Force and the authorities of Lower Saxony.
A cohort study carried out by the Institute (RKI 2011b) involved guests of a restaurant which had been established as the place of exposure to the hazard for several cases. The food consumption of restaurant customers during the period of concern was ascertained not only through interviews, but also by checking food delivery lists and receipts. It established a high relative risk to develop bloody diarrhoea related to consumption of sprouts.
Results of the trace back and forward approach
Pinpointed a sprout farm
The HEC Task Force extensively investigated the possible source of infection in “Establishment A”, in particular water, personnel, and seeds.
• They showed that personnel were infected.
Whereas this may have contributed to the spread of the contamination, there was no indication that
personnel had introduced the outbreak strain of E. coli.
• Analyses of water and seeds have all proved negative to date.
BERLIN, June 11 (Reuters) – No legal action against organic farm in northern Germany “Everything we have looked into until now shows the farm was flawless,” said , spokesman for the consumer protection office of Lower Saxony state.
“It is hygienic and followed all the regulations. No matter how you look at it we don’t see any fault with the farmer, or any legal ground to hold them accountable”
”You cannot punish someone for having bad luck.”
French outbreak – June 2011
24th June: France reported a cluster of patients with bloody diarrhoea, after having participated in an event in a town near Bordeaux on the 8th of June.
Adults (31-64 yr old), many with HUS. Many reported having eaten sprouts.
Infection with E. coli O104:H4 was confirmed, and was the same strain as the German outbreak! Sprouts were not directly connected to Germany.
What question would you ask at this point?
French outbreak – June 2011
Sprouts were not directly connected to Germany.
1. Suspected sprouts of fenugreek, rocket and mustard had been privately produced in small quantities by
the organiser of the event
2. Seeds supplied by British company Thompson & Morgan, UK
What question would you ask now?
Tracing the seeds…
Link between the French and German outbreaks
Foodborne pathogens can live in plant tissues
and found that foodborne pathogens can live inside plant tissues
http://www.sciencedaily.com/releases/2011/08/110815152049.htm
E. coli 0157:H7 was present in tissues of mung bean sprouts and Salmonella in peanut seedlings after the plants’ seeds were contaminated with the pathogens prior to planting.
, a postdoctoral researcher in food science, said seeds could be contaminated in such a manner before or after planting through tainted soil or water. “The pathogens were in every major tissue, including the tissue that transports nutrients in plants,“ said Deering, whose results were published in separate papers in the Journal of Food Protection and Food Research International.
The sprouting process –the risk factors
Pathogenic bacteria can survive in/on seeds for hundreds of days
Impossible to absolutely sanitise seeds prior to sprouting (without killing seeds)
Germination provides ideal condition for bacterial growth (humidity, nutrients, warmth) for several days • Inherent risk if you eat raw sprouts
Extra risk factors from organic certified sprouts:
• Seeds are at greater risk of faecal contamination from manure-compost
• Good seed sanitisation methods (hypochlorite) for seeds ruled out for ideological reasons
• Use of hot water for seed sanitisation is unsafe
The disease track record
Over 40 outbreaks associated with sprouts
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