3. Foodborne Illnesses: Gram negative pathogens

Salmonella

• Part of entero bacteria

• Genus: Salmonella

• Two species: S. bongori and S. enterica

• Subspecies: S. enterica subsp. enterica

• Further subdivision into many serovars (which is not written in italic!!

  • e.g. Salmonella enterica ssp. enterica serovar Typhimurium

Seasonal trend for Salmonella cases

• peak in summer, reason is not known

• Average dip (red line) during covid, e.g. people did not go out to eat and larger focus on hygiene.

Characteristics of Salmonella

• Gram negative, motile rod

• Growth temperature: 5-47C

• Awmin for growth: 0.93

  • Salmonella can survive for extended periods at even lower aw

  • Protection against gastric acid by food matrix

Symptoms of consuming Salmonella (Gastro-enteritis)

Symptoms:

• Abdominal pain, nausea/vomting, diarrhoea

• Incubation time: 8-72 hours

• Duration: 3-7 days

• D/R usually quite high, but sometimes low

• Can even lead to arthritis

Transmisison routes Salmonella

Persistence of Salmonella

• Salmonella can persist in food factories, e.g. as house flora on a machine that cuts pig carcasses

• Salmonella can also persist in stables, in which production animals, such as broilers, are raised

• Cleaning and disinfection does not necessarily solve the problem, darkling beetles can be a vector and bypass cleaning of broiler house

Preventative measures in supply chain

• Prevention of infection at farm

  • Implement national control programmes

  • Hygiene measures, separate animals from outside

  • Salmonella-free feed and water

  • Vaccination

• Limit spread of contamination

  • Compliance with microbiological criteria

  • Logistic slaughter

  • Hygiene design equipment

• Good general hygiene in factory and retail

• Proper heating and storage at reatail, catering, consumer’s

Characteristics of E. coli

• Gram negative rod

• Mesophile (8-45C)

• Facultative anaerobe

• Usually harmless inhabitant in intestines

• Indicator-organism:

  • Hygiene production

  • Faecal contamination

• Some types of E. coli can cause disease: e.g. E. coli O157:H7

  • Low D/R

• No spores

• Grows at low pH

Transmission routes of E. coli

EHEC (E. coli O157:H7)

Toxin: produced in gut (shigatoxin)

Dose: 10-100 cells: low D/R

Symptom:

• Bloody diarrhoea

• Incubation time: 2-3 days (~21 days)

• Complication in children and ederly: haemolytic uremic syndrome (HUS), leading cause acute renal failure

  • Hence this E. coli is studied a lot.

Hamburger disease

Prevention of E. coli

Characteristics Campylobacter

• Gram negative, motile curved rod

• Sometimes coccus (non-culturable, non-infective)

• No spores

• Thermotolerant types: C. jejuni, C. coli, C. lari

• Growth temperature: 30-44 (Psychrotrophic, capable of growth at refrigeration temperatures down to 3)

• Grows best with 3-5% oxygen (microaerophilic organism)

• Sensitive to drying (chilling of meat), heating, some reduction below zero degrees (minimum pH for growth is 4.9)

• Does not grow well in dry environments

• Number 1 cause of bacterial foodborne infections in EU.

Symptoms of consuming Campylobacter

• Diarrhoea, often belly cramps, fever and blood in faeces

• Incubation time: 1-7 days (3d average)

• Duration: up to 1 week

• Low dose response (only 400 to 500 cells needed)

Sometimes sequela develop:

• Reactive arthritis (joints)

• Guillain Barre Syndrome (paralysis)

Transmission routes Campylobacter

Preventative measures for Campylobacter

Microbe found in rice

B. cereus d type, even when cooked can still be found in rice due to spores

Cl. perfringens

Can be found in spices and vegetables.

Where can you find norovirus?

Can be found in rice, spice, vegetables

E. coli in foods

• Undercooked ground meat, raw milk, and fresh produce

• Cattle are an important reservoir for O157:H7, contamination can occur during slaughter and processing.

• Acidic foods can be dangerous too, E. coli can survive prolonged periods at low pH, especially under refrigeration.

In what foods is Salmonella found?

• Foods of animal origin are the most frequently implicated, particularly poultry meat and eggs.

• Eggs and egg products: especially raw or lightly cooked ones, were frequent vehicles in outbreaks

• Poultry

• Fresh produce

Campylobacter in foods

• Common inhabitant of the gastrointestinal tract of warm-blooded animals, with poultry being the primary reservoir and most frequent source of human infection

• Raw milk

• Raw meat, raw vegetables, and water

E. coli ETEC

• Common cause of travelers diarrhea & infant diarrhea

• Symptom: watery diarrhea, dehydration and abdominal cramps

• Produce heat labile and/or heat stable enterotoxins

E. coli (EIEC)

• Causes dysentery-like illness

• Symptoms: Resembles Shigella infections, includes fever, cramps, and watery to bloody diarrhea.

• Invade and multiply within colonic enterocytes, leading to cell destruction

E. coli (EPEC)

• Primarily causes infant diarrhea in developing countries, leading to watery diarrhea, vomiting, and fever

• Adheres intimately to epithelial cells, causing “attaching and effacing” lesions that disrupt microvilli and absorption

When do most E. coli infections happen?

Summer, people eat more ground beef and harder to keep below at temperature of 7C

Disease caused by Salmonella (Enteric fever)

• Caused by host-adapted serotypes which are more invasive

• Typhoid fever has an incubation period of 3 to 56 days (usually 10-20 days)

• Invasive Salmonella enter the intestinal lining, move through the lymphatic system to the mesenteric lymph nodes, multiply inside macrophages, and spread through the body via the bloodstream.

• Symptoms: slow onset of fever, headache, abdominal tenderness, and constipation.

• Mortality rate is around 10-20%

Which two groups of people appear particularly susceptible to Campylobacter infections?

• Young children

• Young adults

(Platy)Helminths

Flatworms

Nematodes

Roundworms

Worms associated with foods

• Animal parasites: need animal host to develop - therefore worms are only found in meat products

• Life cycle: egg, intermediate stage(s), mature worm

• Classified according to shape adult worm:

  • Flatworms: Trematodes and Cestodes

  • Roundworms: Nematodes

• Do not grow in foods

The four most important worms, their hosts and the food vehicles.

Transmission cycle Taenia solium

• Pig tapeworm

• Only in humans the larvae will mature, not in the food.

• Similar cycle for T. safinata but instead it grows in beef.

Human health effect Taenia

• Mature tapeworm only develops in human hosts

• 4-12 m long (1000-2000 segments, proglottids)

• Symptoms: asymptomatic, nausea, abdominal pain, weight loss, anemia

• Effects more severe in young and immuno-compromised

• Efficient drugs are available.

Transmission cycle Trichinella spiralis

Trichinellosis

• Roundworm

• caused by consumption of Trichinella spiralis

• Encysted larvae released in stomach

• Larvae mature to adult worm (3-4 mm) in intestine

• Female worm releases larvae

• Larvae invading intestinal mucosa, causing symptoms

  • Incubation time: few days - month

  • Symptoms: abdominal pain, nausea, diarrhoea

• Larvae invade and encyst in muscle tissue

  • Symptoms: muscle pain, fever

• Efficacy of drugs uncertain

Contamination cycle of Echinococcus multilocularis

• fox tapeworm

Echinococcossis

• Disease caused by consumption of Echinococcus multilocularis

• Which is a parasite found in foxes

• Alveolar cysts (lungs, liver), treatment may not be effective.

Fish parasites

• Anisakis: herring worm

  • Symtpoms: abdominal pain

• Therefore all freshly caught fish, has to be frozen for 24h at -18C which kills the worms

• This makes it safe to eat the fish raw.

Preventative measures against worms

• Examination of slaughter animals before and after slaughter

  • Multiple spots of parasites → rejection

  • Local contamination → approval after treatment

  • Severe cold treatment of contaminated fish or meat, e.g. Taenia saginata, -18C, 10 days in calf meat

• Educate consumers: adequate heating of food before consumption, wash (wild) berries

Characteristics of protozoa

• Unicellular eukaryotic organisms

• Do not grow outside host

• Organism itself vulnerable to environmental stresses e.g. low pH

• Resistant structure: cysts and oocysts

• Low dose response relation

Most relevant protozoa, host and sources

Greedy Lions Eat HoneyCombs, Prowl Through Grass

Giardia lamblia

• Protozoa

• Cysts survive in water

• Gastric juices help to release trophozoites

• Symptoms giardiasis: diarrhea, abdominal cramps, nausea

• Food sources: salads, fruits washed with contaminated water

• Chlorination of water not very effective

• Treatment with drugs available.

Entmoeba histolytica

• Protozoa

• Transmission via water similar to Giardia

• Amoebic dysentery

  • Invading the intestinal wall

  • Spread of trophozoites from the intestine via the bloodstream

  • Amoebic liver abscess

• Effective drugs available.

Cryptosporidium parvum

• Protozoa

• Transmission oocysts through water

• Especially affecting susceptible people (“aids defining illness”): diarrhoea

• Cause of outbreaks:

  • Drinking water USA

  • Salad outbreaks (washed with contaminated water)

• Lesson for companies (include in HACCP plan)

• Chlorine resistant

• Measures: Boil water 1 min

Toxoplasma gondii

• protozoa

• produces oocysts and tissue cysts

• Cat plays central role, growth circle happens in cat.

Symptoms of Toxoplasma gondii

• Spontaneous abortion, eye defects, brain defects

• Changes in behaviour

• Asymptomatic

Lifecycle Giardia lamblia

1. Consumption of water or foods

2. Ingest cysts in intestine

3. Flagellate trophozoite (The active, movile form of a protozoa)

4. Multiplication in intestine

5. Cysts

6. Faeces

7. Contamination of water or food

Cycle repeats

Toxigenic algae

• Toxigenic algae

  • e.g. dinoflagellates, diatoms, cyanobacteria

  • These produce fycotoxins (cyanotoxins)

• Accumulation of toxin by:

  • Filter-feeding shellfish (mussels, clams)

  • Food webs fish

• Toxin undetectable by naked eye and generally unaffected by cooking

Types of intoxications by shellfish and their effects

How toxic are toxins from algae?

• Very toxic!! and lethal

Ciguatera intoxication

• When fish eat the dinoflagellates (= algae) and produce ciguatera toxin that is found in algae

• Accumulation of toxin in the fish, but does not make the fish sick

• Humans can eat these fish and get sick

• Symptoms comparable to neurotoxic shellfish poisoning: vomiting, diarrhoea, neurological effects.