Foodborne pathogens

Bacterial agents of foodborne

illness

Food safety

Aeromonas hydrophila

• Foodborne pathogen of emerging importance

• Ability to grow at chill temperatures

• Isolation from patients with diarrhoea / high infection

dose (5x1010) 2 cases from 50 volunteers

• Gram/negative, catalase positive, oxidase positive rods,

ferment glucose

• Optimal T for growth – 28oC

• Fresh food :fish, meat, poultry, raw milk salad

vegetables, water

Bacillus cereus

• Gram-positive, aerobic, spore-forming rods. The genus

contains 80 species

• Grows from 8 to 55oC, optimally 28 - 35oC, spores are

central

• Diarrhoeal syndrome + abdominal pain, nausea and

vomiting less frequent. Onset of illness 8-16h after

consumption of food

• Infective dose – 105 - 107 CFU total

• Association with food: cereals, flour, rice, pasta dishes-

Chinese restaurant syndrome

Bacillus cereus

Campylobacter

• Non-sporeforming, oxidase positive, Gram-negative rods

• Cannot ferment or oxodize sugars

• Oxygen-sensitive microaerophiles, growing best in

atmosphere of 5-10% carbon dioxide and 3-5% oxygen

• All campylobacters grow at 37oC

• C. jejuni + C. coli optimum at 42-45oC, do not grow

below 30oC

• Principal environmental reservoir: alimentary tract of wild

and domestical animals and birds, also found in rodents,

dogs, cats, dairy cattle, sheep, pigs and wild birds.

Campylobacter

• Cause acute enterocolitis, not easily distinguished

fromillness caused by other pathogens.

• Incubation period 1 to 11 days, usually 3 – 5 days

• Fever, severe abdominal pain and diarrhoea

• Excretion of organism continues 2 – 3 weeks

• Complications – in rare cases neurological disease

Guillain-Barre syndrome

• Low infectious dose

• In 2007 leading cause of infectious diarrhoea in Europe

Campylobacter jejuni

Campylobacter

Clostridium botulinum

• First report about toxin from 1793 “Wurstvergiftung”

botulus = sausage

• In 1896 isolated and described by van Ermengem

• Gram-positive rods, motile with peritrichous flagella, obligately anaerobic , central spores, production of neurotoxins – eight types: A, B, C1, C2, D, E, F, G

• Single strain of C.botulinum produce one type

• Generally psycrotrophic from 3 – 15oC

• Three types of botulism are recognised: foodborne botulism, infant or infectious botulism and wound botulism

Clostridium botulinum

• Foodborne botulism is an example of bacterial food poisoning in its strictest sense:it results from the ingestion of an exotoxin produced by Clostridium botulinum growing in the food.

• Symptoms of botulism occur from 8h to 8 days, most commonly 12-48 h, after consumption of the toxin/containing food.

• Vomiting, constipation, double vision, difficulty in swallowing, dry mouth, difficulty in speaking

• Neuromuscular blockade antagonist, 4-aminopyridine

• Survival critically dependent on early diagnosis + treatment, mortality 20-50%, type of toxin dependent

Clostridium botulinum

• Low-acid canned foods, home-canning (vegetable +

meat), duck pate, minced meat pie etc.

• Infant botulism differs from the classical syndrome /

result of colonization of the infants gut with C. botulinum

and production of toxin in situ.

• Mostly in infants from 2 weeks to 6 months

• Wound botulism – subcutaneous infection with C.

botulinum. Result of trauma or alsou intravenous drug

use

• Isolation and identification - long protocol using mice

Clostridium botulinum

Clostridium perfringens

• Cause of food poisoning – five types of exotoxin,

• Self-limiting, non/febrile illness nausea, abdominal pain,

diarrhoea less commonly vomiting

• Onset usually 8 to 24 h after consumption of food with

large number of vegetative organism

• Ingested vegetative coells that survive stomach`s acidity

pass to the small intestine, grow, sporulate and release

an enterotoxin

• Enterotoxin is produced by sporulating cells

• Toxin is 35 kDa protein – inactivated by 10min heating at

60oC

Clostridium perfringens

• Typical scenario of food poisoning: a meat dish containing spores of C. perfringens is cooked,

• The spores survive the cooking to find themselves in a genial environment without any competing microflora

• After cooking, the product is subjected to temperature/ time abuse, such as slow cooling or prolongaated storage at room T. This allow the spores to germinate and mutiply rapidly to produce a large vegetative population.

• The product is either served cold or reheated insufficiently to kill vegetative cells.

• Most outbreaks: institutional catering(schools, hospitals)

Enterobacter sakazakii

• Foodborne pathogen of emerging importance

• Threatening infections in low birth-weight infants

• First cases in 1958

• Up to 2005 75 cases of Ent.sakazakii infection worlwide

• Gram-negative, motile member of the

Enterobacteriaceae

• Typical mesophil, growth between 6o - 47oC

• Heat resistance varies between strains

• Powder infant formula foods, water, soil, tofu

• Cronobacter ?

Enterobacter sakazakii

• Electron microscopy picture

Escherichia coli

• Universal inhabitant of the gut of humans and other

warm/blooded animals - predominat facultative anaerobe

• Generally a harmless commensal

• Opportunistic pathogen causing infections such as

Gram-negative sepsis, urinary tract infections,

pneumonia in immunosuppressed patients and

meningitis in neonates

• It is a catalase-positive, oxidase-negative, fermentative,

short,gram-negative, non–spore-forming, usually with

flagellae that are peritrichous, and fimbriate bacillus

Escherichia coli

Escherichia coli

Enterotoxigenic (ETEC),

Enteroinvasive (EIEC),

Enteropathogenic (EPEC),

Enterohemorrhagic (EHEC),

Enteroaggregative (EaggEC),

Adherent E. coli (DAEC)

Enterotoxigenic

E. coli

• ETEC are a common cause of infectious diarrhea (Black, 1993), especially in tropical climates.

• Illness occurs between 12 and 36 h after ingestion of organism.

• ETEC produces a watery diarrhea associated with cramps and a low-grade or no fever, vomitting.

• The illness is self-limiting, persisting for 2 or 3 days

• It is a common a cause of infantile diarrhea where it can cause serious dehydration.

• Diarrhea caused by ETEC has a lot in common with cholera; both result from ingestion of rather large inocula of bacteria, which then colonize the small intestine and produce toxins that cause net secretion into intestinal lumen.

Enteroinvasive

E. coli

• EIEC- classic symptoms of an invasive bacillary

dysentery / normally Shigella

• EIEC invades and multiplies within the epithelial cell of

colon causing ulceration and inflammation

• EIEC strains do not produce Shiga toxin

• Invasiveness is detremined by a number of outer

membrane proteins, coded by large plasmid ( 140 Mda)

Enteropathogenic

E. coli

• EPEC infection usually results in watery diarrhea

accompanied by vomiting and fever, but in some cases there is prolonged chronic enteritis.

• Disease appears 12-36 h after ingestion of the organism.

• EPEC is traditionally associated with outbreaks in maternity units and child daycare centers, although outbreaks in adults are also common.

• In infants, the illness is more severe than many other diarrheal infections can persist for longer than 2 weeks in some cases.

Enterohemorrhagic

E. coli

• The EHEC group causes severe bloody diarrhea (hemorrhagic colitis), hemolytic uremic syndrome (HUS), and thrombotic thrombocytopenic purpura.

• Although sometimes the infection causes only diarrhea or no symptoms.

• The EHEC strain most commonly found is O157:H7.

• EHEC strains produce cytotoxin Verotoxin (so/called because of its ability to kill Vero - African Green Monkey Kidney cells

Listeria monocytogenes

• L.monocytogenes is the only important human

pathogen among the six species currently recognized

within the genus Listeria, although L. seeligeri, L.

welshimeri and L.ivanovii occasionally cause human

infections.

• L.monocytogenes is a Gram-positive , facultatively

anaerobic, catalase-positive, oxidase-negative, non-

sporeformer.

• L.monocytogenes elaborates a 58 kDa β-haemolysin,

listeriolysin O, which acts synergistically with the

haemolysin produced by Staphylococcus aureus

L.monocytogenes morphology

Listeria monocytogenes

Scanning EM showing Flagella

L.monocytogenes

• Organism grows over a wide range of temperature from

0 – 42oC with an optimum between 30 and 35oC .

• Organism is ubiquitous in the environment. Isolation from

fresh and salt water, soil, sewage sludge, decaying

vegetation, silage.

• Oportunistic pathogen – incubation periods for disease

from 1 day to 90 days. Symptoms vary from a mild, flu-

like illness to mengitis and meningoencephalitis.

• Attack : pregnant women, very young (0 – 2 years) or

elderly (more 65 years) and the immunocompromised

population.

L.monocytogenes

• Association with food : documented were: coleslaw

salad, raw vegetable (celery, tomatoes, lettuce), dairy

products as raw milk, soft cheeses, smoked salmon,

pork tongue in aspic.

• Ability to multiply at refrigerator temperatures

• Morrtality: 20 – 40%

Mycobacterium species

• Genus Mycobacterium largely harmless environmental organisms

but is best known as the cause of two of the most feared and

ancient of human diseases, tuberculosis (TB) and leprosy.

• Human illness is associated with Mycobacterium tuberculosis.

Also causes tuberculosis in cattle and other animals.

• Organism is Gram-positive, non-sporeforming pleomorphic aerobes

with special composition of cell wall. High lipid content made up of

esterified mycolic acids, complex branched-chain, hydroxy lipids

resulting in very hydrophobic and waxy surface

• Milk was main food source

Plesiomonas shigelloides

• Isolated in tropic countries – belongs to

Enterobacteriacae – Gram-negative, catalase –positive ,

oxidase-positive rod.

• Temperature range from 8-10oC to 40-45oC , ubiquitous

in surface water an soil.

• Associationwith food : fish and shellfish (crab, shrimp,

oysters)

• Diarrhoea in the absence of fever

Salmonella

Gram-negative, non-sporeforming rods, member

of Enterobacteriacae, facultatively anaerobic,

catalase-positive, oxidase-negative, generally

motile,

minimum aw 0.93, survive in dry foods

Salmonella

Salmonella

Serotyping scheme :Kaufmann and White more

than 2000.

Salmonella - growth on XLD agar

Salmonella - pathogenesis

• Salmonellas are responsible for a number of different

clinical syndromes grouped as enteritis and systemic

disease.

• Enteritis – gastrointestinal infections of different

severity, about 200 serotypes are associated with human

illnesses. S. Enteritidis, S. Typhimurium, S. Infantis,

• Incubation period is typically 6 to 48 h.

• Principal symptoms, mild fever, nausea, vomiting,

abdominal pain and diarrhoea, last few days, may persist

a week or more

• Illness is self limiting

Salmonella - pathogenesis

• Systemic disease, host-adapted serotypes are more invasive and

tend to cause systemic disease in their hosts. S.Typhi, S.Paratyphi

A,B and C.

• Typhoid fever has incubation period from 3 to 56 days, usually

between10 and 20 days.

• Invasive salmonellas penetrate the intestinal epithelium and are

then carried by the lymphatics to the mesentheric lymph nodes.

After multiplication in the macrophages, they are released to

drain the blood stream, and disseminate around the body.

• They are removed from the blood by macrophages but continue to

multiply within them. This kills the macrophages which then release

large numbers of bacteria into the blood causing septicaemia.

Macrophage infected by S.tyhimurium gfp labelled in

promotor region. Extracelullar microbes are stained by

antibody conjugated with fycoerythrin (red).

Salmonella - pathogenesis

• In this , the first phase of the illness, the organism may be cultured from the blood.

• Slow onset of symptoms: fever. Headache, abdominal tenderness and constipation.

• During the second stage of the illness, the organism reaches the gall bladder wher it multiplies in the bile.

• The flow of infected bile reinfects the small intestine causing inflammation and ulceration. Fever persists with onset of diarrhoea in which large numbers of bacteria are excreted with the characteristic”pea soup” stools.

• This infectionis treated with antibiotics (chloramphenicol, ampicillin and amoxycillin.)

• After remission of symptoms , a carrier state can persist for several months (years) and bacteria are discharged intermittently with the bile into faeces.

Salmonella - pathogenesis

• Nowadays chronic carriers can be treated with

antibiotics

• Recalcitrant cases – cholecystectomy (surgical

removal of the gall bladder) is necessary.

• People bearing sallmonella – prohibition of work in

food industry and distribution.

• Association with food: zoonotic infection, major source of

human illnessis infected animal.

• Transmission = faecal – oral route

• Meat, milk, poultry, eggs – p[rimary vehicles

• Cross-contamination via kitchen equipment or by contact

Salmonella / serotypes

• Salmonella Enteritidis PT4 (phage type) prevailing type

• Massive increase in salmonella infection started in

1985

• Biosecurity measures to exclude salmonella and reduce

the number of infectionon egg and poultry farms.

• Compulsory bacteriological monitoring of all commericial

egg-laying and breeding flocks ( Denmark,UK, Germany)

• In 2005 EU average 20.3%, UK 8%, Norway, Sweden,

and Luxembourg 0%, Spain, Poland, Czech Republic

50%

Shigella

• Shigella dysenteriae

• Shigella flexneri

• Shigella boydii

• Shigella sonnei

• All are human pathogens causing bacillar dysentery,

• DNA relatedness show close relation to Escherichia

• Family Enterobacteriaceae – Gram-negative, non-motile

rods, catalase positive, oxidase negative , facultative

anaerobs

• Typical mesophiles, 10 – 45oC, pH range 6 - 8

Association with food

• Primary source – sewage - vegetable (iceberg lettuce)

• Uncooked foods ( prawn coctail, tuna salad)

• Infection dose is low, 10 – 100 organisms

• Incubation period vary from 7h to 7days

• Symptoms – abdominal pain, vomiting, fever, diarrhoea,

with bloody stools

• Illness lasts from 3 days up to 14 days

• Carrier state may develop – persistence for several

months

Staphylococcus aureus

In 1882 name

staphylococcus , Greek

staphyle = bunch of

grapes,

coccus = a grain or

berry

Staphylococcus aureus

• Food poisoning agent

• Currently 27 species and 7 subspecies of the genus Staphylococcus

• Enterotoxin production principally associated with the species Staph.aureus

• Relatively mild, short-lived type of illness

• Staphylococcal food poisoning is perhaps under-reported

• Staph.aureus Gram-positive coccus forming spherical to ovoid cells, 1 μm in diameter

• Catalase-positive, oxidase-negative, facultative anaerobs

Staphylococcus aureus

• Typical mesophile 7 – 48oC, pH range 6 – 7

• Organism has unexceptional heat resistance with high D

value

• Tolerant to salt and reduced aw

• Grows readily in media with 5-7% NaCl, some strains up

to 20%.

• Food poisoning by Staph. aureus short incubation

period, typically 2-4 h. Nausea, vomiting, stomach

cramps, retching are main syndroms. In severe cases

dehydration, marked pallor and colapse.

Staphylococcus aureus

• Illness is a result of ingestion of a pre-formed toxin in the food.

• Staph. aureus produces at least 11 enterotoxins designated SEA to SEJ. SEC – 3 variants, No SEF.

• Toxins types A and D, either singly or in combination, are most frequently implicated in outbreaks of food poisoning.

• Though described as enterotoxins the Staph. aureus toxins are strictly neurotoxins.

• They elicit the emetic response by acting on receptors in the gut, which stimulate the vomiting centre in the brain via the vagus and symphatetic nerves.

Staphylococcus aureus

• A number of immunoasay techniques for

staphylococcal enterotoxins are available

• ELISA techniques detect 0.1 – 1.0 ng toxin g-1 food

• Reverse passive agllutination tests 0.5 ng ml-1

• It will occur naturally in poultry and other raw meats

• Skin microflora, also raw milk, dry milk

• Hard cheeses, cold sweets, custards, creamy-filled

bakery products

• In Japan - rice balls moulded by hand

• In Hungary – ice cream

Vibrio

• Historically, cholera has been one of the disease most

feared by mankind.

• Still endemic to the Indian subcontinent, during 19th

century several pandemics of “Asiatic chelera” in Europe

and Americas.

• Vibrio cholerae Gram-negative pleomorphic (curved or

straight) short rods, motile with shethed polar flagella.

• Catalase and oxidase-positive, facultative anaerobs,

tolerant to 3% NaCl, temperature range from 5 - 43oC,

optimum 37oC.

Vibrio

• Cholera has an incubation period from one to three days.

• Illness vary from mild, self-limiting diarrhoea to a severe

life-threatening disorder

• Infectious dose in healthy individuals is large – 1010 cells.

• Pathogenicity is strongly linked to formation of 22 kDa

thermostable extracelluar haemolysin.

• Cholera is regarded as a water-borne infection, though

food which was in contact with contminated water is also

vehicle.

• Sea food, shellfish, oysters etc.

Yersinia enterocolitica • Yersinia enterocolitica is one of the three species of the

genus Yersinia recognized as human pathoges.

• Yersinia enterocolitica causes gastroenteritis

• Yersinia pseudotuberculosis - mesenteric adenitis

• Yersinia pestis – bubonic plague which killed in 14th century 25% of European population

• Member of the Enterobacteriacae, Gram-negative short rod, catalase-positive, oxidase-negative. It can grow from -1 to 40oC, with an optimum about 29oC.

• Y. enterocolitica was isolated from soil, fresh water, intestinal tract of many animals., dairy products, meat (pork), fish, poultry fruits and vegetable.

Yersinia enterocolitica

• Illness occure most commonly in children under 7 years

old.

• It is self-limiting enterocolitis with an incubation period of

1 – 11 days and lasting for between 5 – 14 days.

• Symptoms are abdomibnal pain and diarrhoea, mild

fever.

• Pigs are chronic carriers of Y. enterocolitica serotypes

most commonly found in human infections.

Y. enterocolitica on XLD agar plate