Bacillus cereus is a rod-shaped, Gram-positive, spore-forming bacterium commonly found in soil and foods. It can cause two types of food poisoning - a diarrheal syndrome caused by enterotoxins and an emetic syndrome caused by a preformed toxin. B. cereus grows between 4-55°C and pH 4.5-9.5, producing spores that allow it to survive harsh conditions. While usually a mild foodborne illness, prevention focuses on proper cooking and refrigeration to limit growth and toxin production in foods.

1. BACILLUS CEREUS
by
Tamilselvan.T
51094

2. The word Bacillus means ‘Small rod’ and
cereus means ‘Wax- like’.
It is derived from Latin language.
The name itself reflects the morphology of B.cereus.

3. Scientific classification
Domain : Bacteria
Phylum : Firmicutes
Class : Bacilli
Order : Bacillales
Family : Bacillaceae
Genus : Bacillus
Species : B.cereus
Size:
Length : 3-5 µm
Width : 1-1.2 µm

4. Introduction
 Gram positive bacteria
 Spore bearing
 Rod shaped
 Motile
 Facultative aerobe or anaerobe
 Beta hemolytic
It is widespread in nature and frequently isolated from soil and
growing plants, but it is also well adapted for growth in the intestinal tract
of insects and mammals.
It is becoming one of the important causes of food poisoning in
the industrialized world.

5. B.cereus is the model species of “Bacillus cereus group” also
known as Bacillus cereus sensu lato, comprising five closely related
species:
1. B. anthracis
2. B. thuringiensis
3. B. mycoides
4. B. pseudomycoides
5. B. weihenstephanensis.
These all share a genetic similarity but they have
difference in both Pathogenic properties and phenotypic traits of strains.

6. Optimum conditions for Growth
Temperature:
Optimum : 30 - 37 ºC
Range : 4 - 55 ºC
 Maximum toxin production occurs at 20 - 25 ºC
 Toxin production range at 10 - 40 ºC.
pH:
Optimum : 6 – 7
Range : 4.5 – 9.5
Minimum water activity :
1. with NaCl > 0.93 and 0.95 aw.
2. with glycerol 0.93 aw.

7. For survival:
Temperature:
 Spores more resistant to dry heat than moist heat. It is also
more resistant in Oily foods.
 Cooking at or below 100 ºC may allow spore survival.
pH:
 Vegetative cells decline generally rapidly in stomach acid.
However, some may survive depending on food and level of
stomach acidity.
 Spores are resistant to gastric acidity between pH 1-5.2
Water activity :
 Spores survive long periods in dry foods
e.g: Population unchanged after 48 weeks in cereal
0.27 – 0.28 aw.
(Jaquette and Beuchat, 1998)

8. Life cycle
 It is ubiquitous in nature.
 B.cereus found in many types of soils, sediments, dust, plants, water
bodies, decaying organic matter, vegetables and fomites.
 It also exhibits a saprophytic life cycle in the arthropods intestinal
epithelium.
 Defecation or death of the host releases cells and spores into the soil,
where vegetative cells sporulate and survive until their uptake by
another host.
 Generally, spores germinate when they come into contact with organic
matter or animal host.

9. The core of the spore is surrounded by the inner membrane,
cortex and inner and outer coats.
 The B.cereus spore is refractory to extreme environmental
conditions include of heat, freezing, drying and radiation.
 It has been reported to be present in stools of healthy humans at
varying levels.
 The presence in environments, feed and food would ensure
B.cereus a transient presence in the mammalian gut.

10. The white inclusions in the rod shaped bacteria are the spores.

11.  The spore coat is made up of proteins and small amount of
lipids and carbohydrates which contribute to its resistance to the
oxidizing agents and chemicals by blocking toxic chemicals.
 The outer spore coat allows them the heat and gamma
radiation resistant.
 It can metabolize a variety of compounds like
carbohydrates, proteins, peptides and amino acids for their growth
and energy.

12. Countries prevalent
Reports of Foodborne disease outbreaks in countries like
Norway , Spain, Sweden, UK, USA, Scotland and India.
 India being a sub-tropical country known for a diverse range of
food habits provides scope for the prevalence of B.cereus.
 In 1978 – First reported outbreak of B.cereus food poisoning
among the children due to the consumption of milk powders in
India .
 Incidence of food poisoning in India is higher during various
cultural and religious events when food is prepared in bulk as it
becomes difficult to maintain hygiene during preparation and
storage of food.

13. Year Region Study
group
% Notes
2010 Sea food 29.41% 36.7% and 29.41% of
tropical seafood
samples.
2015 Uttarakhand meat 27.78 –
35%
35% of cooked meat
and 27.78% of raw
meat products.
Bacillus cereus food poisoning in Uttarakhand
(Infectious diseases in India , 2017)

14. B.cereus is an opportunistic pathogen cause infections like
1. Diarrhoeal syndrome
2. Emetic syndrome
Transmission is predominantly foodborne for both.
B.cereus food poisoning occurs year around without any particular
geographical distribution.
Diarrhoeal syndrome :
It is also called ‘Long- incubation’ form of B.cereus food
poisoning.
 The food along with B.cereus is consumed and it passes the stomach
and the site of toxin production is small intestine .

15.  Incubation time : 8-16 hours (occasionally > 24 hrs.)
 Duration of illness :12 - 24 hrs. (occasionally several days)
 Infectious dose : 105 – 107 cfu in total. The number required is
lower for spores compared to vegetative cells.
 Toxin type : Protein : enterotoxins like Hbl, Nhe, CytK
 Symptoms:
Abdominal pain , watery diarrhoea and occasionally nausea.
 Foods most frequently implicated:
Proteinaceous foods, meat products, soups, vegetables,
puddings, sauces, milk and milk products.

16.  Heat stability : Destroyed at 55 ºC after 20 minutes.
 pH stability : unstable < 4 and >11
 Northern Europe and Northern America are Diarrhoeal dominant
countries.
 All peoples are susceptible to infection but intensity varies with
individuals.
 Treatment is not usually given. Fluids are administered when diarrhoea
and vomiting are severe.
The Diarrhoeal form is diagnosed by isolation of the organism from stool
and food.

17. Emetic syndrome :
The toxin is vomiting form of disease following ingestion of food
with pre formed toxin.
 Incubation time : 0.5 – 6 hrs.
 Duration of illness : 6 – 24 hrs.
 Infectious dose : 105 – 108 cells / gram is often found in implicated
foods, but live cells are not required for intoxication.
 Toxin type : Cyclic peptide , emetic toxin – cereulide.
 Symptoms : Nausea, vomiting, malaise and few lethal cases due to liver
damage.

18.  Cereulide is resistant towards acidic conditions, proteolysis and
heat and also to gastric acid.
 Food items which are starch-rich are most frequently implicated.
Ex: Starch rich foods , fried and cooked rice, pasta, pastry
and noodles.
 The Emetic form is diagnosed by isolating the organism from
the incriminated food.
 The molecular mass of emetic toxin is 1.2 kda.

19.  Cereulide synthesis takes place ranging from 12 – 37 ºC. The
maximal production of emetic toxin occurs at 12 – 22 ºC.
 Heat stability : 90 min at 121 ºC
 pH stability : stable at pH 2-11.
Japan and UK are the emetic dominant countries.

20. Underreporting of outbreaks
Several factors contribute to the number of foodborne B.cereus
disease being largely under-reported are
 The consequence of the generally short and mild course of disease ,
which does not motivate the patient to seek medical attention.
 The symptoms are similar to other pathogen infections.
Ex: Emetic disease are not easily distinguished from S.aureus
intoxication.
Diarrhoeal disease shows same symptoms as C.perfringens type
A food poisoning.
Nowadays, B.cereus foodborne disease is reportedly increasing in
Industrialized countries.

21. For Inactivation :
Temperature:
 Vegetative cells destroyed by frying, grilling, roasting and
pressure cooking.
Spores ( depends on strain and food ):
D 100 ºC - 1.2 -7.5 mins. in Rice
D 120 ºC - 2.5 secs.
D 120 ºC - 3.4 mins. (e.g. soybean oil).
(van Asselt and Zwietering, 2006)
pH:
 Vegetative cells inactivated in yogurt at pH 4.5 and in fruit juice
at pH 3.7
Water activity :
 Vegetative cells inactivated at aw < 0.91

22. Preservatives :
 Vegetative cell growth inhibited by Sorbic acid, Benzoate,
Sorbate, EDTA and polyphosphates.
 Spore germination and outgrowth inhibited by Nisin.
(Nisin is not sporicidal).
Disinfectants / Sanitizers :
 Most food industry sanitizers destroy vegetative cells on
surfaces.
 Formaldehyde, Chlorine, Iodine, Acids, Alkalis, H2O2, Peroxy
acids, Ozone are all sporicidal at high concentrations with long
contact times.
 Phenolics, Alcohols, Organic acids, Esters and Mercurial have
little sporicidal effect.
 Chlorine disinfectants such as household bleach contain 5.25%
sodium hypochlorite are effective against B.cereus cells but not
spores.

23. B.cereus as Probiotic ???
It is also adapted to a lifestyle in a host , as a pathogen or
perhaps a part of intestinal flora.
 The possible adaptation of B.cereus to the environment of the
animal gut could be the basis for its probiotic effect.
 Such use cannot uncritically be considered safe for humans
because all B.cereus strains are able to produce at least one type of
toxins associated with diarrhoeal disease.
 Certain strains producing negligible amounts of toxin at 37 ºC
have been approved for probiotic use by the European Food
Safety Authority (EFSA). (Hong et.al., 2004)

24. Infectious dose
Counts ranging from 200 to 109 cells /gram B.cereus have
been reported in the incriminated foods after food poisoning.
Thus any food containing more than 103 cells /gram cannot
be completely safe for consumption.
Both the Diarrhoeal and emetic syndromes are generally
mild and self limiting. Treatment is not usually needed for both.

26. Acid stress resistance
It is especially important for B.cereus that must survive the
acidic pH of the stomach which is 1.5 in fasting state and rises to 3-5
after ingestion of food.
 Before entering the small intestine or colon it have to cross acidic
condition of stomach.
 The acid stress in many foods by means of food preservatives.
 Thus, bacteria have evolved resistance mechanisms to prevent
cell damage due to acid stress, this are called as acid tolerance
responses (ATR)

27. The ATR’s are
1. Production of alkali
2. Homeostasis of Internal pH
3. Decarboxylation of amino acids
4. Buffering ability of cytoplasm
5. Cell density

28. Transfer from soil to food
B.cereus isolated from rice, dairy products , vegetables,
spices and sometimes it can cause cross contamination to other
foods like meat products also.
 At harvest, B.cereus cells or spores may accompany plant
material into food production areas and establish on food
processing equipment.
 Bacillus cereus is a common contaminant of milk.
 Spores or cells of it can contaminate udders of cows during
grazing or enter diary farm through bedding material or feed.

29.  The endospores have adhering capacity which are not removed
by regular cleaning of surfaces.
 It has the ability to form Biofilms is important for its persistence
in food industry equipment such as diary pipelines.
 The biofilms protect spores and vegetative cells against
inactivation by sanitizers.
B.cereus is not a competitive microorganism, but it
grows well after cooking and cooling (<48 ºC) . This heat treatment
will cause spore germination and in the absence of competing flora
it grows well.

30. Toxins
B.cereus produces one type of emetic toxin and three types of
enterotoxin.
Three pore forming enterotoxin responsible for diarrhoeal syndrome
are 1. Hemolysin bl (Hbl)
2. Non – Hemolytic enterotoxin (Nhe)
3. Cytotoxin K (cyt K)
Hbl consists three different protein components L1, L2, B.
Nhe contain three different protein constituents namely
NheA, NheB, NheC. and Cyt K is a single component toxin

31. The emetic toxin is (dodecadepsipeptide) cereulide and
having a ring shaped structure of three repeats of four amino acids .
Laboratory diagnosis
When grown under aerobic conditions on 5% sheep blood
agar at 37 ºC, B.cereus colonies are dull, grey and opaque with
a rough matted surface.

32. Grey, opaque, granular, spreading colonies with irregular
perimeters growing on 5% sheep blood agar.

34.  No type of food with pH > 4.8 can be excluded as a possible
vehicle or as representing a risk of food spoilage or food borne
disease.
 Failures by consumers to follow basic food preparation rules
i.e., slow or inadequate cooling, storage at ambient temperature or
pro longed heat keeping at <60 ºC may allow growth of B.cereus.
 It occurs as a contaminant during the pre-processing and
post- processing operations in the food chain.

35. Prevention :
According to NIH, NIAID and NFPA the suggestions below
are good examples of how to destroy B.cereus.
 steaming under pressure, roasting, frying and grilling foods can
destroy the vegetative cells and spores.
 Foods infested with diarrheal toxin can be inactivated by heating
for 5 mins at 133 ºF
 Foods infested with emetic toxin can be inactivated by heating to
259 ºF for more than 90 mins.

36. In meat processing facilities to prevent toxin and contamination:
1. Assure current GMP being used in slaughter houses and
processing units.
2. Apply approved treatments of carcasses to remove fecal bacteria.
3. Use proper cleaning and disinfection of food contact surfaces with
hypochlorite or other approved sanitizers.
4. Keep hot foods above 60 ºC and cold foods below 4 ºC to prevent
formation of spores.
5. Cook beef and beef products thoroughly. Properly refrigerate left
overs.

37. References:
1. Academic press. 2011. Foodborne infection and intoxication.
564p.
2. GIDEON informatics. 2017. Infectious diseases in India.36p.
3. Vijaykumar, D.S. 2010. DNA based detection of food isolates
of Bacillus cereus and its behavioral pattern in selected foods,
Ph.D. CFTRI, Mysore .25p.
4. Arnesen, L. and fagerlund, A. From soil to gut: Bacillus cereus
and its food poisoning toxins. Norwegian school of veterinary
science, Norway.
5. Granum, P. and Lund, T. Bacillus cereus and its food poisoning
toxins. FEMS microbiology letters. 157 (223-228).
6. Bottone, E. Bacillus cereus: a volatile human pathogen. Clinical
microbiology reviews. 2010, 382-398p.