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The Two-Faced Troublemaker: Bacillus cereus, the Jekyll and Hyde of Bacteria

Bacillus cereus colonies on a sheep-blood agar plate

Bacillus cereus is the bacterial world’s very own shape-shifting supervillain! This microscopic menace is the master of disguise, equally at home in your garden soil as it is crashing your dinner party.

Picture, if you will, a rod-shaped rascal with a penchant for party-crashing. B. cereus is the uninvited guest that turns your lovely meal into a stomach-churning adventure. When it comes to food poisoning, it’s got not one, but two dastardly schemes up its cellular sleeve:

The “Oops, I Did It Again” Emetic Syndrome: Here, B. cereus plays the role of a speed demon. Within a mere 30 minutes to 6 hours after ingestion, you’ll be singing the porcelain prayer, with nausea and vomiting as your backup chorus.

The “Slow Burn” Diarrheal Syndrome: For those who prefer their misery with a side of suspense, B. cereus offers a 6 to 15-hour delay before unleashing a torrential downpour upon your digestive tract.

But wait, there’s more! This bacterial bad boy isn’t content with just ruining your day. It’s got ambitions beyond your belly. In its non-intestinal form, B. cereus can turn into an ocular outlaw, causing endophthalmitis – an eye infection so severe it might make you wish you were seeing double instead of not at all.

You might be wondering, “How does this dastardly duo-syndrome dealer get past our defenses?” The answer lies in its secret weapon: spores. These are the bacterial equivalent of a superhero’s indestructible suit, allowing B. cereus to survive temperatures that would turn lesser germs into microbial mush.

So, the next time you’re tempted to leave that rice dish out on the counter, remember: you might be setting the stage for B. cereus’s next big performance. And trust me, this is one show you definitely don’t want tickets to!

In the end, Bacillus cereus proves that even in the world of microbes, it’s the two-faced troublemakers that keep us on our toes. It’s the bacteria that reminds us all: in the game of food safety, you either win, or you spend a very uncomfortable night praying to the porcelain gods!

B. cereus: The Anthrax Impersonator

Move over, Clark Kent! There’s a new master of disguise in town, and it’s none other than Bacillus cereus, the bacterial world’s very own shape-shifter. This crafty microbe has been caught red-handed, sporting some of Bacillus anthracis’ most notorious accessories – the anthrax toxin genes.

Picture this: a seemingly innocent B. cereus, usually content with ruining your fried rice, suddenly decides to go full supervillain. It dons the genetic equivalent of a black cape and mask, acquiring the anthrax toxin genes cya, lef, and pagA, along with their ringleader, atxA. It’s like B. cereus went to a “How to Be Anthrax” workshop and came out with a certificate of completion.

But wait, there’s more! Some B. cereus strains have been caught in the act, causing severe and potentially fatal anthrax-like pneumonia. It’s as if these bacteria are auditioning for the role of B. anthracis in a microbial theater production, and they’re nailing the performance.

Take, for example, the case of B. cereus G9241, isolated from a Louisiana welder suffering from an anthrax-like infection. This bacterial method actor didn’t just look the part; it had the props to match, carrying plasmids eerily similar to B. anthracis’ pXO1. Talk about commitment to the role!

But G9241 isn’t the only star in this microbial drama. Enter BcFL2013, another B. cereus isolate that decided to take its act to the skin, causing a cutaneous lesion that could have been mistaken for an anthrax eschar. It’s like these bacteria are trying to win a “Most Convincing Anthrax Impersonation” contest.

The CDC has even reported fatal anthrax pneumonia in welders caused by these B. cereus method actors. It’s a reminder that in the world of bacteria, sometimes the understudy can steal the show – with potentially deadly consequences.

Now for the bacterial soap opera of the last century! The Bacillus cereus group is a family of microscopic misfits that’ll make your head spin faster than a centrifuge on steroids! Picture seven siblings, so close they’re practically wearing each other’s DNA, but each with their own twisted personality quirks. It’s like “The Brady Bunch” meets “The Addams Family,” but with more spores and less singing!

First up, we’ve got B. cereus sensu stricto, the OG troublemaker. This bad boy’s got a rap sheet longer than its flagella, causing food poisoning that’ll have you hugging the porcelain throne and cursing the day you ever laid eyes on that leftover rice.

Then there’s B. anthracis, the family psychopath. This guy’s idea of a good time is causing anthrax and watching the world burn. Talk about daddy issues!

Don’t forget B. thuringiensis, the bug-zapping black sheep of the family. While the others are out causing mayhem in humans, this oddball’s busy playing exterminator for insects. It’s like if your sibling decided to become a professional fly swatter.

B. mycoides and B. pseudomycoides are the artistic twins, always showing off their rhizoid growth patterns. It’s like they’re trying to one-up each other in a never-ending bacterial Rorschach test.

B. weihenstephanensis is the family’s cold-loving oddball. While the others are sweating it out at body temperature, this weirdo’s chilling at 4°C like it’s a day at the beach.

And finally, we’ve got B. cytotoxicus, the hot-headed rebel of the bunch. This thrill-seeker laughs in the face of danger, growing at temperatures that would make the others curl up and sporulate.

Together, they’re the Bacillus cereus group – a dysfunctional family of bacterial misfits that’ll make you question everything you thought you knew about microbiology. It’s like “Game of Thrones,” but with more plasmids and less dragons! So, the next time you encounter B. cereus, remember: it might just be wearing its anthrax costume. It’s the bacterial equivalent of a wolf in sheep’s clothing, proving that in the microscopic world, things aren’t always as they seem. Who knew bacteria could be such drama queens?

Tectiviridae: The Shapeshifting Ninjas of the Bacterial World

Prepare to be amazed by the ultimate biological quick-change artists – the Tectiviridae family of bacteriophages! These microscopic marvels are the Transformers of the viral world, with more tricks up their sleeves than a magician at a Las Vegas show.

Picture this: a virus that looks like a geometric puzzle, an icosahedral protein shell that would make Buckminster Fuller jealous. But wait, there’s more! Beneath this hard exterior lies a secret weapon – a lipid membrane vesicle. It’s like these phages are wearing a bulletproof vest… made of butter!

But the real magic happens when these viral ninjas attack the unsuspecting Bacillus cereus. In a move that would make Optimus Prime proud, the lipid membrane transforms into a tail-like structure. It’s the viral equivalent of pulling a lightsaber out of your pocket!

Now, let’s talk about their genetic makeup. These phages are packing about 15 kilobases of linear, double-stranded DNA. But this isn’t just any old DNA – oh no! It’s got long, inverted terminal-repeat sequences. It’s like the phage is saying, “I like my DNA like I like my palindromes – readable from both ends!”

And who are the stars of this microscopic circus? Let’s give a round of applause to:

GIL01 – The OG of the group

Bam35 – Not to be confused with a certain British secret agent

GIL16 – GIL01’s cooler younger sibling

AP50 – The one that always scores a perfect 50

Wip1 – Because every group needs a member with a cool nickname

These temperate tectiviruses are the ultimate party crashers in the B. cereus group’s bacterial bash. They’re like that friend who shows up uninvited, rearranges your furniture, and somehow ends up being the life of the party.

So, the next time you’re feeling down about your own ability to adapt, just remember: somewhere out there, a tectivirus is turning its innards into outtards, all in the name of infecting a bacterium. Now that’s what I call a real identity crisis!

B. cereus: The Probiotic Paradox (And yes, it does sound like “be serious”)

Bacillus cereus, once known only as the party crasher of your potato salad picnic, is now auditioning for a new role: the helpful sidekick in the gut health saga. In the world of animal agriculture, B. cereus is shedding its bad boy image faster than a pig sheds pounds on a diet. Farmers are discovering that this microscopic marvel can be a secret weapon in their probiotic arsenal. When added to animal feed, B. cereus strains can turn into tiny personal trainers for livestock, pumping up growth rates and beefing up feed efficiency. It’s like having a gym membership for your gut!

But wait, there’s more! B. cereus isn’t content with just helping out our furry and feathered friends. No, this bacterial overachiever has set its sights on the plant kingdom too4. Picture this: B. cereus, donning a tiny gardener’s hat, rolling up its flagella, and getting down to business in the rhizosphere. It’s been caught red-handed promoting plant growth, protecting against nasty pathogens, and even inducing systemic resistance in plants. Talk about a green thumb!

In the tomato fields, B. cereus AR156 is the unsung hero, fighting off bacterial wilt and root-knot nematodes like a botanical bodyguard. It’s as if this bacterium woke up one day and decided, “You know what? I’m tired of being the villain. Time to join the Avengers of the microbial world!”

So, the next time you hear “B. cereus,” don’t just think “be serious” about food safety. Think “WTF?” at how this troublemaker which can cause food poisoning (and much worse) is purposely being used in agriculture and animal husbandry for beneficial purposes:

As plant growth-promoting bacteria (PGPB): Some B. cereus strains have been shown to enhance growth in crops like soybean, maize, rice, and wheat. They can increase plant height, dry weight, and nutrient uptake.

For biocontrol of plant pathogens: Certain B. cereus strains can suppress harmful phytopathogens, including bacteria, fungi, and nematodes.

To improve plant stress tolerance: Some strains help plants better withstand abiotic stresses like drought, salinity, and heavy metal pollution.

As probiotics in animal feed: Harmless strains of B. cereus are used as feed additives for chickens, rabbits, and pigs to reduce harmful bacteria like Salmonella in their intestines.

For bioremediation: B. cereus has shown potential in cleaning up heavy metal contamination in soils and organic pollutants in water bodies.

As a microbial pesticide: The EPA has approved at least one strain (BP01) as a plant growth regulator for use in cotton crops.

Other Notes (Wikipedia)

Colonies of B. cereus were originally isolated from a gelatine plate left exposed to the air in a cow shed in 1887. In the 2010s, examination of warning letters issued by the US Food and Drug Administration issued to pharmaceutical manufacturing facilities addressing facility microbial contamination revealed that the most common contaminant was B. cereus.

Several new enzymes have been discovered in B. cereus, such as AlkC and AlkD, both of which are involved in DNA repair.

Electron micrograph of Bacillus cereus

Metabolism

Bacillus cereus has mechanisms for both aerobic and anaerobic respiration, making it a facultative anaerobe. Its aerobic pathway consists of three terminal oxidases: cytochrome aa3, cytochrome caa3, and cytochrome bd, the use of each dependent on the amount of oxygen present in the environment. The B. cereus genome encodes genes for metabolic enzymes including NADH dehydrogenases, succinate dehydrogenase, complex III, and cytochrome c oxidase, as well as others. Bacillus cereus can metabolize several different compounds to create energy, including carbohydrates, proteins, peptides, and amino acids.

An isolate of a bacterium found to produce PHBs was identified as B. cereus through analysis of 16S rRNA sequences as well as similarity of morphological and biochemical characteristics. PHBs may be produced when there is excess carbon or limited essential nutrients present in the environment, and they are later broken down by the microbe as a fuel source under starvation conditions. This indicates the potential role of B. cereus in producing biodegradable plastic substitutes. PHB production was highest when provided with glucose as a carbon source.

Following exposure to non-lethal acid shock at pH 5.4-5.5, the arginine deiminase gene in B. cereus, arcA, shows substantial up-regulation. This gene is part of the arcABC operon which is induced by low-pH environments in Listeria monocytogenes, and is associated with growth and survival in acidic environments. This suggests that this gene is also important for survival of B. cereus in acidic environments.

The activation of virulence factors has been shown to be transcriptionally regulated via quorum-sensing in B. cereus. The activation of many virulence factors secreted is dependent on the activity of the Phospholipase C regulator (PlcR), a transcriptional regulator which is most active at the beginning of the stationary phase of growth. A small peptide called PapR acts as the effector in the quorum-sensing pathway, and when reimported into the cell, it interacts with PlcR to activate transcription of these virulence genes. When point mutations were introduced into the plcR gene using the CRISPR/Cas9 system, it was observed that the mutated bacteria lost their hemolytic and phospholipase activity.

Growth

The optimal growth temperature range for B. cereus is 30-40 °C. At 30 °C (86 °F), a population of B. cereus can double in as little as 20 minutes or as long as 3 hours, depending on the food product. Spores of B. cereus are not metabolically active, but can rapidly become active and begin replicating once they encounter adequate growth conditions.[better source needed]

FoodMinutes to double, 30 °C (86 °F)Hours to multiply by 1,000,000
Milk20–366.6 – 12
Cooked rice26–318.6 – 10.3
Infant formula5618.6

Ecology

Like most Bacilli, the most common ecosystem of Bacillus cereus is the soil. In concert with Arbuscular mycorrhiza (and Rhizobium leguminosarum in clover), they can up-regulate plant growth in heavy metal soils by decreasing heavy metal concentrations via bioaccumulation and biotransformation in addition to increasing phosphorus, nitrogen, and potassium uptake in certain plants.

  • Azcón R, Perálvarez M, Roldán A, Barea JM (May 2010). “Arbuscular mycorrhizal fungi, Bacillus cereus, and Candida parapsilosis from a multicontaminated soil alleviate metal toxicity in plants”. Microbial Ecology. 59 (4): 668–677. doi:10.1007/s00248-009-9618-5. PMID 20013261. S2CID 12075701.

B. cereus was also shown to aid in survival of earthworms in heavy metal soils resulting from the use of metal-based fungicides, showing increases in biomass, reproduction and reproductive viability, and a decrease in metal content of tissues in those inoculated with the bacterium. These results suggest strong possibilities for its application in ecological bioremediation. Evidence of bioremediation potential by Bacillus cereus was also found in the aquatic ecosystem, where organic nitrogen and phosphorus wastes polluting a eutrophic lake were broken down in the presence of B. cereus.

In a study measuring the ability of B. cereus to degrade keratin in chicken feathers, bacteria were found to sufficiently biodegrade keratin via hydrolytic mechanisms. These results indicate its potential to degrade keratinous waste from the poultry industry for potential recycling of the byproducts.

B. cereus competes with Gram-negative bacteria species such as Salmonella and Campylobacter in the gut; its presence reduces the number of Gram-negative bacteria, specifically via antibiotic activity via enzymes such as cereins that impede their quorum sensing ability and exhibit bactericidal activity. In food animals such as chickens, rabbits and pigs, some harmless strains of B. cereus are used as a probiotic feed additive to reduce Salmonella in the animals’ intestines and cecum. This improves the animals’ growth, as well as food safety for humans who eat them. In addition, B. cereus create and release enzymes that aid in the digestion of materials that are typically difficult to digest, such as woody plant matter, in the guts of other organisms.

The strain B. cereus B25 is a biofungicide. A study by Figueroa-López et al. showed that the presence of this strain reduced Fusarium verticillioides growth. B25 shows promise for reduction of mycotoxin concentrations in grains.

Pathogenesis

B. cereus is responsible for a minority of foodborne illnesses (2–5%), causing severe nausea, vomiting, and diarrhea. Bacillus foodborne illnesses occur due to survival of the bacterial endospores when contaminated food is not, or is inadequately, cooked. Cooking temperatures less than or equal to 100 °C (212 °F) allow some B. cereus spores to survive. This problem is compounded when food is then improperly refrigerated, allowing the endospores to germinate. Cooked foods not meant for either immediate consumption or rapid cooling and refrigeration should be kept at temperatures below 10 °C (50 °F) or above 50 °C (122 °F). Germination and growth generally occur between 10 °C and 50 °C, though some strains can grow at low temperatures, and Bacillus cytotoxicus strains have been shown to grow at temperatures up to 52 °C (126 °F). Bacterial growth results in production of enterotoxins, one of which is highly resistant to heat and acids (pH levels between 2 and 11); ingestion leads to two types of illness: diarrheal and emetic (vomiting) syndrome. The enterotoxins produced by B. cereus have beta-hemolytic activity.

  • The diarrheal type is associated with a wide range of foods, has an 8-to-16-hour incubation time, and is associated with diarrhea and gastrointestinal pain. Also known as the ‘long-incubation’ form of B. cereus food poisoning, it might be difficult to differentiate from poisoning caused by Clostridium perfringens. Enterotoxin can be inactivated after heating at 56 °C (133 °F) for 5 minutes, but whether its presence in food causes the symptom is unclear, since it degrades in stomach enzymes; its subsequent production by surviving B. cereus spores within the small intestine may be the cause of illness.
  • The ’emetic’ form commonly results from rice which is cooked at a time and temperature insufficient to kill any spores present, then improperly refrigerated. The remaining spores can produce a toxin, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption. Distinguishing from other short-term bacterial foodborne intoxications, such as by Staphylococcus aureus, can be difficult. Emetic toxin can withstand 121 °C (250 °F) for 90 minutes. As a result of the emetic type’s association with rice, it is sometimes referred to colloquially as ‘fried rice syndrome’.

The diarrhetic syndromes observed in patients are thought to stem from the three toxins: hemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe), and cytotoxin K (CytK). The nhe/hbl/cytK genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by PlcR. These genes occur in the taxonomically related B. thuringiensis and B. anthracis, as well. These enterotoxins are all produced in the small intestine of the host, thus thwarting digestion by host endogenous enzymes. The Hbl and Nhe toxins are pore-forming toxins closely related to ClyA of E. coli. The proteins exhibit a conformation known as a “beta-barrel” that can insert into cellular membranes due to a hydrophobic exterior, thus creating pores with hydrophilic interiors. The effect is loss of cellular membrane potential and eventually cell death.[citation needed]

Previously, it was thought that the timing of the toxin production was responsible for the two different courses of disease, but it has since been found that the emetic syndrome is caused by the toxin cereulide, which is found only in emetic strains and is not part of the “standard toolbox” of B. cereus. Cereulide is a cyclic polypeptide containing three repeats of four amino acids: d-oxy-Leu—d-Ala—l-oxy-Val—l-Val (similar to valinomycin produced by Streptomyces griseus) produced by nonribosomal peptide synthesis. Cereulide is believed to bind to 5-hydroxytryptamine 3 (5-HT3) serotonin receptors, activating them and leading to increased afferent vagus nerve stimulation. It was shown independently by two research groups to be encoded on multiple plasmids: pCERE01 or pBCE4810. Plasmid pBCE4810 shares homology with the B. anthracis virulence plasmid pXO1, which encodes the anthrax toxin. Periodontal isolates of B. cereus also possess distinct pXO1-like plasmids. Like most of cyclic peptides containing nonproteogenic amino acids, cereulide is resistant to heat, proteolysis, and acid conditions.

B. cereus is also known to cause difficult-to-eradicate chronic skin infections, though less aggressive than necrotizing fasciitis. B. cereus can also cause keratitis.

  • Pinna A, Sechi LA, Zanetti S, Usai D, Delogu G, Cappuccinelli P, Carta F (October 2001). “Bacillus cereus keratitis associated with contact lens wear”. Ophthalmology. 108 (10): 1830–1834. doi:10.1016/S0161-6420(01)00723-0. PMID 11581057.

While often associated with gastrointestinal illness, B. cereus is also associated with illnesses such as fulminant bacterial infection, central nervous system involvement, respiratory tract infection, and endophthalmitis. Endophthalmitis is the most common form of extra-gastrointestinal pathogenesis, which is an infection of the eye that may cause permanent vision loss. Infections typically cause a corneal ring abscess, followed by other symptoms such as pain, proptosis, and retinal hemorrhage. While different from B. anthracis, B. cereus contains some toxin genes originally found in B. anthracis that are attributed to anthrax-like respiratory tract infections.

A case study was published in 2019 of a catheter-related bloodstream infection of B. cereus in a 91-year-old male previously being treated with hemodialysis via PermCath for end-stage renal disease. He presented with chills, tachypnea, and high-grade fever, his white blood cell count and high-sensitivity C-reactive protein (CRP) were significantly elevated, and CT imaging revealed a thoracic aortic aneurysm. He was successfully treated for the aneurysm with intravenous vancomycin, oral fluoroquinolones, and PermCath removal. Another case study of B. cereus infection was published in 2021 of a 30-year-old woman with lupus who was diagnosed with infective endocarditis after receiving a catheter. The blood samples were positive for B. cereus and the patient was subsequently treated with vancomycin. PCR was also used to verify toxins that the isolate produces.

Diagnosis

In case of foodborne illness, the diagnosis of B. cereus can be confirmed by the isolation of more than 100,000 B. cereus organisms per gram from epidemiologically implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting.

Prognosis

Most emetic patients recover within 6 to 24 hours, but in some cases, the toxin can be fatal via fulminant hepatic failure.

In 2014, 23 newborns in the UK receiving total parenteral nutrition contaminated with B. cereus developed sepsis, with three of the infants later dying as a result of infection.

Prevention

While B. cereus vegetative cells are killed during normal cooking, spores are more resistant. Viable spores in food can become vegetative cells in the intestines and produce a range of diarrheal enterotoxins, so elimination of spores is desirable. In wet heat (poaching, simmering, boiling, braising, stewing, pot roasting, steaming), spores require more than 5 minutes at 121 °C (250 °F) at the coldest spot to be destroyed. In dry heat (grilling, broiling, baking, roasting, searing, sautéing), 120 °C (248 °F) for 1 hour kills all spores on the exposed surface. This process of eliminating spores is very important, as spores of B. cereus are particularly resistant, even after pasteurization or exposure to gamma rays.

B. cereus and other members of Bacillus are not easily killed by alcohol; they have been known to colonize distilled liquors and alcohol-soaked swabs and pads in numbers sufficient to cause infection.

A study of an isolate of Bacillus cereus that was isolated from the stomach of a sheep was shown to be able to break down β-cypermethrin, or β-CY, which has been known to be an antimicrobial agent. This strain, known as GW-01, can break down β-CY at a significant rate when the bacterial cells are in high concentrations relative to the antimicrobial agent. It has also been noted that the ability to break down β-CY is inducible. However, as the concentration of β-CY increases, the rate of β-CY degradation decreases. This suggests that the agent also functions as a toxin against the GW-01 strain. This is significant as it shows that in the right concentrations, β-CY can be used as an antimicrobial agent against Bacillus cereus.

Diseases in aquatic animals

Bacillus cereus groups, notably B. cereus (Bc) and B. thuringiensis (Bt), are also pathogenic to multiple aquatic organisms including Chinese softshell turtle ( Pelodiscus sinensis ), causing infection characterized by gross lesions such as hepatic congestion and enlarged spleen, which causes high mortality.

  • Cheng LW, Rao S, Poudyal S, Wang PC, Chen SC (October 2021). “Genotype and virulence gene analyses of Bacillus cereus group clinical isolates from the Chinese softshell turtle (Pelodiscus sinensis) in Taiwan”. Journal of Fish Diseases. 44 (10): 1515–1529. doi:10.1111/jfd.13473. PMID 34125451. S2CID 235426384.

Bacteriophages

Bacteria of the B. cereus group are infected by bacteriophages belonging to the family Tectiviridae. This family includes tailless phages that have a lipid membrane or vesicle beneath the icosahedral protein shell and that are formed of approximately equal amounts of virus-encoded proteins and lipids derived from the host cell’s plasma membrane. Upon infection, the lipid membrane becomes a tail-like structure used in genome delivery. The genome is composed of about 15-kilobase, linear, double-stranded DNA (dsDNA) with long, inverted terminal-repeat sequences (100 base pairs). GIL01, Bam35, GIL16, AP50, and Wip1 are examples of temperate tectiviruses infecting the B. cereus group.

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