MICR5832 L8: Bacterial Infections of GIT I 9/6/25

What is this?

-Toxigenic bacteria contaminate cooked food

-Pre-formed toxins ingested

-Vomiting/diarrhea only a few hours after ingestion

-Usually lasts 24h

Foodborne Intoxications (GI Disease)

How does ingesting food lead to Foodborne Intoxication?

1) Food stored at room temp or higher for long periods

2) Growth of pathogen

3) Secretion of neurotoxic emetics &/or enterotoxins into food

What is this?

-Bacterial pathogens ingested via fecal-oral route

-Contaminated food, water, direct contact

-Pathogen colonizes intestine

-Production of toxins/invasion of intestinal epithelium

-Diarrhea days after ingestion

Infections (GI Disease)

What are the two main types of GI disease?

1) Foodborne Intoxication

2) Infections

What is this?

-Gram Positive bacilli

-Aerobic endo spore, β-haemolytic

-Emetic toxin/Diarrheal Enterotoxin

-Rice dishes + ubiquitous in environment

Bacillus cereus

What is this?

-Bacillus Cereus

-Gram Positive bacilli

-Aerobic endo spore, β-haemolytic

-Emetic toxin/Diarrheal Enterotoxin

What two toxins are produced by B. cereus?

1) Emetic toxin (Cereulide)

2) Diarrheal Enterotoxin

What organism are these toxins produced by?

1) Emetic toxin (Cereulide)

2) Diarrheal Enterotoxin

Bacillus cereus

What is this?

-Bacillus cereus toxin

-Vomiting, nausea 1-5 hrs after ingestion

-30% have diarrhoea (food-borne intoxication)

Emetic toxin (Cereulide)

What is this?

-Bacillus cereus toxin

-Diarrhea, cramps, 8-16 hr after ingestion

Diarrheal Enterotoxin

How much B. cereus must be present to confirm food poisoning?

>105 cells/gm of food and absence of other pathogens

True or False: Bacillus cereus is found in low numbers in stool of healthy people

True

What is this culture for?

-Mannitol egg-yolk polymyxin agar (MYP)

-Bacara agar

Bacillus cereus

What culture would you use for this?

-Bacillus cereus (Gram Positive)

-Mannitol egg-yolk polymyxin agar (MYP)

-Bacara agar

What is this?

-Polymyxin B

-Mannitol + phenol red pH indicator lecithin

-Used for Gram Positives such as Bacillus cereus

Mannitol egg-yolk polymyxin (MYP) agar

How does this ingredient found in MYP help cultivate Gram Positive Bacillus cereus?

-Polymyxin B

Kills Gram Negative bacteria

How does this ingredient found in MYP help cultivate Bacillus cereus?

-Mannitol + phenol red pH indicator lecithin

-Degraded by lecithinase

-Insoluble products are precipitated

You cultivate a Gram Positive organism in MYP agar. What is it?

Mannitol: Negative

Lecithinase: Positive

Bacillus cereus

You cultivate a Gram Positive organism in MYP agar. What is it?

Mannitol: Positive

Lecithinase: Negative

Bacillus subtilis

What is this used to confirm?

-Microgen Bacillus ID multitest strip; Vitek 2 BCL card; MALDI-TOF; PCR

Bacillus cereus

What is this?

-Newer chromogenic agar with egg yolk

-Bacillus cereus turns it orange-pink

-Inhibits other Gram Positives

Bacara agar

Which Bacillus cereus ID test is this?

-Carbohydrate substrate

-For Bacillus, Paenibacillus or Vergibacillus

Microgen Bacillus ID

What substrate does this ID test use?

-Microgen Bacillus ID

-For Bacillus, Paenibacillus or Vergibacillus

Carbohydrates

Which Bacillus cereus ID test is this?

-Substrate utilization test

-Microwell card formatautomated reading

-350 clinically relevant bacteria and yeast

Vitek 2 ID Card

What is this?

-Gram Positive cocci in clusters

-"Bunch of grapes"

-Coagulase positive, plasma clots from binding to fibrinogen

Staphylococcus aureus

What is this?

-Staphylococcus aureus

-Gram Positive cocci in clusters

-"Bunch of grapes"

-Coagulase positive

Why does Staphylococcus cause plasma to clot?

-Coagulase positive

-Enzyme binds to plasma fibrinogen

What is this?

-Creams/custards, warm food, meats, dairy products

-Nausea, vomiting, cramps, diarrhoea; 30 min to 8 hr after ingestion

-20 Enterotoxins with emesis

Staphylococcus aureus

True or False: Salmonella, Shigella and Staphylococcus aureus do not require antibiotics for treatment, just oral rehydration

True

What is the primary reservoir for Staphylococcus aureus ("Bunch of grapes")?

Human carriers, skin

What culture would you use for this?

-Staphylococcus aureus (Gram Positive)

-Baird Parker Agar

-Mannitol Salt Agar

What is this culture for?

-Baird Parker agar

-Mannitol Salt Agar (MSA)

Staphylococcus aureus

What is this?

-Used for Staphylococcus aureus

-Tellurite + rabbit plasma + fibrinogen

Baird Parker Agar

What is the purpose of the following ingredients found in Baird Parker Agar used to culture S. aureus?

-Glycine, lithium, tellurite

Suppress most bacteria

What can you observe about the black dotted appearance of Baird-Parker agar containing coagulase positive S. aureus?

-Tellurite is reduced → black colonies

-Coagulase activity → zone of precipitation around colony

What is this?

-Used for Staphylococcus aureus

-7.5% salt inhibits most bacteria

-S. aureus ferments mannitol, turning red -> yellow

Mannitol Salt Agar (MSA)

What can you observe about the red and yellow appearance of MSA containing salt fermenter S. aureus?

S. aureus ferments mannitol → yellow colonies

What is this?

-Neurotoxin BonT causes flaccid paralysis/respiratory failure

-Spores distributed in soil and water

-Diagnosis via neurotoxin detection in feces, food, serum

Clostridium botulinum

What is this?

-Clostridium botulinum

-Neurotoxin BonT causes flaccid paralysis/respiratory failure

-Spores distributed in soil and water

-Diagnosis via neurotoxin detection in feces, food, serum

What bacteria are these assays for?

-Mouse lethality assay

-Lateral flow assay (in vitro, dipstick)

-ELISA

-PCR assays (doesn't show if toxin is active)

Clostridium botulinum

True or False: Clostridium botulinum spores are not found in the human/animal GI tract because it is not a commensal bacteria

False

True or False: Blood Agar (BA) and Egg Yolk Agar (EYA) are unsuitable for Clostridium botulinum as they are not selective

True

True or False: Infant botulism, wound botulism, and intestinal botulism are not intoxications

True

True or False: Infant botulism, wound botulism, and intestinal botulism all involve bacterial colonization followed by toxin production

True

How to prevent foodborne infections?

1) Cook food well → reduce number of potential pathogens

2) Do not mix cooked food with uncooked food

3) Store food at cool temperatures 4C

4) Do not re-heat food and then store again at lower temp

GIT infections must pass through the stomach acid.

What makes the host more susceptible to this happening?

-Antacids, drugs, surgery (gastrectomy)

-Impairs gastric acidity

Which GIT Infection bacteria is this?

-Low acid tolerance

-10 to 10E3 cells

Shigella

Which GIT Infection bacteria is this?

-High acid tolerance

-Up to 10E9 cells

Vibrio cholerae

How do these pathogens colonize the GIT?

-Clostridium perfringens

-Enterotoxigenic E. coli (ETEC)

-Vibrio cholerae

Enterotoxins → electrolyte and water loss → watery diarrhea

What GIT pathogens use this route to colonize?

-Enterotoxins → electrolyte and water loss → watery diarrhea

-Clostridium perfringens

-Enterotoxigenic E. coli (ETEC)

-Vibrio cholerae

How do these pathogens colonize the GIT?

-Campylobacter

-Salmonella,

-Shigella

-Yersinia enterocolitica

Invade intestinal epithelium → inflammation → bloody diarrhea (dysentery)

What GIT pathogens use this route to colonize?

-Invade intestinal epithelium → inflammation → bloody diarrhea (dysentery)

-Campylobacter

-Salmonella,

-Shigella

-Yersinia enterocolitica

What part of the GIT do these pathogens invade?

-Helicobacter pylori

Stomach

What part of the GIT do these pathogens invade?

-Clostridium perfringens

-Plesiomonas shigelloides

-Vibrio spp.

Small Intestine

What part of the GIT do these pathogens invade?

-Aeromonas hydrophila

-Campylobacter spp.

-Clostridium difficile

-Shigella spp.

Large Intestine

Which GIT pathogens are found in both the Small Intestine and Large Intestine?

-Diarrhoeagenic E. coli

-Salmonella spp.

-Yersinia enterocolitica

These GIT organs are part of which Intestine?

-Duodenum, ileum, jejunum

Small Intestine

These GIT organs are part of which Intestine?

-Cecum, colon, rectum, anal canal

Large Intestine

What is this culture for?

-Carey-Blair transport medium

-Transport immediately in sterile jar for microscopy, direct detection

Fecal pathogens

What culture would you use for this?

-Carey Blair transport medium

-Transport immediately in sterile jar for microscopy, direct detection

Fecal pathogens

What would you look for when doing microscopy on feces?

-PMNs and RBCs in wet mount

-Inflammation indicators

What is this?

1) Aeromonas hydrophila

2) Campylobacter spp.

3) Plesiomonas shigelloides

4) Salmonella spp.

5) Shigella spp.

6) Yersinia enterocolitica

Fecal pathogens

What culture would you use for this?

-Salmonella, Shigella, Aeromonas, Plesiomonas

-McConkey agar (MAC)

-Hektoen Enteric agar (HE)

-Salmonella Shigella agar (SS)

-Xylose Lactose Deoxycholate agar (XLD)

What is this culture for?

-MAC, HE, SS, and XLD

-Salmonella

-Shigella

-Aeromonas

-Plesiomonas

What culture would you use for this?

-Campylobacter

-CAMP Agar

-Skirrow Agar

What is this culture for?

-CAMP Agar

-Skirrow Agar

Campylobacter

What is this culture for?

-CIN Agar

Yersinia enterocolytica

What culture would you use for this?

-Yersinia enterocolitica

CIN Agar

What is this?

-Gram Positive bacilli, strict anaerobic spores

-Meats, gravy, human reservoir

-Abdominal cramping, watery diarrhea, vomiting, fever ~1 day

Clostridium perfringens

What is this?

-Clostridium perfringens

-Gram Positive bacilli, strict anaerobic spores

-Meats, gravy (human reservoir)

-Abdominal cramping, watery diarrhea, vomiting, fever ~1 day

What is this culture for?

-Tryptose Sulfite Cycloserine (TSD Agar)

-Kanamycin, polymyxin, cycloserine inhibits normal flora

-H2S production → black dotted colonies

Clostridium perfringens

What culture would you use for this?

-Clostridium perfringens

Tryptose Sulfite Cycloserine (TSD Agar)

What is this?

-Used to culture Clostridium perfringens

-Contains kanamycin, polymyxin, cycloserine

-H2S production results in black colonies

Tryptose Sulfite Cycloserine (TSD Agar)

What is the role of this ingredient of Tryptose Sulfite Cycloserine (TSD Agar) used to culture Clostridium perfringens?

-Kanamycin, polymyxin, cycloserine

Inhibits normal flora

What can you observe about the black dotted appearance of TSD agar containing Clostridium perfringens?

H2S production → black colonies

What is the minimum amount of Clostridium perfringens required for diagnosis?

>10E5 orgs/gm food

>10E6 orgs/gm faeces

What is the most reliable way to detect Clostridium perfringens?

CPE enterotoxin in feces

What is this?

-Alpha toxin (lecithinase) neutralized with specific antibody

-Used to confirm Clostridium perfringens

Nagler test

What is this?

-Nagler Test

-Alpha toxin (lecithinase) neutralized with specific antibody

-Used to confirm Clostridium perfringens

What Gram Positive rod-forming bacteria is the Nagler test used to confirm?

Clostridium perfringens

How does the Nagler test work to confirm C. perfringens?

-Anti-Alpha-toxin antibody spread on one half of egg-yolk agar

-Test organism streaked across plate, incubated

-Lecithinase produced by C. perfringens breaks down lecithin in egg yolk → white precipitate

You are conducting a Nagler test.

What does this contain?

-Lecithinase breaks down lecithin in egg yolk

-White precipitate

Clostridium perfringens

You are conducting a Nagler test.

What does this contain?

-Lecithinase neutralized by antibody

-No precipitate

No Clostridium perfringens

What is this?

-API 20A, RapID ANA, others

-Catalase -ve, Spot indole +ve

Biochemical profiling used to detect C. perfringens

True or False: Biochemical profiling is more effective at confirming C. perfringens ID than MALDI-TOF

False

What is this?

-Gram Negative bacilli

-Oxidase Negative Enterobacteriaceae

-Contaminated meats, dairy, eggs, poultry

-Inhabits animal intestines

Salmonella

What is this?

-Salmonella

-Gram Negative bacilli

-Oxidase Negative Enterobacteriaceae

-Contaminated meats, dairy, eggs, poultry

-Inhabits animal intestines

How do you distinguish between serovars/serotypes of Salmonella?

-O (LPS)

-H (flagella) antigens

What are the 2 species of Salmonella?

1) S. enterica

2) S. bongori

Which Salmonella species is this?

-Has 6 subspecies including enterica

-Main human pathogens

S. enterica

Which Salmonella species is this?

-Mainly cold-blooded animals

S. bongori

True or False: 99.5% of all Salmonella strains isolated from humans/warm blooded animals belong to S. enterica (including Typhoid)

True

What symptoms are caused by Salmonella Typhi and Enteridis enterotoxins?

-Watery or bloody diarrhoea (dysentery), fever, cramps

How do Salmonella Typhi and Enteridis cause watery and bloody diarrhoea (dysentery), fever, and cramps?

Invasion of intestinal epithelium → limited to subepithelial tissues → intense inflammation

How do Salmonella Typhi and Paratyphi cause typhoid/enteric fever?

Invasion of blood → life threatening systemic infection

What is this?

-Gram Negative bacilli, facultative anaerobe

-Oxidase-neg rod (nonmotile)

Shigella

What is this?

-Dysentery, Haemolytic-Uraemic Syndrome (HUS)

-Invasion of intestinal epithelium → inflammation → bloody mucoid diarrhoea

Shigella

What is this?

-Shigella

-Gram Negative bacilli, facultative anaerobe

-Oxidase-neg rod (nonmotile)

-Invasion of intestinal epithelium → inflammation → bloody mucoid diarrhoea

What are the 4 serogroups of Shigella, based on LPS O Antigen?

A: S. dysenteriae

B: S. flexneri

C: S. boydii

D: S. sonnei

True or False: Shigella is found outside of humans and higher primates

False