4.1 Infections of the GI tract PART II

Question 1

What are enteric bacteria?

Give one thing they are resistant to?

Answer 1

The Enterobactericaea are a gram negative group of related bacteria that are known to reside in the intestines of the mammalian gut

They are resistant to bile salts and commonly have capsules

Question 2

What are purpose of the LPS, O, K and H antigens of enteric bacteria

This classification of Salmonella based upon antigenic structure is known as the ________ scheme?

Answer 2

LPS (lipopolysaccharide): aids adherence and acts as an endotoxin

O-antigen: inhibits phagocytosis and provides a degree of heat stability

K-antigen: part of the capsule and creates a sticky layer to aid attachment to cellss of biofilm

H-antigen: ONLY present in bacteria containing flagellum (mobile) and allows adherence and protection from macrophages

Classified using the Kaufmann-White scheme

Question 3

What is the most commonly found infection that co-exists with enterobacteria?

Answer 3

UTI’s

Question 4

What are opportunistic pathogens give 2 examples

Answer 4

Found in normal microflora but have the potential to become pathogenic in situations such as a weakened immune system, altered microbiota and breached integumentary barriers

Examples:

• Escherichia Coli
• Klebsiella pneumoniae
• Proteus ss
• Citrobacter ss

Question 5

What are obligate pathogens give 2 examples

Answer 5

Obligate pathogens always cause disease and can only survive and replicate within a host

Examples:

• Salmonella spp
• Shigella spp
• Yersinia spp
• Some E.Coli strains

Question 6

What is meant by a ubiquitous organism?

What is meant by a facultative anaerobe?

What is meant by a strict/obligate aerobe?

Answer 6

Ubiquitous organism: organism that is present everywhere

Facultative anaerobe: is an organism that makes ATP by aerobic respiration when oxygen is available but can switch to anaerobic respiration if oxygen is absent

Strict aerobes: organisms that cannot make ATP in the absence of oxygen

Question 7

Describe the structure of Salmonella

How are most grouped and how can they be sub-classified?

Where do they commonly reside

Answer 7

Salmonella is a gram-negative, facultative anaerobe that is rod-shaped, flagellated and belongs to the Enterobacteriaceae family

Nearly all grouped under S. enterica but can be further sub-classified based on their O (cell wall) and H (flagellar) antigens

They live in the intestinal tracts of warm and cold blooded animals but some species are ubiquitous.

Question 8

What are the 2 main diseases caused by Salmonella in humans and what are they a result of?

Answer 8

Salmonella are the cause of two diseases called salmonellosis:

1) Enteric fever (typhoid): resulting from bacterial invasion in the bloodstream
2) Acute gastroenteritis: resulting from a food-borne infection

Question 9

List 3 diseases caused by Salmonella and state specifically which strain causes these

Answer 9

1) S.typhi: typhoid fever (humans are the only host)
2) S. paratyphi A, B and C: paratyphoid fevers
3) S.typhimurium, S.montevideo, S.wien: cause salmonellosis

Question 10

Salmonella is ingested in ______ food/water. The bacterium passes through the GIT and attaches to the ______ cells of the ______

It invades through the mucosa by endocytosis using ______ proteins on their surface AND induces ______ to persist in epithelial cells and macrophages

Inside the cell it produces enterotoxins leading to local ______ and then exits killing the host cell which triggers the symptoms of _________ and __________.

Salmonella is then shed in the ________ and after several days the symptoms alleviate without the need for specific therapy

Answer 10

Contaminated, M, jejunum, Invasin, phagocytosis, inflammation, abdominal cramps, diarrhoea, faeces

Question 11

Typhoid fever occurs when salmonella temporarily enters the _______.

_______ may phagocytose but not digest S.Typhi and it can be carried to the _______, ______ and _______

In these locations it reproduces and re-enters the _______ where it travels and invades the ________, ________, and the _________ tissue of the bowel

Answer 11

blood, small intestine, WBCs, liver, spleen, bone marrow, blood, gallbladder, biliary system, lymphatic

Question 12

What are the 4 stages of untreated Typhoid Fever and long does each last?

Answer 12

Each stage lasts about a week:

Stage 1: fever, bradycardia, malaise, headache, cough and epistaxis (25% of people)

Stage 2: continuing fever, bradycardia, distended abdomen, weight loss, dicrotic pulse (x2 beats) and delirium

Stage 3: high fevers + complications ➞ intestinal haemorrhage or perforation, encephalitis, dehydration, motionless

Stage 4: defervescence (very high fever) and potential death due to other complications that may arise

Question 13

What complications of untreated Typhoid fever may lead to death?

Answer 13

• overwhelming infections
• pneumonia
• intestinal haemorrhage or perforation
• kidney failure
• peritonitis

Question 14

What is meant by a ‘carrier’ of S.Typhi and why is this dangerous?

How would you treat?

Answer 14

A carrier is a healthy person who survived the disease, but still have the bacteria which are able to survive without causing further symptoms

Dangerous because carriers continue to spread the disease through excrement of their faeces without realising it

Treat with:

• prolonged antibiotics.
• removal of the gallbladder or site of the infection

Question 15

Why may you remove gallbladder in a carrier of S. Typhi?

Answer 15

When spread through the bloodstream to distant sites, S.Typhi is able to establish a semi-permanent infection in the gallbladder meaning carriers can remain infected for years

Question 16

What is shigella and what does it cause

What signs would be seen on infection, how is it transmitted and how would you treat

Answer 16

Shigella is gram (-), non-motile, non-spore forming, catalase (+) facultative anaerobe that causes Shigellosis

Signs: bloody faeces (dysentry) associated with intestinal pain

Mode of transmission is person-to-person

Treatment: manage dehydration, antibiotics for severe dysentery (e.g. ampicillin).

Question 17

What are the 4 main species of Shigella?

Answer 17

group A ➞ shigella dysenteriae
group B ➞ shigella flexneri
group C ➞ shigella boydii
group D ➞ shigella sonnei

Question 18

List 5 differences between diarrhoea and dysentery

Answer 18

1) diarrhoea presents as watery stool with NO blood, dysentery presents as mucoid stools may be blood
2) fever is less common in diarrhoea and more common in dysentery
3) diarrhoea affects small bowel, dysentery affects the colon
4) diarrhoea is viral cause, dysentery is mostly bacterial
5) diarrhoea doesn’t need antibiotics, dysentery almost always requires antibiotics

Question 19

What enterotoxin is produced by shigella?

What is shigella’s mechanism of infection and how does this lead to dysentry?

What happens if shigella enters the blood?

Answer 19

Shigatoxin ➞ neurotoxic, enterotoxic and cytotoxic

1) bacteria are ingested and then invade the epithelial lining of intestines (does NOT penetrate)
2) multiplies in the small intestine and produces shigatoxin that inhibits host cell protein synthesis and damages epithelia
4) damage attracts leukocytes, triggers inflammation and causes release of mucus and blood leading to dysentery

If it enters the blood it can be phagocytosed very quickly and taken care of by our immune system. However, bacteria has adapted to only effect epithelial cells which allows a less effective host immune response

Question 20

Give 6 ways in which various E.Coli strains can express pathogenicity?

Answer 20

1) O, H, K antigens
2) plasmids for virulence
3) shiga-like Toxin
4) type III secretion system
5) disrupt PM
6) receptors for attachment

Question 21

What is meant by Type III secretion system that E.Coli has?

Answer 21

(T3SS) important virulence feature of Gram (-) bacteria that delivers effector proteins into host cells to subvert host cellular processes

Question 22

List 3 conditions caused by E.coli

Answer 22

1) UTIs
2) neonatal meningitis: usually E. coli carrying the K1 capsular antigen (and group B strep)
3) Intra-abdominal infections (associated with intestinal perforation)

Question 23

E.Coli can be classified by their virulence features and associated diseases ➞ what do the following classifications indicate

ETEC
EPEC
EIEC
EHEC

Answer 23

ETEC: enteroToxigenic, Travellers diarrhoea, produces 2 exotoxins HT (heat labile toxin) and ST (heat stable toxin) that cause infection that is non invasive and results in watery diarrhoea and NO fever….. similar to cholera

EPEC: enteroPathogenic, moderately invasive… similar to shigella

EIEC: enteroInvasive, causes dysentery and a host response that is clinically identical to shigella

EHEC: enteroHaemorrhagic, O157:H7 strain that produces the shigatoxin which stimulates an inflammatory response and can lead to haemolytic uraemic syndrome

Question 24

What would the presence of blood and/or pus

cells in the faeces indicates?

Answer 24

An invasive infection with mucosal destruction ➞ Dysentery (NOT diarrhoea)