Helicobacteria, Campylobacter And Mycobacteria

Question 1

What is the most common cause of food poisoning in the UK, Europe and the USA?
This bacterium is present on what percentage of chicken tested?
Describe this bacterium.

Answer 1

Campylobacter,
Present on 80% of chickens tested.
Campylobacter is a gram negative bacterium. It is microaerophilic and thermophilic. It has a long and spiral shaped morphology. They are also highly motile bacterial colonising the avian caecum and causing diarrhoea in humans.

Question 2

How is Campylobacter transmitted?

What is the incidence of Campylobacter contamination?

Answer 2

It is transmitted through poultry when raw or undercooked. This bacteria contaminates half of poultry sold.

Question 3

What are the symptoms of enteric disease in industrialised countries and developing countries?

Answer 3

Acute abdominal pain,
Fever and general malaise,
Profuse bloody diarrhoea but rarely vomiting,
Rarely bacteraemia,
Mucosal damage and inflammation especially in the ileum and jejunum.
In developing countries the symptoms are less severe, with water diarrhoea being one of the symptoms.

Question 4

Describe the pathogenesis of Campylobacter.

Answer 4

Campylobacter requires a high dose to infect the host due to its sensitivity to hydrochloric acid in the stomach, infection rarely occurs under 10000 bacteria ingested. The disease causes damage to the ileum, colon and jejunum. Most strains of the bacteria produce a toxin that hinders the cells of the immune system dividing, this allows for it to evade the immune system for some time.

Question 5

How are Campylobacter and Guillain-Barré syndrome related?

Answer 5

This is a syndrome resulting in a rapid onset of muscle weakness caused by the immune system damaging the peripheral nervous system. Symptoms include: absent reflexes, a tingling sensation, generalised weakness. These symptoms worsen over 1-4 weeks. Two thirds of the people with Guillain-Barré syndrome had previously been infected with Campylobacter jejuni.

Question 6

Why is research into Campylobacter challenging?

Answer 6

Because there are no reliable animal disease models. C. Jejuni strains vary phenotypically after isolation.

Question 7

Describe how Campylobacter jejuni adhere and interact with the mucosal membrane.

Answer 7

C. jejuni move chemotactically towards the mucosal layer, the shape of the bacterium allows it to move through viscous environments. Adherence and invasion of epithelial cells is dependent on a flagellar system. Invasion of the cells and interaction with sub mucosal layer results in a damaged epithelial barrier. Cytolethal Distending Toxin (CDT) activity may contribute to epithelial damage.

Question 8

Describe some virulence properties of C. jejuni.

Answer 8

They possess flagella making them highly motile; CDT, a DNase that damages the epithelial layer; adherence and invasion; chemotaxis, they are attracted to mucins, L-serine, L-fucose, repelled by bile salts; immune evasion, flagella glycosylated and poor substrate for TLR5 receptor.

Question 9

What innate defences does the intestinal tract possess that are relevant to C. jejuni?

Answer 9

Possesses a ciliated epithelial barrier (trapping/exclusion),
Normal flora (antagonism),
Mucous and peristalsis,
Inhibitory effects of mucosal antibodies (sIgA),
Nutrient restriction,
Mucosal antibody responses,
Adaptive antibody responses during infection.

Question 10

How many cases of food poisoning are there per year?

How can food be contaminated leading to food poisoning?

Answer 10

1.2 million cases.

Can be contaminated through soils or fecal contamination, through improper storage or if it is improperly prepared.

Question 11

What is Helicobacter pylori?

Where does this bacterium colonise?

Answer 11

It is a gram negative bacterium, transmitted orally, that causes a variety of stomach diseases including ulcers and cancers. The bacterium has a corkscrew morphology and is highly motile what with it possessing a flagella. H. pylori colonises the mucous layer and adheres to epithelial cells.

Question 12

What barriers does the stomach possess to prevent injury from its own acid?
How can ulcers form?

Answer 12

The stomach possesses a mucosal lining and a bicarbonate layer to prevent the acid reaching the stomach lining. If this is reduced then ulcers can occur. These are very painful and hard to treat and often require surgery, with them even returning after this. 85-95% of ulcers are caused by H. pylori.

Question 13

What is the second leading cause of cancer mortality worldwide?
This has a high incidence where?
What is the link between this disease and H. pylori?

Answer 13

Gastric cancer.
High incidence of Gastric Cancer in Asia.
H. pylori causes stress upon the mucosa of the stomach, inflaming it leading to chronic active gastritis. The immune response can then lead to this developing into gastric atrophy and intestinal metaplasia which can lead to to dysplasia and then gastric cancer.

Question 14

Describe the general features of H. pylori infection.

Answer 14

The infection is lifelong and transmission routes are not entirely known but are thought to be either fecal-oral or oral-oral. The presence of the pathogen elicits a strong immune response, leading to inflammation. The symptoms of this disease are the peptic ulcers and malignancies.

Question 15

Describe the immune response to H. pylori.

Answer 15

The immune response to H. pylori is mostly T-helper 1 cell responding, these producing Tissue Necrosis Factor and Interleukin 1 as well as oxygen free radicals which all cause massive damage to the epithelium.

Question 16

In terms of carcinogens, H. pylori can be described as what? The bacterium increases the chance of developing gastric cancer by how much? What percentage of gastric cancers in the developed world are associated with H. pylori.

Answer 16

Can be described as a type I carcinogen. Increases chances 3-9 fold. 60-80% of gastric cancers are linked to H. pylori infection.

Question 17

Outline the development of adenocarcinoma in an animal model.

Answer 17

27 H. pylori infected Mongolian gerbils were investigated for 62 weeks.
100% possessed gastritis,
85% possessed intestinal metaplasia,
37% possessed adenocarcinoma.

Question 18

How does H. pylori infection lead to chronic inflammation?

Answer 18

H. pylori induces a T helper 1 cell response which results in damage to the epithelium. The response does not eradicate H. pylori resulting in further immune responses and further epithelium damage.

Question 19

How does H. pylori survive ingestion and the stomach acid?

What enzymes does the bacteria produce that allow it to reach the mucosal lining?

Answer 19

Following ingestion of the pathogen, the flagella of H. pylori propels it towards the mucosa. The pathogen produces intracellular and perhaps even extracellular urease, which converts urea to CO2 and ammonia. This reduces the pH of the acid around it, allowing it to survive.
Collagenase and mucinase.

Question 20

Once at the epithelial lining what does H. pylori do?

Answer 20

At the epithelial lining, the bacteria can grow and divide due to the lowered pH. The bacteria produces various adhesins, such as BapA and HpaA, to bind to host cells. Once the bacteria has adhered it produces Vacuolating Cytotoxin (VacA) and Neutrophil-Activating Protein (NAP).

Question 21

What do the proteins: VacA, NAP and CagA all do?

Answer 21

NAP activates neutrophils and mast cells that further damage local tissue. VacA forms a Hexameric pore in the host membrane and induces apoptosis. CagA is an effector injected by a Type IV secretion system into the host cells. It is phosphorylated and interacts with host signalling proteins and activates host signalling transduction pathways.

Question 22

What is an issue with delivering antimicrobials to the gastric site for H. pylori treatment?
Name an antibiotic that can be used.

Answer 22

There is limited secretion and diffusion of antibiotics into the gastric mucosa. Thickness of the mucus layer and adverse effects of low gastric pH results in antibiotic inefficacy.
Tetracycline

Question 23

What are the mycobacteria?

Answer 23

These are slow growing rod shaped bacteria. They belong to the high GC gram positive phylum: actinobacteria.

Question 24

What does an acid fast organism mean?

What is the acid fast staining procedure?

Answer 24

It means that their cell walls contain a high amount of lipids called mycotic acids. These acids resist staining by ordinary methods such as Gram stain. The acid fast staining procedure can be used to stain these bacteria. The bacteria are treated with carbol-fuchsin which stains all cells red. They are washed with dilute acid/alcohol solution then tested with methylene blue. Mycobacteria retain their red dye.

Question 25

What are the two types of mycobacterium?

Answer 25

There are slow growing and fast growing.
Fast growing mycobacteria: M. smegmatis grows overnight in liquid culture and is a useful model for studying basic biology. This group also contains the opportunistic pathogens: M. fortuitum and M. chelonei which cause osteomyelitis.
Slow growing mycobacteria: include M. tuberculosis and M. leopard which cause Hansen’s disease.

Question 26

What does Mycobacterium leprae cause?

Answer 26

Causes leprosy, Hansen’s disease. This bacterium is mostly restricted to tropical countries. The disease can result in nerve damage leading to disfigurement. It was common in Europe until the 19th century. It is transmitted through nasal secretions, with a 2-20 year incubation time.

Question 27

When did Hansen discover M. leprae?
Why was it difficult to prove that it caused leprosy?
When was its genome published?
What are the similarities and differences of M. Leprae and M. Tuberculosis infection of cells?

Answer 27

Hansen discovered M. leprae in 1873 in the tissues of leprosy patients. It could not be proven till 100 years later when the disease was finally cultured in an armadillo.
It’s genome was published in 2001.
Both infect macrophages but only M. Leprae infects Schwann cells, leading to infection of the nervous system.

Question 28

What types of staining are used to identify M. Tuberculosis?

Answer 28

Acid fast or Ziehl-Neelsen staining.

Question 29

Describe how M. Tuberculosis is able to survive because of its cell wall and receptors.

Answer 29

The cell wall has a high lipid content which prevents desiccation and weak disinfectants. The cell wall also prevents fusion of the phagosome and lysosomes within macrophages. This prevents the macrophage digesting them. ManLAM is a high weight lipoglycan in the cell wall. This prevents macrophage activation and T cell proliferation. The bacteria also releases cell wall Glycolipids which contribute to granuloma formation.

Question 30

How do granulomas help to transmit TB throughout the body?

Answer 30

Macrophages ingest the bacteria and become granulomas. They release a chemical which attracts other macrophages to the site. These ingest the dead cells and thus contract TB and become granulomas themselves. Infected macrophages break away and form granulomas elsewhere in the host, resulting in it spreading.

Question 31

What is the only effective vaccine for TB?

Answer 31

The BCG vaccine, an attenuated live strain of M. Bovis. It’s efficiency ranges from 10-80%. The vaccine only protects children and can’t be boosted with a second vaccination.

Question 32

What is the MV85A booster for the BCG vaccine?

Answer 32

This is the most promising clinical trial vaccine. The antigen 85A binds to mycotic acids in the TB cell wall, tagging it for recognition by antibodies.

Question 33

What are the three types of drug resistance for TB?

Answer 33

MDR TB- Multidrug Resistant TB- 500000 new cases per year.
XDR TB- Extensively drug resistant TB- 40000 new cases per year.
TDR TB- Totally drug resistant TB- first reported in 2009, resistant to a wider range of drugs than XDR TB and most prevalent in India. not recognised by WHO because total drug resistance is hard to prove in TB.

Question 34

What are some treatments for TB?

Answer 34

Bedoquiline- first new drug in 40 years approved 26 months ago, it blocks TB ATP synthase.
Delamanid- approved 10 months ago. Blocks mycolic acid biosynthesis.