CDS (II) 2020 General Knowledge · Question 95 of 120

Correct — A, Helicobacter pylori. It is the one organism on the list that can live in the stomach at all. H. pylori is a spiral, gram-negative bacterium that burrows into the mucus layer over the gastric lining and neutralises the acid immediately around itself by producing large amounts of urease, an enzyme that splits urea into ammonia and bicarbonate. Sheltered there, it provokes a long-running inflammation that thins the mucosal defence and lets acid and pepsin dig into the wall — an ulcer. The discovery overturned the old teaching that ulcers were a disease of stress and spicy food, and it turned a chronic surgical problem into something curable with a week or two of antibiotics plus an acid suppressor. Barry Marshall and Robin Warren, who identified the organism and its role, received the Nobel Prize in Physiology or Medicine in 2005.

• (b)E. coli — Escherichia coli is a normal inhabitant of the large intestine, far downstream of the stomach. Its harmful strains cause diarrhoea and urinary tract infection; it has no urease shield and does not colonise the gastric mucosa.
• (c)Streptococcus pneumoniae — The pneumococcus is a respiratory pathogen — the leading bacterial cause of pneumonia, and also of meningitis and middle-ear infection. It has nothing to do with the stomach.
• (d)Salmonella typhimurium — A Salmonella of the food-poisoning group, causing gastroenteritis; its close relative Salmonella typhi causes typhoid fever. Both are intestinal infections, not ulcer-forming colonisers of the stomach lining.

A peptic ulcer is a break in the lining of the stomach or the first part of the small intestine, produced when the aggressive factors — hydrochloric acid and the enzyme pepsin — overwhelm the defensive ones, chiefly the mucus and bicarbonate layer. Two causes account for most cases worldwide: chronic infection with Helicobacter pylori, and long-term use of non-steroidal anti-inflammatory drugs such as aspirin and ibuprofen, which suppress the prostaglandins that maintain the mucus barrier.

The stem hands you the reasoning: it says the cause is bacterial and the site is the stomach, so the question reduces to which of the four can survive gastric acid. Three of them are classic pathogens of other organs — gut, lung and gut again — and only H. pylori has the urease trick that lets it live where the pH is close to 1. It is worth keeping the proportions honest: infection is common and disease is not. Most people carrying H. pylori never develop symptoms, with a risk of peptic ulcer usually put at roughly one in ten, and the organism is also the main driver of gastric cancer, associated with a large majority of cases.

• Helicobacter pylori is a spiral gram-negative bacterium that colonises the mucus layer of the human stomach.
• It survives the acid by secreting urease, which splits urea into ammonia and bicarbonate and neutralises the microenvironment around the cell.
• Barry Marshall and Robin Warren were awarded the 2005 Nobel Prize in Physiology or Medicine for discovering the bacterium and its role in gastritis and ulcer disease.
• Most carriers stay symptom-free; the risk of developing a peptic ulcer is of the order of ten to twenty per cent.
• The other main cause of peptic ulcer is prolonged use of non-steroidal anti-inflammatory drugs, which strip the mucosal defence.

• Falling back on the folklore that ulcers are caused by stress or spicy food alone.
• Mixing up Salmonella typhimurium (food poisoning) with Salmonella typhi (typhoid).
• Assuming that carrying H. pylori means having an ulcer — most carriers never develop one.

As a pathogen-to-disease match, or as a Nobel Prize item on Marshall and Warren, or inside a list asking which diseases are bacterial.

• practice — not a real PYQ

  Helicobacter pylori survives the acidity of the human stomach chiefly by producing which enzyme?

  • (a)Amylase
  • (b)Urease
  • (c)Lipase
  • (d)Catalase

  Answer(b) Urease — it splits urea into ammonia and bicarbonate, neutralising the acid in the bacterium's immediate surroundings.

• practice — not a real PYQ

  Which one of the following diseases is caused by a bacterium?

  • (a)Dengue
  • (b)Typhoid
  • (c)Malaria
  • (d)Influenza

  Answer(b) Typhoid — caused by Salmonella typhi. Dengue and influenza are viral and malaria is caused by a protozoan, Plasmodium.