Final answer:
The correct cause of a gastric ulcer among the provided options is Helicobacter pylori, a bacterium that survives in the stomach's acidic conditions and can lead to gastritis, ulcers, and increased stomach cancer risk.
Step-by-step explanation:
Among the options provided for the cause of a gastric ulcer, Helicobacter pylori is the correct answer. Helicobacter pylori is a gram-negative bacterium that thrives in the acidic environment of the human stomach. It is identified as the primary cause of peptic ulcers in the stomach or duodenum. This bacterium can withstand stomach acidity by producing urease, which leads to the creation of ammonia that neutralizes the acidity. Chronic infection by H. pylori can lead to chronic gastritis, which can progress to ulcers and even increase the risk of stomach cancer.
Other organisms listed, such as Escherichia coli (E. coli), Streptococcus pyogenes, Staphylococcus aureus, and Vibrio cholerae, are associated with different types of infections or diseases. It is essential to note that alongside H. pylori infection, excessive use of non-steroidal anti-inflammatory drugs (NSAIDs) can also contribute to the development of peptic ulcers.