Which one of the following is a Gram negative coccus?
Correct Answer B:
Classification of bacteria:
Remember:
Therefore, only a small list of Gram positive rods (bacilli) need to be memorized to categorize all bacteria - mnemonic = ABCD L:
Remaining organisms are Gram negative rods.
A man presents with severe vomiting. He reports not being able to keep fluids down for the past 12 hours. You suspect a diagnosis of gastroenteritis and on discussing possible causes he mentions reheating curry with rice the night before.
What is the most likely causative organism?
Correct Answer E: Bacillus cereus infection most commonly results from reheated rice.
Gastroenteritis: Gastroenteritis may either occur whilst at home or whilst travelling abroad (travellers' diarrhoea) Travellers' diarrhoea may be defined as at least 3 loose to watery stools in 24 hours with or without one of more of abdominal cramps, fever, nausea, vomiting or blood in the stool. The most common cause is Escherichia coli.
Another pattern of illness is 'acute food poisoning'. This describes the sudden onset of nausea, vomiting and diarrhoea after the ingestion of a toxin. Acute food poisoning is typically caused by Staphylococcus aureus, Bacillus cereus or Clostridium perfringens.
Stereotypical histories:
Incubation period:
*Vomiting subtype, the diarrhoeal illness has an incubation period of 6-14 hours.
A patient with HIV is reviewed. Which one of the following is an example of a nucleoside analogue reverse transcriptase inhibitors?
Correct Answer A: Zidovudine (AZT) was one of the first HIV drugs and remains important today.
HIV drugs, rule of thumb:
HIV: anti-retrovirals: Highly active anti-retroviral therapy (HAART) involves a combination of at least three drugs, typically two nucleoside reverse transcriptase inhibitors (NRTI) and either a protease inhibitor (PI) or a nonnucleoside reverse transcriptase inhibitor (NNRTI). This combination both decreases viral replication but also reduces the risk of viral resistance emerging.
Nucleoside analogue reverse transcriptase inhibitors (NRTI):
Non-nucleoside reverse transcriptase inhibitors (NNRTI):
Protease inhibitors (PI):
A 17-year-old girl presents with a sore throat. On examination she has inflamed tonsils covered in white patches. Tender cervical lymphadenopathy and a low grade pyrexia are also present.
Which one of the following organisms is most likely to be responsible?
Correct Answer E:
Streptococci: Streptococci are gram-positive cocci. They may be divided into alpha and beta haemolytic types.
Alpha haemolytic streptococci (partial haemolysis): The most important alpha haemolytic Streptococcus is Streptococcus pneumoniae(pneumococcus). Pneumococcus is a common cause of pneumonia, meningitis and otitis media. Another clinical example is Streptococcus viridans.
Beta haemolytic streptococci (complete haemolysis): These can be subdivided into groups A-H. Only groups A, B & D are important in humans.
Group A:
Group B
Group D:
Which of the following anti-retroviral drugs is most characteristically associated with pancreatitis?
Correct Answer B: Ritonavir may cause acute pancreatitis but this is not as common as with didanosine therapy.
HIV: biliary and pancreatic disease: The most common cause of biliary disease in patients with HIV is sclerosing cholangitis due to infections such as CMV, Cryptosporidium and Microsporidia.
Pancreatitis in the context of HIV infection may be secondary to anti-retroviral treatment (especially didanosine) or by opportunistic infections e.g. CMV.
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