Ch. 23 - Microbial Diseases of the Cardiovascular and Lymphatic Systems

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 23 - Microbial Diseases of the Cardiovascular and Lymphatic Systems

Problem 7

Chapter 23, Problem 7

Use the following choices to answer the question given below:
a. Brucellosis
b. Malaria
c. Relapsing fever
d. Rocky Mountain spotted fever
e. Ebola
The patient’s fever spikes each evening. Oxidase-positive, gram-negative coccobacilli were isolated from a lesion on his arm. What is your diagnosis?

Verified step by step guidance

Step 1: Analyze the clinical symptom described — the patient's fever spikes each evening. This pattern is characteristic of certain infectious diseases, particularly those with cyclical fever patterns.

Step 2: Consider the microbiological characteristics of the isolated organism: it is oxidase-positive, gram-negative coccobacilli. This information helps narrow down the possible pathogens.

Step 3: Review the list of diseases and their typical causative agents: for example, Brucellosis is caused by Brucella species (oxidase-positive, gram-negative coccobacilli), malaria is caused by Plasmodium (a protozoan, not bacteria), relapsing fever is caused by Borrelia (spirochetes, not coccobacilli), Rocky Mountain spotted fever is caused by Rickettsia (gram-negative coccobacilli but oxidase-negative), and Ebola is a virus.

Step 4: Match the clinical presentation (fever spikes each evening) and microbiological data (oxidase-positive, gram-negative coccobacilli) to the most likely diagnosis from the given options.

Step 5: Conclude that the diagnosis corresponds to the disease caused by the organism matching both the clinical and microbiological features.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Clinical Presentation of Relapsing Fever

Relapsing fever is characterized by recurring episodes of fever that typically spike and then subside, often in a cyclical pattern such as daily or every few days. Recognizing this pattern helps differentiate it from other febrile illnesses. The fever spikes each evening in this case suggest a relapsing pattern typical of relapsing fever.

Gram-negative Coccobacilli and Oxidase Test

Gram-negative coccobacilli are short, rod-shaped bacteria that stain pink in Gram staining. The oxidase test detects the presence of cytochrome c oxidase enzyme; a positive result indicates certain bacterial groups. Identifying oxidase-positive, gram-negative coccobacilli narrows down the possible pathogens causing the infection.

Differential Diagnosis of Vector-borne Febrile Illnesses

Diseases like brucellosis, malaria, relapsing fever, Rocky Mountain spotted fever, and Ebola have distinct clinical and microbiological features. Understanding their vectors, symptoms, and laboratory findings is essential for accurate diagnosis. For example, relapsing fever is caused by Borrelia species, which are spirochetes, not coccobacilli, so the microbiological findings must be carefully correlated with clinical signs.

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