Question

A 55-year-old man was admitted to a local hospital with fever and chills. The patient was human immunodeficiency virus positive and had received multiple courses of antibiotics. Blood cultures grew gram-positive cocci, which tested positive with group D streptococcal antisera. The isolate was resistant to penicillin and vancomycin. Which one of the following is the most likely pathogen? A. Streptococcus pneumoniae B. Enterococcus faecium C. Streptococcus pyogenes D. Streptococcus agalactiae E. Streptococcus mutans

Short answer

B. Enterococcus faecium is the most likely pathogen.

Step-by-step solution

Understanding the Scenario

The patient in the question is diagnosed with HIV and has been treated with multiple courses of antibiotics. This is important because individuals with a weakened immune system from conditions like HIV are more susceptible to different kinds of bacterial infection.

Identifying the Pathogen

The pathogen in question is described as a gram-positive coccus that is group D streptococcal positive. Only certain pathogens have both of these characteristics. It's also necessary to consider the pathogen's resistance to antibiotics, which further narrows down the possibilities.

Comparing with the Provided Options

When we look at the provided choices, only Enterococcus faecium (option B) fits all the criteria. It's a gram-positive, group D streptococcus, and it can be resistant to both penicillin and vancomycin. None of the other options meet all these characteristics.

Key concepts

HIV and Opportunistic Infections

HIV, which stands for Human Immunodeficiency Virus, weakens the immune system by targeting and destroying specific immune cells. This makes individuals more vulnerable to infections that a healthy immune system can typically control. These are called opportunistic infections because they take advantage of the weakened immunity.

People with HIV can be at risk for infections caused by various bacteria, viruses, fungi, and parasites that normally do not cause serious issues in healthy individuals. Some common opportunistic infections include:

• Tuberculosis (TB)
• Pneumocystis pneumonia (PCP)
• Candida infections
• Toxoplasmosis

HIV-positive individuals often require careful monitoring and may receive prophylactic treatments to prevent these types of infections. This becomes especially crucial if their immune system is heavily compromised.

Antibiotic Resistance

Antibiotic resistance occurs when bacteria develop the ability to survive or grow despite the presence of antibiotics meant to inhibit or eliminate them. This is a significant concern in medical communities as it leads to more challenging treatments and increased mortality rates.

Factors contributing to antibiotic resistance include:

• Overuse and misuse of antibiotics
• Incomplete courses of treatment
• Use of broad-spectrum antibiotics when not necessary

When treating individuals with compromised immune systems, such as those with HIV, the issue is more pronounced. Bacteria like Enterococcus faecium have developed resistance to many antibiotics, including penicillin and vancomycin, making infections difficult to treat.

Group D Streptococci

Group D Streptococci refer to a classification that historically included certain types of Streptococcus species and Enterococcus species.

The classification is based on specific antigens found on the bacterial cell wall. These bacteria are typically harmless in the gut but can cause problems if they enter other parts of the body, especially in immunocompromised individuals.

Some key points about group D streptococci include:

• Enterococcus faecium and Enterococcus faecalis are part of this group.
• They can grow in various environments, showcasing their adaptability.
• They often exhibit resistance to multiple antibiotics.

Enterococci are particularly noted for causing hospital-acquired infections and can lead to serious conditions like bloodstream infections or urinary tract infections.

Gram-Positive Cocci

Gram-positive cocci are a category of bacteria characterized by their spherical shape and their ability to retain a purple color in the Gram stain test. This stain's result is due to a thick layer of peptidoglycan in their cell walls.

Some widely known gram-positive cocci include:

• Staphylococcus species
• Streptococcus species
• Enterococcus species

These bacteria can cause various infections, from minor skin conditions to severe illnesses like pneumonia or bacteremia. Because they appear similar under microscopic observation, distinguishing them often requires additional tests such as antibiotic sensitivity or specific antigen detection. This becomes more critical in managing infections in patients with already compromised immune systems such as those with HIV.