A 1-year-old boy is brought to the emergency department by his mother because of high fever, irritability, and photophobia. He recently underwent ventriculoperitoneal shunt placement for congenital hydrocephalus. On physical examination, his temperature is 38.3° C (101° F), and passive flexion of the neck results in spontaneous flexion of the hips and knees. Blood cultures grow coagulase-negative Staphylococcus. Which of the following is the most important virulence mechanism by which this bacterium causes disease?

Question

A 1-year-old boy is brought to the emergency department by his mother because of high fever, irritability, and photophobia.  He recently underwent ventriculoperitoneal shunt placement for congenital hydrocephalus.  On physical examination, his temperature is 38.3° C (101° F), and passive flexion of the neck results in spontaneous flexion of the hips and knees.  Blood cultures grow coagulase-negative Staphylococcus.  Which of the following is the most important virulence mechanism by which this bacterium causes disease?

Quizplus · Accepted Answer

11ec160b_385c_586c_9249_072f2acd240e_MD0001_00 Staphylococcus epidermidis, a coagulase-negative Staphylococcus species and a component of normal skin flora, is one of the most common causes of infections associated with foreign bodies (including ventriculoperitoneal shunts). S epidermidis is adept at causing foreign body infections because of its ability to form biofilms. Once introduced into the body, foreign bodies quickly become coated with a layer of host proteins, including fibrinogen and fibronectin. These proteins then serve as binding sites for S epidermidis. After attachment occurs, the bacteria multiply and communicate with one another to induce synthesis of an extracellular polysaccharide matrix that encases the bacteria. The resulting biofilm functions as a barrier to antibiotic penetration and interferes with host defenses, including opsonization, neutrophil migration, and even T lymphocyte activation. Once mature, these biofilms can disperse individual pathogen "seeds" (planktonic cells) into the bloodstream and surrounding areas, further disseminating the infection. Definitive treatment of infections caused by biofilm-producing organisms often requires removal of the foreign body. (Choice A) S epidermidis is not an intracellular organism. Examples of obligate intracellular organisms include Chlamydiae and Rickettsiae. Facultative intracellular organisms include Legionella, Listeria, Mycobacterium, Neisseria, and Salmonella. (Choice B) S epidermidis is not an encapsulated bacterium. Examples of encapsulated bacteria are Streptococcus pneumoniae, Haemophilus influenzae type B, and Neisseria meningitidis. Asplenic individuals are unable to opsonize encapsulated pathogens and are at risk of infection from these organisms. (Choice C) Protein A is a surface protein found on the cell wall of Staphylococcus aureus that binds to the Fc region of immunoglobulins. S aureus uses Protein A to inhibit opsonization and phagocytic engulfment. (Choice D) Exotoxin production is not a known pathogenic mechanism of S epidermidis. Examples of well- known exotoxins include staphylococcal enterotoxins (food poisoning), botulinum toxin, diphtheria toxin, tetanus toxin, and pertussis toxin. Educational objective: Staphylococcus epidermidis is a common cause of foreign body infections due to its ability to produce adherent biofilms. __________ References: Biofilms: microbes and disease. (http://www.ncbi.nlm.nih.gov/pubmed/19287843)

A 1-Year-Old Boy Is Brought to the Emergency Department by His