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Binding to cell surfaces through filamentous outer membrane appendages
9%
108/1142
Greater influx of white blood cells into the joint
44%
501/1142
Induction of Interleukin-1 (IL-1) inhibitors by S aureus
11%
122/1142
Possession of endotoxin activity
33%
380/1142
Lower sensitivity to penicillins
1%
16/1142
Select Answer to see Preferred Response
This patient's history and clinical examination is concerning for septic arthropathy. In addition to a positive culture following aspiration, S aureus typically induces a much greater white blood cell influx than does N gonorrhoeae, >50,000 cells/mm3. Septic Arthritis is the inflammation of the joints secondary to an infectious etiology, most commonly affecting the knee, hip, and shoulder. Diagnosis is made with an aspiration of joint fluid with a WBC count >50,000, high polymorphonuclear leukocytes (PMNs), and a positive culture; lower counts may still indicate infection in the presence of positive gram stains or cultures results. N gonorrhoeae and S aureus are common organisms causing septic arthropathy in young, healthy adults. Both organisms induce IL-1 production and possess endotoxin activity that contributes to joint damage. Stutz et al. retrospectively reviewed patients with septic arthritis that were treated with a combination of arthroscopic irrigation, debridement, and antibiotic therapy according to the tested bacterial sensitivity. They report that in 78% of the infected joints the causative organism could be identified: Staphylococcus aureus was the most common organism found (42%), followed by streptococci (15%), pneumococci (6%), Escherichia coli (4%), Staphylococcus epidermidis (3%), Borrelia burgdorferi (3%), and others in 5%. They concluded that the combination of arthroscopic irrigation and systemic antibiotic therapy was able to cure 91% of the affected joints. Horowitz et al. reviewed the diagnosis and treatment of infectious arthritis. They reported that synovial fluid WBC in most patients with septic arthritis is >50,000. They concluded that septic arthritis is caused by nongonococcal pathogens (most commonly Staphylococcus species) in >80% of patients. Incorrect Answers: Answer 1: N gonorrhoeae binds to cell surfaces through filamentous outer membrane appendages, whereas S aureus uses microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) Answers 3&4: Both N gonorrhoeae and S aureus induce IL-1 production and possess endotoxin activity that contributes to joint damage Answer 5: An increase in the resistance of N gonorrhoeae to numerous antimicrobials, including penicillin, has been observed
2.3
(4)
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