<s>[INST] context: An understanding of normal, or indigenous, microflora is essential in order to appreciate the abnormal. Usually, anatomic sites contiguous to mucous membranes are not sterile and have characteristic normal flora.The skin flora differs as a function of location. Skin adjacent to mucous membranes may share some of the normal flora of the GI system. Overall, the predominant bacteria on the skin surface are S. epidermidis and Propionibacterium, an anaerobic diphtheroid.The mouth is part of the GI tract, but its indigenous flora shows some distinct differences. While anaerobes are present in large numbers, particularly in the gingival crevice, the eruption of teeth at 6 to 9 months of age leads to colonization by organisms such as S. mutans and Streptococcus sanguis, both a-hemolytic streptococci. An edentulous person loses b-hemolytic streptococci as normal flora.The GI tract is sterile at birth and soon develops characteristic flora as a function of diet. In the adult, anaerobes such as B. fragilis and Bifidobacterium may outnumber coliforms and enterococci by a ratio of 1000:1. The colon contains 1011 to 1012 bacteria per gram of feces.Soon after birth, the vagina becomes colonized by lactobacilli. As the female matures, lactobacilli may still be predominant, but anaerobic cocci, diphtheroid, and anaerobic, gram-negative rods also are found as part of the indigenous flora. Changes in the chemical or microbiologic ecology of the vagina can have marked effects on normal flora and may promote infection such as vaginitis or vaginosis.Escherichia coli are among the most common group of gram-negative rods isolated in the laboratory. It is fairly easily identified in the laboratory. It ferments mannitol and is lactose positive. The organism is part of normal body flora but is a very efficient opportunist. Urinary tract infections are commonly caused with this organism. [/INST] question: A healthy 45-year-old female had root canal treatment about 3 weeks ago. She now presents with a new heart murmur, fever, painful skin nodules, abdominal pain, and an abnormal liver function test. Which of the following organisms would mostly likely cause endocarditis and is implicated in dental caries or root canal infections? | options: A: a-Hemolytic streptococci B: Bacteroides fragilis C: Escherichia coli D: Lactobacillus species | answer: A </s>