After the first year of life, VGS are generally the most frequently isolated organisms in patients with IE caused by underlying congenital heart disease. S aureus was the second most common cause of IE in children but is now the most common cause of IE in some series and is definitely the most common agent of acute (rapidly progressive) bacterial endo- carditis. IE may be caused by organisms that are dependent on l-cysteine or pyridoxal for growth, previously referred to as the nutritionally variant streptococci (Abiotrophia Table 3. Definitions of Terms Used in Modified Duke Criteria for Diagnosis of IE Major criteria 1. Positive blood culture for IE A. Typical microorganism consistent with IE from 2 blood cultures, as noted below (i) Viridans streptococci,* Streptococcus bovis, or HACEK group or (ii) Community-acquired Staphylococcus aureus or enterococci, in the absence of a primary focus or B. Microorganisms consistent with IE from persistently positive blood cultures, defined as: (i) 2 Positive cultures of blood samples drawn >12 h apart or (ii) All of 3 or a majority of 4 blood cultures, irrespective of the timing (iii) 1 Positive blood culture for Coxiella burnetii or antiphase-I immunoglobulin G antibody titer >1:800 2. Evidence of endocardial involvement A. Positive echocardiogram (TEE recommended in prosthetic valves, rated at least possible IE by clinical criteria, or complicated IE; TTE as the first test in other patients) for IE, defined as (i) Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternative anatomic explanation or (ii) Abscess or (iii) New partial dehiscence of prosthetic valve or B. New valvular regurgitation (worsening or changing of preexisting murmur not sufficient) Minor criteria 1. 