Epidemiological clues that may help in narrow- ing empirical antibiotic coverage for patients diagnosed with CNE are contained in Table 9.) Recommendations 1. When pediatric patients have suspected endocardi- tis and have been treated with antibiotic drugs <4 days but have not had a prior blood culture, cessa- tion of antibiotic drugs can be useful to clarify the pathogen s identity (Class IIa; Level of Evidence C) and may be considered if the patient is clinically stable (Class IIb; Level of Evidence C). In such cases, consultation with the infectious disease specialist should be obtained. 2. Consultation with the director of the microbiol- ogy laboratory or an infectious diseases expert in all cases of CNE is recommended to optimize the chance of identification of the causative microorgan- ism (Class I; Level of Evidence C). Other Microbiological Tests Testing for antimicrobial susceptibility with determination of the minimum inhibitory concentration (MIC) of the antibi- otic for the organism is recommended in choosing the opti- mal therapy for IE. Although not routinely recommended, determination of the minimum bactericidal concentration of the antimicrobial agent chosen for treatment against the infecting organism may be considered in selected circum- stances, such as with atypical organisms, organisms resis- tant to first-line antibiotic drugs, and unexplained failure to control bacteremia. Synergy studies, with a -lactam agent and an aminoglycoside, although not always available and somewhat controversial, may be reasonable in determining optimal therapy of enterococcal or penicillin-nonsusceptible streptococcal IE. However, existence of an isolate resistant to a high level of aminoglycosides indicates a lack of potential for synergy. Recommendations 1. Testing for antimicrobial susceptibility with deter- mination of the MIC of the antibiotic drug for the organism is recommended in choosing the optimal therapy for IE (Class I; Level of Evidence B). 2. 