This, however, has been challenged by retrospectively col- lected data from 2 different medical centers116,117 that sug- gest that 2 weeks of antibiotic therapy may be sufficient in patients who undergo valve surgery and have negative valve tissue cultures, particularly in IE cases caused by VGS or Streptococcus gallolyticus (bovis). Whether a 2-week treatment course would be sufficient after valve sur- gery in patients with positive valve cultures either was not or included only 5 patients in the Histopathological evidence of bacteria with valve tissue Gram staining in patients with negative tissue cul- tures can represent killed organisms and is not a factor in defining the length of therapy after valve surgery.110 For patients with NVE who undergo valve resection with prosthetic valve replacement or repair with an annuloplasty ring, there is a lack of consensus as to whether the postopera- tive treatment regimen should be one that is recommended for prosthetic valve treatment rather than one that is recommended Baddour et al Infective Endocarditis in Adults 1445 for native valve treatment. In regimens that contain combi- nation antimicrobial therapy, it is reasonable to administer agents at the same time or temporally close together to maxi- mize the synergistic killing effect on an infecting pathogen. Recommendations 1. Infectious diseases consultation should be obtained to define an optimal empirical treatment regimen at the time of initiation of antimicrobial therapy (Class I; Level of Evidence B). 2. It is reasonable that the counting of days for the duration of antimicrobial therapy begin on the first day on which blood cultures are negative in cases in which blood cultures were initially positive (Class IIa; Level of Evidence C). 3. 