Bacterial Infections The only human trials examining the antibacterial properties of pomegranate extracts have focused on oral bacteria. However, several in vitro assays demonstrate its bacteriocidal activity against several highly pathogenic and sometimes antibiotic-resistant organisms. Brazilian researchers evaluated the synergistic effect of a P. granatum methanolic extract with five antibiotics on 30 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus.75 Antibiotics tested were chloramphenicol, gentamicin, ampicillin, tetracycline, and oxacillin. Although synergistic activity between the pomegranate extract and all five antibiotics was noted in the S. aureus isolates, synergy with ampicillin was the most pronounced. Based on earlier research and the results of this study, the ellagitannin, punicalagin, is thought to be the primary constituent responsible for the observed antibacterial effects. Another organism that can cause significant disease in humans is enterohemorrhagic Escherichia coli (E. coli O157:H7). An ethanolic PPE, one of the two most effective extracts against E. coli O157:H7, was shown to be both bacteriostatic and bacteriocidal, indicating PPE may be an effective adjunct treatment for E. coli O157:H7 infection.