Although I have often reference this, I just realized that I have not done up a post on it. From PubMed, we have the following information:
- “The oils [of Tulsi], at concentrations of 4.5 and 2.25% completely inhibited the growth of Staphylococcus aureus(including MRSA) and Escherichia coli, while the same concentrations only partly inhibited the growth of Pseudomonas aeruginosa…Tulsi essential oil could be a valuable topical antimicrobial agent for management of skin infections caused by these organisms.” 
- “At 3mg. concentration, O.sanctum was the most effective against S. mutans,” 
- “Moreover, water extracts did not restrain the growth of any tested bacteria. Ethanol and methanol extracts were found to be more potent being capable of exerting significant inhibitory activities against majority of the bacteria investigated. Staphylococcus aureus 1 was the most inhibited bacterial isolate with 24 extracts (60%) inhibiting its growth whereas Escherichia coli 2 exhibited strong resistance being inhibited by only 11 extracts (28%).” 
- Amelioration of inflammation by phenolic rich methanolic extract of Ocimum sanctum Linn. leaves in isoproterenol induced myocardial infarction.
- Therapeutic Potential of Ocimum tenuiflorum as MPO Inhibitor with Implications for Atherosclerosis Prevention .
- Anti-Inflammatory, gastrointestinal and hepatoprotective effects of Ocimum sanctum Linn: an ancient remedy with new application . “In modern era, it has been shown to be effective against diabetes mellitus, hypertension, cancers, bronchitis, and found to have anti-microbial properties. Several experimental studies have confirmed its anti-inflammatory properties and its role in modulation of both cellular and humeral immunity. Recently its efficacy against inflammatory response, hepatic injury and gastric ulcer has been elucidated in animal studies. In liver, essential oils and extracts of Ocimum sanctum could prevent oxidative stress by increasing glutathione peroxidae and catalase and were also effective in prevention of hepatic steatosis. In gastric epithelial tissue different derivatives of Ocimum sanctum had anti-ulcer and anti-secretory characteristics and could heal gastric ulceration.”
- “antimicrobial activity of herbal medicines (neem extract, tulsi extract) and chlorhexidine against Enterococcus faecalis in Endodontics…Herbal medicines seemed to be effective against E. faecalis compared to 2% chlorhexidine gluconate.” 
- “For tulsi oil-fed mice, the decrease in bacterial load was significant with long-term feeding (p < 0.01).” 
- Ocimum sanctum essential oil inhibits virulence attributes in Candida albicans .
- “The results obtained were compared with standard drugs Amoxicillin (10μg) and Amphotericin B(10μg).” 
- Activity of Ocimum sanctum (the traditional Indian medicinal plant) against the enteric pathogens . “Aqueous extract showed wider zones of inhibition for Klebisella, E. Coil, Proteus & Staphylococcus aureus.”
- “The extracts from the leaves of Ocimum sanctum showed better activity against the three MRSA strains.” 
- “Ocimum sanctum fixed oil showed good antibacterial activity against Staphylococcus aureus, Bacillus pumilus and Pseudomonas aeruginosa, where S. aureus was the most sensitive organism.” 
- “This finding reflects that supplementation of O.sanctum intuitively by reasonable and understandable treatment effectively ameliorates the cerebral ischemia-induced oxidative damage.” 
- “The results of the study indicate an immunostimulant capability for Ocimum sanctum which may be contributory in explaining the adaptogenic action of the plant.” 
It is an effective antibiotic especially against S. Aureus. While it does inhibit E.Coli, I believe the trade off is a net beneficial one.