A Nice Cup of Tea to Eliminate MRSA?
ABSTRACT & COMMENTARY
Synopsis: An extract of green tea restored the activity of methicillin against MRSA and also reversed, to some extent, penicillin resistance in penicillinase producers.
Source: Yam TS, et al. The effect of a component of tea (Camellia sinensis) on methicillin resistance, PBP 2 synthesis, and ß-lactamase production in Staphylococcus aureus. J Antimicrob Chemother 1998;42:211-216.
The inhibitory activity of the aqueous extracts of various Indian and Chinese black teas and green teas against Staphylococcus aureus was shown by Yam and associates to be of three different types. The first, called Activity I, is direct inhibition, the second, Activity II, shows synergy with methicillin against methicillin-resistant Staphylococcus aureus (MRSA), and the third, Activity III, appears synergistic with benzylpenicillin against ß-lactamase producing S. aureus.
Yam et al made a 2% extract of Japanese Sencha green tea in boiling water and called it "Extract T." This had to be further diluted at least 20 times before it lost its inhibitory effect. They then exposed 22 strains of S. aureus showing high-level resistance to methicillin (MIC > 256 mg/L) and 18 strains exhibiting low-level resistance to methicillin (MIC 32-128 mg/L) to a range of different two-fold concentrations of the drug from. The concentrates tested ranged from 1-1024 mg/L mixed with 40-, 70-, 100-, 200-, and 300-fold dilutions of extract T in a checkerboard fashion to ensure that every combination of drug and tea concentration was present. Similar experiments were done with extract T and benzylpenicillin by exposing 40 strains of MRSA and nine strains of methicillin-susceptible S. aureus, all of which produced ß-lactamase.
Synergy between methicillin and extract T occurred with the 70-100 fold dilutions of tea extract and was optimal when diluted 40 times, with methicillin-resistance being reversed for 20/22 (91%) and 17/18 (94%) (i.e., 93% of high and low-level MRSA alike). By contrast, synergy was only seen against eight ß-lactamase producing strains out of the 49 tested.
In a separate experiment, a 250-fold dilution of extract T almost completely inhibited synthesis of PBP-2 by a constitutive producer (i.e., one that produces the protein all the time) and thwarted its production by an inducible strain.
Further purification yielded the active principle, compound P, which retained both activity II and III against MRSA and methicillin-resistant S. epidermidis at concentrations of 1-3 mg/L. Yam et al suggested that the purified tea extract is able to inhibit the production both of PBP-2, the protein that is responsible for methicillin-resistance and ß-lactamase, by preventing the switching on of the genes mecA and bla+, which are close to one another and share the same induction system.
COMMENT BY J. PETER DONNELLY, PhD
Both tea-tree oils and tea inhibit growth of staphylococci directly, but only the latter has been shown to reverse methicillin-resistance. Yam et al point out that other compounds also have the same effect, including non-ionic detergents, naphthalene derivatives, and some peptides, but the chances are that these may well prove too toxic for use in humans and will probably never be acceptable. Tea, on the other hand, is one of the most popular beverages in the world and is consumed by millions of people every day without any obvious ill-effects. It would be interesting to know whether tea drinking has ever been linked to low carriage of MRSA, as this would indicate the potential of using tea to help control carriage. If this were so, how should we use this extract? Must we first wait for a company to provide pharmaceutical preparation, or could we ask carriers of MRSA now to simply rub cold tea onto their skin? Alternatively, we might be able to allow these carriers to simply imbibe the tea in the usual fashion if the active substance is shown to find its way into the sweat, just as certain antibiotics such as ciprofloxacin do. How IRBs and ethics committees would react to a proposal to test an extract of tea in a randomized clinical trial is anybody's guess, but they may react favorably if MRSA is endemic in their own hospital. It would be really something if the observations in-vitro confirmed that methicillin-resistance can, in fact, be reversed. Not least because we may likely see the slogan "A cup a day keeps the MRSA away" alongside the injunction to "Now wash your hands"?