This antibiotic is routinely used to control S. aureus infections in the body. S. aureus is a species of bacteria commonly found growing on healthy people. It grows on the skin and less commonly, on the upper respiratory tract membranes. S. aureus enters the body through an open wound, or institutionally, through the use of invasive medical techniques and devices. It can also be transmitted from person to person in everyday contact with each other. It can become a serious infection that has the potential to become life-threatening. S. aureus has also been identified as a cause food poisoning because it produces a chemical that is toxic to humans. Strains of Staphylococcus aureus (S. aureus) that are resistant the antibiotic methicillin are identified as methicillin-resistant staphylococcus aureus (MRSA). MRSA does not represent a single strain of S. aureus but refers to a group of strains that exhibit resistance to methicillin.
How MRSA Came About
Historically, S. aureus was treated with penicillin. As the bacteria defended itself against this treatment it adapted by producing an enzyme called penicillinase that breaks the penicillin molecule rendering it ineffective as a bacteriocide. Next physicians turned to methicillin, another antibiotic in the same family as penicillin, to treat S. aureus infections.
Since bacteria reproduce so quickly in such great numbers, mutations that bring about resistance may occur relatively rapidly. When treated with methicillin over time, S. aureus successful mutations resulted in adaptation again leading to a new strain known as methicillin resistant S. aureus, or MRSA. It resists methicillin by the action of a gene called mecA. This gene tells the bacteria’s genetic code to make and use a certain protein to destroy methicillin in a similar fashion as it does penicillin.1
Back to the Drawing Board
Given the ability of S. aureus strains to adapt to various antibiotics, scientists continue to identify alternate ways to control MRSA. This search has been ongoing since at least the 1990’s. Strategies explored include alternate antibiotics which are broader spectrum, meaning they act upon more kinds of microorganisms than only the target. However, this can result in negative effects because our bodies are dependent on certain microorganisms to function properly.
Scientists are also trying to locate new points of vulnerability of MRSA. They are testing combinations of various antibiotics as well as combinations of antibiotics and other substances not traditionally considered antibiotics.
Green Tea
Somewhere along the way, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), two polyphenols that are abundant in green tea (Camellia sinensis) were identified as candidates for treating S. aureus. Chromosomal factors, known as “fem factors” are necessary for S. aureus, to show resistance to methicillin.2 Scientists have identified ECG as a potential inhibitor of these fem factors.3 ECG has also been recognized as a selective growth inhibitor of MRSA because it damages the cell wall of the bacteria. It is only effective when ECG is present in high concentrations.
Carbapenems are a newer class of antibiotics that bind to enzymes required for MRSA cell wall synthesis. Without an intact cell wall, the bacteria cannot survive. When Carbapenems are combined with EGCG the potency of carbapenems is increased. This is true for two carbapenems: panipenem and meropenem.4 Ampicillin and sulbactam are two more antibiotics that are effective against MRSA when given with EGCG in concentrations of 6.25 and 25 mg per liter of EGCG.5
1Methicillin resistance in Staphylococcus aureus mechanisms and modulation. Stapleton, PD and Taylor, PW. Sci Prog. 2002. 85(Pt 1): 57–72.
2 The effect of a component of tea (Camellia sinensis) on methicillin resistance, PBP2′ synthesis, and β-lactamase production in Staphylococcus aureus. Yam, TS; Hamilton-Miller, JMT and Shah S. J. Antimicrob. Chemother. 1998. 42(2):211–216.
3Mapping and Characterization of Multiple Chromosomal Factors Involved in Methicillin Resistance in Staphylococcus aureus. Berger-Bachi, B; Strassle, A; Gustafson, JE and Kayser, FH. Antimicrobial Agents and Chemotherapy. 1992. 36(7): 1367-1373.
4 Epigallocatechin Gallate Synergistically Enhances the Activity of Carbapenems against Methicillin-Resistant Staphylococcus aureus. Zhi-Qing Hu, Wei-Hua Zhao, Nozomi Asano, Yoshiyuki Yoda, Yukihiko Hara, and Tadakatsu Shimamura. Antimicrob Agents Chemother. 2002. 46(2): 558–560.
5Epigallocatechin gallate synergy with ampicillin/sulbactam against 28 clinical isolates of methicillin-resistant Staphylococcus aureus. Hu, ZQ; Zhao, WH; Hara, Y and Shimamura, T. J Antimicrob Chemother. 2001. 48(3):361-4.
