The antimicrobial activity of plant extracts was evaluated with antibiotic susceptible and resistant microorganisms. Extracts from the following plants were utilized: Ocimum basilucum (basil), Psidium guajava (guava), Punica granatum (pomegranate), Syzygium cumini (jambolan). The highest antimicrobial potentials were observed for the extracts of clove, jambolan and pomegranate, which inhibited the multidrug resistant P. aeruginosa. The results obtained with P. aeruginosa were particularly interesting, since it was inhibited by jambolan and pomegranate extracts.

Even though pharmacological industries have produced a number of new antibiotics in the last three decades, resistance to these drugs by microorganisms has increased. Approximately, 20% of the plants found in the world have been submitted to pharmaceutical or biological test and a sustainable number of new antibiotics introduced in the market are obtained from natural or semisynthetic resources. It has been reported that between the years 1983 and 1994 (Cragg et al., 1999), the systematic screening of antibacterial plant extracts represents a continuous effort to find new compounds with the potential to act against multiresistant bacteria. According to World Health Organization (Santos et al., 1995), medicinal plants would be the best source to obtain a variety of drugs. In general, bacteria have the genetic ability to transmit and acquire resistance to drugs, which are utilized as therapeutic agents (Cohen, 1992). Such a fact is a cause for concern, because of the number of patients in hospitals who have suppressed immunity and due to new bacterial strains which are multiresistant.

The problem of microbial resistance is growing, and the outlook for the use of antimicrobial drugs in the future is still uncertain. Therefore, actions must be taken to reduce this problem, for example, to control the use of antibiotic, perform research to better understand the genetic mechanisms of resistance, and continue studies to develop new drugs, either synthetic or natural. The ultimate goal is to offer appropriate and efficient antimicrobial drugs to the patient.

For a long period of time, plants have been a valuable source of natural products for maintaining human health, especially in the last decade with more intensive studies for natural therapies.

Biotechnology Journal, Stress Adaptation of Bacteria, Extremophiles, Bacterial Adaptation, Cytosolic Components, Denature Cellular Proteins, Reactive Oxygen Species, Monounsaturated Fatty Acids, Ultraviolet Radiation, Environmental Stress, Stress Management, Biological Systems, Cellular Economy.