Antibiotic antibiotic therapy. The antibiotic treatment may select for bacterial strains with physiologically or genetically enhanced capacity to survive high doses of antibiotics. Under certain conditions, it may result in preferential growth of resistant bacteria, while growth of susceptible bacteria is inhibited by the drug. For example, antibacterial selection for strains having previously acquired antibacterial-resistance genes was demonstrated in 1943 by the Luria–Delbrück experiment. Antibiotics such as penicillin and erythromycin, which used to have a high efficacy against many bacterial species and strains, have become less effective, due to the increased resistance of many bacterial strains. Resistance may take the form
Discovered attack referred to as a "discovered attack" (or "check") "with capture". When the moving piece moves to a square from which it threatens to inflict checkmate on the next move, the tactic is called a "discovered attack with mate threat". A "discovered checkmate" itself is also possible. In exceptional circumstances, it is possible for the moved piece to give a "double discovered check" (though this name is not actually used). The only way for this to happen in orthodox chess is by way of an "en passant" capture. In the position shown at right, Black has just played 1...g7–g5. White replies