Exposure to antibiotics has exerted a selective pressure on bacteria which has resulted in increased resistance to these drugs among bacteria from both animals and humans. This ability evolves through different mechanisms and once one or more resistance genes are generated, bacteria can transfer the genetic information by horizontal transmission of resistance genes between commensal and pathogenic bacteria. Antibiotic resistance is becoming a common problem in many parts of the world due to the fact that antibiotics are used frequently and, sometimes, incorrectly. Other factors that contribute to the spread of the phenomenon include incorrect diagnosis, unnecessary prescriptions, improper use of antibiotics by patients and the use of antibiotics as live stock food additives for growthpromotion.