ABSTRACT
Most clinically important resistance to antibiotics is the result of plasmid-encoded genes (Falkow, 1975; Levy and Novick, 1986; Cohen, 1992; Neu, 1992a; Gómez-Lus, 1998). Many bacterial species have become resistant to antibiotics as a result of plasmid exchange by transformation or conjugation. Conjugation with plasmid transfer is a very common phenomenon among the Enterobacteriaceae, Pseudomonas, and some anaerobic species, such as Staphylococcus aureus or Serratia marcescens (Bryan, 1988; Finland, 1979; Neu, 1984; Schaberg et al., 1981). Some examples are the emergence of plasmid-encoded penicillinase-producing Neisseria gonorrhoeae, the plasmid mediated resistance to chloramphenicol of Haemophilus, the plasmid NTP2 of Salmonella typhimurium that encodes for resistance to streptomycin and sulfonamide, and the plasmid mediated resistance to penicillins of Pseudomonas among many other examples.
