Nonspecific resistance of Serratia marcescens against antimicrobial drugs. Resistance or decreased susceptibility of phenotypic variants against chloramphenicol, nalidixic acid, nitrofurantoin, sulfonamides and trimethoprim.

Several clinical isolates and O-antigen reference strains of Serratia marcescens were shown to yield spontaneously phenotypic variants with nonspecific, combined resistance or decreased susceptibility for chloramphenicol, nalidixic acid, nitrofurantoin, sulfonamides, and trimethoprim, including cotrimoxazole. Additional presumptive evidence indicated that this resistance phenomenon is not mediated extrachromosomally, but rather chromosomally. The nature of this novel resistance mechanism remains to be elucidated.