Salmonella resistance is on the rise
Salmonella gains resistance to antibiotics by enzymatic hydrolysis of beta-lactams, modification of drug targets (amino acid substitutions in gyrase and other proteins targeted by quinolones), and expression of antibiotic efflux pumps (AcrAB-TolC-type efflux pumps to remove ciprofloxacin). Among typhoidal Salmonella, resistance to traditional first-line antimicrobials ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole is commonly caused by resistance determinants located on plasmids - small DNA molecules separate from chromosomal DNA that can replicate independently and can be shared from one bacteria to another. In the 1970's, chloramphenicol was the treatment of choice, but in 1972 an epidemic was caused by a
chloramphenicol-resistant strain, followed by outbreaks across the globe. The resistance determinant was carried on a self-transmissible plasmid that also carried resistance to other drugs such as streptomycin, sulfonamides, and tetracyclines.