Abstract
Antibiotic resistance is increasing at an alarming rate worldwide, in large part due to their misuse and improper disposal. Antibiotics administered to treat human and animal diseases, including feed supplements for the treatment or prevention of disease in farm animals, have contributed greatly to the emergence of a multitude of antibiotic-resistant pathogens. Shewanella is one of many bacteria that have developed antibiotic resistance, and in some species, multiple-antibiotic resistance (MAR). Shewanella is a rod-shaped, Gram-negative, oxidase-positive, and H(2)S-producing bacterium that is naturally found in the marine environment. In humans, Shewanella spp. can cause skin and soft tissue infections, septicemia, cellulitis, osteomyelitis, and ear and wound infections. Some Shewanella have been shown to be resistant to a variety of antibiotics, including beta-lactams, aminoglycoside, quinolones, third- or fourth-generation cephalosporins, and carbapenems, due to the presence of genes such as the bla(OXA)-class D beta-lactamase-encoding gene, bla(AmpC)-class-C beta-lactamase-encoding gene, and the qnr gene. Bacteria can acquire and transmit these genes through different horizontal gene-transmission mechanisms such as transformation, transduction, and conjugation. The genes for antibiotic resistance are present on Shewanella chromosomes and plasmids. Apart from this, heavy metals such as arsenic, mercury, cadmium, and chromium can also increase antibiotic resistance in Shewanella due to co-selection processes such as co-resistance, cross resistance, and co-regulation mechanisms. Antibiotics and drugs enter Shewanella spp. through pores or gates in their cell wall and may be ejected from the bacteria by efflux pumps, which are the first line of bacterial defense against antibiotics. Multiple-drug resistant Shewanella can be particularly difficult to control. This review focuses on the phenotypic and genomic characteristics of Shewanella that are involved in the increase in antimicrobial resistance in this bacterium.