Salmonella [sal′′mo-nel′ә]

Figure

Figure. Drug-resistant, nontyphoidal, Salmonella sp. bacteria showing numerous flagella. Taken from Antibiotic Resistance Threats in the United States, 2019 (AR Threats Report); Centers for Disease Control and Prevention. Illustration: James Archer/...

Named in honor of Daniel Elmer Salmon, an American veterinary pathologist, Salmonella (Figure) is a genus of motile, gram-negative bacillus, nonspore-forming, aerobic to facultatively anaerobic bacteria of the family Enterobacteriaceae. In 1880, Karl Joseph Eberth was the first to observe Salmonella from specimens of patients with typhoid fever (from the Greek typhōdes [like smoke; delirious]), which was formerly called Eberthella typhosa in his tribute. In 1884, Georg Gaffky successfully isolated this bacillus (later described as Salmonella Typhi) from patients with typhoid fever, confirming Eberth’s findings. Shortly afterward, Salmon and his assistant Theobald Smith, an American bacteriologist, isolated Salmonella Choleraesuis from swine, incorrectly assuming that this germ was the causative agent of hog cholera. Later, Joseph Lignières, a French bacteriologist, proposed the genus name Salmonella in recognition of Salmon’s efforts.

With a complicated taxonomy, the genus Salmonella is currently classified into 2 species (S. enterica and S. bongori), encompassing 2,659 serotypes based on somatic O and H flagellar antigens as specified in the Kauffmann–White–Le Minor scheme. S. enterica is divided into 6 subspecies: enterica, salamae, arizonae, diarizonae, houtenae, and indica. Arguably, this zoonotic pathogen remains one of the most pressing global concerns. It causes a spectrum of diseases in several hosts, and there is much to be learned and deciphered about its continuous evolution.