Antibiotic resistance of Salmonella in Europe and the United States.

Nontyphoid salmonellosis has been said to be a zoonosis; hence, antibiotic resistance in the salmonella serotypes is thought to be derived directly from resistance in the animal reservoir. This thesis seems incorrect for the following reasons: (1) Typhoid and paratyphoidal salmonellae are clearly exceptions to the rule since they are restricted to human hosts. (2) Salmonella isolates involved in food-borne outbreaks disease have not been notable in terms of their antibiotic resistance. (3) In contrast, outbreaks of nosocomial disease, transmitted from person to person and persisting for long periods, have produced and disseminated multiple resistant salmonellae, such as Salmonella wien (another serotype without an animal reservoir) in western Europe. (4) In western Europe and the United States, there are often large differences between the resistance of isolates from animals and that of isolates from humans. (5) In most reported outbreaks of disease caused by antibiotic-resistant Salmonella in humans or animals, the administration of therapeutic concentrations of antibiotics has been implicated. (6) The role of low-concentration, growth-promoting antibiotic feed supplements has been much discussed but never has been delineated or proven. In fact, these supplements probably are totally irrelevant to the development of antibiotic resistance in Salmonella. With regard to Salmonella, there is an exception to every rule; in this case the exception is Salmonella dublin, which in western Europe is a highly antibiotic-resistant serotype in cattle and appears in humans with a similar--and unusual--pattern of resistance.