Salmonella

Salmonella enterica serotype Typhi has developed multiple resistance to first-line antibiotics in many developing countries. In the 1970s, strains with plasmid-mediated resistance to ampicillin and chloramphenicol caused epidemics in Latin America. In the 1980s, strains with plasmid-mediated resistance to ampicillin, chloramphenicol and co-trimoxazole emerged in South East Asia and have since become widespread in Asia and Latin America, where rates of 30–70% multiresistant Salmonella Typhi were reported in the 1990s. Fluoroquinolone resistance is now emerging in MDR strains and has been associated with recent outbreaks of typhoid fever in Tajikistan, Vietnam and the Indian subcontinent.
In 1999, soon after the introduction of codes of good practice for the prophylactic use of fluoroquinolones in animal husbandry in the UK, there was a 75% decline in isolations of multiresistant Salmonella ser. Typhimurium DT104 from clinical specimens, which may indicate a favorable impact of more prudent antibiotic use. The extended- spectrum β-lactamases have appeared in some Salmonella strains, possibly as a result of plasmid transfer from commensal enterobacteria in the human gut. ESBL-producing salmonellae caused epidemics in Greece and spread to other European countries in the 1990s. The first case of infection by ceftriaxone-resistant Salmonella reported in the USA was linked to contact with infected cattle treated with cephalosporins on a Nebraska farm.