A survey of antimicrobial resistance in Salmonellae isolated from animals in England and Wales during 1984-1987.

Resistance to 14 antimicrobial substances was tested in 18,647 salmonella strains isolated from animals, their environment and from animal feeds during the period 1984-1987. Of the 2284 Salmonella dublin strains the percentage sensitive to all the antimicrobial substances ranged from 18.1 to 26.8. Resistance to the higher concentration of streptomycin (S25) ranged from 1.9 to 6.4%, whereas the corresponding figures when the lower concentration (S10) was used were 32.3 and 63.8%. Resistance to the higher sulphonamide concentration (Su500) never exceeded 3.3%, although in 1987 70.3% of strains showed resistance to the lower concentration. In general, less than 1% of strains showed resistance to the other antibacterial substances. No strains resistant to amikacin (AK), apramycin (Apr), gentamicin (CN) and colistin (CT) were detected. Of the 8677 S. typhimurium strains the percentage sensitive to all the antimicrobial agents ranged from 6.6 in 1985 to 13.6 in 1987. Resistance to tetracycline (T), ampicillin (PN), trimethoprim (TM) and chloramphenicol (C) ranged from 36.5 to 58.8%, the highest percentages being detected with tetracyclines. Less than 1% of strains showed resistance to furazolidone and none was resistant to amikacin and colistin. Resistance to apramycin ranged from 3.1% in 1984 to 11.6% in 1985; the figures for gentamicin were approximately half that of apramycin. In 1984, 41.6% of strains showed resistance to neomycin but only 8.5% in 1987. The fall in neomycin resistance was associated with the epidemic spread of the commonest phage-type DT204C becoming sensitive to neomycin. Of the 7687 strains of serotypes other than S. typhimurium and S. dublin the percentage sensitive to all antimicrobial agents ranged from 23.7 in 1985 to 14.7 in 1987. Resistance to tetracyclines and sulphonamides (Su500) ranged from 5.2 to 12.1% and 5.8 to 13.3% respectively. Resistance to the other antimicrobial agents was usually less than 5%.