Antimicrobial resistance among Escherichia coli strains isolated from healthy and septicemic chickens.

There is a clear association between heavy antimicrobial consumption in poultry industry and the recovery of resistant bacteria. This was a case-control study of 396 E. coli strains isolated from clinically affected broiler chickens and 132 strains from healthy controls to compare the antimicrobial resistance rates. Antimicrobial resistance testing of 525 avian E. coli strains isolated in Kashan-Iran showed very high levels of resistance to 11 antimicrobials tested, especially to trimethoprim-sulfamethoxazole (98.7%) and to ciprofloxacin (69.7%). The prevalence rate of resistant E. coli to ciprofloxacin and erythromycin in the samples isolated from chickens with colibacillosis was significantly higher than healthy controls. In addition, to prevent the emergence of cross-resistance with human enteric pathogens, controlled use of these antimicrobial agents in veterinary practice is recommended.

Increasing resistant coagulase negative staphylococci in bovine clinical mastitis.

The aim of this study was to determine Coagulase Negative Staphylococci (CNS) and other bacteria for their resistance to antimicrobial agents approved for the control of pathogens involved in clinical bovine mastitis. This descriptive study was done on 106 milk samples obtained from clinical mastitis in dairy cattle husbandry from April 2006 through August 2006 in Kashan, Iran. From the total of 106 milk samples collected from clinical mastitis, 96 (90.6%) lead to positive culture. Coagulase negative Staphylococci isolated in 51 out of 96 samples (53.1%), Staphylococcus aureus isolated in 21 out of 96 (21.9%), gram negative bacilli isolated in 14 out of 96 (14.6%) and Enterococci isolated in 4 (4.2%). The highest rate of resistant CNS observed to penicillin (56.6%) and the highest rate of sensitivity to enrofloxacin 100%, followed by kanamycin, streptomycin and neomycin, 92.2, 82.3 and 82.3%, respectively. The highest rate of resistance S. aureus exhibited to penicillin (66.6%); while the highest rate of sensitivity showed to trimethoprim-sulphamethoxasole (81%), followed by kanamycin and enrofloxacin both at 76.2%. The highest rate of resistance gram negative bacilli exhibited to ampicillin and erythromycin at 71.4%. Their highest rate of sensitivity observed to enrofloxacin (78.6%), followed by kanamycin, (71.4%). In recent years, CNS is emerging as important minor mastitis pathogens and can be the cause of substantial economic losses. The high resistance rate to penicillin and other antibiotics found in this study emphasize the importance of identification of CNS when a bovine clinical mastitis is present.