Frequently used therapeutic antimicrobials and their resistance patterns on <i>Staphylococcus aureus</i> and <i>Escherichia coli</i> in mastitis affected lactating cows

Abstract

Mastitis is one of the most frequent and costly production diseases of dairy cattle. It is frequently treated with broad-spectrum antimicrobials. The objectives of this work were to investigate the prevalence of <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>, find out the antimicrobials used in mastitis treatment, and explore the antimicrobial resistance profile including detection of resistance genes. Bacterial species and antimicrobial resistance genes were confirmed by the polymerase-chain reaction. A total of 450 cows were screened, where 23 (5.11%) and 173 (38.44%) were affected with clinical and sub-clinical mastitis, respectively. The prevalence of <i>S. aureus</i> was 39.13% (n = 9) and 47.97%(n = 83) while, <i>E. coli</i> was 30.43% (n = 7) and 15.60% (n = 27) in clinical and sub-clinical mastitis affected cows, respectively. The highest antimicrobials used for mastitis treatment were ciprofloxacin (83.34%), amoxycillin (80%) and ceftriaxone (76.67%). More than, 70% of <i>S. aureus</i> showed resistance against ampicillin, oxacillin, and tetracycline and more than 60% of <i>E. coli</i> exhibited resistance against oxacillin and sulfamethoxazole-trimethoprim. Selected antimicrobial resistance genes (<i>mec</i>A, <i>tet</i>K, <i>tet</i>L, <i>tet</i>M, <i>tet</i>A, <i>tet</i>B, <i>tet</i>C, <i>sul</i>1, <i>sul</i>2 and <i>sul</i>3) were identified from <i>S. aureus</i> and <i>E. coli</i>. Surprisingly, 7 (7.61%) <i>S. aureus</i> carried the <i>mec</i>A gene and were confirmed as methicillin-resistant <i>S. aureus</i> (MRSA). The most prevalent resistance genes were <i>tet</i>K 18 (19.57%) and <i>tet</i>L 13 (14.13%) for <i>S. aureus</i>, whereas <i>sul</i>1 16 (47.06%), <i>tet</i>A 12 (35.29%), <i>sul</i>2 11 (32.35%) and <i>tet</i>B 7 (20.59%) were the most common resistance genes in <i>E. coli</i>. Indiscriminate use of antimicrobials and the presence of multidrug-resistant bacteria suggest a potential threat to public health.