Antimicrobial susceptibility of mastitis pathogens from first lactation and older cows

• Published in: Veterinary microbiology 2004-08, Vol.102 (1), p.33-42
• Main Authors: Rajala-Schultz, P.J, Smith, K.L, Hogan, J.S, Love, B.C
• Format: Article
• Language: English
• Subjects: animal age; animal pathogenic bacteria; Animals; Anti-Bacterial Agents - pharmacology; antibiotic resistance; Antimicrobial resistance; Biological and medical sciences; bovine mastitis; calving; Cattle; Coagulase-negative staphylococci; dairy cows; Drug Resistance, Bacterial; Female; Fundamental and applied biological sciences. Psychology; Inhibitory Concentration 50; Intramammary infection; Lactation; lactation number; Mastitis, Bovine - drug therapy; Mastitis, Bovine - microbiology; Microbial Sensitivity Tests - veterinary; Microbiology; Milk - microbiology; minimum inhibitory concentration; Parity; penicillins; Staphylococcal Infections - drug therapy; Staphylococcal Infections - microbiology; Staphylococcal Infections - veterinary; Staphylococcus; Staphylococcus - drug effects; Staphylococcus - isolation & purification; Staphylococcus aureus; Staphylococcus epidermidis; Staphylococcus hyicus; Staphylococcus simulans; Streptococcus; tetracycline; udder quarters
• ISSN: 0378-1135; 1873-2542
• DOI: 10.1016/j.vetmic.2004.04.010

Increasing antimicrobial resistance has become a serious concern worldwide and antimicrobial use in animal agriculture is currently under scrutiny. Mastitis is the most common reason for antibiotic use in dairy herds and thus, antimicrobial resistance of mastitis pathogens has received recent attention. The purpose of this study was to describe and compare antimicrobial susceptibility of mastitis pathogens isolated at calving from first lactation and older cows. A total of 202 bacteria were isolated from intramammary infections (IMIs) within 3 days after calving over a 16-month study period in the Krauss Dairy Research Herd at the Ohio Agricultural Research and Development Center (OARDC) in Wooster, OH. Of these IMIs, 78% were caused by coagulase-negative staphylococci (CNS). Forty-four percent of them were resistant to at least one antibiotic. Most resistance was observed against penicillin, 39% of the isolates from older cows and 26% from first lactation cows being resistant to penicillin ( P > 0.05). Also MIC 90 for penicillin was higher among isolates from older cows. On the other hand, resistance to tetracycline was more common and MIC 90 higher among isolates from first lactation cows than from older cows. Differences in the proportions of resistant isolates between first lactation and older cows were not statistically significant, though. The resistance patterns of the CNS isolated during the study are concordant with antimicrobial usage in the study herd. This is in agreement with the generally accepted notion that selection pressure from the use of antibiotics is a main factor in development of antibiotic resistance.