Antimicrobial Susceptibility of Microorganisms Isolated from the Mammary Glands of Dairy Heifers

Abstract

Minimum inhibitory concentrations were determined with 1494 microorganisms isolated from the mammary glands of dairy heifers. The antimicrobial agents tested were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. All minimum inhibitory concentrations were expressed as micrograms per milliliter. The isolates tested included 135 Staphylococcus aureus, 1222 Staphylococcus sp., 42 Streptococcus sp., 15 Enterococcus sp., 60 enteric species, and 20 miscellaneous organisms. The minimum inhibitory concentrations for 90% of isolates for the various antimicrobial agents with Staph. aureus were as follows: penicillin, .13; cloxacillin, .5; cephapirin, .5; ceftiofur, 1; novobiocin, .5; enrofloxacin, .5; erythromycin, .5, and pirlimycin, .5. In comparison, the minimum inhibitory concentrations for 90% of isolates for the Staphylococcus sp. were 1, 1, .5, 1, .5, .5, 1, and .5 for penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin, respectively. The minimum inhibitory concentrations for 90% of isolates for the Streptococcus sp. were 2, 32, 2, 2, 8, 1, 64, and 32 for the respective antimicrobial agents; the minimum inhibitory concentrations for 90% of isolates were 4, 64, 32, 64, 4, 1, 4, and 4 for the enterococci. Against the Gram-negative enteric bacilli, only ceftiofur and enrofloxacin were active; minimum inhibitory concentrations for 90% of isolates were 1 microgram/ml for ceftiofur and .25 microgram/ml for enrofloxacin. Results indicated that the majority of staphylococcal strains were susceptible to the antimicrobial agents tested but that antimicrobial susceptibility varied for Streptococcus sp. Compounds currently available in intramammary infusion products demonstrated poor activity against the enteric organisms.

Decision tree analysis to evaluate dry cow strategies under UK conditions

“…Restricting antimicrobial use at drying off also reduces theoretically the potential selection pressure for antibiotic resistance. To date there is no evidence to suggest that dry cow antibiotics do pose a risk (Schultze, 1983 ;Watts et al 1995). Whilst dual use of both antibiotic and OrbeSeal in the same quarter might be a more complete option for different infection states or types of cow, this would then negate the non antibiotic attraction of the OrbeSeal.…”

Managing Mastitis in Heifers: An Initial Step in Improving Dairy Herd Health

“…aureus, as well as the associated elevated SCC, antimicrobial therapy should be considered. The testing of various staphylococcal isolates obtained from heifers for susceptibility to antibiotics commonly incorporated into mastitis infusion tubes has shown that antibiotic resistance is usually low (Watts et al, 1995). Greater than 90% of mastitis-causing staphylococci are generally killed by the drug preparations used, based on in vitro sensitivity testing using zone diffusion analysis (Watts et al, 1995).…”

“…The testing of various staphylococcal isolates obtained from heifers for susceptibility to antibiotics commonly incorporated into mastitis infusion tubes has shown that antibiotic resistance is usually low (Watts et al, 1995). Greater than 90% of mastitis-causing staphylococci are generally killed by the drug preparations used, based on in vitro sensitivity testing using zone diffusion analysis (Watts et al, 1995). From a practical standpoint, the administration of antibiotics by a parenteral route would be preferred; however, in the author's experience, neither subcutaneous nor intramuscular injections of drugs have been found to cure IMI in heifers because sufficient antibiotic does not pass into the mammary gland to be bactericidal.…”

Depletion study of trimethoprim and sulphadiazine in milk and its relationship with mastitis pathogenic bacteria strains minimum inhibitory concentrations (MICs) in dairy cows

“…Clinical mastitis is recognized worldwide to cause major economic losses in dairy cattle because of the loss in milk production and quality (De Graves & Fetrow, 1993; Watts et al. , 1995).…”

“…A good antimicrobial therapy for bovine clinical mastitis is aimed at the elimination of the infectious agent by maintaining homogeneous concentrations above the MIC in the mammary gland for an adequate time. The antimicrobial therapy for the more severe cases is based on systemic and/or intramammary treatments with tetracyclines, β ‐lactams, cephalosporins, macrolides, aminoglycosides and sulphonamides (Watts et al. , 1995; Morin et al.…”