Comparison of Antibiotic Resistance of Udder Pathogens in Dairy Cows Kept on Organic and on Conventional Farms

Abstract

There has been a rapid rise in the emergence of multi-drug-resistant pathogens in the past 10 to 15 yr and some bacteria are now resistant to most antimicrobial agents. Antibiotic use is very restricted on Swiss organic dairy farms, and a purely prophylactic use, such as for dry cow mastitis prevention, is forbidden. A low prevalence of antibiotic resistance in organic farms can be expected compared with conventional farms because the bacteria are infrequently or not exposed to antibiotics. The occurrence of antibiotic resistance was compared between mastitis pathogens (Staphylococcus aureus, nonaureus staphylococci, Streptococcus dysgalactiae, Streptococcus uberis) from farms with organic and conventional dairy production. Clear differences in the percentage of antibiotic resistance were mainly species-related, but did not differ significantly between isolates from cows kept on organic and conventional farms, except for Streptococcus uberis, which exhibited significantly more single resistances (compared with no resistance) when isolated from cows kept on organic farms (6/10 isolates) than on conventional farms (0/5 isolates). Different percentages were found (albeit not statistically significant) in resistance to ceftiofur, erythromycin, clindamycin, enrofloxacin, chloramphenicol, penicillin, oxacillin, gentamicin, tetracycline, and quinupristin-dalfopristin, but, importantly, none of the strains was resistant to amoxicillin-clavulanic acid or vancomycin. Multidrug resistance was rarely encountered. The frequency of antibiotic resistance in organic farms, in which the use of antibiotics must be very restricted, was not different from conventional farms, and was contrary to expectation. The antibiotic resistance status needs to be monitored in organic farms as well as conventional farms and production factors related to the absence of reduced antibiotic resistance in organic farms need to be evaluated.

Analysis of Escherichia coli isolated from bovine mastitic milk

“…Studies performed in the United States indicate that there is no correlation among increased resistance of and antimicrobials that are commonly used in dairy cattle for treatment of mastitis (Erskine et al 2001, Makovec & Ruegg 2003. In Switzerland, there was no increased antibiotic resistance of mastitis pathogens during the last 20 years (Roesch et al 2006), indicating different points of view about this theme. In Brazil a strong control of antimicrobial drugs commercialization and access to data related to resistance to antimicrobial drugs presented by the pathogens responsible for bovine mastitis would first be necessary before a conclusive answer about this matter is given.…”

Trends of Antibiotic Resistance (AR) in Mesophilic and Psychrotrophic Bacterial Populations During Cold Storage of Raw Milk, Produced by Organic and Conventional Farming Systems

“…When considering the farming type practices, small or no differences in AR levels were reported by Sato et al (2004) for Campylobacter spp. isolates from organic and conventional dairy herds, by Roesch et al (2006) when the AR of udder pathogens was investigated in dairy cows, by Ray et al (2006) for Salmonella, or by Garmo et al (2010) for coagulasenegative staphylococci: the frequency of AR in organic farms was not so different from conventional farms. Also Ruimy et al (2010) recorded similar levels of resistant Gramnegative bacteria for both organic and conventional produced fruits and vegetables.…”

Prevalence and Characterization of Staphylococcus aureus, Including Methicillin-Resistant Staphylococcus aureus, Isolated from Bulk Tank Milk from Minnesota Dairy Farms

“…Rajala-Schultz et al analyzed the susceptibility patterns of mastitis pathogens isolated at calving from firstlactation and older cows and reported no significant difference in the proportions of resistant isolates between first-lactation and older cows (53). A study conducted by Roesch et al in Switzerland compared the rates of occurrence of resistant mastitis pathogens between organic and conventional dairy farms and reported no significant differences between the two (54).…”