Udder pathogens and their resistance to antimicrobial agents in dairy cows in Estonia

Abstract

BackgroundThe goal of this study was to estimate the distribution of udder pathogens and their antibiotic resistance in Estonia during the years 2007-2009.MethodsThe bacteriological findings reported in this study originate from quarter milk samples collected from cows on Estonian dairy farms that had clinical or subclinical mastitis. The samples were submitted by local veterinarians to the Estonian Veterinary and Food Laboratory during 2007-2009. Milk samples were examined by conventional bacteriology. In vitro antimicrobial susceptibility testing was performed with the disc diffusion test. Logistic regression with a random herd effect to control for clustering was used for statistical analysis.ResultsDuring the study period, 3058 clinical mastitis samples from 190 farms and 5146 subclinical mastitis samples from 274 farms were investigated. Positive results were found in 57% of the samples (4680 out of 8204), and the proportion did not differ according to year (p > 0.05). The proportion of bacteriologically negative samples was 22.3% and that of mixed growth was 20.6%. Streptococcus uberis (Str. uberis) was the bacterium isolated most frequently (18.4%) from cases of clinical mastitis, followed by Escherichia coli (E. coli) (15.9%) and Streptococcus agalactiae (Str. agalactiae) (11.9%). The bacteria that caused subclinical mastitis were mainly Staphylococcus aureus (S. aureus) (20%) and coagulase-negative staphylococci (CNS) (15.4%). The probability of isolating S. aureus from milk samples was significantly higher on farms that had fewer than 30 cows, when compared with farms that had more than 100 cows (p < 0.005). A significantly higher risk of Str. agalactiae infection was found on farms with more than 600 cows (p = 0.034) compared with smaller farms. The proportion of S. aureus and CNS isolates that were resistant to penicillin was 61.4% and 38.5%, respectively. Among the E. coli isolates, ampicillin, streptomycin and tetracycline resistance were observed in 24.3%, 15.6% and 13.5%, respectively.ConclusionsThis study showed that the main pathogens associated with clinical mastitis were Str. uberis and E. coli. Subclinical mastitis was caused mainly by S. aureus and CNS. The number of S. aureus and Str. agalactiae isolates depended on herd size. Antimicrobial resistance was highly prevalent, especially penicillin resistance in S. aureus and CNS.

Prevalence and Antimicrobial Resistance Assessment of Subclinical Mastitis in Milk Samples From Selected Dairy Farms

“…Antimicrobial sensitivity tests of Staphylococcus aureus as seen in this study agrees with earlier reports by Kalmus et al (2011), who reported a heightened resistance of Staphylococcus aureus to Penicillin and Ampicillin. There is no scientific evidence as to the resistance pattern of mastitis pathogens to penicillin and the Cephalosporin group, but there were widespread reports of antimicrobial drug resistance among Staphylococcus pathogens for over 2-3 decades as earlier reported by Kalmus et al (2011) in Estonia, Botrel et al (2010) in Germany; Persson et al, 2011in Sweden Sahebekhtiari et al (2011 in Iran, Chaudhary andPayasi, 2013 in India andRall et al (2013) in Brazil.…”

“…There is no scientific evidence as to the resistance pattern of mastitis pathogens to penicillin and the Cephalosporin group, but there were widespread reports of antimicrobial drug resistance among Staphylococcus pathogens for over 2-3 decades as earlier reported by Kalmus et al (2011) in Estonia, Botrel et al (2010) in Germany; Persson et al, 2011in Sweden Sahebekhtiari et al (2011 in Iran, Chaudhary andPayasi, 2013 in India andRall et al (2013) in Brazil. The trend of resistance patterns to antibiotic use over time showed a long-term effect of over 3-7 years (Rall et al, 2013).…”

Mastitis Pathogens and Their Antimicrobial Susceptibility in Early Lactating Dairy Cows

“…Other isolated microorganisms were susceptible to antimicrobials tested. Similar results were reported by Persson et al (2011) when the most of the isolated udder pathogens were susceptible to wide range of antimicrobials, with exception to Penicillin G. Opposite, the other authors reported the high level of resistance of udder pathogens to antimicrobials (Kalmus et al, 2011).…”

“…and Streptococcus spp. was revealed from cases of subclinical mastitis in dairy cows (Roesch et al, 2007;Kalmus et al, 2011). Saini et al (2013) reported higher prevalence of environmental mastitis pathogens and Escherichia coli in dairy herds, predominantly in early lactation.…”

“…For example, the prevalence of Staphylococcus aureus in Finland and Germany vary from 3,0 to 3,5% up to 38,5% in Zimbabwe and Australia (Kloppert et al, 1999;Milne et al, 2002). Kalmus et al (2011) reported that Streptococcus agalactiae is the second predominant etiological agents of mastitis in dairy farms but cure rate with antibiotic therapy during lactation is very high.…”