The objective of the study was to investigate the microbiological content of cow (Bos primigenius) milk in Latvian organic farms according to season and herd size with a purpose to detect their impact on the distribution of mastitis causing pathogens in milk. Samples were collected in 14 organic dairy farms of Latvia, 4 times through 2012: in winter, autumn, spring and summer period. Raw milk samples (n=564) obtained from cow composite milk were studied. The samples were divided into three groups in accordance with the number of cows in the cow-shed: A (3-30), B (31-60) and C (61-124). The total colony count (TTC) and the isolation of mastitis causing bacteria were analysed using standard methods. Bacterial growth occurred in 90.4% of samples. Isolated microorganisms belonged to 35 species, and the following bacteria were the most prevalent agent, including Coagulase negative staphylococci in 29.4%, Staphylococcus aureus in 24.1%, Kocuria kristinae in 12.9%, and Enterobacteriaceae spp. in 10.3% out of 564 milk samples. Depending on the season, the average number of TCC was the lowest in summer (4.66 ± 4.01 log10 CFU mLE-1), moderately higher in spring and winter (4.72 ± 4.18 and 4.82 ± 3.54 log10 CFU mLE-1, respectively), but significantly higher in autumn (5.43 ± 4.80 log10 CFU mL-E1). Coliforms were not isolated from group A herds instead of B (3.1%) and C (4.6%). Occurrence of Staphylococcus aureus was noticeably higher in B (19.1%) and C (20.8%) than in A (12.6%) herds. Most of group A herds met the milk quality requirements, while group C herds produced more contaminated milk.

The present study describes situation of antimicrobial resistance of animal pathogens and resistance trends in Estonia in years 2006-2009. Bacterial strains isolated during period 2006-2009 were Escherichia coli (E. coli), Enterococcus faecium (E. faecium), Enterococcus faecalis (E. faecalis), collected from healthy pigs faeces as well as from diagnostic submissions of pig samples. Staphylococcus aureus (S. aureus) isolates originated from cows with clinical mastitis and Staphylococcus pseudointermedius (S. pseudointermedius) isolates from dogs with pyoderma or otitis externa. Antimicrobial susceptibility was detected by microdilution method. Normal enteric microflora from health y pigs had resistance against streptomycin, tetracyclin, sulfametoxazol and trimethoprim. E. faecalis and E. faecium were resistant to erythromycin, tetracyclin, streptomycin and kanamycin. Multiresistance occured mainly against kanamycin, streptomycin and tetracyclin. E. coli strains isolated from pathological material showed high resistance to ampicillin, tetracycline, streptomycin, sulphonamides and trimethoprim. Multiresistance was detected between 60–73% during study years. In 2009, one ESBL (extended spectrum betalactamase) producing isolate was observed. S. aureus strains isolated from clinical mastitis samples were mainly penicillin resistant (58–86%). Meticillinresistant S. aureus was not found during the study. In 2009, resistance to lincomycin (30%) and fucidinic acid (22%) was detected. In S. pseudointermedius strains isolated from canine skin samples the prevalence of resistance to penicillin as high as 53–81% was found. Multidrug resistance was relatively stable being 38% in 2006, 29% in 2007 and 25% in 2009. In conclusion, antimicrobial resistance of animal pathogens in Estonia was high. Further improvement of prudent use of antimicrobials and infection control is needed.