The primary objective of this study was to determine management practices concerning mastitis in Brandenburg, Germany, the prevalence of mastitis pathogens in dairy cows, and their resistance to selected antimicrobial agents. A further objective was to study the potential effect of parity and stage of lactation on the resistance of Staphylococcus aureus isolates against ampicillin. Milk samples for microbiological culture were collected from 4 groups of clinically healthy cows (first lactation, >1 lactation, >50 d in milk, and >250 d in milk; 8 cows/group) in 80 dairy herds. Resistance of gram-positive pathogens against 6 antimicrobial agents was tested using the broth microdilution method. Mastitis pathogens were isolated from 26.4% of the milk samples. Coagulase-negative staphylococci (CNS, 9.1% of quarters) and Corynebacterium bovis (7.3%) were the pathogens most frequently isolated. Among the major pathogens, Staph. aureus (5.7%) and Streptococcus uberis (1.0%) had the highest prevalence. Streptococcus agalactiae was isolated in samples from 29% of the herds. Although the prevalence of most pathogens was higher in older cows, the prevalence of CNS was higher in primiparous cows. Results of the mastitis control questionnaire showed that cows with clinical mastitis were transferred to a sick cow pen in 70% of the herds. Cephalosporins were the drug of first choice for treatment of clinical mastitis cases followed by fixed combinations of antimicrobial agents, beta-lactamase-resistant penicillins, and penicillin. Most farmers treated cows 3 to 4 times per case. Cloxacillin, alone or in combination, and penicillin were most often used for dry-cow therapy. Antimicrobial resistance of the pathogens was within the range of other reports. Resistance of Staph. aureus to ampicillin increased significantly during the first lactation. Further research is required to determine the factors that lead to the selection of Staph. aureus strains that are resistant to ampicillin during the first lactation.

Non-saleable milk (waste milk, WM) is contaminated with an undefined spectrum of potentially harmful pathogens and antimicrobial residues. The objective of this study was to determine the impact of feeding bulk milk (BM) or WM - both pasteurized or not - on calf performance, health and the antibiotic resistance of specific faecal bacteria. A total of 114 calves from a large-scale dairy were housed outdoors in individual hutches and were randomly assigned to one of four feeding groups. The calves were fed either WM, pasteurized WM (pWM), BM or pasteurized BM (pBM) from day 3 to 56 of life. Milk samples taken from the pasteurizer and calves' nipple buckets were investigated at regular intervals for total plate count and counts of thermoduric bacteria, coliforms and mastitis pathogens. Faecal samples were taken on days 2, 14, 28 and 56 of life from randomly selected calves of the WM, pWM and BM groups (each N = 8-9) and processed to obtain from each sample preferably two isolates of Escherichia (E.) coli and Enterococcus spp. respectively. Isolates were tested for their antimicrobial susceptibility to 25 antimicrobial agents by broth microdilution. Daily weight gain, milk and calf starter intake and health parameters did not differ significantly between the calves of the four feeding groups. The proportion of resistant E. coli isolates was significantly higher in calves fed WM and in calves fed pWM (most pronounced for cephalosporins) than in calves receiving BM. No differences in resistance were found for Enterococus spp. Thus, the concerns for selecting resistant faecal bacteria by feeding WM seem to be justified. Nonetheless, pasteurized WM of cows not treated with antimicrobials represents an acceptable feed for young calves.

MICs for 349 Bordetella bronchiseptica isolates from respiratory tract infections of swine were determined by broth microdilution. The lowest MIC at which 90% of isolates tested are inhibited (MIC 90 ) was that of tetracycline and enrofloxacin (0.5 g/ml), whereas the highest MIC 90 s were those of tilmicosin and cephalothin (32 g/ml) as well as streptomycin (256 g/ml).Porcine respiratory diseases represent the leading cause of mortality in nursery and finishing units (12). Bordetella bronchiseptica is often involved in porcine respiratory tract infections, along with viruses and other bacteria (1). It has been shown that infections with B. bronchiseptica predispose pigs to secondary infections with toxigenic strains of Pasteurella multocida and thus play an important role in the pathogenesis of severe atrophic rhinitis (1,8). Various antimicrobial agents are licensed and used for the control of bacteria involved in porcine respiratory diseases and atrophic rhinitis, including aminopenicillins, cephalosporins, aminoglycosides, tetracyclines, macrolides, lincosamides alone or in combination with spectinomycin, potentiated sulfonamides, fluoroquinolones, pleuromutilins, and florfenicol. In contrast to well-studied pathogens such as P. multocida (for a review see reference 5), comparatively little is known about the antimicrobial susceptibility of porcine B. bronchiseptica isolates (3, 5, 6, 9-11, 14, 16, 20).Between 2000 and 2003, 349 B. bronchiseptica isolates were collected from cases of bronchopneumonia and/or atrophic rhinitis of swine in Germany. This study includes 78 isolates from 2000, 98 isolates from 2001, 91 isolates from 2002, and 82 isolates from 2003. All isolates were collected from diseased animals on the basis of one isolate per herd. The animals had not been treated with antimicrobial agents in the 3 weeks prior to sample collection. Samples included nasal swabs sent to the diagnostic laboratories by veterinarians and lung tissue obtained during postmortem inspections at diagnostic laboratories. Microbiological sample processing and biochemical confirmation of species assignment followed standard procedures (7). All bacterial isolates were investigated for their in vitro susceptibility to antimicrobial agents by the microdilution broth method with microtiter plates (Sensititre, Westlake, Ohio) that contained the antimicrobial agents in serial twofold dilutions. The layouts of the microtiter plates corresponded to those used in the German resistance monitoring program for veterinary pathogens (GERM-VET). The antimicrobial agents and concentrations tested are shown in Table 1. Performance and evaluation of the susceptibility tests followed the recommendations given in document M31-A2 of the National Committee for Clinical Laboratory Standards (13). Specifically, an inoculum that corresponded to a 0.5 McFarland standard was prepared in cation-supplemented Mueller-Hinton broth and then further diluted to yield a final concentration of 10 5 CFU/ ml. After incubation for 16 to 20 h at 35°C, the wells of...

BackgroundIn the European Union, various fluoroquinolones are authorised for the treatment of food producing animals. Each administration poses an increased risk of development and spread of antimicrobial resistance. The aim of this study was to investigate the impact of parenteral administration of enrofloxacin on the prevalence of enrofloxacin and ciprofloxacin susceptibilities in the commensal intestinal E. coli population.Methods E. coli isolates from faeces of twelve healthy pigs were included. Six pigs were administered enrofloxacin on day 1 to 3 and after two weeks for further three days. The other pigs formed the control group. MIC values were determined. Virulence and resistance genes were detected by PCR. Phylogenetic grouping was performed by PCR. Enrofloxacin and ciprofloxacin were analysed in sedimentation samples by HPLC.ResultsSusceptibility shifts in commensal E. coli isolates were determined in both groups. Non-wildtype E. coli could be cultivated from two animals of the experimental group for the first time one week after the first administration and from one animal of the control group on day 28. The environmental load with enrofloxacin in sedimentation samples showed the highest amount between days one and five. The repeated parenteral administration of enrofloxacin to pigs resulted in rapidly increased MIC values (day 28: MIC up to 4 mg/L, day 35: MIC ≥ 32mg/L). E. coli populations of the control group in the same stable without direct contact to the experimental group were affected.ConclusionThe parenteral administration of enrofloxacin to piglets considerably reduced the number of the susceptible intestinal E. coli population which was replaced by E. coli strains with increased MIC values against enrofloxacin. Subsequently also pigs of the control were affected suggesting a transferability of strains from the experimental group through the environment to the control group especially as we could isolate the same PFGE strains from both pig groups and the environment.

After the UK and France, floR-mediated florfenicol resistance has now also been identified in target bacteria from Germany. PFGE data and the analysis of plasmids strongly suggested that the spread of florfenicol resistance is due to the horizontal transfer of plasmids rather than the clonal dissemination of a resistant P. multocida isolate.