The aim of this paper was to describe an increased occurrence of vancomycin-resistant enterococci (VRE) in Swedish broilers since 2000 and to investigate the genetic relatedness of isolates.Caecal content from slaughtered broilers was cultured for VRE on medium supplemented with vancomycin (16 mg/L). Species identification, antibiotic susceptibility determination, vancomycin resistance genotyping, multilocus sequence typing (MLST) and characterization of Tn1546 were performed.The proportion of VRE-positive samples increased gradually from < 1% in 2000 to slightly over 40% in 2005. Between 2005 and 2006, the proportion of VRE-positive samples decreased and between 2006 and 2007, it was stable at just below 30%. All isolates tested were Enterococcus faecium and carried the vanA gene. A majority of the isolates had similar antibiograms, the same MLST sequence type and Tn1546 transposon.The proportion of VRE-positive samples from broilers has increased since 2000, and this is due to the spread of one major clone. Moreover, this has taken place in an environment without any obvious selective pressure.

There are few studies on antimicrobial susceptibility of Brachyspira pilosicoli, therefore this study was performed to investigate the situation among isolates from pigs. The tiamulin and tylosin susceptibility was determined by broth dilution for 93 and 86 porcine B. pilosicoli isolates, respectively. The isolates came from clinical samples taken in Swedish pig herds during the years 2002 and 2003. The tylosin minimal inhibitory concentration (MIC) was >16 μg/ml for 50% (n = 43) of the isolates tested. A tiamulin MIC >2 μg/ml was obtained for 14% (n = 13) of the isolates and these were also tested against doxycycline, salinomycin, valnemulin, lincomycin and aivlosin. For these isolates the susceptibility to salinomycin and doxycycline was high but the MICs for aivlosin varied. The relationship between the 13 tiamulin resistant isolates was analyzed by pulsed-field gel electrophoresis (PFGE). Among the 13 isolates 10 different PFGE patterns were identified.

A point mutation in the 23S rRNA gene causes macrolide and lincosamide resistance in Brachyspira hyodysenteriae. The possible occurrence of a similar mutation in Brachyspira pilosicoli was studied and the MICs of six antimicrobial agents for Swedish field isolates of B. pilosicoli were determined. Of 10 isolates with high MICs of macrolide and lincosamide antibiotics, six had a mutation in nucleotide position 2058 or 2059 in the 23S rRNA gene as compared to the wild type of Escherichia coli, whereas none of 10 tylosin-susceptible isolates were mutated in this region. The mutations found in position 2058 were A --> T transversions, and in position 2059 either A --> G transitions or A --> C transversions. The MICs at which 90% of the B. pilosicoli field isolates were inhibited by tylosin, erythromycin, clindamycin, virginiamycin, tiamulin, and carbadox, were >256, >256, >4, 4, 2, and 0.125 mug/ml, respectively. In conclusion, point mutations in positions 2058 and 2059 of the 23S rRNA gene can cause macrolide and lincosamide resistance in B. pilosicoli. Macrolide resistance is widespread among Swedish field isolates of B. pilosicoli. Notably also a few isolates with elevated MICs of tiamulin were found.

Brachyspira hyodysenteriae is the causative agent of swine dysentery, a severe diarrhoeal disease in pigs. Few drugs are available to treat the disease, owing to both antimicrobial resistance and withdrawal of drugs authorized for use in pigs. Tiamulin is the drug of choice in many countries, but isolates with decreased susceptibility have recently been reported. The mechanism of tiamulin resistance in B. hyodysenteriae is not known and this facet is essential to understand the dissemination of the trait. To study the resistance epidemiology of B. hyodysenteriae, further characterization of a set of isolates from Germany (n = 16) and the UK (n = 6) with decreased susceptibility to tiamulin was performed. The relatedness between the isolates was studied by comparing PFGE patterns, and the in vitro susceptibility to five other antimicrobials (aivlosin, doxycycline, salinomycin, chloramphenicol and avilamycin) was also determined. For comparison of the antimicrobial-susceptibility pattern, Swedish (n = 20) and British (n = 4) tiamulin-susceptible isolates were tested. The German isolates represented several different PFGE patterns, indicating that tiamulin usage has been sufficient to select clones with decreased tiamulin susceptibility at different farms in Germany. The PFGE pattern for the six British isolates with decreased tiamulin susceptibility was identical to that of the German isolates, and they had a similar antimicrobial-susceptibility pattern, except for resistance to aivlosin, which was only found in a few German isolates. No other co-resistance with tiamulin was found.

Equine Veterinary JournalVolume 36, Issue 2 p. 180-182 Study of faecal shedding of Clostridium difficile in horses treated with penicillin A. Gustafsson, Corresponding Author A. Gustafsson Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Search for more papers by this authorV. Båverud, V. Båverud National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this authorA. Gunnarsson, A. Gunnarsson National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this authorJ. Pringle, J. Pringle Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Search for more papers by this authorA. Franklin, A. Franklin National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this author A. Gustafsson, Corresponding Author A. Gustafsson Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Search for more papers by this authorV. Båverud, V. Båverud National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this authorA. Gunnarsson, A. Gunnarsson National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this authorJ. Pringle, J. Pringle Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Box 7018, S-750 07Search for more papers by this authorA. Franklin, A. Franklin National Veterinary Institute, SE-751 89, Uppsala, SwedenSearch for more papers by this author First published: 05 January 2010 https://doi.org/10.2746/0425164044868657Citations: 25AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References Andersson, G., Ekman, L., Månsson, I., Persson, S., Rubarth, S. and Tufvesson, G. (1971) Lethal complications following administration of oxytetracycline in the horse. Nord. vet. Med. 23, 9–22. Aronsson, B., Möllby, R. and Nord, C.E. (1982) Clostridium difficile and antibiotic associated diarrhea in Sweden. Scand. J. Infect. Dis., Suppl. 35, 53–58. Beier, R., Amtsberg, G. and Peters, M. (1994) Bacteriogishe Untersuchungen zum Vorkommen und zur Bedeutung von Clostridium difficile beim Pferd. Pferdeheilkunde 10, 3–8. Båverud, V., Gunnarsson, A., Karsson, M. and Franklin, A. (2004) Antimicrobial susceptibility of equine and environmental isolates of Clostridium difficile. Microb. Drug Resist. In Press. Båverud, V., Gustafsson, A., Franklin, A., Lindholm, A. and Gunnarsson, A. (1997) Clostridium difficile associated with acute colitis in adult horses treated with antibiotics. Equine vet. J. 29, 279–284. Båverud, V., Gustafsson, A., Franklin, A., Aspán, A. and Gunnarsson, A. (2003) Clostridium difficile: prevalence in horses, in environment and antimicrobial susceptibility. Equine vet. J. 35, 465–471. Cohen, N.D. and Woods, A.M. (1999) Characteristics and risk factors for failure of horses with acute diarrhea to survive: 122 cases (1990-1996). J. Am. vet. med. Ass. 214, 382–389. Gustafsson, A., Båverud, V., Gunnarsson, A., Horn af Rantzien, M., Lindholm, A. and Franklin, A. (1997) The association of erythromycin ethylsuccinate with acute colitis in horses in Sweden. Equine vet. J. 29, 314–318. Horspool, L.J.I. and McKellar, Q.A. (1995) Disposition of penicillin G sodium following intravenous and oral administration to Equidae. Br. vet. J. 151, 401–411. Jones, R.L., Shideler, R.K. and Cockerell, G.L. (1988) Association of Clostridium difficile with foal diarrhea. In: Proceedings of the 5th International Conference on Equine Infectious Diseases, Ed: D.G. Powell, University Press of Kentucky, Lexington . pp 236–240. Karlsson, S., Burman, L.G. and Åkerlund, T. (1999) Supression of toxin production in Clostridium difficile VPI 10463 by amino acids. Microbiol. 145, 1683–1693. Madewell, B.R., Tang, Y.J., Jang, S., Madigan, J.E., Hirsh, D.C., Gumerlock, P.H. and Silva, J. (1995) Apparent outbreak of Clostridium difficile-associated diarrhea in horses in a veterinary medical teching hospital. J. vet. Diagn. Invest. 7, 343–346. Magdesian, K.G., Madigan, J.E., Jang, S.S. and Hirsh, D.C. (1997) Colitis associated with Clostridium difficile in horses. J. vet. intern. Med. 11, 110. McFarland, L.V., Surawicz, C.M. and Stamm, W.E. (1990) Risk factors for Clostridium difficile carriage and C. difficile-associated diarrhea in a cohort of hospitalized patients. J. Infect. Dis. 162, 678–684. McGorum, B.C., Dixon, P.M. and Smith, D.G.E. (1998) Use of metronidazole in equine acute idiopathic toxaemic colitis. Vet. Rec. 142, 635–638. Nolan, N.P.M., Kelly, C.P., Humphreys, J.F.H., Cooney, C., O'Connor, R., Walsh, T.N., Weir, D.G. and Briain, D.S. (1987) An epidemic of pseudomembranous colitis: Importance of person to person spread. Gut 28, 1467–1473. Raisbeck, M.F., Holt, G.R. and Osweiler, G.D. (1981) Lincomycin-associated colitis in horses. J. Am. vet. med. Ass. 179, 362–363. Staempfli, H.R., Prescott, J.F. and Brash, M.L. (1992) Lincomycin-induced severe colitis in ponies: association with Clostridium cadaveris. Can. J. vet. Res. 56, 168–169. Weese, J.S. (2000) Antimicrobial-associated diarrhea in 40 horses: 1997-1999. In: Clostridium difficile Associated Enterocolitis in Adult Horses and Foals. DVSc Thesis, Ontario Veterinary College, Canada . pp 115–124. Wistrom, J., Norrby, S.R., Myhre, E.B., Eriksson, S., Granstrom, G., Lagergren, L., Englund, G., Nord, C.E. and Svenungsson, B. (2001) Frequency of antibiotic-associated diarrhea in 2462 antibiotic-treated hospitalized patients: a prospective study. J. Antimicrob. Chemother. 47, 43–50. Citing Literature Volume36, Issue2March 2004Pages 180-182 ReferencesRelatedInformation

ABSTRACT No standardized method for susceptibility testing of Brachyspira spp. is currently available. A broth dilution procedure was evaluated and used to test the activities of six antimicrobial agents for 108 isolates of Swedish porcine Brachyspira spp. representing biochemical groups I, II, and III. Group I corresponds to Brachyspira hyodysenteriae , group II corresponds to B . intermedia , and group III corresponds to B . murdochii and B . innocens . A panel was designed with the antimicrobial agents dried in tissue culture trays with wells that allowed a liquid volume of 0.5 ml in each and agitation of the broth when incubated on a shaker. The MICs were determined by using brain heart infusion broth with 10% fetal calf serum. For 10 isolates, the results obtained in broth were compared to the MICs obtained on two different types of agar. Different inoculum densities and incubation times were also compared. The concentrations at which 90% of the B . hyodysenteriae isolates ( n = 72) were inhibited in the broth dilution test by tiamulin (0.25 μg/ml), tylosin (>256 μg/ml), erythromycin (>256 μg/ml), clindamycin (>4 μg/ml), virginiamycin (4 μg/ml), and carbadox (0.06 μg/ml) were determined. The MICs tended to be lower in broth than on agar. Differences in inoculum densities and incubation times had little influence on the MICs. The evaluated broth dilution test was simple to perform, the end points were easily read, and the results were reproducible and reliable. No isolates with decreased susceptibility to tiamulin were found among the Swedish isolates tested.

OBJECTIVETo evaluate an experimental model of the pharmacokinetic/pharmacodynamic (PK/PD) relationship of danofloxacin against Mannheimia haemolytica infection, using subcutaneously implanted tissue cages in calves.METHODSTissue cages implanted subcutaneously in calves were infected with M. haemolytica and different concentration-time profiles of danofloxacin were simulated. Drug concentrations and bacterial counts were monitored over time and various PK/PD parameters calculated.RESULTSBy using different types of cage and various doses, a range of PK/PD indices were simulated. The PK/PD index that best predicted the antimicrobial effect was the AUC/MIC ratio. The magnitude of this index needed for near-maximum effect (80%), assessed using the area under the bacterial kill curve to 48 h, was 244 h.CONCLUSIONSThe model described enabled different concentration-time profiles to be simulated, and PK/PD interactions to be studied in the presence of the host's defences. The validity of this model needs to be confirmed by clinical studies, but the results suggest that it may be a useful intermediary step between in vitro and clinical studies.

An in vivo model for studies of pharmacokinetic/pharmacodynamic (PK/PD) interactions of antimicrobials was developed. Tissue cages with a constant surface area but with different volumes were implanted in calves and infected with Mannheimia haemolytica. Penicillin was injected directly into the cages. With this procedure, different concentration–time profiles could be simulated so that the effect of a range of PK/PD indices on the infection could be monitored. The area under the curve to minimum inhibitory concentration (MIC) and time above MIC were equally predictive for effect, but Cmax to MIC was not. If drug dosages in relation to the MIC of strains used for infection are optimised, the model offers an interesting alternative to explore relevant factors for drug dosage optimisation.

Reasons for performing study: Clostridium difficile has been associated with acute colitis in mature horses.Objectives: To survey C. difficile colonisation of the alimentary tract with age, occurrence of diarrhoea and history of antibiotic therapy; and to study the occurrence and survival of C. difficile in the environment and antimicrobial susceptibility of isolated strains.Methods: A total of 777 horses of different breeds, age and sex were studied. Further, 598 soil samples and 434 indoor surface samples were examined. Antimicrobial susceptibility of 52 strains was investigated by Etest for 10 antibiotics.Results: In horses that developed acute colitis during antibiotic treatment, 18 of 43 (42%) were positive to C. difficile culture and 12 of these (28%) were positive in the cytotoxin B test. Furthermore, C. difficile was isolated from a small! number of diarrhoeic mature horses (4 of 72 [6%]) with no history of antibiotic treatment, but not from 273 healthy mature horses examined or 65 horses with colic. An interesting new finding was that, in normal healthy foals age <14 days, C. difficile was isolated from 113 of foals (16 of 56 [29%]). All older foals (170) except one were negative. Seven of 16 (44%) nondiarrhoeic foals treated with erythromycin or gentamicin in combination with rifampicin were also excretors of C. difficile.On studfarms, 14 of 132 (11%) outdoor soil samples were positive for C. difficile in culture, whereas only 2 of 220 (1%) soil samples from farms with mature horses were positive for C. difficile (P = <0.001). By PCR, it was demonstrated that strains from the environment and healthy foals can serve as a potential reservoir of toxigenic C. difficile. The experimental study conducted here found that C. difficile survived in nature and indoors for at least. 4 years in inoculated equine faeces. The susceptibility of 52 strains was investigated for 10 antibiotics and all were susceptible to metronidazole (MICless than or equal to4 mg/l) and vancomycin (MICless than or equal to2 mg/l).Conclusions: C. difficile is associated with acute colitis in mature horses, following antibiotic treatment. Furthermore, C. difficile was isolated from 1 in 3 normal healthy foals age <14 days.Potential relevance: Strains from healthy foals and the environment can serve as. a potential reservoir of toxigenic C. difficile.

The objectives of the present study were to generate knowledge of enterococcal populations in the food chain, by studying the population structure (in measures of abundance and diversity) among enterococci in different geographical regions and in different parts of the food chain, as well as the similarities between different enterococcal populations. Altogether, 2868 samples were collected from humans (healthy and hospitalised individuals and clinical isolates), animals (slaughterhouse carcasses and farm animals), and the environment (pig farms, sewage, and surface water) in four European countries—Sweden, Denmark, UK, and Spain. The samples were characterised with regard to presence and numbers of enterococci, and eight (for faecal samples) or 24 (for environmental samples) isolates per sample were phenotyped and preliminarily identified with the PhP-RF system. In total, more than 20,000 isolates were typed. A majority of the samples (77%) showed the presence of presumed enterococci. The diversities of enterococci in environmental samples were generally high, and also faecal samples normally showed presence of more than one enterococcal strain. The most common species found were Enterococcus faecium (33%), E. faecalis (29%), and E. hirae (24%), but different enterococcal populations differed in their species distribution. Clinical isolates, hospitalised patients, and hospital sewage in Sweden showed a clear dominance of E. faecalis (80%, 57%, and 54%, respectively) whereas healthy individuals and urban sewage contained less E. faecalis (39% and 40%, respectively). The species distribution among isolates from slaughterhouses varied between animal species and also between countries, but E. faecalis seemed to be mainly associated with broiler, and E. hirae with cattle and pigs. The results from the study have indicated a simplified method to study the diversity of bacterial populations. Instead of collecting many samples and analysing one or a few isolates per sample, it is possible to collect fewer samples and analyse several isolates per sample. Both approaches yielded similar information on the diversity of the populations. Another useful information was that since samples from hospital sewage, urban sewage, and manure contained enterococcal populations that reflected those in faecal samples of hospitalised patients, healthy humans, and animals, respectively, such samples may be used as pooled faecal samples and may replace cumbersome samplings from many individuals.

An ampicillin- and ciprofloxacin-resistant Enterococcus faecium (ARE) strain, named FMSE1, with a characteristic biochemical phenotype, was in a recent study found to dominate among faecal ARE isolates from patients in several Swedish hospitals. In the present study, the prevalence of this strain among 9676 enterococcal isolates from healthy children, hospital sewage, urban sewage, surface water, slaughtered animals (broilers, pigs and cattle) and pig faeces and manure was investigated. Enterococcal isolates having the same biochemical phenotype as the FMSE1 were most common in samples of hospital sewage (50%), surface water (35%), treated sewage (28%) and untreated sewage (17%), but rare in samples from healthy children (0.8%) and animals (2%). PFGE typing of FMSE1-like isolates from hospital sewage indicated that they were closely related to the nosocomial FMSE1 strain. Thus, this study indicated a possible transmission route for nosocomial E. faecium from patients in hospitals to hospital sewage and urban sewage, and further via treatment plants to surface water and possibly back to humans. This proposed route of circulation of drug-resistant enterococci might be further amplified by antibiotic usage in human medicine. In contrast, such transmission from food animals seems to play a negligible role in Sweden.

In a prospective study involving eight veterinary clinics during 1995 and 1996, samples from first-time and recurrent cases of canine pyoderma were collected by a needle technique. Three hundred and ninety-four staphylococci were isolated and their susceptibility to various antimicrobial drugs was assessed by a microdilution technique. Resistance to macrolides, lincosamides, fusidic add, tetracycline and streptomycin was significantly more common in isolates from the recurrent cases than from the first-time cases; 20 per cent of the isolates from the first-time cases were resistant to three or more of the antimicrobials tested, compared with 45 per cent of those from the recurrent cases. Coresistance between macrolide-lincosamides, tetracyclines and streptomycin was common. No resistance to penicillinase-stable beta-lactams was observed. A comparison with earlier studies indicated that there had been a marked increase in resistance during the previous five years.

ABSTRACT Enterococci from pigs in Denmark, Spain, and Sweden were examined for susceptibility to antimicrobial agents and copper and the presence of selected resistance genes. The greatest levels of resistance were found among isolates from Spain and Denmark compared to those from Sweden, which corresponds to the amounts of antimicrobial agents used in food animal production in those countries. Similar genes were found to encode resistance in the different countries, but the tet (L) and tet (S) genes were more frequently found among isolates from Spain. A recently identified transferable copper resistance gene was found in all copper-resistant isolates from the different countries.

Tissue cages implanted subcutaneously in calves were infected with Escherichia coli. Twenty-four hours later, the calves were treated either with single doses of 2.5 + 12.5 or 5 + 25 mg/kg trimethoprim (TMP) + sulfadoxine (SDX) or with five doses of 7.5 + 37.5 mg/kg TMP + SDX at 12-h intervals. In addition, one cage in each of three calves in the highest dose group was infected 3 h after initiation of treatment. Untreated calves were kept as controls. Concentrations of TMP and SDX in plasma and tissue cage fluid (TCF) and counts of viable bacteria in TCF were determined. In the highest dose group, concentrations of TMP in TCF remained above the minimum inhibitory concentration of the test strain for 94-101 h and peak to minimum inhibitory concentration (MIC) ratio was close to 10. In spite of this, an effect of treatment was noted only in cages infected after initiation of treatment. In vitro studies and analysis of thymidine content in serum and TCF from calves suggest that levels of thymidine in TCF are high enough to antagonize the antibacterial effect of TMP. The results indicate that soft tissue infections in secluded infection sites of calves are refractory to treatment with TMP + SDX.

ABSTRACT In Europe the use of the growth promoter avoparcin is considered to have selected for vancomycin-resistant enterococci (VRE). Sweden ceased using avoparcin in 1986, and only occasional cases of VRE from hospitals have been reported since 1995. Within the framework of a European study, samples from urban raw sewage, treated sewage, surface water, and hospital sewage in Sweden ( n = 118) were screened for VRE. Surprisingly, VRE were isolated from 21 of 35 untreated sewage samples (60%), from 5 of 14 hospital sewage samples (36%), from 6 of 32 treated sewage samples (19%), and from 1 of 37 surface water samples. Thirty-five isolates from 33 samples were further characterized by geno- and phenotyping, MIC determination, and PCR analysis. Most isolates (30 of 35) carried the vanA gene, and the majority (24 of 35) of the isolates were Enterococcus faecium . Most of the VRE were multiresistant. The typing revealed high diversity of the isolates. However, one major cluster with seven identical or similar isolates was found. These isolates came from three different sewage treatment plants and were collected at different occasions during 1 year. All VRE from hospital sewage originated from one of the two hospitals studied. That hospital also had vancomycin consumption that was 10-fold that of the other. We conclude that VRE were commonly found in sewage samples in Sweden. The origin might be both healthy individuals and individuals in hospitals. Possibly, antimicrobial drugs or chemicals released into the sewage system may sustain VRE in the system.

A total of 522 strains belonging to streptococci, enterococci and staphylococci isolated from sub-clinical and clinical cases of bovine mastitis from the west littoral region of Uruguay were analysed for their susceptibility to several antimicrobial agents. The susceptibility patterns were studied by agar disk diffusion methods (ADDM) and broth micro-dilution to determine the minimum inhibitory concentration (MIC). The concentration that inhibits 90% (MIC90) of the analysed strains reported in micrograms per millilitre, for Staphylococcus aureus were > 8, 8, ≤ 0.5, ≤ 4, ≤ 1, ≤ 0.5, > 64, ≤ 0.25, 0.5, ≤ 1 and ≤ 1 to penicillin, ampicillin, oxacillin, cephalotin, gentamicin, erythromycin, oxitetracycline, enrofloxacin, trimethoprim/sulfamethoxazole, neomycin, and clindamycin, respectively. Coagulase-negative staphylococci (CNS) had different values for penicillin (4) and ampicillin (2), while the other antimicrobial agents had the same MIC90 values as reported for S. aureus. The MIC90 values for streptococci were 0.12, 0.25, ≤ 4, 16, ≤ 0.25, 0.5, 0.25 for penicillin, ampicillin, cephalotin, gentamicin, erythromycin, oxytetracycline and trimethoprim-sulfamethoxazole, whereas MIC90 for enterococci were 4, 4, 4, ≤ 0.5, 2, > 8 for penicillin, ampicillin, gentamicin, erythromycin, oxytetracycline and trimethoprim-sulfamethoxazole, respectively. Of 336 strains of S. aureus, 160 (47.6%) were resistant to penicillin. For 41 CNS strains, 10 (27%) presented penicillin-resistance. All the streptococcal strains were susceptible to penicillin, while 3 (7%) of the 43 enteroccocal strains were resistant. Non significant statistical differences were found between the results obtained by ADDM and broth micro-dilution for classifying bacterial isolates as susceptible or resistant according to the National Committee of Clinical Laboratory Standards.

Abstract The pleuromutilins are the only antimicrobial agents with sufficient minimum inhibitory concentration (MIC) values left to treat swine dysentery in Sweden. Other antimicrobials are either not approved for use against swine dysentery or only partly active against Brachyspira hyodysenteriae. To date, in Sweden two pleuromutilins, tiamulin and valnemulin, are authorized for use in pigs. This study includes a comparison between MICs of tiamulin and valnemulin for Swedish field isolates of B. hyodysenteriae, as determined by broth dilution. For different isolates the MIC of tiamulin was between 0 and 8 times higher than that of valnemulin. No resistance to pleuromutilins was recorded (tiamulin MIC range 0.031–2 μg/ml, valnemulin MIC range ≤0.016–1 μg/ml). In vitro development of tiamulin resistance was also studied. Two B. hyodysenteriae and two B. pilosicoli strains became resistant to tiamulin following reiterated passages on agar containing tiamulin in increasing concentrations. The resistance emerged slowly and three of the strains that went through more than 60 passages increased their tiamulin MICs from 0.031–0.25 to more than 128 μg/ml. The tiamulin MIC for one B. hyodysenteriaestrain that went through 29 passages increased from 0.0125 to 4 μg/ml. One B. pilosicoli strain developed cross-resistance to valnemulin; the MIC increased from 0.25 to more than 64 μg/ml. The valnemulin MIC for one B. hyodysenteriae strain increased from 0.031 μg/ml to 32 μg/ml. Valnemulin MIC was not determined for the B. hyodysenteriae strain that only went through 29 passages. The valnemulin MIC of the other B. pilosicoli strain increased from 0.031 to 4 μg/ml.

The objectives of the present study are to generate knowledge of the ecology and epidemiology of enterococci in the food chain by studying the following: (1) the population structure (in measures of abundance, number of vancomycin resistant strains, antibiotic resistance patterns, diversity, and stability) among enterococcal populations in different geographical regions and in different links of the food chain (2) possible transmission of strains through the food chain and between hospital environments and the food chain (3) the association between vancomycin resistance and individual strains of enterococci and (4) the diversity of the drug resistance genes in enterococci. So far, 1578 samples have been collected from different countries within the EU (Sweden, Denmark, UK and Spain), and from different habitats (pig farms, carcasses in slaughter houses, soil, manure, water, sewage, and humans). Total and vancomycin resistant enterococcal populations in each sample have been enumerated and more than 12000 isolates have been characterised by phenotyping. Representative isolates are further species identified and characterised by genotyping and MIC determination and from antibiotic resistant isolates the resistance genes are characterised.

Five Finnish Ayrshire cows in mid or end-lactation were treated with 40 mg sulphadiazine/kg and 8 mg trimethoprim/kg using intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) routes. Elimination of sulphadiazine was not affected by the route of administration (median t½4.4–5.0 h) while elimination of trimethoprim was strongly limited by slow absorption from the injection site after s.c. and i.m. administration (median for apparent t½. 21–25 h) compared to that after i.v. administration (median t½ 1.2 h; p<0.05). The median bioavailability of trimethoprim was also decreased, being 37% and 55% after s.c. and i.m. administration, respectively. When i.v. administration was used, trimethoprim concentration exceeded 0.1 mg/l in milk between 0.15–8 h while sulphadiazine concentrations above 2 mg/l were maintained from 0.5–2 h to 8 h. After s.c. and i.m. administration sulphadiazine in milk behaved similar to that after i.v. administration, while trimethoprim time-concentration curves were flat and trimethoprim concentrations were around 0.1 mg/l for an extended period of time (8–12 h). Median Cmax values in milk were only 0.07 mg/l and 0.10 mg/l for s.c. and i.m. administrations, respectively After s.c. administration, 4 out of 5 cows showed signs of pain. After i.m. administration, 2 of the cows showed clear signs of pain and one had some local tenderness at the site of injection.