Resistance to antimicrobial agents used for animal therapy in pathogenic-, zoonotic- and indicator bacteria isolated from different food animals in Denmark: a baseline study for the Danish Integrated Antimicrobial Resistance Monitoring Programme (DANMAP)

This study describes the establishment and first results of a continuous surveillance system of antimicrobial resistance among bacteria isolated from pigs, cattle and broilers in Denmark. The three categories of bacteria tested were: 1) indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium), 2) zoonotic bacteria (Campylobacter coli/jejuni, Salmonella enterica, Yersinia enterocolitica), and 3) animal pathogens (E. coli, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Staphylococcus hyicus, Actinobacillus pleuropneumoniae). A total of 3304 bacterial isolates collected from October 1995 through December 1996 were tested for susceptibility to all major classes of antimicrobial agents used for therapy in Denmark. Bacterial species intrinsically resistant to an antimicrobial were not tested towards that antimicrobial. Acquired resistance to all antimicrobials was found. The occurrence of resistance varied by animal origin and bacterial species. In general, resistance was observed more frequently among isolates from pigs than from cattle and broilers. The association between the occurrence of resistance and the consumption of the antimicrobial is discussed, as is the occurrence of resistance in other countries. The results of this study show the present level of resistance to antimicrobial agents among a number of bacterial species isolated from food animals in Denmark. Thus, the baseline for comparison with future prospective studies has been established, enabling the determination of trends over time.

Surveillance of antimicrobial resistance in bacteria isolated from food animals to antimicrobial growth promoters and related therapeutic agents in Denmark

This study was conducted to describe the occurrence of acquired resistance to antimicrobials used for growth promotion among bacteria isolated from swine, cattle and poultry in Denmark. Resistance to structurally related therapeutic agents was also examined. Three categories of bacteria were tested: 1) indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium), 2) zoonotic bacteria (Campylobacter, Salmonella, Yersinia enterocolitica), and 3) animal pathogens (E. coli, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Staphylococcus hyicus, Actinobacillus pleuropneumoniae). All antimicrobials used as growth promoters in Denmark and some structurally related therapeutic agents (in brackets) were included: Avilamycin, avoparcin (vancomycin), bacitracin, carbadox, flavomycin, monensin, olaquindox, salinomycin, spiramycin (erythromycin, lincomycin), tylosin (erythromycin, lincomycin), and virginiamycin (pristinamycin). Bacterial species intrinsically resistant to an antimicrobial were not tested towards that antimicrobial. Breakpoints for growth promoters were established by population distribution of the bacteria tested. A total of 2,372 bacterial isolates collected during October 1995 to September 1996 were included in the study. Acquired resistance to all currently used growth promoting antimicrobials was found. A frequent occurrence of resistance were observed to avilamycin, avoparcin, bacitracin, flavomycin, spiramycin, tylosin and virginiamycin, whereas resistance to carbadox, monensin, olaquindox and salinomycin was less frequent. The occurrence of resistance varied by animal origin and bacterial species. The highest levels of resistance was observed among enterococci, whereas less resistance was observed among zoonotic bacteria and bacteria pathogenic to animals. The association between the occurrence of resistance and the consumption of the antimicrobial is discussed. The results show the present level of resistance to growth promoters in bacteria from food animals in Denmark. They will form the baseline for comparison with future prospective studies, thereby enabling the determination of trends over time.

A study of phage- and ribotype patterns of Staphylococcus aureus isolated from bovine mastitis in the Nordic countries

This study was conducted to investigate the geographical distribution of phage and ribotypes of Staphylococcus aureus causing bovine mastitis in the 5 Nordic countries. A total of 403 isolates of S. aureus was isolated from 403 different dairy herds. One hundred five strains were isolated in Denmark, 81 in Finland, 17 in Iceland, 96 in Norway and 104 in Sweden. The isolates were phage typed and characterized for their EcoRI restriction fragment length polymorphisms of the genes encoding ribosomal RNA (ribotyping). A total of 351 (87%) of the 403 isolates could be typed by phages assigning them to 25 different phage types. Two to 3 different phage types predominated within each country. One type (29/52) accounted for 36% of all the isolates and was found in 4 of the countries. A total of 87 different ribotypes was found among the isolates investigated. As for phage typing 2 to 3 different types predominated within countries. However, except for one type (ribotype 1), which was commonly found in Denmark, Sweden and Finland, different ribotypes predominated within each country. The combination of phage and ribotyping assigned the isolates to 178 different types. Ninety-six percent of the isolates of ribotype 1 belonged to phage type 29/52. This combined type accounted for 17% of all the 403 isolates. These findings show that a large number of different types of S. aureus can be isolated from cases of bovine mastitis. However, few types predominate within different countries. These predominating types seem to be specific in each country, however, a single type was common for both Denmark, Sweden and Finland. This could suggest differences in the virulence or in modes of transmission of predominating and rare types of S. aureus associated with bovine mastitis.

Serological characterization and antimicrobial susceptibility of Streptococcus suis isolates from diagnostic samples in Denmark during 1995 and 1996

At the Danish Veterinary Laboratory Streptococcus suis infections in pigs were diagnosed in 114 cases in 1995 and in 151 cases in 1996. Isolates were serotyped using specific antisera against type 1 through 28 and a total of 67 cases from 1995 and 113 cases in 1996 were tested for resistance to 11 antimicrobial agents. The majority of cases were lung diseases (57%), followed by septicaemia (16%), meningitis (15%) and endocarditis (8%). Almost 96% of the isolates could be typed using the 28 antisera. The most common serotype was serotype 2 (29%), followed by serotype 7 (17%), and serotypes 3, 4 and 8 (9-10%). The remaining serotypes were observed in frequencies of less than 5%. Serotype 7 was more commonly isolated from septicaemia than the other serotypes. Serotype 2 was more commonly isolated from pigs older than 4 weeks compared to the other serotypes. Most isolates were susceptible to amoxycillin + clavulanate, ampicillin, ceftiofur, enrofloxacin, penicillin, spectinomycin, tiamulin and trimethoprim + sulphadiazine. A high frequency (> 30%) of resistance to tetracycline was observed. Among isolates of serotype 2, 9.7% were resistant to lincomycin and 12.9% to spiramycin. Among other serotypes 56.8% were resistant to lincomycin and spiramycin. The differences in susceptibility between isolates of serotype 2 and the other serotypes were statistically significant. Compared to a previous Danish study the distribution of serotypes of S. suis causing infections among pigs in Denmark has changed during the last 15 years.

Prevalence and duration of intramammary infection in Danish heifers during the peripartum period

Milk samples were collected from 180 heifers from 20 herds around parturition to study the prevalence and persistence of intramammary infection (IMI). A total of 3382 quarter milk samples was collected each week from 4 wk before parturition to 4 wk after parturition. Staphylococcus chromogenes, the most commonly found bacterial species before parturition, was isolated from 15% of all quarters. However, IMI with Staph. chromogenes decreased shortly after parturition to around 1% of quarters. Infectious with Staphylococcus simulans and Staphylococcus epidermidis occurred in 1 to 3% of quarters both before and after parturition. Infections with Staph. simulans persisted in the same quarter for several weeks, but IMI with Staph. epidermidis were transient. Streptococcus dysgalactiae was isolated from 4 to 6% of quarters before and immediately after parturition, but the prevalence of IMI with Strep. dysgalactiae decreased. A strong association existed between IMI with Strep. dysgalactiae before parturition and IMI with Strep. dysgalactiae after parturition, and, using DNA typing, the persistence of 9 IMI was confirmed. Infections with Staphylococcus aureus rarely occurred before parturition, but the rate of IMI with Staph. aureus greatly increased during the 1st wk after parturition. No association was found between bacterial status before parturition and IMI with Staph. aureus after parturition. Overall, the presence of bacterial IMI in a quarter before parturition increased the risk of IMI for the lactating cow. This study demonstrated that variability in prevalence and duration of IMI according to bacterial species occurred around first parturition.

Molecular characterization of Escherichia coli strains isolated from pigs with edema disease

The present study was conducted to investigate the epidemiological relationship of isolates of Escherichia coli causing edema disease. Classical edema disease has not previously been described in Denmark, but between February 1994 and November 1995 cases appeared in 51 pig herds, among which direct or indirect trading contacts were confirmed for 36 of the herds. A total of 213 isolates from pigs with edema disease in Denmark and other countries and 23 E. coli O139 isolates from pigs with diarrhea or healthy pigs were analyzed to characterize their O serogroups, HindIII ribotypes, and pulsed-field gel electrophoresis (PFGE) types, and 183 of the isolates were also analyzed for their plasmid profiles. The resulting PFGE types of the isolates from pigs with edema disease were examined by cluster analysis. Ten isolates from three herds could not be typed with the available O antisera, whereas all other isolates were of serotype O139. However, all isolates from pigs with edema disease belonged to the same HindIII ribotype, which was not observed among the isolates from pigs with diarrhea or healthy pigs. All isolates from Danish pigs with edema disease except for three isolates originating from two herds belonged to the same or closely related XbaI PFGE types; the other three isolates were assigned to possibly related types. Isolates from pigs with edema disease in different countries belonged to different PFGE types. All isolates from Danish pigs with edema disease grouped together in one cluster, in contrast to isolates from other countries, which did not form any clusters. E. coli strains of serogroup O139 from pigs with diarrhea or isolated from the feces of healthy Danish pigs were very different. Plasmid profiles differed largely among isolates. However, among the isolates from Danish pigs with edema disease, one type predominated within herds. The present study indicated that most, if not all, of the observed cases of edema disease in Denmark were part of the same outbreak. The combination of PFGE typing and ribotyping was useful for studying the possible clonal relationship among strains, whereas plasmid profiling was less informative.

A study of phage- and ribotype patterns of Staphylococcus aureus isolated from bovine mastitis in the Nordic countries

This study was conducted to investigate the geographical distribution of phage and ribotypes of Staphylococcus aureus causing bovine mastitis in the 5 Nordic countries. A total of 403 isolates of S. aureus was isolated from 403 different dairy herds. One hundred five strains were isolated in Denmark, 81 in Finland, 17 in Iceland, 96 in Norway and 104 in Sweden. The isolates were phage typed and characterized for their EcoRI restriction fragment length polymorphisms of the genes encoding ribosomal RNA (ribotyping). A total of 351 (87%) of the 403 isolates could be typed by phages assigning them to 25 different phage types. Two to 3 different phage types predominated within each country. One type (29/52) accounted for 36% of all the isolates and was found in 4 of the countries. A total of 87 different ribotypes was found among the isolates investigated. As for phage typing 2 to 3 different types predominated within countries. However, except for one type (ribotype 1), which was commonly found in Denmark, Sweden and Finland, different ribotypes predominated within each country. The combination of phage and ribotyping assigned the isolates to 178 different types. Ninety-six percent of the isolates of ribotype 1 belonged to phage type 29/52. This combined type accounted for 17% of all the 403 isolates. These findings show that a large number of different types of S. aureus can be isolated from cases of bovine mastitis. However, few types predominate within different countries. These predominating types seem to be specific in each country, however, a single type was common for both Denmark, Sweden and Finland. This could suggest differences in the virulence or in modes of transmission of predominating and rare types of S. aureus associated with bovine mastitis.

A preliminary study on the pathogenicity of Bacillus licheniformis bacteria in immunodepressed mice

The pathogenicity of 13 strains of Bacillus licheniformis was studied in immunodepressed mice. The strains had been isolated from cases of bovine abortions (n = 5), bovine feedstuffs (n = 3), soil (n = 1), and grain products (n = 2). The origin of two strains was unknown. Groups of 10 mice were inoculated intravenously with B. licheniformis bacteria at doses from < 10(6) to 10(10) colony-forming units. Following 7 days of infection, the animals were euthanized and examined bacteriologically, histologically, and immunohistochemically using a PAP technique based on primary polyclonal rabbit anti-B. licheniformis antibodies. B. licheniformis bacteria were reisolated from the liver, spleen or kidneys of mice in all groups. Inflammatory lesions were present in mice of all immunodepressed groups, but only brain and pulmonic lesions were definitely attributed to B. licheniformis infection, as strong immunostaining was found within these lesions. It is concluded that all strains of B. licheniformis examined were pathogenic for immunodepressed mice, and that spontaneous infections may be established by bacterial strains to which susceptible individuals are accidentally exposed.

Mycoplasma hyopneumoniae infection in pigs: duration of the disease and evaluation of four diagnostic assays

200 SPF pigs were infected by aerosol with Mycoplasma hyopneumoniae and the development of clinical signs, serological and pathological reactions were studied. Mean time to onset of coughing was 13 days. A mean delay of 9 days was observed from onset of coughing until seroconversion against M. hyopneumoniae as measured by ELISA. At an individual level, the sensitivity for this ELISA was estimated to 98-100% and the specificity to 93-100%. Pasteurella multocida was isolated from the majority of the lungs 4 weeks post inoculation with M. hyopneumoniae and the lung lesions in pigs were significantly larger when P. multocida was present as compared to pigs with M. hyopneumoniae alone. An evaluation of cultivation, immunofluorescence, ELISA and polymerase chain reaction for demonstration of M. hyopneumoniae in lungs showed that all four methods have a high sensitivity in the acute stages of pneumonia. In the later stages the sensitivity of cultivation was superior to the other methods. No differences in specificity were observed between the methods. The antigen-ELISA OD values and the immunofluorescence scores revealed a strong positive correlation. Nasal swabs were additionally used for demonstration of M. hyopneumoniae and the polymerase chain reaction was found superior to the other methods.

Epidemiological aspects of group B streptococci of bovine and human origin

Restriction fragment length polymorphism of the gene encoding rRNA (ribotyping) was used in combination with conventional epidemiological markers to study phenotypic variations among Streptococcus agalactiae of bovine origin and the possible epidemiological interrelationship between the bovine and human reservoirs of Streptococcus agalactiae. The bovine material constituted 53 strains (9 antigen combinations) isolated from 11 herds. Herds with a uniform as well as heterogenic antigenic pattern were included. Furthermore, strains isolated in the course of time from the same persistently infected quarters were examined. The human material constituted 16 strains, 4 each of 4 serotypes, isolated from healthy carriers. Finally, nine serotype- and the group reference strains were examined. All strains were serotyped by double diffusion in agarose gel, biotyped (lactose +/-), and ribotyped using two restriction enzymes, Hind III and HhaI. All isolates could be typed by ribotyping and seven ribotypes were identified among the reference strains. The restriction enzymes used alone or in combination gave typing results that allowed discrimination between and within serotype. Combined use of serotype, Hind III and HhaI ribotypes produced 11 types among the 16 human strains. Ribotype analysis discriminated between herds infected with the same serotype. Strains of varying antigenic patterns from the same herd had the same ribotype. Phenotypic variations in serotype observed in persistent intramammary infection were not related to genetic changes as monitored by ribotype. Two ribotypes were represented among both bovine and human strains. The discriminating capability of lactose fermentation was of limited value.

Genotypic and phenotypic diversity of Streptococcus dysgalactiae strains isolated from clinical and subclinical cases of bovine mastitis

This study was conducted to characterize Streptococcus dysgalactiae isolated from cases of bovine mastitis. One hundred strains from 100 dairy herds in Denmark, 29 strains from 29 dairy herds in Pennsylvania, USA, 7 reference strains and 18 strains consisting of 9 paired strains from 9 quarters were investigated using biotyping (utilization of tagatose and sorbitol) and HindIII ribotyping. Four different biotypes were observed. Only 34 of the 100 Danish strains utilized either tagatose or sorbitol, 18 utilized tagatose, 15 sorbitol and 1 both tagatose and sorbitol. In contrast, among the American strains one (3.4%) did neither utilize tagatose or sorbitol, twenty (69.0%) utilized tagatose, four (13.8%) sorbitol and four (13.8%) both tagatose and sorbitol. HindIII ribotyping produced 15 different types among all the strains, 9 different types were found among the Danish strains and 8 types among American strains. Five types were observed among both the Danish and the American strains. The 7 reference strains were assigned to 5 different ribotypes. Three type strains (ATCC 27957, NCTC 4670, NCTC 4335) were assigned to a type that was present among both the Danish and the American strains. Ribotyping was the most discriminatory typing method. Agreement between ribo- and biotyping was observed, and especially pronounced among the Danish strains. The 9 paired strains were in case found to have identical ribo- and biotype.

Listeria monocytogenes in bovine mastitis. Possible implication for human health

During the 23-year period 1972 through 1994 quarter milk samples from 1,132,958 cows originating from 36199 herds were examined for the presence of Listeria monocytogenes. Through the period the reference population amounted to 12,742,600 cow years and 401,682 herd years. The percentage of cows infected with L. monocytogenes varied from 0.01 to 0.1% (mean 0.04%) and of herds with an infected cow from 0.2 to 4.2% (mean 1.2%) through the period, showing a low but constant level of infection. A comparison of 33 isolates from bovine mastitis and 27 human clinical isolates was made by sero- and ribotyping. Serotyping showed that all bovine and 17 (63%) of the human isolates belonged to serogroup 1, whereas 10 (37%) of the human isolates belonged to serogroup 4. Ribotyping using EcoRI as restriction enzyme divided the 60 isolates into 16 different types, 7 of which were found among both the bovine and human types. The combination of the typing methods showed that 26 (79%) bovine and 13 (48%) human isolates shared common types. This study showed that a low but constant percentage of Danish dairy herds have cows infected with L. monocytogenes and that some of the bovine types could be found among types causing human infections.

Listeria monocytogenes in poultry and poultry products: epidemiological investigations in seven Danish abattoirs

Listeria monocytogenes was isolated from 11/236 (4 x 7%) caecal samples from parent flocks, providing broilers to the abattoirs investigated. Caecal samples from 2078 broilers representing 90 randomly selected broiler flocks were negative for L. monocytogenes. A total of 3080 samples from seven abattoirs including poultry processing line samples, and final products were also examined for L. monocytogenes. Listeria monocytogenes was isolated in 0 x 3% to 18 x 7% of the samples collected in the different abattoirs. Epidemiological typing of 247 L. monocytogenes isolates, including serotyping, phage typing, pulsed-field gel electrophoresis and ribotyping revealed 62 different clones. Based upon typability and discriminatory power, DNA typing methods used were found equally suitable as epidemiological markers. Serotyping and phage typing were not found useful as epidemiological markers for poultry isolates of L. monocytogenes since only 120/247 (48 x 6%) isolates were typable by phage typing and 230/247 (93 x 1%) L. monocytogenes belonged to serotype 01 while 6/247 (2 x 4%) belonged to 04. The discovery of a few dominating clones in each abattoir might indicate an endemic occurrence of L. monocytogenes. It is concluded that L. monocytogenes in the broiler production is primarily localized to the abattoirs. The incidence of L. monocytogenes may be reduced by improving the hygiene.

Analysis of associations between major histocompatibility complex (BoLA) class I haplotypes and subclinical mastitis of dairy cows

The associations between BoLA class I haplotypes and subclinical mastitis were investigated using information on 333 cows from three different breeds and crossbreeds from 14 dairy herds in Denmark. Somatic cell count and bacteriological status were used as markers for subclinical mastitis. Associations between BoLA class I haplotypes and IMI status were also determined. The association between BoLA class I haplotypes and subclinical mastitis was weak. The A10(W50), A11, A12(A30), A16, A19(A6), A21, A26, and A31(A30) alleles were associated with different markers of subclinical mastitis. Susceptibility or resistance to the two bacteria categories was associated with different alleles. This study indicated that BoLA antigens may be involved in resistance to mastitis and that resistance may be specific for a particular pathogen.

Development of a peroxidase-antiperoxidase (PAP) technique for the identification of Haemophilus somnus in pneumonic calf lungs in Denmark

A peroxidase-antiperoxidase (PAP) technique was developed for the identification of Haemophilus somnus bacteria in lung tissues of calves. Antisera raised against somatic and wall antigens of a Danish and American strain of H. somnus were produced. Experimentally infected murine tissues were used for the determination of the sensitivity and specificity of antiserum that had been heterologously absorbed with antigens of cross-reacting bacteria, i.e. Pasteurella haemolytica and Pasteurella multocida. None of the antisera reacted with Actinomyces pyogenes. An antiserum raised against somatic antigens of the Danish strain of H. somnus revealed the highest sensitivity in the PAP technique and became specific following absorption. Heterologous absorption also rendered this antiserum specific in crossed immunoelectrophoresis. Subsequently, the PAP technique was applied on formalin-fixed pneumonic lung tissues of 86 calves. An immunodiagnosis of H. somnus pneumonia was obtained in 15 of 17 lungs from which the bacterium had been isolated. Moreover, immunostained bacteria were also demonstrated in 20 lungs from which H. somnus had not been isolated. Thus, application of immunohistochemistry significantly enhanced the diagnostic sensitivity of H. somnus pneumonia of calves and should be used as a potent supplementary tool for the routine screening of suspected lung tissues of calves from which bacterial isolation is negative.

Experimental infection in mice with Bacillus licheniformis

The pathogenicity of Bacillus licheniformis was assessed in normal and immunodepressed BALB/c mice. The animals were challenged intravenously with 4 x 10(7) colony forming units of B. licheniformis (ATCC 14580) and both normal and immunodepressed mice were susceptible. However, the infection was more severe in the immunosuppressed animals. In normal mice, lesions were restricted to the liver and kidneys, while lesions also occurred in other organs of immunodepressed mice. By crossed immunoelectrophoresis it was shown that antigens of B. licheniformis are potent immunogens, and the bacteria could be identified in tissue sections by immunostaining. Immunohistochemically, B. licheniformis was demonstrated in hepatic and pulmonic macrophages, and from some animals the bacteria were also reisolated.

Classification of Erysipelothrix strains on the basis of restriction fragment length polymorphisms

Restriction fragment length polymorphisms of the 16S rRNA genes of Erysipelothrix strains were studied by cleavage of the chromosomal DNA with restriction endonuclease EcoRI, followed by hybridization to a 420-bp internal fragment of the 16S rRNA gene. Thirty-two Erysipelothrix type and reference strains were classified, together with seven field strains. Reference strains of all serotypes and the type strains of Erysipelothrix rhusiopathiae and Erysipelothrix tonsillarum were included. Nine ribopatterns were observed. Pattern A was represented by 16 strains and included strains of serotypes 1b, 2 to 8, 11 to 13, 15 to 17, 19, and 23. Pattern B was represented by two strains (serotypes 1a and 9). Pattern C was represented by five strains (serotypes 5, 6, and 21). Pattern D was represented by one strain of serotype 4. Pattern E was represented by 11 strains of serotypes 2, 7, 10, 20, 22, 24, and 25. Patterns F, G, H, and I were each represented by a single strain of serotypes 26, 2, 18, and 3, respectively. All the different ribopatterns had some bands in common. Patterns B, C, and D were most similar to pattern A, while patterns F, G, H, and I resembled pattern E. Partial sequencing of the 16S rRNA gene of nine selected strains resulted in three different sequences, i.e., the typical E. rhusiopathiae sequence, the E. tonsillarum sequence, and a third sequence found for two strains. Strains of the same serotype were found to have different ribopatterns as well as different partial 16S rDNA sequences.

Staphylococcal and other bacterial species associated with intramammary infections in Danish dairy herds

Four thousand six hundred forty-five quarter milk samples from 1179 cows from 20 commercial dairy herds were examined in order to determine the prevalence of bacterial species. A total of 859 isolates from 839 (18.1%) culture positive samples could be assigned to 34 different species and subspecies. Diagnostics of staphylococcal species was based on conventional procedures able to differentiate between all 36 species and subspecies presently acknowledged. Staphylococcus aureus was found in 10.2% of the samples and was the most common species isolated. Streptococcus dysgalactiae (1.6%) and Streptococcus uberis (1.4%) were the second and third most common species isolated. Seventeen different coagulase negative staphylococcal species (CNS) were found in 4.1% of the samples. The most frequently isolated CNS were S. epidermidis (1.3%), S. chromogenes (1.0%) and S. simulans (0.7%). Isolates of S. aureus were phage typed, and isolates of S. epidermidis were investigated by phage typing, antibiogram typing, and biotyping. A total of 378 (79.9%) isolates of S. aureus could be typed by phages, assigning them to 18 different phage types. However, 6 phage types accounted for 92.1% of the typable isolates. One to 2 phage types predominated within each herd. Eleven (18%) isolates of S. epidermidis could be typed by phages, assigning the isolates to 3 different types. Biotyping of S. epidermidis produced a total of 8 different types, the most common accounting for 29.5% of the isolates. A total of 6 different antibiogram types were observed among all isolates of S. epidermidis. Resistance towards penicillin (36.1%), tetracycline (9.8%) and streptomycin (9.8%), were recorded in the isolates of S. epidermidis. However, 35 (57.4%) of the isolates were susceptible to all 12 antibiotics tested.

Lack of staphylococcal enterotoxin production among strains of Staphylococcus aureus from bovine mastitis in Denmark

Staphylococcal enterotoxins (SE’s) are a group of small exoproteins produced by some strains of Staphylococcus aureus. The SE’s, designated A to E according to their antigenic specificities, are important causes of food poisoning worldwide. Milk and dairy products are frequently associated with S. aureus enter-otoxin food poisoning, and it is supposed that infected milk from mastitic animals constitute the main source of enterotoxigenic S. aureus of animal origin (Bryon 1983, Gilmour & Harvey 1990, Bergdoll 1989). Indeed, S. aureus is the most common cause of bovine mastitis worldwide, and if mastitis strains produce SE this makes up an enormous reservoir of potential enterotoxin producers. The production of SE by S. aureus isolated from bovine mastitis have been investigated in several countries (Matsunaga et al. 1993, Kenny et al. 1993, Olson et al 1970, Orden et al. 1992, Olsvik et al. 1981, Adekeye 1980, Garcia et al. 1980, Abbar 1986, Harvey & Gilmour 1985). Since no studies have been performed on the prevalence of enterotoxigenic strains of S. aureus isolated from bovine mastitis in Denmark, a well characterized collection of S. aureus (Aarestrup et al. 1995) was investigated with respect to this property.

No effect of dieldrin on progesterone production in gilts

The effect of feeding pigs with dieldrin containing feed on the progesterone profile of the estrous cycle was investigated. Eight gilts comprising three controls and five treatment animals were given feed containing 40 ppm of dieldrin for 60 days. Dieldrin levels in mg/kg fat in tissues analysed were; fat 15.15, muscle 18.68, liver 12.21, corpus luteum 13.68, kidney 14.16, serum 2.84 and brain 1.66. On analysing serum progesterone levels no significant difference (P > 0.10) between the progesterone profile of the control and the treatment animals was observed.

Interquarter comparison of markers of subclinical mastitis: somatic cell count, electrical conductivity, N-acetyl-beta-glucosaminidase and antitrypsin

We have evaluated the usefulness in mastitis diagnostics of new diagnostic measures using the continuous nature of the variation in quarter milk samples of four inflammatory markers: somatic cell count, N-acetyl-beta-glucosaminidase (EC 3.2.1.30), electrical conductivity and antitrypsin. A two-way analysis of variance was performed for each of the inflammatory markers on results from 273 cows sampled six times at 14 d intervals. Adjustment for the individual cow's mean removed approximately half the total variation for all four markers, indicating that comparisons in marker levels between quarters without taking the cows' overall level into account, as is done in diagnostic keys based on fixed threshold, is a rash procedure. After adjusting for the individual cow means, the total variation of the marker observations was partitioned in three sources of variation: between the four quarter levels, between different sampling days, and the experimental error, i.e. the variation within each quarter over the study period. As expected, the variation between quarters accounted for the largest percentage of the variation (44-65%). In contrast the variation between days was only 16-34% and of the same magnitude as the experimental error. These figures can profitably be taken into account when designing experiments in future mastitis research studies. They imply that mastitis diagnostics based on quarter milk samples collected over time will be influenced only slightly by random biological variation and that the same relative differences that exist in marker levels between the four quarters of a cow as a rule will be disclosed irrespective of sampling day. Thus, the udder health state is relatively stable when determined by these inflammatory markers. In addition to simple correlations between markers measured on the same day, correlations of the logarithm of the interquarter ratios and of the experimental errors were computed. Stronger associations between the markers emerged and these correlations reflect more precisely than simple correlations the real diagnostic relations of the markers.