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Little is known about the antibiotic resistance of E. coli O157 in The Netherlands. In this study, 218 human and 247 nonhuman samples, isolated between 1998 and 2003, were tested for antimicrobial resistance. About 5.5% of E. coli O157 isolates from human samples were resistant, as were about 4.00% of E. coli O157 isolates from non-human samples. These figures are lower than those reported in the literature. Class I integrons were found in six multiresistant isolates. This type of integron is also found in commensal E. coli in food animals and Salmonella spp. One of the integron-positive isolates contained the beta-lactamase bla(TEM-1b) and an extended spectrum beta-lactamase (ESBL), which belongs to the group 2 CTX-M enzymes. This is the first report of these beta-lactamases in E. coli O157 isolated from chicken.

The development and test of detection models for oestrus and mastitis in dairy cows is described in a PhD thesis that was defended in Wageningen on June 5, 2000. These models were based on sensors for milk yield, milk temperature, electrical conductivity of milk, and cow activity and concentrate intake, and on combined processing of the sensor data. The models alert farmers to cows that need attention, because of possible oestrus or mastitis. A first detection model for cows, milked twice a day, was based on time series models for the sensor variables. A time series model describes the dependence between successive observations. The parameters of the time series models were fitted on-line for each cow after each milking by means of a Kalman filter, a mathematical method to estimate the state of a system on-line. The Kalman filter gives the best estimate of the current state of a system based on all preceding observations. This model was tested for 2 years on two experimental farms, and under field conditions on four farms over several years. A second detection model, for cow milked in an automatic milking system (AMS), was based on a generalization of the first model. Two data sets (one small, one large) were used for testing. The results for oestrus detection were good for both models. The results for mastitis detection were varying (in some cases good, in other cases moderate). Fuzzy logic was used to classify mastitis and oestrus alerts with both detection models, to reduce the number of false positive alerts. Fuzzy logic makes approximate reasoning possible, where statements can be partly true or false. Input for the fuzzy logic model were alerts from the detection models and additional information. The number of false positive alerts decreased considerably, while the number of detected cases remained at the same level. These models make automated detection possible in practice.

In 1994 (August-September) and in 1995 (July-October) faeces of Dutch veal calves and adult cattle was examined for the presence of verocytotoxin-producing Escherichia coli O157 (O157 VTEC). The samples were collected at slaughterhouses. In 1994, O157 VTEC were isolated from three (0.9%) of 365 fecal samples of veal calves. Faeces of adult cattle was not collected. In 1995, O157 VTEC were isolated from one (0.5%) of 18.3 fecal samples of veal calves and from 30 (11.1%) of 270 fecal samples of adult cattle. In 1994, the organisms were isolated by selective plating onto both sorbitol MacConkey agar (SMAC) and SMAC containing tellurite and cefixime (TC-SMAC) following selective enrichment in modified trypton soya broth with acriflavin (mTSB + a). In 1995, the samples were enriched in modified E. coli broth with novobiocin (mEC + n), and in addition to directly plating onto TC-SMAC the enriched cultures were plated after incorporation of an immunomagnetic separation step of E. coli O157. All 30 strains isolated from adult cattle were isolated with the immunomagnetic separation procedure. Four of the 30 samples were determined positive also by directly plating onto TC-SMAC. The sample from the veal calve was determined positive only by directly plating onto TC-SMAC. Plating onto SMAC resulted only in negative results. Characterization of the O157 VTEC isolates showed similarities between isolates of humans and cattle. Additional experiments need to be done concerning this aspect. From this study it appeared that also Dutch cattle are a reservoir of O157 VTEC.

A total of 550 faecal samples of cattle was examined on the presence of Escherichia coli serotype O157:H7 using a method comprising a selective enrichment and isolation medium. Escherichia coli O157:H7 was not isolated from any of the samples tested.

Eight-two bovine Pasteurella haemolytica strains were serotyped. The majority of the strains were isolated from calves which had died from fibrinous pneumonia and small numbers from cases of pleuritis, sepsis and abortion. A total of eight different serotypes were noticed. Serotype A1 was found to be the most prevalent 37.8 per cent, followed by serotype A2 with 20.7 per cent. Antibiotic resistance was found for sulfonamide, tetracycline and penicillin in about half of all strains. Conventional combination of biotype to serotype per strain was not confirmed by the results of arabinose and trehalose fermentation.

The development of sensitivity to antibiotic and chemotherapeutic agents of a number of important pathogens isolated from veal and replacement calves showed adverse features. This impression is gained when the results of sensitivity testing of these bacteria during the past twenty years are compared. The findings were provided by the Animal Health Service in the Province of Gelderland.

A prospective study of the bacterial flora of the haircoat, rumen contents and interdigital skin was done as part of investigations on the contamination and prevention of contamination of carcases and livestock products of veal calves in the slaughter line. These constitute a source of contamination of the meat during slaughter. Twenty calves were studied. The coats of these calves were found to be severely contaminated by bacteria of faecal origin. In addition to enterobacteriaceae showing multiple resistance to antibiotics and chemotherapeutic agents, large numbers of pseudomonadaceae and Lancefield D streptococci were present in the rumen contents. Small numbers of lactobacilli were identified in the rumen contents. It is concluded that they may have detrimental effects on the safety and quality of the veal and carcases.

Chloramphenicol is used in the treatment of respiratory infections in veal calves. Antibiotic resistance of Pasteurella to chloramphenicol was rarely observed upto 1984. The increase was recorded from 1984. The following dosages are recommended on the basis of findings reported in the literature: a daily dosage of 40 mg/kg body weight of chloramphenicol palmitate by oral route, and a daily dosage of 20-50 mg/kg body weight of chloramphenicol administered parenterally and preferably given in two injections daily. Malabsorption and aplastic anaemia were observed as toxic effects when a dose of 100 mg/kg daily was administered for five days and ten days respectively. Chloramphenicol may give rise to aplastic anaemia in human individuals, but also to idiosyncrasy, allergy and diminished activity of the bone marrow. Foods of animal origin should be free from residues of chloramphenicol. A three-week interval between administration of chloramphenicol to veal calves and slaughter would appear to be reasonable. Experience of alternatives to chloramphenicol in the treatment of Pasteurellosis in veal calves, such as flumequine and doxycylin, is still too limited in actual practice to conclude that chloramphenicol can be dispensed with.

Clostridium botulinum, mainly type B, was constantly found to be present on cattle farms. The organism was isolated both from samples of the soil of pastures and from the faeces of cattle during the winter housing period. The number of C. botulinum type B in samples of soil varied from 10 to 300 organisms per 100 grams. Contamination with C. botulinum was found to be of a similar order of magnitude on farms on which pastures are regularly dressed with sewage sludge. C. botulinum was detected in 13 per cent of the faecal samples (420 samples of one gram each). Particularly grass silage pits prepared with wilted grass were found to provide a possible link between contamination of pastures and cattle.

The antibiograms of the most important pathogenic bacteria isolated from pigs and cattle in the laboratory of the Animal Health Service of the province of Gelderland during the period from 1974 up to and including 1979 are reviewed. The findings are compared with those during a previous period. Adverse developments were not found to be present as regards P. multocida, B. bronchiseptica, H. parahaemolyticus, streptococci and S. typhimurium in pigs. Only pathogenic E. coli as the causative organism of oedema disease (colibacillary) enterotoxaemia) showed reduced sensitivity to co-trimoxazole; an increase in sensitivity to streptomycin, tetracycline and neomycin was observed. The pattern of pathogenic E. coli in breeding calves showed a variable, through on the whole not so favourable picture. There was a negative development as regards S. dublin in veal calves in view of the fact that sensitivity, particularly that to chloramphenicol and tetracycline, but also that to furazolidone and co-trimazole, had diminished. In the case of S. typhimurium, there was a relationship between the sensitivity pattern and a number of phage types. Ever since 1977, P. haemolytica has shown a diminishing and partly variable sensitivity to penicillin, streptomycin, tetracycline and sulphonamide. This was the case to a far less extent with P. multocida.

Since 1974, tetracycline resistance in salmonellae of human and porcine origin has decreased nation-wide in the Netherlands. This decrease had coincided with the ban on incorporation of tetracycline in animal feeds for growth-promotion.

Approximately 20,000 strains of Salmonella were screened annually for resistance to tetracycline, chloramphenicol, kanamycin and ampicillin since 1959, and also to trimethoprim since 1978. Tetracycline-resistant strains increased in human subjects and pigs from 1961. After the ban on incorporation of tetracycline in animal feeds for nutritive purposes in 1974, the proportion of tetracycline-resistant strains in pigs and human subjects decreased. In veal calves, the number of strains of S. typhimurium and S. dublin resistant to multiple drugs increased from 1972. Strains resistant to multiple antibiotics in man were mainly isolated from adoptive children from Indonesia. No further spread of these strains was observed. So far, strains similar to those in calves resistant to multiple drugs were only incidentally isolated from human patients.

Strains of Staphylococcus aureus (n = 319) from bovine quarter milk were tested for susceptibility to antimicrobial drugs. The minimum inhibitory concentration (MIC), was determined by agar dilution methods, and the diameter of the inhibition area was determined by agar diffusion methods. In addition beta-lactamase production was tested. The strains tested showed resistance to penicillin, (38.4%), oxytetracyclin (21.2%), and streptomycin (11.5%). Little or no resistance was found to the other antimicrobials in this study. A strong correlation between dilution and diffusion methods was calculated for oxytetracyclin: r = 0.88, and for streptomycin: r = -0.90; correlation for penicillin was weaker: r = -0.66. Since 17% of the strains with an MIC for penicillin less than 0.16 mg/L are still able to produce beta-lactamase, we recommend that when antibiotic susceptibility of staphylococci is examined, beta-lactamase production should also be tested. Dapsone, a sulfone compound, formerly not considered a chemotherapeutical drug under Dutch law, had an MIC less than or equal to 0.64 mg/L for 85% of the strains. Therefore, we recommend that sulfone compounds should be registered under the new Veterinary Medicines Act. Since the resistance patterns of S. aureus strains to most antimicrobial drugs were the same as those seen in earlier studies, we find no reason to resort to new generations of broad-spectrum antibiotics in routine prevention and treatment of mastitis.

The results of a bacteriological and serological study of the presence of L. hardjo on a dairy farm in view of a case of milk fever in a farmer are reviewed. In addition, the epidemiology, prevention and possible treatment of the infection on the dairy farm are discussed.

Haemolysis as the sole criterion of the pathogenicity of staphylococci detected on bacteriological examination of slaughtered animals should be reconsidered.