Effects of a mastitis J5 bacterin vaccination on the productive performance of dairy cows: An observational study using propensity score matching techniques.

Inferring causal effects between variables when utilizing observational data is challenging due to confounding factors not controlled through a randomized experiment. Propensity score matching can decrease confounding in observational studies and offers insights about potential causal effects of prophylactic management interventions such as vaccinations. The objective of this study was to determine potential causality and impact of vaccination with an Escherichia coli J5 bacterin on the productive performance of dairy cows applying propensity score matching techniques to farm-recorded (e.g., observational) data. Traits of interest included 305-d milk yield (MY305), 305-d fat yield (FY305), 305-d protein yield (PY305), and somatic cell score (SCS). Records from 6,418 lactations generated by 5,121 animals were available for the analysis. Vaccination status of each animal was obtained from producer-recorded information. Confounding variables considered were herd-year-season groups (56 levels), parity (5 levels: 1, 2, 3, 4, and ≥5), and genetic quartile groups (4 levels: top 25% through bottom 25%) derived from genetic predictions for MY305, FY305, PY305, and SCS, as well as for the genetic susceptibility to mastitis. A logistic regression model was applied to estimate the propensity score (PS) for each cow. Subsequently, PS values were used to form pairs of animals (1 vaccinated with 1 unvaccinated control), depending on their PS similarities (difference in PS values of cows within a match required to be <20% of 1 standard deviation of the logit of PS). After the matching process, 2,091 pairs of animals (4,182 records) remained available to infer the causal effects of vaccinating dairy cows with the E. coli J5 bacterin. Causal effects estimation was performed using 2 approaches: simple matching and a bias-corrected matching. According to the PS methodology, causal effects of vaccinating dairy cows with a J5 bacterin on their productive performance were identified for MY305. The simple matched estimator suggested that vaccinated cows produced 163.89 kg more milk over an entire lactation when compared with nonvaccinated counterparts, whereas the bias-corrected estimator suggested that such increment in milk production was of 150.48 kg. Conversely, no causal effects of immunizing dairy cows with a J5 bacterin were identified for FY305, PY305, or SCS. In conclusion, the utilization of PS matching techniques applied to farm-recorded data was feasible and allowed us to identify that vaccination with an E. coli J5 bacterin relates to an overall milk production increment without compromising milk quality.

Tetracycline resistance genes in isolates of Pasteurella multocida, Mannheimia haemolytica, Mannheimia glucosida and Mannheimia varigena from bovine and swine respiratory disease: intergeneric spread of the tet(H) plasmid pMHT1.

Tetracycline-resistant isolates of Pasteurella multocida and Mannheimia spp. from respiratory diseases in cattle and swine were investigated for the classes of tet gene and their chromosomal or plasmid location. The 34 isolates comprised eight P. multocida, 23 Mannheimia haemolytica, two Mannheimia varigena and a single Mannheimia glucosida isolate. Identification of the tet genes was achieved by PCR analysis and hybridization with specific probes. Transformation and hybridization experiments served to confirm the plasmid location of tet genes. Selected tet genes and their adjacent regions were sequenced. The tet genes tet(B), tet(G) and tet(H) were detected. The gene tet(H) was present in 26 isolates. The 4.4 kb tet(H)-carrying plasmid pMHT1 was detected in six isolates representing all four species. In the remaining 28 isolates, copies of tet(B), tet(G) and tet(H) were identified as chromosomal. No correlation between the tet gene type and the MIC of tetracycline, or between the number of tet gene copies and the MIC of tetracycline was observed. Tetracycline resistance in P. multocida and Mannheimia spp. is mediated by at least three different tet genes. A new type of tet(H)- carrying plasmid, pMHT1, was identified. The detection of pMHT1 in M. glucosida and M. varigena is the first report of resistance plasmids in isolates of these two species. For the first time, tet(G) genes were detected in members of the family Pasteurellaceae.

Antimicrobial susceptibility of Staphylococcus aureus isolated from bovine mastitis in Europe and the United States.

Minimum inhibitory concentrations were determined for 811 strains of Staphylococcus aureus isolated from cases of bovine mastitis in 11 countries. The countries and number of isolates included Denmark (105), England (92), Finland (95), Germany (103), Iceland (22), Ireland (42), Norway (101), Sweden (123), Switzerland (69), United States (53), and Zimbabwe (6). The antimicrobial agents tested were penicillin, ampicillin, oxacillin, cephalothin, ceftiofur, amoxicillin + clavulanate, penicillin + novobiocin, enrofloxacin, premafloxacin, erythromycin, clindamycin, lincomycin, pirlimycin, neomycin, lincomycin + neomycin, and sulfamethazine. The MIC90 for these antimicrobial agents for all strains were 0.5, 1.0, 1.0, 0.5, 1.0, < or =0.06, 0.125, 0.125, < or =0.0078, 0.5, 1.0, 16.0, 1.0, 2.0, 0.5, and 4.0 microg/ml, respectively. Overall, only small variations between countries were seen in the MIC90 for the majority of compounds tested. Of the strains tested, 35.6% were positive for beta-lactamase production on initial testing, with an additional 21.3% positive after induction by penicillin. In conclusion, the overall level of resistance was generally low for all antimicrobial agents tested regardless of country. Given the differences in antimicrobial use in various countries, the widespread adoption of mastitis control programs to prevent infections limits the exposure of S. aureus infected animals to antimicrobial drugs.

MICs of oxazolidinones for Rhodococcus equi strains isolated from humans and animals.

Eperezolid and linezolid are representatives of a new class of orally active, synthetic antimicrobial agents. The in vitro activity values (MICs) of linezolid, eperezolid, and comparator antibiotics against 102 strains of Rhodococcus equi isolated from humans and animals were determined. Linezolid was more active than eperezolid against the strains tested; premafloxacin was the most active comparator antibiotic.

Minimum inhibitory concentration determinations for various antimicrobial agents against 1570 bacterial isolates from turkey poults.

Minimum inhibitory concentrations (MICs) were determined for 1570 bacteria from eight geographic locations (1204 Escherichia coli, 231 other enteric gram-negative bacilli [including Citrobacter spp., Enterobacter spp., Klebsiella spp., Proteus spp., and Salmonella spp.], 31 Pseudomonas spp., 18 coagulase-positive staphylococci, 26 coagulase-negative staphylococci, and 55 streptococci and enterococci) by the National Committee for Clinical Laboratory Standards broth microdilution procedure. Antimicrobial agents tested included ampicillin, ceftiofur, enrofloxacin, erythromycin, florfenicol, gentamicin, neomycin, spectinomycin, sulfamethazine, tetracycline, and trimethoprim/sulfadiazine. Against the E. coli strains tested, ceftiofur, enrofloxacin, gentamicin, and trimethoprim/sulfadiazine were the most active compounds with MIC at which 50% of the strains are at or below (MIC50) = 0.5, < or = 0.03, 0.5, and 0.13 microg/ml, respectively, and MIC at which 90% of the strains are at or below (MIC90) = 1.0, 0.13, 32.0, and 2.0 microg/ml, respectively. Ampicillin, florfenicol, neomycin, and spectinomycin were the next most active compounds against the E. coli strains, with MIC50 = 4.0, 4.0, 16.0, and 16.0 microg/ml, respectively. MIC90 values for these compounds against E. coli strains were > 32.0, 8.0, 512.0, and > 128.0 microg/ml, respectively. The remaining compounds exhibited limited, strain-dependent activity against the E. coli strains tested. As with the E. coli, enrofloxacin, ceftiofur, and trimethoprim/sulfadiazine were also the most active compounds against the 231 other enteric organisms tested, with MIC50 < or = 1.0 microg/ml for all of these genera. The remaining compounds exhibited limited activity against these genera. Against the gram-positive cocci tested, ampicillin, enrofloxacin, ceftiofur, and trimethoprim/sulfadiazine were most active, whereas the remaining compounds exhibited strain-dependent activity. When MIC data for E. coli were summarized separately, differences were observed between the geographic locations for the various antimicrobial agents. In conclusion, ceftiofur, enrofloxacin, and trimethoprim/sulfadiazine were the most active of the compounds tested against all of the bacterial strains.

Minimum inhibitory concentrations for selected antimicrobial agents against organisms isolated from the mammary glands of dairy heifers in New Zealand and Denmark.

Minimum inhibitory concentrations were determined for selected antimicrobial agents against 872 bacteria isolated from intramammary infections in heifers in New Zealand (n = 401) and Denmark (n = 471). These values were reported in micrograms per milliliters. Antimicrobial agents tested against isolates from New Zealand were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. The minimum inhibitory concentrations that inhibit 90% of the strains tested for these antimicrobial agents with Staphylococcus aureus were 4.0, 0.5, 0.5, 2.0, 1.0, 0.25, 0.5, and 1.0, respectively. The minimum inhibitory concentration values that inhibit 90% of the strains tested against the Staphylococcus spp. ranged from 0.5 to 1.0 for all antimicrobics. The minimum inhibitory concentrations against streptococci were < or = 0.06, 0.5, 0.13, 0.13, 4.0, 1.0, 0.13, and < or = 0.06, respectively. Antimicrobial agents tested against isolates from Denmark included penicillin, ampicillin, oxacillin, cephalothin, ceftiofur, penicillin plus novobiocin, erythromycin, and pirlimycin. Against S. aureus, the minimum inhibitory concentrations were 0.13, 0.5, 0.5, 0.5, 1.0, 0.25, 0.5, and 0.5, respectively. The minimum inhibitory concentrations against Staphylococcus spp. were 0.25, 0.25, 0.5, 0.5, 1.0, < or = 0.06, 0.13, 1.0, and 0.5, respectively. The minimum inhibitory concentrations against the streptococci were < or = 0.06, 0.13, 0.5, 0.5, 1.0, < or = 0.06, 0.13, 0.5, and 0.5, respectively. Minimum inhibitory concentration values for staphylococci from New Zealand and Denmark were similar to values reported for US isolates. Streptococci from New Zealand and Denmark had lower minimum inhibitory concentration values than did US isolates. Only ceftiofur and enrofloxacin were active against the Gram-negative bacilli.

In vitro activity of premafloxacin, a new extended-spectrum fluoroquinolone, against pathogens of veterinary importance.

The in vitro activity of premafloxacin against 673 veterinary pathogens was evaluated. Premafloxacin was equivalent to ciprofloxacin, enrofloxacin, and danofloxacin in activity against the gram-negative bacilli but was much more active (MIC for 90% of the strains tested [MIC90], 0.015 to 0.25 microg/ml) than the comparison antimicrobial agents (MIC90, 0.13 to 16.0 microg/ml) against the staphylococci, streptococci, and anaerobes tested.

Activity of selected antimicrobial agents against strains of Staphylococcus aureus isolated from bovine intramammary infections that produce beta-lactamase.

The activity of selected antimicrobial agents was determined against strains of Staphylococcus aureus that were isolated from bovine intramammary infections and that were positive or negative for beta-lactamase. A total of 107 S. aureus strains (70 that were positive for beta-lactamase and 37 that were negative for beta-lactamase) were used in the study. Production of beta-lactamase was determined using a chromogenic cephalosporin disk method. Minimum inhibitory concentrations (MIC) for each test strain were determined using a commercially available microdilution panel. The following compounds were tested: penicillin, ampicillin, oxacillin, cephapirin, ceftiofur, penicillin plus novobiocin, erythromycin, and pirlimycin. Of the five beta-lactam compounds tested, penicillin and ampicillin were most affected by beta-lactamase activity, but oxacillin, cephapirin, and ceftiofur were not affected. Penicillin plus novobiocin also demonstrated excellent activity against strains of S. aureus that were both positive and negative for beta-lactamase. Erythromycin and pirlimycin demonstrated good activity against the S. aureus strains that were negative for beta-lactamase; 90% of the isolates had an MIC of < or = 0.5 microgram/ml (MIC90). The MIC90 for erythromycin and pirlimycin for strains that were positive for beta-lactamase was > 64.0 micrograms/ml. However, 8 strains, in addition to producing beta-lactamase, were also resistant to macrolides and lincosaminides. Recalculation of the MIC90 without these 8 strains yielded equivalent values for both erythromycin and pirlimycin with strains that were positive or negative for beta-lactamase (MIC90 < or = 0.5 microgram/ml).

In vitro activity of ceftiofur and its primary metabolite, desfuroylceftiofur, against organisms of veterinary importance.

Ceftiofur (XNL) and its primary metabolite, desfuroylceftiofur (DXNL), were evaluated for in vitro activity against 539 isolates from veterinary sources. Actinobacillus pleuropneumoniae, Pasteurella spp., Haemophilus somnus, Salmonella spp., Escherichia coli, staphylococci, and streptococci were tested. Overall, XNL and DXNL were equivalent in activity against the gram-negative organisms with all minimum inhibitory concentrations (MICs) within 1 serial dilution. Against the staphylococci, MIC difference of 2-3 serial dilutions were detected with an MIC90 for XNL and DXNL of 1.0 and 4.0-8.0 micrograms/ml, respectively. Although the MIC90 obtained for Streptococcus suis for each compound was within 1 dilution, the MIC values against individual strains were 2-3 dilutions greater for DXNL than for XNL. The MICs obtained with the bovine and equine streptococci for DXNL (MIC90 = 0.03 microgram/ml) were 5 serial dilutions higher than those obtained for XNL (MIC90 < or = 0.0019). Although DXNL was less active than XNL against the streptococci, these differences were not clinically important because both XNL and DXNL were highly active for these bacteria. Although these differences are of little importance with the streptococci, they may have important implications for susceptibility testing of the staphylococci. In conclusion, with the exception of the staphylococci, both XNL and DXNL were highly active against the organisms tested, with MICs for both compounds several fold lower than plasma levels achieved during dosing of XNL.

Comparison of MICs of ceftiofur and other antimicrobial agents against bacterial pathogens of swine from the United States, Canada, and Denmark.

The MICs of ceftiofur and other antimicrobial agents, tested for comparison, for 515 bacterial isolates of pigs from the United States, Canada, and Denmark with various diseases were compared. The organisms tested included Actinobacillus pleuropneumoniae, Escherichia coli, Pasteurella multocida, Salmonella choleraesuis, Salmonella typhimurium, Streptococcus suis, Streptococcus dysgalactiae subsp. equisimilis, Streptococcus equi subsp. equi, and Streptococcus equi subsp. zooepidemicus. In addition to ceftiofur, the following antimicrobial agents or combinations were tested: enrofloxacin, ampicillin, sulfamethazine, trimethoprim-sulfadiazine (1:19), erythromycin, lincomycin, spectinomycin, lincomycin-spectinomycin (1:8), tilmicosin, and tetracycline. Tilmicosin was only tested against the U.S. isolates. Overall, ceftiofur and enrofloxacin were the most active antimicrobial agents tested against all isolates, with MICs inhibiting 90% of isolates tested (MIC90s) of < or = 2.0 and < or = 1.0 microgram/ml, respectively. Erythromycin, sulfamethazine, spectinomycin, and lincomycin demonstrated limited activity against all of the organisms tested, with MIC90s of > or = 8.0, > or = 256.0, > or = 32.0, and > or = 16.0 micrograms/ml, respectively. Trimethoprim-sulfadiazine was active against isolates of A. pleuropneumoniae, S. choleraesuis, S. typhimurium, P. multocida, S. equi, and S. suis (MIC90s, < or = 0.5 microgram/ml) but was less active against the E. coli strains tested (MIC90, > 16.0 micrograms/ml). Ampicillin was active against the P. multocida, S. suis, and S. equi isolates tested (MIC90s, 0.5, 0.06, and 0.06 micrograms/ml, respectively) and was moderately active against S. typhimurium (MIC90s, 2.0 micrograms/ml). However, this antimicrobial agent was much less active when it was tested against A. pleuropneumoniae, S. cholerae-suis, and E. coli (MIC90s, 16.0, > 32.0, and 32.0 micrograms/ml, respectively). Against the U.S. isolates of A. pleuropneumoniae and P. multocida, tilmicosin was moderately active (MIC90s, 4.0 and 8.0 micrograms/ml, respectively). However, this compound was not active against the remaining U.S. isolates (MIC90s, > 64.0 micrograms/ml). Differences in the MICs from one country to another were not detected with enrofloxacin, ceftiofur, or lincomycin for the strains tested, but variations in the MICs of the remaining antimicrobial agents were observed.

Antimicrobial susceptibility of microorganisms isolated from the mammary glands of dairy heifers.

Minimum inhibitory concentrations were determined with 1494 microorganisms isolated from the mammary glands of dairy heifers. The antimicrobial agents tested were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. All minimum inhibitory concentrations were expressed as micrograms per milliliter. The isolates tested included 135 Staphylococcus aureus, 1222 Staphylococcus sp., 42 Streptococcus sp., 15 Enterococcus sp., 60 enteric species, and 20 miscellaneous organisms. The minimum inhibitory concentrations for 90% of isolates for the various antimicrobial agents with Staph. aureus were as follows: penicillin, .13; cloxacillin, .5; cephapirin, .5; ceftiofur, 1; novobiocin, .5; enrofloxacin, .5; erythromycin, .5, and pirlimycin, .5. In comparison, the minimum inhibitory concentrations for 90% of isolates for the Staphylococcus sp. were 1, 1, .5, 1, .5, .5, 1, and .5 for penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin, respectively. The minimum inhibitory concentrations for 90% of isolates for the Streptococcus sp. were 2, 32, 2, 2, 8, 1, 64, and 32 for the respective antimicrobial agents; the minimum inhibitory concentrations for 90% of isolates were 4, 64, 32, 64, 4, 1, 4, and 4 for the enterococci. Against the Gram-negative enteric bacilli, only ceftiofur and enrofloxacin were active; minimum inhibitory concentrations for 90% of isolates were 1 microgram/ml for ceftiofur and .25 microgram/ml for enrofloxacin. Results indicated that the majority of staphylococcal strains were susceptible to the antimicrobial agents tested but that antimicrobial susceptibility varied for Streptococcus sp. Compounds currently available in intramammary infusion products demonstrated poor activity against the enteric organisms.

A 4-year survey of antimicrobial susceptibility trends for isolates from cattle with bovine respiratory disease in North America.

The antimicrobial susceptibility trends of bovine respiratory disease (BRD) pathogens isolated from 1988 to 1992 were determined. A total of 880 isolates representing Pasteurella haemolytica, Pasteurella multocida, and Haemophilus somnus were used in the study. Overall, resistance to ampicillin, tetracycline, erythromycin, and sulfamethazine was frequently encountered among strains of P. haemolytica and P. multocida. Ceftiofur, an extended-spectrum cephalosporin originally marketed in 1988 for the treatment of BRD, was very active against the BRD pathogens tested; the MIC of ceftiofur for 90% of isolates tested was < or = 0.06 microgram/ml. Resistance to spectinomycin varied on the basis of the breakpoint used. Substantial variation in the year-to-year susceptibility of BRD pathogens to tilmicosin, a new macrolide antimicrobial agent, was observed. The proportion of susceptible P. haemolytica isolates ranged from 84.7% in the second year to 7.1% in the third year and 78.2% in the fourth year. Similar fluctuations were observed with strains of P. multocida.

Antimicrobial susceptibility of Staphylococcus hyicus isolated from exudative epidermitis in pigs.

Exudative epidermitis or greasy pig syndrome is caused by the coagulase-variable staphylococcal species Staphylococcus hyicus. Treatment of this disease is problematic because of the limited number of antimicrobial agents available for this purpose. Thirteen antimicrobial agents were evaluated for their activities against 100 S. hyicus strains isolated from pigs with exudative epidermitis. Novobiocin was the most active compound tested, with an MIC for 90% of the strains tested (MIC90) of < or = 0.06 microgram/ml. Enrofloxacin, ampicillin, and ceftiofur were the next most active compounds, with MIC90s of 0.25, 0.5, and 1.0 microgram/ml, respectively. However, 41.4% of the 99 strains tested were positive for beta-lactamase production. The MIC90s of erythromycin, tetracycline, and streptomycin were > 32.0 micrograms/ml. Initial testing with sulfadiazine-trimethoprim yielded an MIC90 of > 64.0 micrograms/ml, but subsequent testing with thymidine phosphorylase-supplemented medium yielded an MIC90 of 0.06 microgram/ml. Both lincomycin and spectinomycin were relatively inactive against the S. hyicus strains tested, with MIC90s of > 64.0 and > 128.0 micrograms/ml, respectively. However, the combination of the two compounds at ratios of 1:2 (lincomycin to spectinomycin) and 1:8 were more active, with MIC90s of 16.0 and 4.0 micrograms/ml, respectively. These results indicate that novobiocin and sulfadiazine-trimethoprim were the most active compounds tested against the S. hyicus strains isolated from pigs with exudative epidermitis. Furthermore, the combination of lincomycin and spectinomycin was more active than the individual compounds against the strains tested.

Use of modified Rambach agar to differentiate Streptococcus uberis from other mastitis streptococci.

The medium of Rambach was modified to permit differentiation of mastitis streptococci. A total of 377 streptococci isolated from bovine IMI was used in the study. Of the 159 strains identified as Streptococcus uberis, 151 strains (94.9%) were beta-galactosidase-positive and yielded blue colonies on modified Rambach agar. In comparison, Streptococcus agalactiae, Streptococcus dysgalactiae, Enterococcus saccharolyticus, or Enterococcus faecalis strains were negative for propylene glycol utilization (red colonies) or beta-galactosidase production; all strains yielded colorless colonies on modified Rambach agar. However, 5 of 35 (14.3%) Streptococcus equinus strains were also positive for beta-galactosidase. Results indicate that modified Rambach agar is a convenient medium for the differentiation of the Strep. uberis from the other mastitis streptococci. Furthermore, modified Rambach agar could be easily incorporated as a screening medium for Strep. uberis in mastitis bacteriology laboratories.

Evaluation of the RapID NH system for identification of Haemophilus somnus, Pasteurella multocida, Pasteurella haemolytica, and Actinobacillus pleuropneumoniae isolated from cattle and pigs with respiratory disease.

Haemophilus somnus, Pasteurella haemolytica, Pasteurella multocida, and Actinobacillus pleuropneumoniae from cattle and pigs with respiratory disease were used to evaluate the RapID NH system (Innovative Diagnostics, Atlanta, Ga.). Minor modifications of the RapID NH system to include animal source and growth requirements would permit the identification of all isolates tested.

Characterization of Gardnerella vaginalis and G. vaginalis-like organisms from the reproductive tract of the mare.

Gardnerella vaginalis has been isolated from women with bacterial vaginosis, from the genital tracts of asymptomatic women, and from several other infected body sites in humans. However, until recently, it has not been isolated from any other animal species. Between June 1988 and October 1989, 31 isolates identified as G. vaginalis and 70 isolates identified as G. vaginalis-like organisms have been recovered from the genital tracts of 93 mares from Michigan and Ohio. Identification was based on biochemical reactions, hemolysis on media containing blood from various animal sources, and susceptibility to select antimicrobial agents. This report details the characterization of G. vaginalis and G. vaginalis-like organism isolates obtained from the reproductive tracts of these mares and compares the equine isolates with human isolates.

Isolation of Gardnerella vaginalis from the reproductive tract of four mares.

A gram-variable pleomorphic bacillus was isolated from the reproductive tracts of 4 mares during routine prebreeding soundness examinations. Using a commercial bacterial identification system, these organisms were identified as Streptococcus acidominimus. However, colonial and Gram-staining characteristics did not support this identification. Subsequent testing indicated the organism was similar to Gardnerella vaginalis. Additional growth and biochemical analysis performed in our laboratory and at the Michigan Department of Public Health and by the Center for Disease Control, Atlanta, Georgia, confirmed the identification of G. vaginalis.