Host-response patterns of intramammary infections in dairy cows.

Many different bacterial species have the ability to cause an infection of the bovine mammary gland and the host response to these infections is what we recognize as mastitis. In this review we evaluate the pathogen specific response to the three main bacterial species causing bovine mastitis: Escherichia coli, Streptococcus uberis and Staphylococcus aureus. In this paper we will review the bacterial growth patterns, host immune response and clinical response that results from the intramammary infections. Clear differences in bacterial growth pattern are shown between bacterial species. The dominant pattern in E. coli infections is a short duration high bacteria count infection, in S. aureus this is more commonly a persistent infection with relative low bacteria counts and in S. uberis a long duration high bacteria count infection is often observed. The host immune response differs significantly depending on the invading bacterial species. The underlying reasons for the differences and the resulting host response are described. Finally we discuss the clinical response pattern for each of the three bacterial species. The largest contrast is between E. coli and S. aureus where a larger proportion of E. coli infections cause potentially severe clinical symptoms, whereas the majority of S. aureus infections go clinically unnoticed. The relevance of fully understanding the bovine host response to intramammary infection is discussed, some major gaps in our knowledge are highlighted and directions for future research are indicated.

Evidence for interindividual heterogeneity in the glucose gradient across the human red blood cell membrane and its relationship to hemoglobin glycation.

OBJECTIVE: To determine whether interindividual heterogeneity in the erythrocyte (red blood cell [RBC]) transmembrane glucose gradient might explain discordances between A1C and glycemic control based on measured fructosamine. RESEARCH DESIGN AND METHODS: We modeled the relationship between plasma glucose and RBC glucose as the concentration distribution (C(i)-to-C(o) ratio) of a nonmetabolizable glucose analog (14)C-3-O-methyl glucose ((14)C-3OMG) inside (C(i)) and outside (C(o)) RBCs in vitro. We examined the relationship between that distribution and the degree of glycation of hemoglobin in comparison with glycation of serum proteins (fructosamine), the glycation gap. A1C, fructosamine, and in vitro determination of the (14)C-3OMG distribution in glucose-depleted RBCs were measured in 26 fasted subjects. RESULTS: The C(i)-to-C(o) ratio 0.89 +/- 0.07 for 3-O-methyl-d-glucopyranose (3OMG) ranged widely (0.72-1.04, n = 26). In contrast, urea C(i)-to-C(o) (1.015 +/- 0.022 [range 0.98-1.07], P < 0.0001) did not. Concerning mechanism, in a representative subset of subjects, the C(i)-to-C(o) ratio was retained in RBC ghosts, was not dependent on ATP or external cations, and was reestablished after reversal of the glucose gradient. The 3OMG C(i)-to-C(o) ratio was not correlated with serum fructosamine, suggesting that it was independent of mean plasma glucose. However, C(i)-to-C(o) did correlate with A1C (R(2) = 0.19) and with the glycation gap (R(2) = 0.20), consistent with a model in which differences in internal glucose concentration at a given mean plasma glucose contribute to differences in A1C for given level of glycemic control. CONCLUSIONS: The data demonstrate interindividual heterogeneity in glucose gradients across RBC membranes that may affect hemoglobin glycation and have implications for diabetes complications risk and risk assessment.

Discordance between HbA1c and fructosamine: evidence for a glycosylation gap and its relation to diabetic nephropathy.

OBJECTIVE: Discordances between HbA1c and other measures of glycemic control are common in clinical practice and remain unexplained. We developed a measure of discordance between HbA1c and fructosamine (FA) (glycosylated serum proteins) to conduct a systematic evaluation. We termed this the glycosylation gap (GG) and sought to determine its relationship to diabetic nephropathy. RESEARCH DESIGN AND METHODS: Measurements of HbA1c and FA on the same sample in 153 people were used to calculate GG, defined as the difference between measured HbA1c and HbA1c predicted from FA based on the population regression of HbA1c on FA. RESULTS: GG had a broad distribution (range, -3.2% to 5.5%); 40% of samples had values indicating major differences in prediction of complications risk by the measured versus predicted HbA1c. GG was highly correlated (r = 0.81) between measurements repeated in 65 patients 23 +/- 2 weeks apart, indicating that the discordances are reliable and not explained by differences in turnover of underlying proteins. In 40 patients with type 1 diabetes of >or = 15 years' duration, an increase in GG by 1% was associated with a 2.9-fold greater frequency of increasing nephropathy stage (P = 0.0014). GG was -0.8 +/- 0.2% in subjects with no nephropathy, -0.3 +/- 0.2% with microalbuminuria/hypertension, and 0.7 +/- 0.3% in subjects with proteinuria or renal dysfunction (P < 0.05). GG correlated better with nephropathy than did either HbA1c or FA alone in this population. CONCLUSIONS: The glycosylation gap may be a useful clinical research tool for evaluating physiologic sources of variation in diabetic complications beyond glycemic control.

A randomized, prospective study measuring outcomes after antibiotic therapy intervention by a multidisciplinary consult team.

Our aim was to identify financial and outcome benefits of therapeutic intervention by a multidisciplinary antimicrobial treatment team composed of pharmacists, a clinical microbiologist, and an infectious disease specialist. Of 252 consecutive inpatients receiving suboptimal intravenous antibiotics identified by the clinical pharmacist, 127 were prospectively randomized to intervention and 125 to a control group. The groups were similar with regard to severity of illness, infection type, and time from admission to randomization. Physicians received timely, detailed reviews of relevant microbiologic and clinical data with recommendations of possible optimal antibiotic choices, dosages, and rationales. Median length of stay after randomization for control and intervention groups was 9.0 days and 5.7 days, respectively (3.3-day difference, p=0.0001). Fifteen (12.0%) and eight patients (6.3%), respectively, died, although the time-specific mortality risk was not significantly different when length of postrandomization follow-up and time to death were taken into account. Physician acceptance of suggestions was 89%. Median patient charges for radiology, laboratory, pharmacy, and room were reduced by $4404/intervention, and median hospital costs were reduced by $2642/intervention. A multidisciplinary antimicrobial therapy team can be a useful information source for physicians, improve outcomes in hospitalized patients receiving intravenous antimicrobials, and result in substantial cost savings.

PauA: a novel plasminogen activator from Streptococcus uberis.

Chromosomal DNA from two geographically distinct isolates of Streptococcus uberis was used to clone the plasminogen activator in an active form in Escherichia coli. The cloned fragments from each strain contained four potential open reading frames (ORFs). That for the plasminogen activator encoded a protein of 286 amino acids (33.4 kDa) which is cleaved between residues 25 and 26 during secretion by S. uberis. The amino acid sequence of the mature protein showed only weak homology (23.5-28%) to streptokinase. The plasminogen activator gene, pauA, in S. uberis was located between two ORFs with high homology to the DNA mismatch repair genes, hexA and hexB, and not on a DNA fragment between the genes encoding an ATP binding cassette transporter protein (abc) and a protein involved in the formation and degradation of guanosine polyphosphates (rel) as is the case for streptokinase in other streptococci.

Attenuation and immunogenicity of Deltacya Deltacrp derivatives of Salmonella choleraesuis in pigs.

Six different isogenic Deltacya Deltacrp derivatives of a strain of Salmonella choleraesuis var. kunzendorf-chi3246 virulent for pigs were constructed by transposon-mediated deletion mutagenesis. These strains were evaluated for virulence and ability to elicit a protective immune response in young weaned pigs after oral administration and were compared to a commercially available vaccine which lacks the 50-kb virulence plasmid (vpl(-)). These derivatives were Deltacya Deltacrp vpl(+), Deltacya Deltacrp vpl(-), Deltacya Delta(crp-cdt) vpl(+), Deltacya Delta(crp-cdt) vpl(-), Deltacya Deltacrp pmi-3834 vpl(+), and Deltacya Delta(crp-cdt) pmi-3834. In experiments to evaluate safety, no significant adverse effects of any of the vaccine constructs were observed, except that two of the strains which carried the virulence plasmid (vpl(+)) caused a small, short-term elevation in maximum temperature compared to pretreatment temperature values. Orally immunized animals, except for those vaccinated with the Deltacya Deltacrp pmi-3834 vpl(+) strain or SC-54, developed significant serum antibody responses 21 days postvaccination as measured by enzyme-linked immunosorbent assay. No cell-mediated immune responses to heat-killed S. choleraesuis were noted at the same time point as measured with heat-killed bacteria as antigen in a lymphocyte proliferation assay. In an oral challenge exposure model with a highly virulent heterologous strain of S. choleraesuis, the Deltacya Deltacrp strains with deletions in pmi were not protective. As measured by morbidity scores, the responses to challenge of the pigs vaccinated with the other four Deltacya Deltacrp derivatives were significantly better than those of the nonvaccinated, challenged group. With the exception of temperature elevation and slight differences in diarrhea scores postchallenge, none of these strains differed significantly from each other in the other clinical parameters analyzed. While the commercial vaccine was protective by most of the parameters measured, it was not fully protective against challenge with virulent S. choleraesuis as judged by diarrhea scores and temperature elevation. Collectively, these data demonstrate that Deltacya Deltacrp derivatives, with or without the virulence plasmid but not with deletions in the pmi gene, are candidates for vaccines for protection against salmonellosis in pigs.

Vaccines and diagnostic methods for bovine mastitis: fact and fiction.

A number of problems are uniquely associated with vaccination of dairy cows for mastitis. One of these is that the number of mastitis pathogens is numerous and heterogeneous. Vaccine efforts have concentrated mainly on the major mastitis pathogens. While at least one S. aureus bacterin has been commercially available for a number of years, no large-scale, independent field trials have been published in refereed journals which support the efficacy of this vaccine. Experimental vaccines for S. aureus composed of pseudocapsule-enriched bacterins supplemented with alpha- and/or beta-toxoids appear promising, but none of these has been commercialized. With S. uberis, some protection against homologous strain challenges was reported recently with a live strain and a bacterin, but other data from the same laboratory showed this vaccine would not protect against heterologous challenge strains. At this time there is only one highly effective vaccine for mastitis, the core-antigen vaccine for coliform mastitis. All of the commercially available vaccines for this indication are bacterins of rough mutants of E. coli strain J5 or Salmonella spp. Preliminary success with an experimental vaccine based on the plasminogen activator of S. uberis is a very different approach for a mastitis vaccine. Little success has been reported with vaccination against other mastitis pathogens. For diagnostic methods, the high somatic cell count, as measured by direct count or indirect assays, remains the cornerstone of mastitis diagnosis. However, for subclinical mastitis, bacterial cell culture is a reliable diagnostic method. Pathogen identification may rely on older biochemical testing methods or newer commercial identification systems, depending on the laboratory budget. ELISA assays also have been used to assess herd infection status. Epidemiologic studies have used DNA fingerprinting and ribotyping, but none of these methods has yet produced an easily utilized commercial format. Within the next decade, additional efficacious vaccines for several of the most common agents for bovine mastitis are likely. A review written at that time then can be more fact than fiction.

Computerized documentation for a rural nursing intervention project.

The Rural Partnership Linkage for Cancer Care project is a program of advanced practice nursing care made available to rural cancer patients to provide education, symptom management, referral, and support within their communities. The advanced practice nurses used a computerized clinical information system (CCIS) to record care. In this article the CCIS is described, the software and hardware requirements are discussed, and the outcomes and value of the system are discussed. The CCIS is a relational database run on laptop computers that includes screens for standard recording of demographics, physical exam, symptoms, and treatments. The advanced practice nurses track patient symptoms over time, noting which treatments are successful in resolving or reducing the problems. Information from patient visits is selected by help menus for inclusion into referral forms, reports of patient care, and discharge summaries. Reports can be faxed or mailed to distant sites. The research team uses the combined data set to examine symptom patterns, nursing diagnosis, and treatments that result in improved physical and psychological functioning and symptom resolution. Rural cancer patients and their families benefit from care management, participation in research, and communication of patient health status in an integrated and timely fashion made possible by the CCIS.

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.

Characterization of flaA- and flaB- mutants of Serpulina hyodysenteriae: both flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization.

Motility of Serpulina hyodysenterlae is thought to play a pivotal role in the enteropathogenicity of this spirochete. To test this, a series of isogenic mutants containing specifically disrupted flagellar alleles (flaA1 and flaB1) were constructed and examined for virulence and ability to colonize the intestinal tract of mice. Mice challenged with the wild-type, parent strain showed a dose-related response to the challenge organism. In contrast, all flagellar mutant strains demonstrated aberrant motility in vitro and a significantly reduced ability to colonize and infect mice. To some extent, this degree of reduction in colonizing ability was dependent on the wild-type background strain used for mutant construction. A flaB1- strain generated from a 'laboratory isolate' was unable to colonize the mouse gut even at high challenge doses, although its parent was virulent for mice. However, when the same parent strain was 'animal-passed' prior to disruption of flaB1, the resulting flaB1- strain was able to transiently colonize the mouse gut and induce intestinal lesions. A comparison of a series of flagellar mutants constructed using the animal-passed parent strain further revealed that specific inactivation of flaB1 resulted in a more pronounced reduction in virulence and colonizing ability than that which occurred with two flaA1 mutants. Taken together, these data suggest that motility is an essential virulence factor of S. hyodysenteriae and that both sheath and core flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization.

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.

Comparison of success of antibiotic therapy during lactation and results of antimicrobial susceptibility tests for bovine mastitis.

Antimicrobial susceptibility testing was conducted on a variety of mastitis pathogens. The infected quarters were subsequently treated during lactation with a commercially available product containing penicillin and novobiocin that was designed for lactating cows. Cows were treated as per the recommendations of the product manufacturer, and cures were determined by the absence of bacteria in both sets of duplicate quarter milk samples that were collected at 28 d posttreatment. Comparisons were made between the susceptibility of the bacteria and the therapeutic success or failure. All isolates tested were considered to be susceptible to the penicillin and novobiocin combination. Bacteriologic cure rates for newly acquired Staphylococcus aureus intramammary infection (IMI) (< 2 wk in duration) at 28 d posttreatment were 70%. Cure rates for chronic Staph. aureus IMI (> 4 wk duration) were much lower (35%), reaffirming previous reports of the intractable nature of chronic Staph. aureus IMI. Cure rates for subclinical IMI caused by other organisms were 90% for Streptococcus agalactiae, 91% for Streptococcus uberis, 90% for Streptococcus dysgalactiae, 77% for other Streptococcus spp., and 71% for Staphylococcus spp. other than Staph. aureus. In vitro testing was considered to be a predictor of therapy outcome for IMI caused by Staphylococcus spp., newly acquired Staph. aureus, Strep. uberis, Strep. dysgalactiae, and Strep. agalactiae, but was not considered to be a useful predictor of efficacy for chronic IMI caused by Staph. aureus.

The activity of a combination of penicillin and novobiocin against bovine mastitis pathogens: development of a disk diffusion test.

The combination of penicillin and novobiocin is currently available for the treatment of bovine mastitis, but methods are not available for susceptibility testing of the combination by veterinary diagnostic laboratories. The minimum inhibitory concentration (MIC) and disk diffusion data were determined for penicillin, novobiocin, and a combination of the two in a 1:2 ratio for 225 staphylococcal, streptococcal, and Gram-negative isolates from bovine intramammary infections. Based on the drug concentrations in milk following infusion, linear regression analysis, and error rate bounding, the interpretive zone diameters selected were < or = 16 mm for resistant isolates and > or 17 mm for susceptible isolates with a disk containing 10 U of penicillin and 30 micrograms of novobiocin. Additionally, MIC breakpoints of < or = 2 micrograms/ml of penicillin and 4 micrograms/ml of novobiocin were selected to categorize isolates as susceptible and > or = 4 micrograms/ml of penicillin and 8 micrograms/ml of novobiocin were selected to categorize isolates as resistant. The MIC and disk diffusion results, as well as studies to monitor bacterial killing by antimicrobial agents over time, indicated that the combination of penicillin and novobiocin in a 1:2 ratio was more active than were the individual drugs. Kinetics of the kill curves with the penicillin and novobiocin combination (1:2 ratio) showed that the combination was bactericidal for Staphylococcus aureus and Staphylococcus xylosus.

Characterization of the gene encoding Mhp1 from Mycoplasma hyopneumoniae and examination of Mhp1's vaccine potential.

The gene encoding Mhp1, a 124 kDa protein from Mycoplasma hyopneumoniae, has been cloned, sequenced, and its product characterized. No significant homology to the gene or encoded polypeptide was found in the Genbank, NBRF, or PIR databases, though this protein appears similar to p97, a putative adhesin of M. hyopneumoniae described by Zhang et al. (Infect. Immun. 63, 1013-1019, 1995). Two repeated motifs were identified within the 3' end of the gene and encoded polypeptide. The mhp1 gene was fused to the glutathione S-transferase (GST) gene from Schistosoma japonicum, enabling high-level expression and purification of the protein. Both the authentic and recombinant proteins were recognized by sera from pigs infected with M. hyopneumoniae. In an induced-disease model in pigs, coughing was reduced in animals vaccinated with recombinant GST-Mhp1, although differences were not significant. Only minimal protection against lung lesion formation was provided, and again differences between the Mhpl-vaccinated and nonvaccinated groups were not significant.

Interpretive criteria for antimicrobial susceptibility testing of ceftiofur against bacteria associated with swine respiratory disease.

Ceftiofur, an extended-spectrum cephalosporin, is active against a variety of animal pathogens, including organisms associated with swine respiratory disease. However, minimum inhibitory concentration (MIC) breakpoint and disk diffusion interpretive criteria have not been established for swine pathogens. Susceptibility tests were performed by broth microdilution MIC and disk diffusion methods on 246 bacterial species that cause swine respiratory disease. Ceftiofur was active against Salmonella sp., Pasteurella multocida, Actinobacillus pleuropneumoniae, Streptococcus suis, and Escherichia coli but was not active against Bordetella bronchiseptica measured by MIC. Based on pharmacokinetic studies of ceftiofur in swine after a single intramuscular injection of 3 or 5 mg/kg body weight of ceftiofur and on the MIC and disk diffusion data, we recommend MIC breakpoints and disk diffusion distances, respectively, of < or = 2 micrograms/ml and > or = 21 mm for susceptible, 4 micrograms/ml and 18-20 mm for intermediate, and > or = 8 micrograms/ml and > or = 17 mm for resistant classification for swine pathogens. When these breakpoints were applied to data from a previous study using bovine pathogens, only 1 minor interpretive error occurred.

Dual flaA1 flaB1 mutant of Serpulina hyodysenteriae expressing periplasmic flagella is severely attenuated in a murine model of swine dysentery.

The motility imparted by the periplasmic flagella (PF) of Serpulina hyodysenteriae is thought to play a pivotal role in the enteropathogenicity of this spirochete. The complex PF are composed of multiple class A and class B polypeptides. Isogenic strains containing specifically disrupted flaAl or flaB1 alleles remain capable of expressing PF, although such mutants display aberrant motility in vitro. To further examine the role that these proteins play in the maintenance of periplasmic flagellar structural integrity, motility, and fitness for intestinal colonization, we constructed a novel strain of S. hyodysenteriae which is deficient in both FlaA1 and FlaB1. To facilitate construction of this strain, a chloramphenicol gene cassette, with general application as a selectable marker in prokaryotes, was developed. The cloned flaAl and flaB1 genes were disrupted by replacement of internal fragments with chloramphenicol and kanamycin gene cassettes, respectively. The inactivated flagellar genes were introduced into S. hyodysenteriae, and allelic exchange at the targeted chromosomal flaA1 and flaB1 loci was verified by PCR analysis. Immunoblots or cell lysates with antiserum raised against purified FlaA or FlaB confirmed the absence of the corresponding sheath and core proteins in this dual flagellar mutant. These mutations selectively abolished the expression of the targeted genes without affecting the synthesis of other immunologically related FlaB proteins. The resulting flaA1 flaB1 mutant exhibited altered motility in vitro. Surprisingly, it was capable of assembling periplasmic flagella that were morphologically normal as evidenced by electron microscopy. The virulence of this strain was assessed in a murine model of swine dysentery by determining the incidence of cecal lesions and the persistence of S. hyodysenteriae in the gut. Mice challenged with the wild-type strain or a passage control strain showed a dose-related response to the challenge organism. The dual flagellar mutant was severely attenuated in murine challenge experiments, suggesting that the FlaA1 and FlaB1 proteins are dispensable for flagellar assembly but critical for normal flagellar function and colonization of mucosal surfaces of the gastrointestinal tract. This strain represents the first spirochete engineered to contain specifically defined mutations in more than one genetic locus.

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.

In vivo activities of U-100592 and U-100766, novel oxazolidinone antimicrobial agents, against experimental bacterial infections.

The Upjohn oxazolidinones, U-100592 and U-100766, are orally bioavailable synthetic antimicrobial agents with spectra of activity against antibiotic-susceptible and -resistant gram-positive pathogens. In several mouse models of methicillin-resistant Staphylococcus aureus infection, U-100592 and U-100766 yielded oral 50% effective doses (ED50) ranging from 1.9 to 8.0 mg/kg of body weight, which compared favorably with vancomycin subcutaneous ED50 values of 1.1 to 4.4 mg/kg. Similarly, both compounds were active versus a Staphylococcus epidermidis experimental systemic infection. U-100592 and U-100766 effectively cured an Enterococcus faecalis systemic infection, with ED50 values of 1.3 and 10.0 mg/kg, and versus a vancomycin-resistant Enterococcus faecium infection in immunocompromised mice, both drugs effected cures at 12.5 and 24.0 mg/kg. Both compounds were exceptionally active in vivo against penicillin- and cephalosporin-resistant Streptococcus pneumoniae, with ED50 values ranging from 1.2 to 11.7 mg/kg in systemic infection models. In soft tissue infection models with S. aureus and E. faecalis, both compounds exhibited acceptable curative activities in the range of 11.0 to 39.0 mg/kg. U-100766 was also very active versus the Bacteroides fragilis soft tissue infection model (ED50 = 46.3 mg/kg). In combination-therapy studies, both U-100592 and U-100766 were indifferent or additive in vivo against a monomicrobic S. aureus infection in combination with other antibiotics active against gram-positive bacteria and combined as readily as vancomycin with gentamicin in the treatment of a polymicrobic S. aureus-Escherichia coli infection. U-100592 and U-100766 are potent oxazolidinones active against antibiotic-susceptible and -resistant gram-positive pathogens in experimental systemic and soft tissue infections.

Motility and chemotaxis in Serpulina hyodysenteriae.

Chemotactic- or motility-regulated mucus association appears to be the predominant mechanism of mucosal association by the causative agent of swine dysentery, Serpulina hyodysenteriae. In the present study, a modification of the Adler capillary assay was used to evaluate the chemotactic responses of S. hyodysenteriae to a variety of potential stimuli. First, however, it became necessary to study factors that influenced motility of the spirochete in vitro, since standard cultivation methods produced motility inferior to that observed for in vivo grown cells. A number of factors were found to influence S. hyodysenteriae motility, but of these growth medium and growth phase appeared to be the most important. The type and even batch of culture medium also were found to have a significant influence on S. hyodysenteriae motility. Optimal motility and chemotaxis for S. hyodysenteriae was observed when the cells were harvested in mid- to late-log phase, and in vivo-like motility could be induced by suspending the cells in physiologic saline. S. hyodysenteriae was strongly attracted to hog gastric mucin, certain concentrations of blood, L-fucose, L-serine and other compounds. Selected sugars and other amino acids did not serve as chemoattractants for S. hyodysenteriae. The chemotactic response of S. hyodysenteriae toward L-fucose and L-serine, constituents of mucin, may be important factors in the affinity of the spirochete for the mucus in the intestinal tract of swine.