Knowledge gaps and research priorities in Staphylococcus aureus mastitis control.

This study assessed knowledge gaps and suggested research priorities in the field of Staphylococcus aureus mastitis. Staphylococcus aureus infecting the mammary gland remains a major problem to the dairy industry worldwide because of its pathogenicity, contagiousness, persistence in the cow environment, colonization of skin or mucosal epithelia, and the poor curing efficacy of treatments. Staphylococcus aureus also constitutes a threat to public health due to food safety and antibiotic usage issues and the potential for bidirectional transmission of strains between humans and dairy animals (cows and small ruminants). Gaps have been identified in (i) understanding the molecular basis for pathogenesis of S. aureus mastitis, (ii) identifying staphylococcal antigens inducing protection and (iii) determining the cell-mediated immune responses to infection and vaccination. The recommended priorities for research are (i) improved diagnostic methods for early detection of infection and intervention through treatment or management, (ii) development of experimental models to investigate the strategies used by S. aureus to survive within the mammary gland and resist treatment with anti-microbials, (iii) investigation of the basis for cow-to-cow variation in response to S. aureus mastitis, (iv) identification of the immune responses (adaptive and innate) induced by infection or vaccination and (v) antibacterial discovery programmes to develop new, more effective, narrow spectrum antibacterial agents for the treatment of S. aureus mastitis. With the availability and ongoing improvement of molecular research tools, these objectives may not be out of reach in the future.

Reduced activity of AMP-activated protein kinase protects against genetic models of motor neuron disease.

A growing body of research indicates that amyotrophic lateral sclerosis (ALS) patients and mouse models of ALS exhibit metabolic dysfunction. A subpopulation of ALS patients possesses higher levels of resting energy expenditure and lower fat-free mass compared to healthy controls. Similarly, two mutant copper zinc superoxide dismutase 1 (mSOD1) mouse models of familial ALS possess a hypermetabolic phenotype. The pathophysiological relevance of the bioenergetic defects observed in ALS remains largely elusive. AMP-activated protein kinase (AMPK) is a key sensor of cellular energy status and thus might be activated in various models of ALS. Here, we report that AMPK activity is increased in spinal cord cultures expressing mSOD1, as well as in spinal cord lysates from mSOD1 mice. Reducing AMPK activity either pharmacologically or genetically prevents mSOD1-induced motor neuron death in vitro. To investigate the role of AMPK in vivo, we used Caenorhabditis elegans models of motor neuron disease. C. elegans engineered to express human mSOD1 (G85R) in neurons develops locomotor dysfunction and severe fecundity defects when compared to transgenic worms expressing human wild-type SOD1. Genetic reduction of aak-2, the ortholog of the AMPK α2 catalytic subunit in nematodes, improved locomotor behavior and fecundity in G85R animals. Similar observations were made with nematodes engineered to express mutant tat-activating regulatory (TAR) DNA-binding protein of 43 kDa molecular weight. Altogether, these data suggest that bioenergetic abnormalities are likely to be pathophysiologically relevant to motor neuron disease.

Bovine intramammary Escherichia coli challenge infections in late gestation demonstrate a dominant antiinflammatory immunological response.

Coliform mastitis that presents itself at parturition or in the early weeks of bovine lactation is often characterized by severe inflammation and impaired milk production and can lead to death of the animal. Chronic intramammary infections caused by persistent strains of Escherichia coli may result in high production losses. The aim of this study was to determine the inflammatory response to a teat-canal challenge of bovine mammary glands with a persistent strain of E. coli during late gestation (dry period) and into early lactation. Two weeks before parturition, animals were challenged in 2 quarters with 30 cfu of a persistent strain of E. coli; control quarters were vehicle-infused and not infused, respectively. Samples of dry cow secretions were taken from all quarters before challenge and at 6, 12, 18, 24, 48, 72, 96, and 120 h following challenge. Colostrum samples and milk samples were taken from all quarters at parturition and 6, 12, 18, 24, 48, 72, 96 and 120 h postpartum. Bacterial culture, combined with random amplified polymorphic DNA genetic strain-typing analysis, indicated recovery of the bacterial challenge strain until 48 to 96 h postchallenge, and again at parturition and up to 6 and 12h postpartum. One animal exhibited clinical mastitis and the bacterial challenge strain was evident to at least 12 d postpartum. During twice-daily milkings, production levels were lower in bacteria-challenged quarters compared with controls. Somatic cell counts decreased to normal levels at a slower rate in challenged quarters compared with control quarters. Cytokine analysis indicated a minimal proinflammatory cytokine response, including interleukin-1ß and tumor necrosis factor-α in challenged-quarter dry cow samples up to 120 h postchallenge. Interleukin-10 levels were significantly increased by 12h postchallenge in secretions from challenged and control quarters. These preliminary results in 2 cows indicate that proinflammatory signaling after intramammary bacterial infection may be actively suppressed during late gestation. We hypothesize that this immune-inhibitory response allows intramammary infections to become persistent in the dry period and cause clinical signs immediately after parturition.

Outcome of extreme prematurity: as information increases so do the dilemmas.

Application of technology in neonatal intensive care has been very successful in reducing mortality, particularly in extremely low birthweight infants. As survival has improved, the need for accurate studies of long term outcome has increased. This need has been met by studies that are larger, more inclusive, and address a wider variety of later outcomes. Rather than a comprehensive quantitative review of these studies, this article uses a smaller number of studies that focus on infants of borderline viability, to illustrate current dilemmas and challenges in interpretation, and the actions, both individual and societal, that may be prompted by these interpretations.

Antibiotic susceptibility patterns for environmental streptococci isolated from bovine mastitis in central California dairies.

Environmental streptococci are frequently isolated from bovine mastitis in dairy cows with only limited information available on the antimicrobial susceptibility of these organisms. A total of 362 environmental streptococci isolated from cases of bovine mastitis from the central San Joaquin Valley of California over a 3-yr period were used in the study. Overall, 39.9% of the strains tested were Streptococcus uberis, 42.2% were Streptococcus dysgalactiae, and 11.1% were Enterococcus spp. The antimicrobial susceptibility for these organisms was determined for the following antimicrobial agents: penicillin, ampicillin, cephalothin, ceftiofur, penicillin + novobiocin, erythromycin, pirlimycin, tetracycline, and sulfadimethoxine. Results demonstrate substantial differences in the susceptibility patterns for the various organisms collectively referred to as the environmental streptococci. The MIC90 for penicillin was 0.06 microg/ml for 152 strains of S. dysgalactiae compared with 0.25 microg/ml for 133 strains of S. uberis. However, the Enterococcus spp. were the most resistant organisms tested. These data also indicate that the use of interpretive criteria based on human data may provide misleading results. In conclusion, these data confirm that the environmental streptococci are a diverse group of organisms comprised of several different genera and species and that identification of environmental streptococci to the species level is needed to appropriately modify control methods. Moreover, the use of the agar disk diffusion (Kirby-Bauer) susceptibility test for agents with human-based interpretive criteria is contraindicated, and these tests should only be performed with agents with mastitis specific interpretive criteria.

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.

Early light reduction for preventing retinopathy of prematurity in very low birth weight infants.

BACKGROUND: Retinopathy of prematurity (ROP) causes vision loss in many premature infants each year, despite the advances being made in treatment. In the search for ways to prevent the disease altogether, the exposure of the retina to bright ambient light following premature birth has been a natural hypothesis, since the premature infant normally would be in the dark in-utero environment. Several controlled studies have now addressed this theory. OBJECTIVES: To answer the question: "Among very low birth weight infants, what is the effect of reducing early environmental light exposure on the incidence of any "Acute ROP", or "Poor ROP Outcomes"? SEARCH STRATEGY: Searches were made of the Cochrane Neonatal Group Register of Controlled Trials, Medline, EMBASE, the Cochrane Library, previous reviews including cross references, abstracts, conference and symposia proceedings, and expert informants. The search terms used were [retrolental fibroplasia or retinopathy of prematurity] and [light or light/ae or lighting or lighting/ae or light/tu or lighting/st]. This search was updated as of November 2000. SELECTION CRITERIA: Randomized or quasi-randomized controlled trials that reduced light exposure to premature infants within the first 7 days following birth were considered for this review. DATA COLLECTION AND ANALYSIS: Data on clinical outcomes including any Acute ROP and Poor ROP Outcome were excerpted by both reviewers independently and consensus reached. Data analysis was conducted according to the standards of the Neonatal Cochrane Review Group. MAIN RESULTS: Data from four recent randomized trials, and one much older quasi-randomized trial failed to show any reduction in Acute ROP, or Poor ROP Outcome with the reduction of ambient light to premature infants' retinas. The number of infants studied to date allows 95% confidence that IF there were a true difference being missed, it would be smaller than 7 percentage points on a background of 54% of all infants under 2 kg developing ROP. REVIEWER'S CONCLUSIONS: Decreasing retinal ambient light exposure in premature infants is very unlikely to reduce the incidence of ROP.

D-Penicillamine for preventing retinopathy of prematurity in preterm infants.

BACKGROUND: Retinopathy of prematurity remains a common problem. A low rate of this disorder was unexpectedly observed among infants treated with intravenous d-penicillamine to prevent hyperbilirubinemia. This observation led to the investigation of its use to prevent retinopathy of prematurity. OBJECTIVES: To answer the question: Among very low birth weight infants, what is the effect of prophylactic administration of d-penicillamine on the incidence of acute ROP or severe ROP, and side effects including death? SEARCH STRATEGY: Searches were made of multiple electronic databases, previous reviews including cross references, abstracts, conference/symposia proceedings, and expert informants. The search was updated to November 2000. SELECTION CRITERIA: Randomized or quasi-randomized controlled trials that administered d-penicillamine to infants less than 2000g birth weight within the day following birth were considered relevant to this review. Additional case series were examined for potential side effects. DATA COLLECTION AND ANALYSIS: Data on clinical outcomes were excerpted by 3 reviewers independently, and consensus reached. Data analysis was conducted according to the standards of the Neonatal Cochrane Review Group. MAIN RESULTS: Two randomized trials on the effects on ROP were identified. When combined, they showed a significantly lower incidence of acute ROP in the treated infants, relative risk of 0.09, 95% CI [0.01,0.71]. Severe stages of ROP could not be analyzed. There was no effect on death rates, relative risk 0.99 95% CI [0.70,1.39]. No side effects were reported, and follow up at one year revealed no significant differences in spasticity or developmental delay, although there were more rehospitalizations among the controls. In other reports of using d-penicillamine in over 140 infants for hyperbilirubinemia, skin rashes were reported in 2 infants and one had vomiting that may have been related. REVIEWER'S CONCLUSIONS: D-penicillamine is unlikely to affect survival, and may reduce the incidence of acute ROP among survivors. Studies to date justify further investigation of this drug in a broader population; careful attention to possible side effects is needed.

Phylogenetic studies on Corynebacterium bovis isolated from bovine mammary glands.

Coryneform bacteria are frequently isolated from bovine mastitis with the lipophilic species, and Corynebacterium bovis is the most frequently isolated organism of this group. However, previous studies on the phylogeny of corynebacteria have incorporated only a single reference strain. We examined the phylogeny of C. bovis using 47 strains isolated from bovine mammary glands. Phylogenetic studies were performed by direct sequencing of the 16S ribosomal RNA and comparison to sequences of reference strains. All strains identified as C. bovis demonstrated similarity of 98% or higher to the ribosomal RNA gene sequences of the type strain of C. bovis. Phylogenetic analyses indicated that all strains tested clustered with members of the Corynebacterium urealyticum group confirming that C. bovis is a legitmate member of the genus Corynebacterium. Further investigation into the diversity within the species using repetitive element palindrome PCR indicated only minor differences between the strains tested. Corynebacterium bovis ATCC 13722 demonstrated the highest similarity (95%) with Brevibacterium helvolum, indicating that this organism does not belong in the genus Corynebacterium.

Susceptibilities of Corynebacterium bovis and Corynebacterium amylocolatum isolates from bovine mammary glands to 15 antimicrobial agents.

Coryneform bacteria are frequently isolated from bovine mastitis and are associated with economic losses. Generally, the MICs of the 15 antimicrobial agents tested at which 90% of the isolates tested are inhibited for 46 Corynebacterium bovis and 13 Corynebacterium amylocolatum strains were low. These are the first quantitative antimicrobial susceptibility data available for coryneforms from bovine mastitis. Data from this study suggest that comparable corynebacteria from humans have a much higher level of antimicrobial resistance to a variety of antimicrobial agents.

Identification of corynebacterium bovis and other coryneforms isolated from bovine mammary glands.

Bovine mastitis remains the most economically important disease in dairy cows. Corynebacterium bovis, a lipid-requiring Corynebacterium spp., is frequently isolated from the milk of infected mammary glands of dairy cows and is associated with reduced milk production. A total of 212 coryneform bacteria isolated from the milk of dairy cows were obtained from mastitis reference laboratories in the United States and Canada. All isolates had been presumptively identified as Corynebacterium bovis based on colony morphology and growth in the presence of butterfat. Preliminary identification of the isolates was based on Gram stain, oxidase, catalase, and growth on unsupplemented trypticase soy agar (TSA), TSA supplemented with 5% sheep blood, and TSA supplemented with 1% Tween 80. Of the 212 isolates tested, 183 were identified as Corynebacterium spp. based on preliminary characteristics. Of the strains misidentified, one was identified as a yeast, two as Bacillus spp., 11 as Enterobacteriaceae, 18 as staphylococci, one as a Streptococcus spp., and one as an Enterococcus spp. Eighty-seven coryneforms were selected for identification to the species level by direct sequencing of the 16S rRNA gene, the Biolog system and the API Coryne system. Fifty strains were identified as C. bovis by 16S rRNA gene similarity studies: the Biolog and API Coryne systems correctly identified 54.0 and 88.0% of these strains, respectively. The other coryneforms were identified as other Corynebacterium spp., Rhodococcus spp., or Microbacterium spp. These data indicate that the coryneform bacteria isolated from bovine mammary glands are a heterogeneous group of organisms. Routine identification of C. bovis should include Gram-stain, cell morphology, catalase production, nitrate reduction, stimulated growth on 1% Tween 80 supplemented media, and beta-galactosidase production as the minimum requirements.

A palmitoyl-CoA-specific delta9 fatty acid desaturase from Caenorhabditis elegans.

Biosynthesis of polyunsaturated fatty acids in C. elegans is initiated by the introduction of a double bond at the delta9 position of a saturated fatty acid. We identified three C. elegans fatty acid desaturase genes related to the yeast delta9 desaturase OLE1 and the rat stearoyl-CoA desaturase SCD1. Heterologous expression of all three genes rescues the fatty acid auxotrophy of the yeast delta9 desaturase mutant ole1. Examination of the fatty acid composition of the transgenic yeast reveals striking differences in the substrate specificities of these desaturases. Two desaturases, FAT-6 and FAT-7, readily desaturate stearic acid (18:0) and show less activity on palmitic acid (16:0). In contrast, the other desaturase, FAT-5, readily desaturates palmitic acid (16:0), but shows nearly undetectable activity on the common delta9 substrate stearic acid. This is the first report of a palmitoyl-CoA-specific membrane fatty acid desaturase.

Early light reduction for preventing retinopathy of prematurity in very low birth weight infants.

BACKGROUND: This section is under preparation and will be included in the next issue. OBJECTIVES: To answer the question: "Among very low birth weight infants, what is the effect of reducing early environmental light exposure on the incidence of any "Acute ROP", or "Poor ROP Outcomes"? SEARCH STRATEGY: Searches were made of the Cochrane Neonatal Group Register of Controlled Trials, Medline, EMBASE, the Cochrane Library, previous reviews including cross references, abstracts, conference and symposia proceedings, and expert informants. The search terms used were [retrolental fibroplasia or retinopathy of prematurity] and [light or light/ae or lighting or lighting/ae or light/tu or lighting/st]. SELECTION CRITERIA: Randomized or quasi-randomized controlled trials that reduced light exposure to premature infants within the first 7 days following birth were considered for this review. DATA COLLECTION AND ANALYSIS: Data on clinical outcomes including any Acute ROP and Poor ROP Outcome were excerpted by both reviewers independently and consensus reached. Data analysis was conducted according to the standards of the Neonatal Cochrane Review Group. MAIN RESULTS: Data from four recent randomized trials, and one much older quasi-randomized trial failed to show any reduction in Acute ROP, or Poor ROP Outcome with the reduction of light to premature infants' retinas. The number of infants studied to date allows 95% confidence that IF there were a true difference being missed, it would be smaller than 7 percentage points on a background of 54% of all infants under 2 kg developing ROP. REVIEWER'S CONCLUSIONS: Decreasing retinal light exposure in premature infants is very unlikely to reduce the incidence of ROP.

D-Penicillamine for preventing retinopathy of prematurity in preterm infants.

BACKGROUND: This section is under preparation and will be included in the next issue. OBJECTIVES: To answer the question: Among very low birth weight infants, what is the effect of prophylactic administration of d-penicillamine on the incidence of acute ROP or severe ROP, and side effects including death? SEARCH STRATEGY: Searches were made of multiple electronic databases, previous reviews including cross references, abstracts, conference/symposia proceedings, and expert informants. SELECTION CRITERIA: Randomized or quasi-randomized controlled trials that administered d-penicillamine to infants less than 2000g birth weight within the day following birth were considered relevant to this review. Additional case series were examined for potential side effects. DATA COLLECTION AND ANALYSIS: Data on clinical outcomes were excerpted by 3 reviewers independently, and consensus reached. Data analysis was conducted according to the standards of the Neonatal Cochrane Review Group. MAIN RESULTS: Two randomized trials on the effects on ROP were identified. When combined, they showed a significantly lower incidence of acute ROP in the treated infants, relative risk of 0.09, 95% CI [0.01,0.71]. Severe stages of ROP could not be analyzed. There was no effect on death rates, relative risk 0.99 95% CI [0.70,1.39]. No side effects were reported, and follow up at one year revealed no significant differences in spasticity or developmental delay, although there were more rehospitalizations among the controls. In other reports of using d-penicillamine in over 140 infants for hyperbilirubinemia, skin rashes were reported in 2 infants and one had vomiting that may have been related. REVIEWER'S CONCLUSIONS: D-penicillamine is unlikely to affect survival, and may reduce the incidence of acute ROP among survivors. Studies to date justify further investigation of this drug in a broader population; careful attention to possible side effects is needed.

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.

Identification and characterization of an animal delta(12) fatty acid desaturase gene by heterologous expression in Saccharomyces cerevisiae.

We have cloned a Caenorhabditis elegans cDNA encoding a Delta12 fatty acid desaturase and demonstrated its activity by heterologous expression in Saccharomyces cerevisiae. The predicted protein is highly homologous both to the cloned plant genes with similar function and to the published sequence of the C. elegans omega-3 fatty acid desaturase. In addition, it conforms to the structural constraints expected of a membrane-bound fatty acid desaturase including the canonical histidine-rich regions. This is the first report of a cloned animal Delta(12) desaturase gene. Expression of this cDNA in yeast resulted in the accumulation of 16:2 and 18:2 (linoleic) acids. The increase of membrane fluidity brought about by this change in unsaturation was measured. The production of polyunsaturated fatty acids in yeast cells and the concomitant increase in membrane fluidity was correlated with a modest increase in growth rate at low temperature and with increased resistance to ethanol and oxidative stress.

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.

The C. elegans par-4 gene encodes a putative serine-threonine kinase required for establishing embryonic asymmetry.

During the first cell cycle of Caenorhabditis elegans embryogenesis, asymmetries are established that are essential for determining the subsequent developmental fates of the daughter cells. The maternally expressed par genes are required for establishing this polarity. The products of several of the par genes have been found to be themselves asymmetrically distributed in the first cell cycle. We have identified the par-4 gene of C. elegans, and find that it encodes a putative serine-threonine kinase with similarity to a human kinase associated with Peutz-Jeghers Syndrome, LKB1 (STK11), and a Xenopus egg and embryo kinase, XEEK1. Several strong par-4 mutant alleles are missense mutations that alter conserved residues within the kinase domain, suggesting that kinase activity is essential for PAR-4 function. We find that the PAR-4 protein is present in the gonads, oocytes and early embryos of C. elegans, and is both cytoplasmically and cortically distributed. The cortical distribution begins at the late 1-cell stage, is more pronounced at the 2- and 4-cell stages and is reduced at late stages of embryonic development. We find no asymmetry in the distribution of PAR-4 protein in C. elegans embryos. The distribution of PAR-4 protein in early embryos is unaffected by mutations in the other par genes.