Biomedical subjects

T J Lam

Publications and source records attributed to T J Lam.

At least 73 records · Page 4Linked to original sources

PubMed1996

The first contiguous estrogen receptor gene from a fish, Oreochromis aureus: evidence for multiple transcripts.

The O. aureus estrogen receptor (OaER) gene of 40.4 kb containing ten exons is the first complete piscine gene to be cloned. There are two extra introns: intron I that divides the 5' UTR into two exons, and intron V that intersperses D and E1 exons. Except for I and V, other introns have identical positions to those of human ER gene. All the donor and acceptor splice sites exhibit consensus sequences. The promoter lacks consensus TATA and CAAT boxes. This region exhibits several putative regulatory elements. A functional imperfect ERE deviating at two bases is located in the leader exon, thus suggesting that this gene is autoregulated. The OaER gene lacks an A region whereas its C and E domains are highly conserved. Within the ER subfamily, OaER exhibits the longest F domain of 77 amino acids. OaER has a long 3'UTR constituting >1/2 of its transcript. Using RT-PCR and SI nuclease mapping, we report for the first time the usage of both alternative transcriptional start sites and polyadenylation signals during estrogen-induced OaER expression. Thus, O. aureus may have four species of ER transcripts differing structurally in their transcriptional start sites and lengths of their 3' UTR.

Amino Acid Sequence↗

PubMed1996

Use of composite milk samples for diagnosis of Staphylococcus aureus mastitis in dairy cattle.

OBJECTIVE: To measure relative sensitivity and relative specificity for use of composite milk samples, compared with that of individual gland milk samples, for diagnosis of Staphylococcus aureus mastitis. ANIMALS: 505 cows suspected of having subclinical mastitis. Of these cows, 172 were considered infected with Sta aureus, based on the results from individual gland samples. PROCEDURE: Composite and individual gland milk samples were collected from cows suspected of having subclinical mastitis, and results of bacteriologic culturing of samples from the same cow were compared. Results were interpreted at the cow level. Relative sensitivity and relative specificity for composite samples were computed from 2 x 2 tables, using results from individual gland samples as references. RESULTS: Relative sensitivity for use of composite milk samples in diagnosing Sta aureus mastitis was 0.63. The relative specificity was 0.98. Factors influencing the relative sensitivity for composite samples were the number of infected glands per cow, the amount of Sta aureus shedding from infected glands, and the proportion of the composite milk obtained from each gland. CLINICAL IMPLICATIONS: Collecting composite instead of individual gland milk samples increases the number of false-negative results in diagnosing Sta aureus mastitis. By collecting consecutive samples from the same cow or by increasing the inoculum volume at culturing, this problem can be diminished.

Animals↗

PubMed1996

Ontogeny of immunoreactive steroidogenic proteins (adrenodoxin and cytochrome p-450(21)) in the interrenals of the teleost Lates calcarifer.

Antisera against bovine adrenodoxin and cytochrome P-450(21) (steroid 21-hydroxylase) cross-reacted with the interrenal cells of the adult Asian seabass (Lates calcarifer); the cells were arranged as cords, two cells thick, in the headkidney. During larval development, cells immunoreactive for adrenodoxin were first observed 1 day posthatching (dph); immunoreactivity for cytochrome P-450(21) was first detected at 1.5 dph. Initially, the interrenal cells occurred as a mass in each headkidney, which only became identifiable histologically at 5 dph. The number of interrenal cells increased with age, becoming associated with the cardinal veins at 14 dph. The present study thus indicates that the posthatching rise in cortisol may originate from the nascent interrenal tissue.

Adrenodoxin↗

PubMed1996

Genotyping by PCR, of Staphylococcus aureus strains, isolated from mammary glands of cows.

A total of 71 Staphylococcus aureus strains isolated from bovine mammary glands were identified and subtyped. The methods used to differentiate between the S. aureus isolates were the DNA polymorphism pattern after amplification with a Polymerase Chain Reaction using several primer combinations and phage typing. The DNA fingerprinting technique using RAPD, ERIC1R and ERIC primers proved to be useful in differentiating isolates of S. aureus. Differentiation of isolates using phage typing gave no additional information compared to the DNA technique. The outbreak of S. aureus in the herd studied was mainly caused by one S. aureus strain. Other strains were only found on three occasions, twice in subclinical infections and once from a case of clinical mastitis. In the latter case the dominant strain was isolated from a different quarter of the same cow. Four of the ten cows studied suffered from clinical mastitis. From those four cows, three remained infected with the same S. aureus strain despite antibiotic treatment.

Animals↗

PubMed1996

Mathematical modeling to estimate efficacy of postmilking teat disinfection in split-udder trials of dairy cows.

A mathematical model was used to estimate the efficacy of postmilking teat disinfection from observations in split-udder trials with natural exposure. Data were studied from an outbreak of Staphylococcus aureus IMI during a split-udder trial in a commercial herd with low SCC. The efficacy of postmilking teat disinfection was similar when calculated based on incidence density rates or on transmission rates of IMI in dipped and control quarters. If, however, first and subsequent S. aureus IMI in a cow were not assumed to be independent and were therefore treated separately in the models, the efficacy of post-milking teat disinfection was calculated as being higher with the modeling procedure. The analysis using mathematical modeling, which includes the effect of the number of existing IMI on the number of new IMI, is presented and discussed. This analysis also allows estimation of the basic reproduction ratio. The impact of postmilking teat disinfection on transmission of pathogens is quantified, and proposals for additional preventive measures can be generated. We concluded that efficacy estimations from split-udder trials, assuming quarters to be independent observations, might underestimate the effect of postmilking teat disinfectants on udder pathogens.

Animals↗

PubMed1996

Epidemiological characteristics of bovine clinical mastitis caused by Staphylococcus aureus and Escherichia coli studied by DNA fingerprinting.

OBJECTIVE: To study the epidemiology of clinical mastitis caused by Escherichia coli and Staphylococcus aureus by differentiating isolates with DNA fingerprinting techniques, using polymerase chain reaction. DESIGN: Milk samples were collected from cases of clinical mastitis in dairy cows. Escherichia coli and S aureus isolates from these cases were compared within and between cows and herds. SAMPLE POPULATION: Seven dairy herds with an average bulk milk somatic cell count < 150,000/ml, and incidence of cows with clinical mastitis of > 25%/y. PROCEDURE: Chromosomal DNA was isolated from E coli and S aureus strains isolated from cases of clinical mastitis, and amplified by polymerase chain reaction, using enterobacterial repetitive intergenic consensus primers for E coli and a random amplified polymorphic DNA primer for S aureus. Escherichia coli and S aureus strains were identified and differentiated, using their DNA polymorphism pattern. RESULTS: Multiple E coli genotypes were found in each of the herds. Persistent infections with E coli were sporadic. Only a limited number of different S aureus genotypes was found in each of the herds studied. Recurrent cases of S aureus mastitis were found in 25% of quarters with clinical S aureus mastitis. Comparing S aureus isolates from different herds indicated that 1 S aureus genotype was most prevalent. CONCLUSIONS: Because different quarters were infected with different genotypes, it was concluded that E coli is an environmental pathogen, and does not generally spread from quarter to quarter. The hypothesis that S aureus mastitis is a contagious disease, spreading from infected to uninfected quarters, could not be rejected.

Animals↗

PubMed1995

[The dairying veterinary approach to a high bulk milk cell count caused by Streptococcus agalactiae].

The herd health approach for dairy herds with a high bulk milk somatic cell count, in which Streptococcus agalactiae plays a major role, was evaluated. After introduction of the standard mastitis prevention programme, all quarters of infected cows were treated during lactation. In three of the four herds investigated, the bulk milk somatic cell count dropped below the limit of 400,000 cells/ml for a long period of time. The herd in which there were many infections with Staphylococcus aureus and Streptococcus agalactiae was an exception. The management, somatic cell count, and prevalence of subclinical mastitis in the different herds is discussed. It is concluded that for infection with Streptococcus agalactiae at the herd level, treatment during lactation can be an effective method to lower the bulk milk somatic cell count. In essence, however, the approach to the problem lies in the standard mastitis prevention programme.

Animals↗

PubMed1995

[Udder disinfection and mastitis in cattle: a literature review].

Postmilking teat disinfection is accepted as an important part of standard preventive measures against mastitis in dairy cattle. The efficacy of postmilking teat disinfection against infections with contagious pathogens such as Staphylococcus aureus and Streptococcus agalactiae is beyond doubt. However, the efficacy of teat disinfection against infections with environmental pathogens such as Escherichia coli is disputed, and a negative effect has even been described in some situations. This article reviews the practice of teat disinfection in dairy cattle. Premilking and postmilking teat disinfection are discussed, as is the efficacy, different ways of teat disinfection, and different disinfectants. It is concluded that post-milking teat disinfection is an effective management measure in most herds. Selection of teat disinfectants should be based on proven efficacy, which is required for registration of the preparation as a veterinary medical product in the Netherlands.

Animals↗

PubMed1995

[Subclinical and clinical mastitis on dairy farms in The Netherlands: epidemiological developments].

In this review a number of the main epidemiological developments in the field of udder health in the Netherlands are summarized. The changes considering the bulk milk somatic cell count are described, as are the population dynamics of subclinical mastitis. Additionally, clinical mastitis caused by Escherichia coli and Staphylococcus aureus and their risk factors are reviewed. Finally, some future developments and the possible applications of these developments are discussed.

Animals↗

PubMed1995

In vitro metabolism of testosterone by gonads of the grouper (Epinephelus tauvina) before and after sex inversion with 17 alpha-methyltestosterone.

The steroidogenic potential of gonadal tissues of the protogynous grouper (Epinephelus tauvina) was examined before and after sex inversion with 17 alpha-methyltestosterone. Incubations of gonadal tissues of the fish with [3H]testosterone resulted in the biosynthesis of 5 beta-androstane-3 beta, 17 beta-diol and 5 beta-dihydrotestosterone as the only metabolites in the female phase. Although the production of these 5 beta-reduced androgens persisted in the male phase, there was a shift toward the production of 11 beta-hydroxytestosterone and 11-ketotestosterone as major metabolites.

Androstane-3,17-diol↗

PubMed1995

An observational study of Eimeria species in housed cattle on Dutch dairy farms.

The prevalence of oocysts of Eimeria species in calves (n = 334), yearlings (n = 254) and cows (n = 1314) was determined on 38 Dutch dairy farms. Twelve species of Eimeria were identified in faecal specimens by sucrose-flotation. The prevalences of Eimeria spp. differed markedly in the different age classes on individual farms as well as between farms. The overall prevalence of Eimeria oocysts in faecal specimens was 46% for calves, 43% for yearlings and 16% for cows. The number of oocysts excreted was generally low in cows and yearlings, whereas high numbers of oocysts per gram of faeces (OPG) were exclusively observed in calves. No cases of clinical coccidiosis were observed in this survey. Linear regression analysis showed that there is significant reduction in the OPG levels (P < 0.05) in calves infected with Eimeria, aged between 7 and 38 weeks. Finally, the data are discussed in relation to management practices and the acquisition of immunity.

Aging↗

PubMed1995

The combined effect of fenbendazole treatment and a move to aftermath 7 or 9 weeks after turnout on Dictyocaulus viviparus infections in calves.

A grazing study was performed with the main objective of examining the effect of fenbendazole (FBZ) in a 'dose and move' system on nematode infections in calves with special emphasis on Dictyocaulus viviparus. Three groups of six calves were grazed from May to October 1993. One group (DM7) was treated with FBZ and moved to aftermath (pasture which had only been mown) 7 weeks after turnout. The second group (DM9) was similarly treated and moved 9 weeks after turnout and the third group served as untreated pasture control group (PC) and was moved to aftermath 9 weeks after turnout. FBZ treatment removed adult lungworms from DM7 and DM9. Tracer calves grazed during the first 7 or the first 9 weeks after turnout acquired mean burdens of 18 and 125 lungworms, respectively. In PC faecal larval counts increased until the end of August. Most of the animals in this group were then suffering from lungworm disease and emergency treatment with ivermectin was given. In both FBZ-treated groups, larvae reappeared in the faeces of some of the calves 4-5 weeks after treatment. Subsequent reinfection resulted in higher mean faecal larval counts in both groups 2 months after treatment, although variation in faecal larval counts was high. In DM7 values tended to be higher than in DM9. These higher larval counts were associated with mild signs of parasitic bronchitis in some calves of DM7, whereas no signs were seen in DM9. At the end of the experiment, all calves, and also a group of six permanently housed non-infected control calves (HC), were infected experimentally with 5000 D. viviparus larvae to evaluate development of immunity. The worm counts at necropsy showed that all calves on pasture had developed immunity.

Animal Feed↗

PubMed1995

Identification of Escherichia coli strains from cows with clinical mastitis by serotyping and DNA polymorphism patterns with REP and ERIC primers.

A number of Escherichia coli strains was isolated during a study of clinical mastitis on seven farms in the Netherlands. From these E. coli strains, 30 were characterised with regard to their serotype and their DNA polymorphism pattern with REP and ERIC primers. Special attention was given to recurrent E. coli mastitis in cows. The combination of serotype and DNA pattern observed, was used to study the epidemiology of clinical E. coli mastitis. The results demonstrated that the PCR reaction with the ERIC primers can be used for differentiation of E. coli strains. The DNA polymorphism patterns showed that E. coli strains isolated from cases of clinical mastitis have a great variability in genotype. More 3 than one case of clinical mastitis associated with E. coli during the same lactation period occurred infrequently. However when it took place, E. coli strains isolated from the separate episodes of inflammation, were in most instances of the same serotype and had the same DNA amplification pattern.

Animals↗

PubMed1995

The differentiation of Staphylococcus aureus from other Micrococcaceae isolated from bovine mammary glands.

Haemolysin production, the slide coagulase test and the tube coagulase test were assessed for their capability to differentiate Staphylococcus aureus among other Micrococcaceae in 199 isolates from udders of cows in herds with a low bulk milk somatic cell count. The API-Staph test was used as a reference. Haemolysin production was less effective in identifying Staph. aureus among Micrococcaceae than a combination of other tests. Differences were found in the predictive values of results from diagnostic protocols in which the slide coagulase test was performed on all Micrococcaceae, or on beta-haemolysin-negative Micrococcaceae only. Diagnostic protocols in which haemolysin production was combined with the results of the other tests resulted in excellent diagnostic performance and a reduction in diagnostic procedures. Recommendations for routine Staph. aureus identification in bovine mastitis bacteriology are given.

Animals↗

PubMed1995

Molecular cloning and sequencing of the hormone-binding domain of Oreochromis aureus estrogen receptor gene.

The nucleotide sequence of the estrogen receptor gene of Oreochromis aureus (OaER) indicates that the hormone-binding E domain is composed of 4 exons interspersed by short introns of only 0.18-1.3 kb each. All 4 E exons exhibit consensus sequences flanking the donor and acceptor splice sites. Analysis of introns revealed (i) numerous palindromic and half-palindromic steroid responsive elements including ERE, TRE and GRE, (ii) six alternative polyadenylation signals and (iii) putative control regions identified by the clustering of transcription factor binding sites. Of particular interest is the presence of a TATA and CAAT box in intron IV. The hydropathicity profile shows that the E exons are relatively hydrophobic. Two receptor dimerization regions have been observed: a conserved heptad repeat of hydrophobic residues (R168-M193) and a perfect leucine zipper (L36-L57). The presence of multiple sites for kinase activity in these regions suggests the importance of phosphorylation in the regulation of receptor functions and ligand-affinity.

Amino Acid Sequence↗

PubMed1995

The hormone-binding domain of Oreochromis aureus estrogen receptor gene: homology comparison with other steroid binding receptors.

Although the estrogen receptor gene of Oreochromis aureus (OaER) shows 85% homology to rainbow trout ER (rtER), the molecular organization of its exons and introns in the hormone-binding E domain is more closely related to the human ER gene. Comparison with other vertebrates yielded reduced homologies of 64-67%, probably due to evolutionary speciation. The E1 and E2 exons of OaER are interspersed by a short intron of 1.3 kb which is flanked by consensus splice sites. This is in sharp contrast to the 11 kb intron separating E1 and E2 exons of rtER which also displayed a rare GC donor junction. Three conserved cys at 83, 112 and 195, which are important for formation of 3-D ligand-binding pocket were found in OaER. However, the 4th conserved cys is replaced by a ser. This substitution which is the result of a single base mutation probably suggests different affinity for estrogen or transactivation of the OaER gene. Two overlapping steroid binding and receptor dimerization domains have been observed. The E domain of OaER and rtER has diversified significantly from that of other non-piscine vertebrates, such that they form a separate subgroup in the UPGMA tree of steroid receptors.

Amino Acid Sequence↗

PubMed1994

Cortisol-induced hepatic vitellogenin mRNA in Oreochromis aureus (Steindachner).

Cortisol triggers rapid but transient transcription of the silent vitellogenin (Vg) gene in male Oreochromis aureus, producing short-lived Vg mRNA. Implantation of cocoa butter containing cortisol at 0.8, 8, 20, and 40 micrograms/g fish body wt induced hepatic Vg mRNA within 1 or 2 hr. Implantation of cortisol at the lowest of these dosages (0.8 micrograms/g body wt) produced a transient surge in serum cortisol within 1 hr. This is equivalent to a 30-fold increase over that of the resting male fish in which the endogenous cortisol levels measured 10.5 +/- 2.39 and 11.4 +/- 3.1 ng/ml, respectively, for fish kept communally or singly. Although sham implantation with cocoa butter also resulted in the elevation of serum cortisol, the rise was much more gradual, only reaching a peak after 6 hr. Thus, parameters like the treatment regime, sampling time intervals after implantation, and the interaction between these two factors can significantly affect the serum cortisol concentrations (P = 0.001). Although implantation of cocoa butter with or without cortisol increased serum cortisol, albeit unsynchronized, Vg mRNA was detected only in the hormone-treated group. The profile of Vg mRNA accumulation appeared to coincide with that of serum cortisol, further suggesting the activating effect of exogenous cortisol on Vg gene. Compared with an earlier study on estradiol-induced Vg gene expression, the action of cortisol was more rapid, but transient. This is reflected in the rapid clearance of the cortisol-induced Vg mRNA and, hence, the lack of plasma Vg protein during cortisol treatment.

Animals↗

PubMed1994

The prevalence of patent lungworm infections in herds of dairy cows in The Netherlands.

The results of a survey on the prevalence of patent lungworm infections in herds of dairy cows in the Netherlands are presented. Low patent infections were recorded in February-March on six out of 40 farms in at least one out of 40 cows. Between mid-April and mid-June low patent infections were detected on 28 out of 39 of these farms in one to four of 40 cows. Two farms on which cows were positive in the first round were negative in the second round. One to three positive cows were found on six out of a total of 15 farms revisited in July-August. These results show that lungworm infections are cycled within herds of dairy cows in the Netherlands at a low level. This indicates that dairy cows are important as carriers for lungworm, particularly in spring. The increased patency of lungworm in cows from winter to spring may be explained by maturation of inhibited larvae.

Animals↗