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Biomedical subjects

H D Larsen

Publications and source records attributed to H D Larsen.

At least 19 recordsLinked to original sources
PubMed2002

Geographical variation in the presence of genes encoding superantigenic exotoxins and beta-hemolysin among Staphylococcus aureus isolated from bovine mastitis in Europe and USA.

The object was to examine the geographical variation in the presence of superantigenic exotoxins and beta-hemolysin among epidemiologically independent Staphylococcus aureus isolates from bovine mastitis. A total of 462 S. aureus isolates from nine European countries and USA were examined for the presence of genes encoding staphylococcal enterotoxins A-E, and H, toxic shock toxin-1 (TSST-1), and beta-hemolysin, and 128 of these were examined for exfoliative toxins A and B. The detection was done by PCR. Phenotypic methods were used to confirm the PCR-results. None of the 128 isolates carried the genes for exfoliative toxin A or B. The total proportion of isolates in which superantigenic exotoxins were detected varied from 2% (one isolate) of the Danish isolates to 65% (32 isolates) of the Norwegian isolates. This marked and highly significant geographical variation was also present for the individual exotoxins. The genes encoding enterotoxin C, TSST-1, and enterotoxin D were the most common superantigens. The present and earlier studies demonstrate that the superantigenic exotoxins that were investigated in this study, do not play a role in the pathogenesis of bovine S. aureus mastitis. In contrast to the geographical variation among superantigenic exotoxins, 97% of the isolates were PCR-positive for and/or produced beta-hemolysin on 5% calf blood agar. Except for three isolates, the Norwegian isolates were PCR-negative, but positive on 5% calf blood agar. Sequence variation in the primer regions in the beta-hemolysin encoding gene of the Norwegian isolates is suggested, and should be investigated further. The consistent presence of beta-hemolysin suggests that this factor, or a co-existing gene correlated to beta-hemolysin, may be an active virulence factor in the pathogenesis of bovine S. aureus mastitis.

Animals↗
PubMed2000

Differences between Danish bovine and human Staphylococcus aureus isolates in possession of superantigens.

PCR-assays for the detection of staphylococcal enterotoxins A-E, and H, toxic shock toxin 1, and exfoliative toxins A and B were evaluated against phenotypic methods, and performed well. Four hundred and fourteen isolates of Staphylococcus aureus from Danish cases of bovine mastitis were screened for genes encoding these superantigens. One hundred isolates from Danish human carriers were also included in the study. In contrast to the frequent presence of genes encoding and in vitro expression of superantigens among the human carrier isolates, only one of 414 isolates from bovine mastitis carried the genes encoding enterotoxin C and toxic shock toxin-1. These results further support the hypothesis that the bovine and human S. aureus reservoirs constitute two separate sub-populations of the species S. aureus. The results also show that these superantigens are generally not present in Danish S. aureus isolates from bovine mastitis, and thus play no essential role in the pathogenesis of bovine S. aureus mastitis.

Animals↗
PubMed2000

The dynamics of Staphylococcus aureus intramammary infection in nine Danish dairy herds.

The aim of the present study was to examine the diversity of Staphylococcus aureus isolates from bovine intramammary infections (IMI) in nine dairy herds, and compare these with isolates from other sites on the cows by phage- and ribotyping. Whether colonisation of milkers with S. aureus could be a source of infection for bovine IMI was investigated. In addition, 100 epidemiologically unrelated S. aureus isolates from asymptomatic human carriers were also phage- and ribotyped to compare the human and bovine reservoir of S. aureus in Denmark. A total of 625 S. aureus isolates from bovine IMI, bovine skin lesions, milking personnel, and non-farm-related human carriers were included in the study. Certain types predominated in one or several herds during the study period of one-and-a-half to two years, whereas the presence of other types was of a more sporadic nature. Within the individual herds, there was a close correspondence between ribo- and phage types of S. aureus isolated from bovine intramammary infections and skin lesions. Isolates from milking personnel, however, were not identical to any of the predominant intramammary strains. Furthermore, several of the isolates from milking personnel showed ribo- and phage patterns identical to S. aureus isolates from human carriers. The findings of the present study underline the importance of strict milking hygiene and improvement of current mastitis therapy. The results support the hypothesis that some S. aureus mastitis strains are more contagious, virulent or persistent than others. The human reservoir of S. aureus does not play a major role as a source of bovine intramammary infections.

Agricultural Workers' Diseases↗
PubMed1999

Characterization of Staphylococcus simulans strains isolated from cases of bovine mastitis.

This study was conducted to characterize Staphylococcus simulans isolated from cases of bovine mastitis. A total of 134 isolates of S. simulans selected from 80 quarters from 61 cows or heifers in 37 different herds were characterized by EcoRI ribotyping. From 22 quarters two to seven consecutive isolates taken at weekly intervals were selected. Furthermore, three isolates from clinical infections in humans and two reference strains were included. A total of 16 different ribotypes were found, however, two types predominated. In most herds more than one type was found. From the 22 different quarters, where 76 paired or multiple isolates were at disposal, the same ribotype was constantly found in the same quarter. This study showed that S. simulans causing bovine mastitis could be divided into relatively large number of different types, but that two types predominated. More than one type could be found in the same herd and within different quarters of the same cow, but ribotyping confirmed that S. simulans could be the cause of persistent and stable infections.

Animals↗
PubMed1999

Frequency of alpha- and beta-haemolysin in Staphylococcus aureus of bovine and human origin. A comparison between pheno- and genotype and variation in phenotypic expression.

The phenotypic expression of haemolysins and the presence of genes encoding alpha and beta-haemolysin were determined in 105 Staphylococcus aureus isolates from bovine mastitis, 100 isolates from the nostrils of healthy humans, and 60 isolates from septicaemia in humans. Furthermore, the possible change in expression of haemolysins after subcultivation in human and bovine blood and milk was studied in selected isolates. Alpha-haemolysin was expressed phenotypically in 39 (37%) of the bovine isolates, in 59 (59%) of the human carrier isolates, and in 40 (67%) of the isolates from septicaemia. Beta-haemolysin was expressed in 76 (72%) bovine, 11 (11%) carrier, and 8 (13%) septicaemia isolates. Significantly more bovine than human isolates expressed beta-haemolysin and significantly fewer expressed alpha-haemolysin. Genotypically, the gene encoding alpha-haemolysin was detected in all isolates. A significant difference in the prevalence of the gene encoding beta-haemolysin between the bovine (96%), human carrier (56%) and isolates from septicaemia (57%) was found. Of the bovine isolates, 75% of those carrying the gene encoding beta-haemolysin expressed beta-haemolysin phenotypically, whereas only 20% of the carrier isolates and 24% of the septicaemia isolates did so. No change in expression of haemolysins could be observed after subcultivation of bovine isolates in human blood and milk. After 5 to 10 subcultures in bovine blood and 1 to 4 in bovine milk, 9 of 10 human isolates originally phenotypically beta-haemolysin negative initiated the expression of beta-haemolysin. This study showed that a larger proportion of S. aureus of bovine origin carry the beta-haemolysin gene compared to isolates from humans. Furthermore, a larger number of the isolates of bovine origin carrying the beta-haemolysin gene express this gene phenotypically compared to isolates of human origin.

Animals↗
PubMed1998

The effect of post milking teat dip and suckling on teat skin condition, bacterial colonisation, and udder health.

The teat skin of cows was scored (1: smooth as silk; 2: smooth; 3: slightly rough; 4: rough; 5: cracked; and 6: scores) by trained technicians who moved their fingers down the barrel of the teat with a light touch. Technicians ranked the same population of teats in the same rank order, but their mean values differed by half a score which probably could be related to the skin condition of their own fingers. Half udder experiments were carried out for 6 months at 4 farms with 35 to 52 cows each. A postmilking teat spray with 10% glycerol improved teat skin condition (p < 0.10) compared with no teat spray. A postmilking teat spray with 120 ppm chlorine dioxide did not influence teat skin condition compared with no teat spray. No differences in udder health could be proven between treatments. Control studies revealed that 10% glycerol as an emollient of a postmilking teat spray improved teat skin condition within 3 weeks from being slightly rough to being smooth for lactating cows (p < 0.05) but not for dry cows having smooth teat skin. Neither glycerol nor chlorine dioxide influenced absolute number of bacteria on teat skin after a challenge with Streptococcus uberis and Staphylococcus aureus but half life of S. aureus on unsprayed teats was longest (p = 0.05). Suckling made teat skin more rough than machine milking. Nevertheless, suckling lowered the number of esculin positive bacteria on the teat skin. We concluded that the condition of healthy teat skin (scores 1-4) has no influence on bacterial colonisation in the absence of cracks and sores (scores 5-6).

Animals↗
PubMed1997

The occurrence of Bacillus cereus in Danish pasteurized milk.

Four hundred and fifty eight samples of pasteurized full fat milk, pasteurized low fat milk (1.5% milk fat) and pasteurized double cream were collected from three Danish dairies (A, B and C) over a period of 1 year. The milk samples were stored at 7 +/- 0.5 degrees C for 8 days, and were then examined for the presence of Bacillus cereus and other aerobic mesophilic microorganisms. In addition, 115 raw milk samples taken from weighing tanks at the three dairies were examined for psychrotrophic B. cereus. B. cereus was isolated from 257 (56%) of the 458 pasteurized milk samples examined, and no differences between full fat milk, low fat milk and double cream were observed as regards the percentage of B. cereus positive samples. However, the mean count of B. cereus was significantly higher in double cream than in the other products. No significant differences was observed between the dairies. The prevalence of B. cereus in pasteurized milk products during summer and winter was 72 and 28%, respectively, and the mean counts of B. cereus was significantly higher during summer as well. Psychrotrophic B. cereus was detected in 29 of 115 samples of raw milk (25%). In 120 of the 257 samples of pasteurized milk found to be positive, the viable count of B. cereus obtained was in the range between 10(3) and 3 x 10(5) cfu/ml.

Animals↗
PubMed1996

Enterotoxin-producing strains of Bacillus thuringiensis isolated from food.

Strains of Bacillus thuringiensis were isolated from various food items (pasta, pitta bread and milk) and were found to belong to either H-serotype kurstaki or neoleonensis. The strains were bioassayed against Pieris brassicae and insecticidal activity of strains was found to correspond to the presence of the cry1A-gene. All strains, except one, were found to express cytotoxic effects on Vero cells as an indicator of enterotoxin activity. Further, the B. thuringiensis strains HD-1 (serotype kurstaki), NB-125 (serotype tenebrionis) and HD-567 (serotype israelensis ) which are used commercially for insect pest management, were also found to have cytotoxic effects on Vero cells.

Animals↗
PubMed1985

A system for developing and evaluating the clinical judgment of dental students.

A system for evaluating the clinical judgment of dental students in removable prosthodontics was presented. The major points of the system are as follows. Students must decide when the quality of their treatment is worthy of a grade. Three quality-level categories are used. Letters that have no intrinsic meaning are used to designate each quality level. Each item may be evaluated a maximum of four times by the student before remediation is instituted. Each attempt to evaluate the same procedure receives a lower point value. The final grade is determined as a percent of points earned out of a possible maximum. Faculty acceptance of the system is high. The system provides an easy means of feedback to students.

Clinical Competence↗
PubMed1984

Modifications of the superstructure for the staple implant.

Two techniques have been described to expedite fabrication and reduce the cost of prostheses made for staple implants. The techniques permit placement of a simulated transosseous pin within the master cast. At the time of denture placement in technique No. 1, the coping-bar attachment assembly is cemented (Fig. 12). In technique No. 2 the superstructure is placed over the transosteal pins and secured between the locknuts to maintain the base of the lower locknut 1.5 mm from the crest of the alveolar ridge (Fig. 13). Technique No. 2 permits removal of the superstructure as desired. Patients should be instructed in proper oral hygiene and denture care.

Bone Plates↗
PubMed1983

Prosthodontic management of the hydroxylapatite denture patient: a preliminary report.

A 4-year study and evaluation of nonresorbable hydroxylapatite to augment different alveolar ridges has been reported. The technique used resulted in improved contour, height, and width of the alveolar ridge. It was found that denture comfort improved with ridge augmentation as this allowed improved stability, support, and preservation of the ridge. Patient satisfaction was correlated to both surgical and prosthodontic success with the use of hydroxylapatite. The state and health of the tissues were found to be improved with the use of hydroxylapatite or hydroxylapatite and bone marrow. The prosthetic and surgical procedures were found to be easier to perform, and they produced more permanent and superior results than those previously experienced with only bone grafts and other alloplasts.

Adult↗