Biomedical subjects

Freddy Haesebrouck

Publications and source records attributed to Freddy Haesebrouck.

68 records · Page 4Linked to original sources

PubMed2003

Emended description of Streptococcus ferus isolated from pigs and rats.

Streptococcus ferus is a mutans-like streptococcus originally isolated from wild rats fed with sugar cane. Taxonomically, this species has not been studied extensively. Ten Gram-positive coccal strains, isolated from the tonsils and nasal conchae of piglets, were identified as S. ferus by 16S rDNA sequencing, tRNA-intergenic spacer length polymorphism analysis (tDNA-PCR), whole-cell protein profiling using SDS-PAGE, G+C content determination and extensive biochemical testing. In all these tests, the type strain of S. ferus (LMG 16520T), from a rat, was included. The results of the tests are described and an emended species description is presented.

Animals↗

PubMed2003

Antimicrobial growth promoters used in animal feed: effects of less well known antibiotics on gram-positive bacteria.

There are not many data available on antibiotics used solely in animals and almost exclusively for growth promotion. These products include bambermycin, avilamycin, efrotomycin, and the ionophore antibiotics (monensin, salinomycin, narasin, and lasalocid). Information is also scarce for bacitracin used only marginally in human and veterinary medicine and for streptogramin antibiotics. The mechanisms of action of and resistance mechanisms against these antibiotics are described. Special emphasis is given to the prevalence of resistance among gram-positive bacteria isolated from animals and humans. Since no susceptibility breakpoints are available for most of the antibiotics discussed, an alternative approach to the interpretation of MICs is presented. Also, some pharmacokinetic data and information on the influence of these products on the intestinal flora are presented.

Animal Feed↗

PubMed2003

Host adaptation of pigeon isolates of Salmonella enterica subsp. enterica serovar Typhimurium variant Copenhagen phage type 99 is associated with enhanced macrophage cytotoxicity.

Phage type 99 of Salmonella enterica subsp. enterica serovar Typhimurium variant Copenhagen strains isolated from pigeons were examined for the presence of genotypic and phenotypic characteristics. The pulsed-field gel electrophoresis patterns obtained with XbaI and BlnI from 38 pigeon strains were compared with those obtained from 89 porcine, poultry, and human strains of variant Copenhagen. Identical patterns with XbaI and four closely related patterns with BlnI were obtained with the pigeon strains, whereas 16 XbaI patterns were found with the other strains. The XbaI patterns of the pigeon strains showed a low genetic similarity to the patterns of the porcine, poultry, and human strains and invariably showed a low-molecular-weight band that was absent in the majority of the other strains. The virulence genes shdA, spvR, pefA, sopE, and spvB were uniformly present in six pigeon isolates representing the genetic diversity found with BlnI. These six pigeon-derived strains were highly cytotoxic for pigeon macrophages compared to three porcine strains. After experimental infection of pigeons with a pigeon strain, clinical symptoms, fecal shedding, and colonization of internal organs were more pronounced than those after infection with a porcine strain. These data suggest that the phage type 99 strains used in this study are highly adapted to pigeons and should be classified as a host-restricted lineage of the serovar Typhimurium.

Adaptation, Physiological↗

PubMed2002

Evaluation of serology, bacteriological isolation and polymerase chain reaction for the detection of pigs carrying Actinobacillus pleuropneumoniae in the upper respiratory tract after experimental infection.

Pigs, asymptomatically infected with Actinobacillus pleuropneumoniae in their upper respiratory tract, can transmit the infection. Detection of such animals is indispensable to prevent the intake of the disease in a herd. This study was conducted to evaluate bacteriology, polymerase chain reaction (PCR) and serology for the detection of subclinically infected pigs. Pigs were inoculated onto the tonsils with an A. pleuropneumoniae serotype 9 strain (n=12, group 1) or phosphate buffered saline solution (PBSS) (n=5, group 2). To prevent infection of the lungs, pigs of group 1 were treated three times with sodium ceftiofur as an aerosol. A third group (n=5) was inoculated intranasally with the same strain. All animals were euthanized 30 days post-inoculation (dpi). In pigs of group 1, clinical signs were not observed. A small lung lesion was found in only one pig and A. pleuropneumoniae was isolated from this lesion. The bacterium was not isolated from the lungs of animals that did not develop lung lesions. A. pleuropneumoniae was demonstrated in tonsils of 9/12 animals using bacteriological isolation, whereas it was demonstrated in mixed bacterial cultures from tonsils of all 12 animals by PCR. In non-infected animals (group 2), clinical signs were not observed and A. pleuropneumoniae was not demonstrated in any sample. All intranasally infected animals (group 3) developed disease signs and lung lesions. High antibody titers against ApxI, ApxII and heat-stable antigens were detected in animals that developed lung lesions. Antibody titers against these antigens were low or absent in all other pigs. It was concluded that pigs carrying A. pleuropneumoniae in the upper respiratory tract generally do not show measurable antibodies in serum. Therefore, sensitive methods for the detection of the etiological agent such as PCR are required to identify carrier animals, while serological methods are not suitable.

Actinobacillus Infections↗

PubMed2002

Characterization of the in vitro adhesion of Actinobacillus pleuropneumoniae to swine alveolar epithelial cells.

Actinobacillus pleuropneumoniae biovar 1 serotypes 2, 5a, 9 and 10 strains were tested for their ability to adhere to alveolar epithelial cells in culture. For the serotypes 5a, 9 and 10 strains, optimal adherence was observed after growth of bacterial cells in a NAD-restricted medium (0.001% NAD). This condition was also associated with the expression of a 55 kDa outer membrane protein (OMP) and of fimbriae. For the serotype 2 strain, adherence and expression of fimbriae and a 55 kDa OMP was less influenced by the growth conditions. The N-terminal amino acid sequence of the 55 kDa OMP had no homology with any known sequence, suggesting that it is an as yet unknown protein. Adherence capabilities were significantly reduced following treatment of the bacteria with proteolytic enzymes or heat. These findings suggest that proteins are involved in adhesion. The hydrophobic bond-breaking agent tetramethylurea was unable to inhibit the adherence of A. pleuropneumoniae to alveolar epithelial cells. Treatment of the bacteria with sodium metaperiodate resulted in lower adhesion scores for the serotypes 2 and 9 strains but the inhibition of adhesion was clearly lower than after treatment with proteolytic enzymes. This indicates that, besides proteins, carbohydrates might also be involved in adhesion of A. pleuropneumoniae to alveolar epithelial cells. The finding that inhibition of adhesion was very high when bacteria were treated with a combination of sodium metaperiodate and pronase also suggests that more than one adhesin is involved.

Actinobacillus pleuropneumoniae↗

PubMed2002

The effect of vaccination with a Salmonella enteritidis aroA mutant on early cellular responses in caecal lamina propria of newly-hatched chickens.

When newly hatched chicks are inoculated with a Salmonella strain, they induce a rapid onset of resistance to intestinal colonization by other Salmonella strains. The exact mechanism of this early colonization-inhibition is not known. To study host-related contributions to this phenomenon, the kinetics of immune cell infiltration in the caecal wall was analyzed during the first 10 days after vaccination of newly hatched chickens with a Salmonella enterica serovar Enteritidis aroA mutant, and infection 1 day later with a virulent S. enterica serovar Enteritidis strain. These data were correlated with bacterial colonization and clearance of the Salmonella Enteritidis challenge strain. Bacteriological data showed that vaccinated animals had a much lower number of challenge bacteria in their organs and caecal contents the first days post-challenge, relative to unvaccinated animals. Immunohistochemical analysis of the caecal lamina propria revealed that heterophils started infiltrating the caecal lamina propria from 12 h post-vaccination. Macrophages and T-lymphocytes started infiltrating from 20 h and B-lymphocytes from 24 h post-vaccination. These data imply that immune cells already colonized the caecal wall at the time of challenge in vaccinated animals. The presence and activity of these cells in the caecal wall shortly after administration of a Salmonella Enteritidis aroA mutant might contribute to the inhibition of colonization of a virulent Salmonella strain, subsequently administered.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗

PubMed2002

Pathogenesis of infections with Salmonella enterica subsp. enterica serovar Muenchen in the turtle Trachemys scripta scripta.

The pathogenesis of Salmonella enterica subsp. enterica serovar Muenchen infections in the aquatic turtle Trachemys scripta scripta was studied. After oral infection with 5x10(5)cfu of serovar Muenchen of 10-14-month-old turtles, kept at 26 degrees C, the intestine and especially the ileum, caecum and colon was colonized. Invasion of the intestinal wall, causing histopathological lesions, and colonization of internal organs were not observed. Serovar Muenchen was only isolated from turtles for 8 days after exposure. Keeping the turtles at 37 degrees C caused colonization of liver and spleen in two of six orally infected turtles and augmented the numbers of bacteria in the intestinal tract. In contrast to oral infections, intraperitoneal infections of turtles with serovar Muenchen enabled the bacterium to persist inside the host for at least 5 weeks. Clearance of serovar Muenchen from the liver and blood was more pronounced at 26 degrees C than at 37 degrees C. ELISA antibodies were demonstrated in intraperitoneally but not in orally infected turtles kept at 26 degrees C. In conclusion, the lack of persistence and invasiveness of serovar Muenchen in T. s. scripta after oral exposure might be due to the turtle's relatively low body temperature and/or the absence of well-organized gut-associated lymphoid tissue.

Animals↗

PubMed2002

Actinobacillus pleuropneumoniae infections in closed swine herds: infection patterns and serological profiles.

Many farrow-to-finish herds are endemically infected with Actinobacillus pleuropneumoniae. In order to control the disease efficiently, a better knowledge of the ages at which pigs become infected is necessary. Furthermore, no information is available concerning the influence of maternally derived antibodies on the colonization of the upper respiratory tract. Therefore, A. pleuropneumoniae infection patterns were studied in five farrow-to-finish pig herds (A-E) with a history of pleuropneumonia. A longitudinal study was carried out in herds A and B. In these herds, piglets from sows carrying A. pleuropneumoniae in their noses or tonsils were sampled. Nasal and tonsillar swabs as well as sera, were collected from these animals at the age of 4, 8, 12, 16 (herds A and B) and 23 weeks (herd B). At these ages other pigs from the same sows were euthanized. The lungs were macroscopically examined and samples from nose, tonsils and lungs were collected at necropsy. A cross-sectional study was performed in herds C-E. In these herds nasal and tonsillar swabs, as well as sera, were taken from 10 animals of 4, 8, 12 and 16 weeks of age. Lung, nasal and tonsillar samples were tested for the presence of A. pleuropneumoniae by routine bacteriology and PCR with mixed bacterial cultures. The sera were examined for the presence of Apx toxin neutralizing antibodies. In herd A, A. pleuropneumoniae serotype 2 and 10 strains were isolated, whereas serotype 2, 3, 5b and 8 strains were demonstrated in herd B. In most herds, A. pleuropneumoniae was detected in mixed bacterial cultures of tonsillar and/or nasal samples by PCR from the age of 4 weeks onwards. Colonization of the lungs and development of lung lesions was observed in 12- and 16-week-old animals of herd A and 23-week-old animals of herd B. In most herds, high antibody titres were detected in 4-week-old piglets. These titres decreased during the first 12 weeks of age, but thereafter, increased. It was concluded that PCR with mixed bacterial cultures from tonsillar swabs is a valuable tool for the detection of infected animals. It was also concluded that colonization of tonsils and nasal mucosae can occur in the presence of maternally derived antibodies. Infection of the upper respiratory tract without lung involvement did not result in development of Apx toxin neutralizing antibodies. Therefore, such serological assays cannot be used for the detection of subclinically infected animals.

Actinobacillus Infections↗

PubMed2002

Dynamics of immune cell infiltration in the caecal lamina propria of chickens after neonatal infection with a Salmonella enteritidis strain.

Dynamics of leucocyte infiltration and bacterial invasion in the caecal wall were studied after oral infection of 2-day-old chicks with Salmonella enterica ser. Enteritidis. Bacteria invaded the lamina propria of the caecal wall from 12h post-challenge onwards. Bacteriological examination of internal organs (liver, spleen) showed a peak in Salmonella bacteria at 3days post-infection, after which the number of bacteria decreased. Immunohistochemistry revealed macrophages and T-lymphocytes invading the caecal propria mucosae from 24h after challenge onwards, while B-lymphocytes came somewhat later, subsequently organising into follicular aggregates. An early increase in granulocytes was partly masked by the response to natural flora. While the B-lymphocyte and granulocyte populations were maintained, T-lymphocyte and macrophage populations were already reducing by 10days post-challenge. The infiltration of macrophages and T-lymphocytes in the caecal wall, followed by B-lymphocytes, is the result of an inflammatory response, caused by invading bacteria at this site. The structural maturation of the mucosa-associated lymphoid tissues is antigen driven, since B-cells organise in a follicular pattern.

Animals↗

PubMed2002

Identification of Lactobacillus species using tDNA-PCR.

tDNA intergenic spacer PCR (tDNA-PCR) using consensus primers complementary to the conserved edges of the tRNA genes can amplify the intergenic spacers. Separation of the PCR products with capillary electrophoresis enables discrimination between fragments differing only one basepair in length. This method was applied to a collection of 82 Lactobacillus strains belonging to 37 species in order to evaluate the discriminatory power of this technique within this genus. Twenty-one species could be distinguished to species level on the basis of a unique tDNA fingerprint pattern. The other species grouped by two (e.g. L. fermentum and L. cellobiosus) or three (L. acidophilus, L. gallinarum and L. helveticus). Inclusion of the resulting fingerprints in a numerical database containing fingerprints of numerous other Gram-positive and Gram-negative species makes the identification of unknown strains possible.

Bacterial Typing Techniques↗

PubMed2002

Study of the intra- and interlaboratory reproducibility of partial single base C-sequencing of the 16S rRNA gene and its applicability for the identification of members of the genus Streptococcus.

The use of Single Base C-Sequencing of the first 500 bases of the 16S rRNA-gene (SBCS) combined with capillary electrophoresis was evaluated for the identification of reference strains of 30 different species within the genus Streptococcus. For SBCS, only dd-CTP's are used in the sequencing reactions instead of the four dideoxy bases and the primer is fluorescently labeled. The reproducibility, interlaboratory exchangeability and discriminative power of this method were studied by comparing the patterns obtained in three laboratories under highly standardized conditions. The interlaboratory reproducibility proved to be high, enabling the construction of a common database for the identification of strains belonging to the streptococcal species studied. Most of the examined species generated distinguishable profiles. SBCS did not differentiate between the closely related species S. constellatus and S. intermedius. Also S. thermophilus and S. vestibularis as well as S. mitis and S. pneumoniae showed highly resembling profiles. The previously reported heterogeneity within the species S. equinus was reflected by SBCS. For all other species, strains belonging to the same species generated indistinguishable patterns. In conclusion, Single Base C-sequencing of the first 500 bases of the 16S rRNA-gene could be a useful and widely applicable method for the identification of bacteria at the species level, with the added advantage of being more rapid and easier to automatize than full sequence determination.

Base Sequence↗

PubMed2002

Comparison of susceptibility to antimicrobials of the enterococcal species isolated from pigeons (Columba livia).

Antimicrobial resistance profiles were assessed in Enterococcus faecium, Enterococcus faecalis, and Enterococcus columbae strains isolated from racing pigeons (Columba livia). E. columbae is the most prevalent enterococcal species in the intestines of pigeons. Acquired resistance against the antimicrobials bambermycin, vancomycin, monensin, narasin, virginiamycin (cross-resistant with quinupristin/dalfopristin), avilamycin (cross-resistant with evernimicin), and ampicillin was not seen. Only for the antimicrobials tetracycline and tylosin was a frequent occurrence of resistance found in all three enterococcal species tested. Resistance to the fluoroquinolone antimicrobial enrofloxacin was present in E. columbae. Bacitracin resistance was seen in the species E. faecalis and E. faecium but not in E. columbae. High-level streptomycin resistance was found in E. columbae and in one E. faecium strain, whereas high-level gentamicin resistance was mainly associated with E. faecalis. The differences noted between the different species illustrate the difficulties related to the choice of indicator bacteria for antimicrobial resistance in the intestinal flora.

Animals↗

PubMed1999

Ultrastructure of surface components of Streptococcus gallolytics (S. bovis) strains of differing virulence isolated from pigeons.

Virulence of Streptococcus gallolyticus (S. bovis) strains isolated from pigeons is associated with the presence of the extracellular proteins A, T1, T2 and T3. Based on the presence or absence of these proteins, six supernatant-phenotypes are distinguished. Experimental infection studies have indicated that strains belonging to the A-T1, A+T1, A+T2 and A+T3 groups are highly virulent for pigeons, strains belonging to the A-T3 groups are moderately virulent and A-T2 strains are of low virulence. In this study the surface structure of 15 pigeon S. gallolyticus strains representing high, moderate and low virulence supernatant-phenotypes was examined by electron microscopy. The presence of capsular material was determined by transmission electron microscopy after polycationic ferritin labelling and immunostabilization. Capsules from cells labelled with polycationic ferritin were usually thicker than those from cells exposed to antiserum. The capsule of the virulent strains had a regular, continuous appearance whilst irregularity of the capsule was a characteristic of the low virulence A-T2 strains. Negative staining revealed the presence of fimbriae in all strains belonging to the high virulence A-T1, A+T1, A+T2 and A+T3 supernatant groups and in one strain of the moderately virulent A-T3 group. The fimbriae were thin, flexible structures with a diameter of approximately 3-4 nm and a length of up to 700 nm. Fimbriae as described above were absent in two other A-T3 strains examined and in the low virulence A-T2 strains. Results from this study indicate that morphological differences in surface structure exist among virulent and low virulence pigeon S. gallolyticus strains, and that the capsule and/or fimbriae are possibly involved in virulence.

Animals↗

PubMedDate not supplied

Interactions of butyric acid- and acetic acid-treated Salmonella with chicken primary cecal epithelial cells in vitro.

In vitro studies of the interaction between pathogenic bacteria and the chicken intestinal epithelium are hampered by the lack of a host- and tissue-specific in vitro model. Therefore, a reproducible method for isolation and cultivation of chicken primary cecal epithelial cells was developed. Cecal crypts were isolated and cultured in vitro to form a semiconfluent layer of epithelial cells. Incubation of Salmonella enteritidis with these cells resulted in invasion. Pretreatment of the Salmonella bacteria with butyric acid resulted in a significant decrease of invasion of the bacteria in the chicken cecal epithelial cells, whereas pretreatment with acetic acid increased invasiveness. These interactions of S. enteritidis with primary chicken cecal epithelial cells were similar to the interactions with other epithelial cell types.

Acetic Acid↗