Under certain circumstances the individuals of a bacterial population may find advantages in acting together and making "collective decisions". This phenomenon is better known as quorum sensing. When the concentration of signal molecules produced by the surrounding bacteria exceeds a certain threshold, the bacterial population acts as a single organism, collectively expressing virulence genes, biofilm forming genes, etc. Several mechanisms of quorum sensing are discussed, each with its distinct signal molecules and respective receptors. Some of these mechanisms are restricted to sensing intraspecies signalling, but interspecies and even interkingdom signalling have also been described. Several veterinary pathogens such as Staphylococcus aureus, Staphylococcus pseudintermedius, Pseudomonas aeruginosa and Salmonella Typhimurium use quorum sensing as a means to optimize virulence gene expression and host colonization. Therefore, targeting of the QS mechanisms may provide a novel strategy for combating bacterial infections, also in veterinary medicine.
Epizootic rabbit enteropathy (ERE), a highly lethal (30-80% mortality) disease of broiler rabbits aged 6-14 weeks, first appeared in 1997 in French intensive enclosed rabbitries and is of unknown aetiology. Bacteriological, virological and parasitical examination of the intestinal contents of rabbits that had died either in spontaneous field cases or after experimental reproduction of ERE, were undertaken in an attempt to identify infectious agents that may play a role in the disease. Two bacterial strains, Clostridium perfringens and non-enteropathogenic Escherichia coli were repeatedly isolated at high faecal counts from naturally infected animals. In field cases, a correlation between typical gross lesions of epizootic enteropathy and the presence of the alpha toxin of Cl. perfringens was observed (P<0.0001; Chi-squared test). Although attempts to reproduce the disease by inoculation with different pools of cultivable bacterial strains failed, the disease was successfully reproduced by inoculation with one French and two Belgian samples of caecal contents.
BackgroundNonendoscopic bronchoalveolar lavage (BAL) is a practical alternative for a deep nasopharyngeal swab (DNS) to sample the airways of a large number of calves in a short period of time. The extent of commensal overgrowth and agreement of BAL with DNS culture results in preweaned calves are unknown.ObjectivesTo compare commensal overgrowth and bacterial culture results between DNS and BAL samples.AnimalsA total of 183 preweaned calves (144 with bovine respiratory disease and 39 healthy animals).MethodsCross‐sectional study. Deep nasopharyngeal swab and BAL samples were taken from each calf and cultured to detect Pasteurellaceae and Mycoplasma bovis. Agreement and associations between culture results of DNS and BAL samples were determined by kappa statistics and logistic regression.ResultsBronchoalveolar lavage samples were less often polymicrobial, more frequently negative and yielded more pure cultures compared to DNS, leading to a clinically interpretable culture result in 79.2% of the cases compared to only in 31.2% of the DNS samples. Isolation rates were lower in healthy animals, but not different between DNS and BAL samples. Only Histophilus somni was more likely to be isolated from BAL samples. In clinical cases, a polymicrobial DNS culture result did not increase the probability of a polymicrobial BAL result by ≥30%, nor did it influence the probability of a negative culture. A significant herd effect was noted for all observed relationships.Conclusions and Clinical RelevanceNonendoscopic BAL samples are far less overgrown by bacteria compared to DNS samples under the conditions of this study, facilitating clinical interpretation and resulting in a higher return on investment in bacteriologic culturing.
Good biosecurity procedures are crucial for healthy animal production. The aim of this study was to quantify the level of biosecurity on conventional broiler farms in Europe, following a standardized procedure, thereby trying to identify factors that are amenable to improvement. The current study used a risk-based weighted scoring system (biocheck.ugent ®) to assess the level of biosecurity on 399 conventional broiler farms in 5 EU member states. The scoring system consisted of 2 main categories, namely external and internal biosecurity, which had 8 and 3 subcategories, respectively. Biosecurity was quantified by converting the answers to 97 questions into a score from 0 to 100. The minimum score, "0," represents total absence of any biosecurity measure on the broiler farm, whereas the maximum score, "100," means full application of all investigated biosecurity measures. A possible correlation between biosecurity and farm characteristics was investigated by multivariate linear regression analysis. The participating broiler farms scored better for internal biosecurity (mean score of 76.6) than for external biosecurity (mean 68.4). There was variation between the mean biosecurity scores for the different member states, ranging from 59.8 to 78.0 for external biosecurity and from 63.0 to 85.6 for internal biosecurity. Within the category of external biosecurity, the subcategory related to "infrastructure and vectors" had the highest mean score (82.4), while the subcategory with the lowest score related to biosecurity procedures for "visitors and staff" (mean 51.5). Within the category of internal biosecurity, the subcategory "disease management" had the highest mean score (65.8). In the multivariate regression model a significant negative correlation was found between internal biosecurity and the number of employees and farm size. These findings indicate that there is a lot of variation for external and internal biosecurity on the participating broiler farms, suggesting that improvements are possible. Since the subcategory "visitors and staff" scored the lowest, better education of broiler farmers and their staff may help to improve overall biosecurity on broiler farms in Europe.
The location and cell damage caused by Vibrio anguillarum, the causative agent of classical vibriosis, within the developing gut of the newly hatched sea bass, Dicentrarchus labrax (L.), is unknown. A gnotobiotic sea bass model was used to investigate the early interactions of V. anguillarum with sea bass larvae. In the present study, germ-free sea bass larvae were orally exposed to a V. anguillarum HI-610 pathogen labelled with the green fluorescent protein (GFP-HI-610) and sampled at regular intervals. Pathogenic colonization of gut enterocytes was observed 2 h post-exposure (p.e.) and onwards, whereas bacteria within the swim bladder were visualized 48 h p.e and onwards. Ultrastructural findings demonstrated direct bacterial contact with the host cell in the oesophageal mucosa and putative attachment to microvilli of mid- and hindgut enterocytes. The present findings form a starting point for studies assessing the impact of potential candidates (probiotics, prebiotics, antimicrobial peptides) to mitigate bacterial virulence.
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