What have we learned from brucellosis in the mouse model?

Brucellosis is a zoonosis caused by Brucella species. Brucellosis research in natural hosts is often precluded by practical, economical and ethical reasons and mice are widely used. However, mice are not natural Brucella hosts and the course of murine brucellosis depends on bacterial strain virulence, dose and inoculation route as well as breed, genetic background, age, sex and physiological statu of mice. Therefore, meaningful experiments require a definition of these variables. Brucella spleen replication profiles are highly reproducible and course in four phases: i), onset or spleen colonization (first 48 h); ii), acute phase, from the third day to the time when bacteria reach maximal numbers; iii), chronic steady phase, where bacterial numbers plateaus; and iv), chronic declining phase, during which brucellae are eliminated. This pattern displays clear physiopathological signs and is sensitive to small virulence variations, making possible to assess attenuation when fully virulent bacteria are used as controls. Similarly, immunity studies using mice with known defects are possible. Mutations affecting INF-γ, TLR9, Myd88, Tγδ and TNF-β favor Brucella replication; whereas IL-1β, IL-18, TLR4, TLR5, TLR2, NOD1, NOD2, GM-CSF, IL/17r, Rip2, TRIF, NK or Nramp1 deficiencies have no noticeable effects. Splenomegaly development is also useful: it correlates with IFN-γ and IL-12 levels and with Brucella strain virulence. The genetic background is also important: Brucella-resistant mice (C57BL) yield lower splenic bacterial replication and less splenomegaly than susceptible breeds. When inoculum is increased, a saturating dose above which bacterial numbers per organ do not augment, is reached. Unlike many gram-negative bacteria, lethal doses are large (≥ 10⁸ bacteria/mouse) and normally higher than the saturating dose. Persistence is a useful virulence/attenuation index and is used in vaccine (Residual Virulence) quality control. Vaccine candidates are also often tested in mice by determining splenic Brucella numbers after challenging with appropriate virulent brucellae doses at precise post-vaccination times. Since most live or killed Brucella vaccines provide some protection in mice, controls immunized with reference vaccines (S19 or Rev1) are critical. Finally, mice have been successfully used to evaluate brucellosis therapies. It is concluded that, when used properly, the mouse is a valuable brucellosis model.     

Use of computerized image analysis to quantify staphylococcal adhesion to canine corneocytes: does breed and body site have any relevance to the pathogenesis of pyoderma?

An optimized system of computerized image analysis was used to investigate variations in the adherence of Staphylococcus intermedius to canine corneocytes from four different breed groups and six different anatomical sites. S. intermedius showed significantly greater adherence to the head and neck compared with the dorsum, but adherence to the limb, axilla and groin did not differ from other sites. Furthermore, there was significantly greater adherence of S. intermedius to corneocytes from the dorsum, forelimb, axilla and groin of Boxers and Bull Terriers than Spaniels and Hounds. S. intermedius, and also Pseudomonas aeruginosa, exhibited abundant adherence, which was significantly greater than Staphylococcus aureus, Streptococcus canis, Klebsiella pneumoniae and Escherichia coli. In addition, S. intermedius adherence demonstrated a sigmoid dose-response curve with increasing bacterial concentration. These results suggest that S. intermedius adheres to canine corneocytes by a specific receptor-ligand interaction and adheres to the skin of some breeds more avidly than others. However, variations in adherence between body regions would not account for the predilection sites of canine bacterial pyoderma.     

Cortisol levels in skimmed milk during the first 22?weeks of lactation and response to short-term metabolic stress and lameness in dairy cows

Background

Cortisol is secreted into blood in reaction to acute stress, but also in phases of diminished feed intake and changed animal behavior. As cows do not always show clear signs of discomfort, reliable diagnostic markers could be used to provide information regarding individual cows’ distress. The objective of this study was to establish an ether free immunoassay for the detection of cortisol and to determine values during the first 22 weeks of lactation. Furthermore, the response in milk cortisol levels was assessed during times of metabolic stress and pain associated symptoms of lameness.

Methods

Milk yield and composition, blood serum glucose, NEFA and BHBA as well as milk cortisol were determined in 24 multiparous Holstein-Friesian cows over the course of the first 22 weeks of lactation. Animals were further checked for signs of clinical diseases on a daily basis. Two feed restrictions over three days (FR; 70 % of precious ad libitum intake) were performed during the 4^th wk and the 21^st wk, respectively. An ELISA for cortisol measurement in easily accessible bovine skimmed milk was established and applied.

Results

On the last day of FR in early lactation, a reduction in milk yield and changes in serum metabolites compared to respective previous values were detected. The FR in mid-lactation resulted in no changes in milk production and serum metabolites. Milk cortisol was highest during first wk of lactation and remained on comparable levels thereafter. Milk yield and composition were not influenced by FR. Lameness resulted in enhanced milk cortisol levels.

Conclusion

Milk cortisol could be used as an indicator of painful symptoms such as lameness. Higher values of milk cortisol levels during first wk of lactation should be taken into account for interpretation.     

Can the use of antimicrobials in adult equine patients with acute colitis be justified in the era of antimicrobial stewardship?

The use of antimicrobials in adult horses with acute colitis is controversial and clear antimicrobial guidelines are lacking. It is generally accepted that antimicrobials should be reserved for patients with specific bacterial enterocolitis such as Neorickettsia risticii or Clostridium difficile; however, in practice, horses show similar clinical signs independently of the underlying aetiology. The clinician is therefore often confronted with the dilemma of rapid initiation of treatment to avoid mortality vs. delayed and selective targeted antimicrobial treatment based on faecal diagnostic testing. The risk of antibiotic associated diarrhoea and the emergence of antimicrobial resistance are other important considerations.