BruSIC: a novel selective medium for the primary isolation of Brucella in veterinary samples

Rev1Δwzm vaccine candidate is safe in young and adult sheep and protects against Brucella ovis infection in rams

Small ruminants affected by brucellosis, caused mainly by Brucella melitensis and B. ovis, suffer reproductive disorders, leading to significant economic losses worldwide. Vaccination is an essential tool to prevent the disease in ovine and caprine livestock, but the only vaccine recommended to date is B. melitensis Rev1, which in sheep is only safe for use in lambs aged 3-4 months. This restriction poses considerable practical challenges for the implementation of Rev1 in countries with endemic brucellosis and/or limited resources, where there is a need for mass vaccination with a safe vaccine to control the disease in both animals and humans. We recently developed a B. melitensis strain Rev1Δwzm showing superior vaccine properties in mice and safety in pregnant ewes. Here, we report that Rev1Δwzm (i) is safe in young and adult sheep, both male and female; (ii) induces a transient serological response in the Rose Bengal test in ≤50 % of sheep, confirmed to some extent by the complement fixation test, and a stronger, more persistent anti- rough-LPS response; and (iii) protects rams against a B. ovis challenge 25 weeks after vaccination. To resolve the problem of serological interference, the use of green fluorescent protein tagging strategy allowed us to identify vaccinated sheep with only a single inoculation. These results, together with the previously reported safety in pregnant ewes, position Rev1Δwzm as a firm vaccine candidate and a promising alternative to Rev1. Further experiments are warranted to assess its efficacy against B. melitensis in pregnant ewes.

Brucella melitensis Rev1Δwzm: Placental pathogenesis studies and safety in pregnant ewes

One of the main causes of human brucellosis is Brucella melitensis infecting small ruminants. To date, Rev1 is the only vaccine successfully used to control ovine and caprine brucellosis. However, it is pathogenic for pregnant animals, resulting in abortions and vaginal and milk shedding, as well as being infectious for humans. Therefore, there is an urgent need to develop an effective vaccine that is safer than Rev1. In efforts to further attenuate Rev1, we recently used wzm inactivation to generate a rough mutant (Rev1Δwzm) that retains a complete antigenic O-polysaccharide in the bacterial cytoplasm. The aim of the present study was to evaluate the placental pathogenicity of Rev1Δwzm in trophoblastic cells, throughout pregnancy in mice, and in ewes inoculated in different trimesters of pregnancy. This mutant was evaluated in comparison with the homologous 16MΔwzm derived from a virulent strain of B. melitensis and the naturally rough sheep pathogen B. ovis. Our results show that both wzm mutants triggered reduced cytotoxic, pro-apoptotic, and pro-inflammatory signaling in Bewo trophoblasts, as well as reduced relative expression of apoptosis genes. In mice, both wzm mutants produced infection but were rapidly cleared from the placenta, in which only Rev1Δwzm induced a low relative expression of pro-apoptotic and pro-inflammatory genes. In the 66 inoculated ewes, Rev1Δwzm was safe and immunogenic, displaying a transient serological interference in standard RBT but not CFT S-LPS tests; this serological response was minimized by conjunctival administration. In conclusion, these results support that B. melitensis Rev1Δwzm is a promising vaccine candidate for use in pregnant ewes and its efficacy against B. melitensis and B. ovis infections in sheep warrants further study.

Vaccine properties of Brucella melitensis 16MΔwzm and reactivation of placental infection in pregnant sheep

Brucellosis, a worldwide zoonotic disease, is endemic in many developing countries. Besides causing significant economic losses for the livestock industry, it has severe consequences for human health. In endemic regions, small ruminants infected by Brucella melitensis are the main source of human brucellosis. Rev1, the only vaccine currently recommended to control the disease in sheep and goats, has several drawbacks. Rough lipopolysaccharide (R-LPS) mutants have been tested as alternatives, but most lack efficacy. Those in the Wzm/Wzt system responsible for O-polysaccharide export to the periplasm have been proposed as promising vaccine candidates, although to date they have been scarcely investigated in the natural host. In the present work, we studied the biological properties of a 16MΔwzm in-frame deletion mutant, including its safety in pregnant mice and sheep. In mice, 16MΔwzm prevented placental and fetal infections before parturition and protected against B. melitensis and Brucella ovis infections. In sheep, 16MΔwzm was equally safe in lambs, rams, and non-pregnant ewes, inducing some transient Rose Bengal reactions (<7 weeks). The serological reactions occurred earlier and more strongly in pregnant than in non-pregnant ewes and were significantly reduced when conjunctival rather than subcutaneous vaccination was used. In ewes vaccinated at mid-pregnancy, 16MΔwzm was not shed in vaginal discharges during the pregnancy and did not induce abortions/stillbirths. However, some ewes showed a transitory reactivation of infection in placentas and/or milk at parturition, accompanied by a seroconversion in smooth LPS (S-LPS) and/or R-LPS tests. Overall, 16MΔwzm can be considered as a safe vaccine for lambs, rams, and non-pregnant ewes, but its use at mid-pregnancy should be avoided to prevent vaccine dissemination at parturition. If the efficacy results against B. melitensis and B. ovis observed in mice are confirmed by further studies in the natural host, 16MΔwzm could constitute a useful vaccine.

Next-Generation Polymyxin Class of Antibiotics: A Ray of Hope Illuminating a Dark Road

Although new-generation antimicrobials, in particular β-lactam/β-lactamase inhibitors, have largely replaced polymyxins in carbapenem-resistant Gram-negative bacterial infections, polymyxins are still needed for carbapanem-resistant Acinetobacter baumannii infections and in settings where novel agents are not readily available. Despite their potent in vitro activity, the clinical utility of polymyxins is significantly limited by their pharmacokinetic properties and nephrotoxicity risk. There is significant interest, therefore, in developing next-generation polymyxins with activity against colistin-resistant strains and lower toxicity than existing polymyxins. In this review, we aim to present the antibacterial activity mechanisms, in vitro and in vivo efficacy data, and toxicity profiles of new-generation polymyxins, including SPR206, MRX-8, and QPX9003, as well as the general characteristics of old polymyxins. Considering the emergence of colistin-resistant strains particularly in endemic regions, the restoration of the antimicrobial activity of polymyxins via PBT2 is also described in this review.