Vaccination with a live-attenuated small-colony variant improves the humoral and cell-mediated responses against Staphylococcus aureus

Abstract

Staphylococcus aureus is known to produce persistent and chronic infections in both humans and animals. It is recognized that small-colony variants (SCVs), which produce higher levels of biofilm and that are capable of intracellular persistence, contribute to the chronicity or recurrence of infections and that this phenotype is inherent to the pathogenesis process. Prevention of S. aureus infections through vaccination has not yet met with considerable success. Some of the current vaccine formulations for S. aureus bovine mastitis consist of inactivated S. aureus bacteria, sometimes combined to E. coli J5. As such, the stimulation of cell-mediated immunity by these vaccines might not be optimal. With this in mind, we recently engineered a genetically stable double mutant SCV (ΔvraGΔhemB), which was highly attenuated in a mastitis model of infection. The present work describes the immune responses elicited in mice by various experimental vaccine compositions including the live-attenuated SCV double mutant and its inactivated form, combined or not with inactivated E. coli J5. The live-attenuated SCV was found to provoke a strong and balanced humoral response in immunized mice, as well as strong proliferation of ex-vivo stimulated splenocytes isolated from these animals. These splenocytes were also found to release high concentration of IL-17 and IFN-γ when compared to every other vaccination formulation. Inversely, the inactivated whole-cell vaccine, alone or in combination with the E. coli J5 bacterin, elicited lower antibody titers and failed to induce Th1 or Th17 cell-mediated responses in the splenocyte proliferation assay. Our results suggest that live-attenuated SCVs can trigger host immunity differently than inactivated bacteria and could represent a suitable vector for inducing strong humoral and cell-mediated immune responses, which are crucial for protection. This could represent an important improvement over existing vaccine formulations for preventing S. aureus bovine mastitis and other infections caused by this pathogen.

Panton-Valentine Leukocidin-Positive Methicillin-Resistant Staphylococcus Aureus with Reduced Vancomycin Susceptibility: An Emerging Trend?

“…3A, B, Ca); which may be similar to that reported in S. aureus small colony variants (SCVs) [68,69]. SCVs are slow-growing, drug-resistant mutants of gram-positive and -negative bacteria, and have been isolated during the longterm treatment with antimicrobial agents, such as gentamicin and trimethoprim-sulfamethoxazole (SXT); SCVs cause persistent and recurrent infections [68,[70][71][72], and examples include our reported case, daptomycin-resistant VISA SCV [69]. Therefore, the sticky intercellular substance may play a role in low-level vancomycin resistance.…”

Biofilm Research in Bovine Mastitis

“…Two mastitis vaccine candidates against S. uberis have shown a significant reduction in the mortality of mice infected with the pathogen (83). Different candidates for a S. aureus vaccine is currently being investigated; in one study, live-attenuated small-colony variants have shown promising results compared to inactivated bacteria in murine models (84). However, in another study, a formalin-killed whole-cell vaccine candidate of S. aureus biofilm showed a significant reduction in the colonization of S. aureus in the udder in vaccinated mice compared to mice vaccinated with a vaccine candidate from planktonic S. aureus (85).…”

“…Most of the so-called in vivo investigations of biofilm in bovine mastitis have used experimental models (mice and sheep), and the majority of these studies focused on anti-biofilm treatment or vaccines against biofilm udder infections (Table 1) (44,69,70,72,(83)(84)(85). Only a few studies investigated and confirmed biofilm in vivo within udder tissue of dairy cows with bovine mastitis.…”

Boron doped silver-copper alloy nanoparticle targeting intracellular S. aureus in bone cells

“…The low intracellular bioavailability and cellular permeability of antibiotics also promote the antibiotic resistance of intracellular pathogens [23,24]. The formation of a low metabolically active small colony variant (SCV) S. aureus phenotype enables it to be less susceptible to antibiotics [25,26]. S. aureus can also form biofilms that promote the survival and persistence of the pathogen in harsh conditions and also provide antibiotic resistance by limiting antibiotic penetration [27,28].…”