Absence of Protein A Expression Is Associated With Higher Capsule Production in Staphylococcal Isolates

Abstract

Staphylococcus aureus is a major human pathogen, and a leading cause of soft tissue and blood stream infections. One of the causes of its success as a pathogen is the peculiar array of immune evasion factors through which the bacterium avoids host defenses, where the staphylococcal protein A (SpA) plays a major role thanks to its IgG binding activities. Moreover, SpA has recently been proposed as a promising vaccine antigen. In this study, we evaluated the expression of SpA in a collection of staphylococcal strains, about 7% of which did not express SpA (SpA - strains), despite the presence of the gene. By a comparative genomic analysis, we identified that a mutation in the spa 5′ UTR sequence affecting the RBS is responsible for the loss of SpA in a subset of SpA - strains. Using a high-throughput qRT-PCR approach on a selected panel of virulence-related genes, we identified that the SpA - phenotype is associated with lower spa transcript levels and increased expression and production of capsule as well as other changes in the transcription of several key virulence factors. Our data suggest that the SpA - phenotype has occurred in geographically distinct strains through different molecular mechanisms including both mutation, leading likely to translation alterations, and transcriptional deregulation. Furthermore, we provide evidence that SpA - strains are highly susceptible to phagocytic uptake mediated by anti-capsule antibodies. These data suggest that S. aureus may alter its virulence factor expression pattern as an adaptation to the host or environment. Vaccination strategies targeting both SpA and capsule could therefore result in broader coverage against staphylococcal isolates than SpA alone.

Bacterial outer membrane vesicles engineered with lipidated antigens as a platform for Staphylococcus aureus vaccine

“…injection of 2 × 10 8 colony-forming units (CFUs) of S. aureus Newman strain, a strain expressing all 5 antigens (see refs. 31, 33, and 34), and the health status of the animals was followed every day over a period of 7 d using a 1-to-4 pain scale (see Material and Methods ). Animals that reached the pain value of 4 were killed since they reached the “near mortality point” and would have died within 24 h. On the other hand, those animals that maintained a score lower than 4, fully recovered within 7 d. Fig.…”

Virulence Gene Expression of Staphylococcus aureus in Human Skin

“…After pre-amplification of the cDNA samples (12 pre-amplification cycles for bacterial cDNA and 14 cycles for mixed samples), quantitative real time PCR was performed using the high-throughput qRT-PCR Fluidigm Biomark HD. The transcription profile of 65 S. aureus virulence factors was assessed using specific TaqMan assays (see Supplementary Table 1; Brignoli et al, 2019). gyrB gene was used as the endogenous control to normalize the data.…”

Genome-Wide Analysis of Staphylococcus aureus Sequence Type 72 Isolates Provides Insights Into Resistance Against Antimicrobial Agents and Virulence Potential

“…Genes encoding serine-aspartate repeat Sdr proteins ( sdrC and sdrE ) were present in most (>70%) ST72 isolates ( Figure 1A ), suggesting that these isolates can bind efficiently to the host ECM. We next assessed the distribution of staphylococcal protein A ( spA ) that binds immunoglobulin G (IgG) to overcome the host defense system ( Brignoli et al, 2019 ). The spA gene was sporadically (~27%) present in ST72 isolates including K07-204 and K07-561 ( Figure 1A ).…”