Staphylococcus aureus from a chronic infection site regains capsule polysaccharide expression regardless of Agr dysfunction after passage through a mouse model of bacteremia

CARLOS M SULIGOY; GOMEZ MARISA INES; DANIEL O. SORDELLI; DIAZ R; WENDLER; NOTO LLANA M; GEHRKE, A; TUCHSCHERR, LORENA; FERNANDA ROXANA BUZZOLA

Castelldefels

Congreso; Gordon Research Seminar; 2019

Staphylococcus aureus is a highly prevalent opportunistic, multifactorial pathogen. Adaptation of S. aureus to affected tissue through microevolution appears to lead to persistence of the microorganism and chronicity of the infection. One of the adaptive traits that leads to persistence are loss of agr expression, with virulence reduction and lack of CP expression. CP mutants likely represent a dead end of evolution at the infection site, because they may encounter difficulties to disseminate through the bloodstream and establish infection at distant sites of the body or in other hosts. However there is still concern whether a supposedly harmless non-encapsulated microevolution endpoint may turn back into a dangerous infective derivative.Materials and methods. Isolate HU-14 was recovered from a 34-year old male patient with a prosthetic implant in the right femur. It is non-encapsulated, SCCmec type 1, Agr II, ST5, CC5 and Spa t149. It has an insertion of IS256 in agrC thus rendering Agr inactive. HU-14 was inoculated by the i.p. route to CF1 mice. After 24 h the animals were sacrificed and bacteria were recovered from blood and re-injected into mice. This cycle was repeated seven times and S. aureus isolate P3.1 was recovered at the third cycle. Capsule (CP5) production was assessed by colony immunoblot. Production of staphyloxanthin was determined by methanol carotenoid extraction and spectrometry. Integrity of major regulators was investigated by Illumina sequence analysis. Expression of RNAIII and other major regulators was assessed by qRT-PCRs performed using standard procedures. In addition, sigB activity was assessed by asp23 qRT-PCR.Results. After 3 passages isolate (P3.1) was recovered, which expressed CP5. The phenotype remained stable after 7 passages on blood agar and tryptic soy agar (TSA). Amplification of the agr locus revealed that IS256 was still inserted in agrC. qRT-PCR showed that both strains were RNAIII defective. P3.1 colonies on trypticase soy agar were highly pigmented, when compared with HU-14. Both isolates produce carothenoids but only P3.1 produced staphyloxantin after 24 h in culture with agitation whereas HU-14 did not produce a carothenoid molecule compatible with staphyloxanthin as assessed by spectrometry. Protease and haemolysin production levels as well as the antibiotic resistance profile of both isolates were identical. Notorious asp23 expression, as measured by qRT-PCR, revealed that derivative P3.1 regained SigB expression, when compared with the parental HU-14 strain.Conclusion. We demonstrate the feasibility that a S. aureus clinical isolate with a non-functional agr due to an IS256 insertion in agrC can regain the production of CP5 and staphyloxhantin in a stable manner after passage through the bloodstream. Such recovery was associated to an increase in sigB expression whereas the IS256 remained inserted in agrC. Therefore, loss of CP expression can only be considered a microevolution endpoint at the primary site of infection, since S. aureus can regain the ability to produce CP in vivo when transferred to a different niche. Our findings underscore the importance of CP as vaccine candidate.