Methicillin Resistance Alters the Biofilm Phenotype and Attenuates Virulence in Staphylococcus aureus Device-Associated Infections

Abstract

Clinical isolates of Staphylococcus aureus can express biofilm phenotypes promoted by the major cell wall autolysin and the fibronectin-binding proteins or the icaADBC -encoded polysaccharide intercellular adhesin/poly- N -acetylglucosamine (PIA/PNAG). Biofilm production in methicillin-susceptible S. aureus (MSSA) strains is typically dependent on PIA/PNAG whereas methicillin-resistant isolates express an Atl/FnBP-mediated biofilm phenotype suggesting a relationship between susceptibility to β-lactam antibiotics and biofilm. By introducing the methicillin resistance gene mecA into the PNAG-producing laboratory strain 8325-4 we generated a heterogeneously resistant (HeR) strain, from which a homogeneous, high-level resistant (HoR) derivative was isolated following exposure to oxacillin. The HoR phenotype was associated with a R 602 H substitution in the DHHA1 domain of GdpP, a recently identified c-di-AMP phosphodiesterase with roles in resistance/tolerance to β-lactam antibiotics and cell envelope stress. Transcription of icaADBC and PNAG production were impaired in the 8325-4 HoR derivative, which instead produced a proteinaceous biofilm that was significantly inhibited by antibodies against the mecA -encoded penicillin binding protein 2a (PBP2a). Conversely excision of the SCC mec element in the MRSA strain BH1CC resulted in oxacillin susceptibility and reduced biofilm production, both of which were complemented by mecA alone. Transcriptional activity of the accessory gene regulator locus was also repressed in the 8325-4 HoR strain, which in turn was accompanied by reduced protease production and significantly reduced virulence in a mouse model of device infection. Thus, homogeneous methicillin resistance has the potential to affect agr - and icaADBC -mediated phenotypes, including altered biofilm expression and virulence, which together are consistent with the adaptation of healthcare-associated MRSA strains to the antibiotic-rich hospital environment in which they are frequently responsible for device-related infections in immuno-compromised patients.

Bypass of genetic constraints during mutator evolution to antibiotic resistance

“…In turn, being an essential gene, PBP3 alleles are likely to entail fitness costs in other conditions. Such costs have already been reported in some cases, including reduced growth at high temperatures [42] and impaired biofilm formation [62]. Alterations in the cell wall structure, however, could also have an adaptive value: a recent report showed that PBP3 substitutions can increase the ability of H. influenza to invade epithelial cells [63].…”

Several Virulence Factors of Multidrug-Resistant Staphylococcus aureus Isolates From Hospitalized Patients in Tehran

“…Biofilm forming strains are more frequently isolated from non-fluid tissues, in particular bone and soft tissues, and also MDR pathogens are more often biofilm formers. Several studies have shown that methicillin-resistance can alter the ability of the S. aureus isolates regarding biofilm production (10). To our knowledge, previous studies on the biofilm formation among MDR isolates and the relationship to clinical manifestations are scarce (11).…”

Biofilm formation and antimicrobial resistance in methicillin-resistant Staphylococcus aureus isolated from burn patients, Iran

“…Since the ability of biofilm production by MRSA increases antibiotic resistance, hospital patients infected with these strains are at serious risk for treatment failure [10]. Biofilm formation is considered to be a virulence factor because the microorganisms that establish in a burn wound biofilm fundamentally differ from suspended populations [11].…”