Offsetting virulence and antibiotic resistance costs by MRSA

Abstract

The prevalence of diverse MRSA (methicillin-resistant Staphylococcus aureus) types in both hospital and community settings is a major health problem worldwide. Here we compare hospitalacquired MRSAs with large type II SCCmec elements with those prevalent in both hospital and community settings with smaller type IV SCCmec elements. We find that the type II but not the type IV SCCmec element causes the bacteria to reduce their levels of costly toxin expression. We compare the relative growth rates of these MRSA types and show that the type II SCCmec carrying MRSAs are more affected than those carrying type IV elements and from this we hypothesize that offsetting the costs associated with antibiotic resistance and toxin expression is why the type II are confined to hospital environments where antibiotic use, the prevalence of immunocompromised individuals and vector-mediated transmission is high. In contrast, those MRSAs that are also successful in the community can maintain their high levels of toxin expression due to a lower fitness burden associated with the smaller SCCmec element.

Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

“…It has been suggested that the acquisition of antibiotic resistance in S. aureus involves changes in virulence factor secretion due to the fitness cost associated with the expression of resistance (Sakoulas et al 2003, Gill et al 2005 and it is reflected in decreased toxin expression (Collins et al 2010, Otto 2010. Therefore, it is not surprising that the results of the present study confirmed this by showing that virulence factor gene carriage was more diverse and abundant in MSSA than in MRSA strains.…”

“…These authors found that in MRSA strains carrying the larger cassette SCCmec II, there was a reduction in virulence factor secretion, while strains carrying the smaller size SCCmec IV secreted a more diverse range of factors. The findings of the present study are consistent with those of Collins et al (2010) because isolates harbouring SCCmec type I presented no or up to two virulence genes, whereas SCCmec type IV strains carried one or more virulence genes simultaneously, as observed in susceptible strains. The fitness cost on the growth and cell yield of S. aureus containing the SCCmec elements has also been experimentally demonstrated; the higher energy demand and decreased cell yield observed in SCCmec type I strains has not been observed in the SCCmec type IV strains (Lee et al 2007, Collins et al 2010).…”

“…tion in susceptible strains that allows a more thorough comparison. In addition, Collins et al (2010) indicated that the fitness cost associated with resistance varies depending on the SCCmec type and antibiotic resistance levels. These authors found that in MRSA strains carrying the larger cassette SCCmec II, there was a reduction in virulence factor secretion, while strains carrying the smaller size SCCmec IV secreted a more diverse range of factors.…”

The antimicrobial and antibiofilm activities of copper(II) complexes

“…The bacterial strains used in this study were S. aureus MRSA252 and MSSA209 [25], Enterococcus faecalis NCTC775, Escherichia coli NCTC86, and Pseudomonas aeruginosa ATCC27853. Strains were maintained on Tryptone Soy Agar (Oxoid).…”

Molecular tracing of the emergence, adaptation, and transmission of hospital-associated methicillin-resistant Staphylococcus aureus

“…Acquisition of SCCmecII was a critical genetic event in the evolution of the EMRSA-16 clone as a hospital-associated antibiotic-resistant clone refractory to treatment with β-lactam antibiotics. Of note, the type II SCCmec element has been demonstrated to reduce the toxicity of MRSA CC30 strains in comparison with methicillinsensitive CC30 strains, by preventing normal stationary phase induction of the agr system, leading to decreased expression of cytolytic toxins (35,36). It is speculated that this reduction in energy requirement could compensate for the metabolically costly maintenance of a large SCCmec element and its associated methicillin resistance, but which would be likely to lead to reduced fitness outside of the hospital setting (37).…”