Altered Growth, Pigmentation, and Antimicrobial Susceptibility Properties of Staphylococcus aureus Due to Loss of the Major Cold Shock Gene cspB

Abstract

An insertional mutation made in the major cold shock gene cspB in Staphylococcus aureus strain COL, a methicillin-resistant clinical isolate, yielded a mutant that displayed a reduced capacity to respond to cold shock and many phenotypic characteristics of S. aureus small-colony variants: a growth defect at 37°C, a reduction in pigmentation, and altered levels of susceptibility to many antimicrobials. In particular, a cspB null mutant displayed increased resistance to aminoglycosides, trimethoprim-sulfamethoxazole, and paraquat and increased susceptibility to daptomycin, teicoplanin, and methicillin. With the exception of the increased susceptibility to methicillin, which was due to a complete loss of the type I staphylococcal cassette chromosome mec element, these properties were restored to wild-type levels by complementation when cspB was expressed in trans. Taken together, our results link a stress response protein (CspB) of S. aureus to important phenotypic properties that include resistance to certain antimicrobials.Staphylococcus aureus is a major global public health problem causing serious, often life-threatening infections in the community and hospital settings that are becoming more difficult to manage with current antibiotic therapy regimens (7). The emergence of methicillin-resistant S. aureus (MRSA) in the hospital and community settings, coupled with the increasing number of persistent MRSA infections (25) and multidrugresistant strains, is a growing problem not just for immunocompromised patients but also for otherwise healthy individuals. The virulence of S. aureus strains is multifactorial and involves the production of extracellular toxins, surface structures that mediate interaction with host cells and resistance to host defenses, transcriptional regulatory processes that control virulence gene expression, and metabolic schemes that allow for adaptation to stresses imposed by the local environment within and outside the human or animal host.The capacity of S. aureus to respond to environmental stress conditions has been the subject of recent investigations (1, 33) and is imperative for its survival in hostile environments such as extreme temperature. S. aureus can effectively respond and adapt to a decrease in temperature by the expression of cold shock proteins (CSPs).

Cold Shock Genes cspA and cspB from Caulobacter crescentus Are Posttranscriptionally Regulated and Important for Cold Adaptation

“…The contribution of CSPs in maintaining cell viability and allowing growth at low temperature was previously analyzed in several bacteria belonging to the Firmicutes (e.g., L. monocytogenes, Lactobacillus plantarum, Staphylococcus aureus, Lactococcus lactis, and B. subtilis) and Gammaproteobacteria (e.g., E. coli) divisions (9,10,22,42,48,50,52). On the other hand, little is known about the importance and regulation of CSPs among Alphaproteobacteria, although many genera in this group may be exposed to temperature extremes due to their free-living lifestyle.…”

“…This family of proteins is widespread throughout bacteria, presenting a highly divergent number of paralogues in each organism. They respond not exclusively to temperature downshift but also to osmotic and oxidative stresses, stationary phase, carbon starvation, and antibiotic resistance, and some may even be constitutively expressed (6,9,10,39,42,54). Escherichia coli has nine csp paralogues, of which five are exclusively cold induced, one is constitutively expressed, and one is a replication inhibitor induced at stationary phase and under carbon starvation (26,54).…”

Cold-shock RNA-binding protein CspR is also exposed to the surface of Enterococcus faecalis

“…In some Gram-positive bacteria such as Staphylococcus aureus and Bacillus subtilis, cold-shock polypeptides have been shown to be involved in several aspects of bacterial life, i.e. survival under starvation and low-temperature conditions or resistance to anti-microbial agents (Duval et al, 2010;Graumann & Marahiel, 1999, 1996Graumann et al, 1997). In addition, the cold-shock polypeptides usually present the conserved RNA-binding motifs RNP-1 and RNP-2 that enable them to act as RNA chaperones (Phadtare & Inouye, 1999;Schröder et al, 1995).…”

CspR, a Cold Shock RNA-Binding Protein Involved in the Long-Term Survival and the Virulence of Enterococcus faecalis

“…For Bacillus subtilis, Csp proteins have been shown to be essential for efficient adaptation to low temperatures and survival during the stationary phase (18). Moreover, a cspB mutant of Staphylococcus aureus exhibited an important growth defect, reduction in pigmentation and in resistance to certain antimicrobials (10). It has been proposed that the Csp proteins act as RNA chaperones, facilitating gene expression at low temperatures as transcriptional activators (3,27,29), transcriptional antiterminators (1), and/or as alternative translation initiation factors (21).…”