Staphylococcus aureus

INTRODUCTION

We aimed to determine the distribution of Phenol-soluble modulin-mec (psm-mec) gene and its relationship with biofilm formation in clinical methicillin-resistant S. aureus (MRSA).

METHODS

In a descriptive study, a total of 94 cefoxitin-resistant S. aureus isolates were collected from patients and tested for antibiotic susceptibility testing, multiplex polymerase chain reaction (MPCR) for detection of mecA and pvl genes, PCR for detection of psm-mec gene and SCCmec typing of psm-mec and pvl-positive isolates. Furthermore, isolates were tested by microtiter plate method for biofilm formation assay.

RESULTS

Multiplex PCR for detection of mecA and pvl genes was performed for all cefoxitin-resistant isolates. The mecA gene was found in 92 (97.9%) isolates but none of the isolates carried the pvl gene. Sixty-five (69.1%) isolates harbored psm-mec genes and 95.4% of these isolates belong to SCCmec type III. Statistical analysis showed a significant difference between the presence or absence of psm-mec gene and biofilm production (P<0.001).

CONCLUSION

In this study, more than half of the MRSA strains harbored psm-mec gene and almost one-fifth of them produced strong biofilm. Since the strains with strong biofilm formation have more antibiotic resistance and cause the long-lasting infection, for the suitable treatment of hospitalized patients with this kind of MRSA strains, we should be paid more attention to these strains.

Expression and regulation of phenol-soluble modulins and enterotoxins in foodborne Staphylococcus aureus

Although high levels of staphylococcal phenol-soluble modulins (PSMs) in clinical methicillin-resistant Staphylococcus aureus (MRSA) has been shown to correlate with bacterial virulence, the PSMs expression in foodborne Staphylococcus aureus (S. aureus), as well as its association with staphylococcal food poisoning (SFP) was not yet clear. We collected a panel of 350 foodborne and 127 clinic-derived S. aureus strains and compared their PSMs expression. Overall, foodborne strains exhibited higher PSMs than clinical isolates, indicating a potential pathological significance of PSMs in staphylococcal food contamination. Furthermore, PSMs expression and staphylococcal enterotoxins (SEs) levels in relation to antibiotic sensitive and resistant strains were analysed. While the co-expression of PSMs and SEs was confirmed, one typical foodborne strain simultaneously yielding PSMs, SEB and SED was selected. By comparing this wildtype strain to a series of gene-deficient mutants, we concluded that PSMs and SEs expressions both relied on staphylococcal accessory regulator A initiation in the early stage of accessory gene regulator control, yet their succedent regulations differentiated to RNAIII-dependent and independent, respectively. These data provided preliminary insight into PSMs and SEs expression in foodborne S. aureus, and may guide the further studies on PSMs effects in SFP.

Increased in vitro phenol-soluble modulin production is associated with soft tissue infection source in clinical isolates of methicillin-susceptible Staphylococcus aureus

BACKGROUND

Phenol-soluble modulins (PSM) are amphipathic proteins produced by Staphylococcus aureus that promote virulence, inflammatory response, and biofilm formation. We previously showed that MRSA isolates from soft tissue infection (SSTI) produced significantly higher levels of PSM than MRSA isolates from hospital-acquired pneumonia (HAP) or infective endocarditis (IE). In this investigation, we sought to validate this finding in methicillin-susceptible S. aureus (MSSA) isolates.

METHODS

MSSA isolates (n = 162) from patients with SSTI, HAP, and IE were matched 1:1:1 based on geographic origin of the infection to form 54 triplets (North America n = 27, Europe n = 25, Australia n = 2). All isolates underwent spa typing and were classified using eGenomics. In vitro PSM production was quantified by high-performance liquid chromatography/mass spectrometry. Fischer's Exact Test and the Kruskal-Wallis test were used for statistical analysis.

RESULTS

Spa1 was more common in SSTI (14.81% SSTI, 3.70% HAP, 1.85% IE) (p < 0.03). Spa2 was more common in HAP (0% SSTI, 12.96% HAP, 3.70% IE) (p < 0.01). Levels of PSMα1-4 all differed significantly among the three clinical groups, with SSTI isolates producing the highest levels and IE producing the lowest levels of PSMα1-4. Spa1 isolates produced significantly more delta-toxin (p < 0.03) than non-Spa1 isolates. No associations between PSM levels and clinical outcome of SSTI, HAP, or IE were identified.

CONCLUSION

Production of PSMα1-4 is highest in SSTI MSSA isolates, supporting the hypothesis that these peptides are important for SSTI pathogenesis. These findings are similar to those described in MRSA, and demonstrate that associations between PSM levels and type of infection are independent of the methicillin-resistance status of the isolate.

Community-associated MRSA: what makes them special?

While infections with methicillin-resistant Staphylococcus aureus (MRSA) were traditionally restricted to the hospital setting, novel MRSA strains emerged over the last two decades that have the capacity to infect otherwise healthy people outside of the hospital setting. These community-associated (CA-)MRSA strains combine methicillin resistance with enhanced virulence and fitness. Interestingly, CA-MRSA strains emerged globally and from different backgrounds, indicating that the "trade-off" between maintaining sufficient levels of methicillin resistance and obtaining enhanced virulence at a low fitness cost was achieved on several occasions in convergent evolution. However, frequently this process comprised similar changes. First and foremost, all CA-MRSA strains typically carry a novel type of methicillin resistance locus that appears to cause less of a fitness burden. Additionally, acquisition of specific toxin genes, most notably that encoding Panton-Valentine leukocidin (PVL), and adaptation of gene expression of genome-encoded toxins, such as alpha-toxin and phenol-soluble modulins (PSMs), further contributed to the evolution of CA-MRSA. Finally, the exceptional epidemiological success of the USA300 CA-MRSA clone in particular may have been due to yet another gene acquisition, namely that of the speG gene, which is located on the arginine catabolic mobile element (ACME) and involved in detoxifying harmful host-derived polyamines.