Abstract
Purpose Infective endocarditis (IE) is a major complication in patients with bacteremia of Staphylococcus (S.) aureus infection. Our aim was to determine the association of the major Staphylococcal superantigens (SAgs), including Staphylococcal enterotoxins (SEs) and toxic shock syndrome toxin-1 (TSST-1), among hospitalized patients diagnosed with bacteremia and those with IE. Methods This study was conducted on 88 patients; of these, 84 (95.5%) had two positive blood cultures. Eighteen out of the 84 patients (21.4%) were diagnosed based on the modified Duke criteria by a cardiologist to have IE. The recovered isolates were screened phenotypically using ELISA followed by molecular analysis of sea, seb, sec, sed, see, and tsst-1, the major SAg coding genes, and the obtained findings were statistically analyzed. Results Phenotypic screening for SE production of 26 selected Staphylococci (15 isolated from the IE patients (10 S. aureus and 5 coagulase negative staphylococci (CoNS)) and 11 from bacteremic patients (10 S. aureus and 1 CoNS)) using ELISA revealed that 12/26 (46%) isolates were SE producers. PCR analysis showed that 19 (73%) isolates were PCR positive for SAg genes with the highest prevalence of the sea gene (79%), followed by seb (63%) and tsst-1 (21%). The least frequent gene was sed (5.3%). Statistical correlations between bacteremic and IE isolates with respect to prevalence of SAgs showed no significant difference (P value = 0.139, effect size = 0.572) indicating no specific association between any of the detected SAgs and IE. Conclusion There is high prevalence of SEs among clinical isolates of Staphylococci recovered from patients suffering bacteremia and those with IE. No significant difference was found among Staphylococcal isolates recovered from patients with bacteremia or IE regarding both phenotypic and genotypic detection of the tested SAgs.
Highlights
S. aureus is a dangerous and versatile human pathogen because of its ability to cause various types of infections, including skin and soft tissue infections, pneumonia, bloodstream infections (BSIs), osteomyelitis, and infective endocarditis (IE) [1, 2]
When assessing the susceptibility of S. aureus to different antimicrobial agents, our results revealed that methicillinresistant S. aureus (MRSA) was responsible for most S. aureus bacteremia (92.3%), and cefoxitin resistance among CoNS was highly noticed with a percentage of 93.3%
Our results showed no significant difference between Staphylococcal IE and bacteremia isolates with respect to both phenotypic and genotypic detection of the most commonly found SAgs
Summary
S. aureus is a dangerous and versatile human pathogen because of its ability to cause various types of infections, including skin and soft tissue infections, pneumonia, bloodstream infections (BSIs), osteomyelitis, and infective endocarditis (IE) [1, 2]. A higher mortality rate (15–25%) was recently reported from serious S. aureus infections, bacteremia and endocarditis [3, 4]. IE is a major devastating complication of Staphylococcal bacteremia [4, 5]. Patient groups at high risk of developing S. aureus bacteremia include patients with higher prevalence of colonization, immunocompromised patients, and patients on hemodialysis. The involvement of bacterial complications still needs further studies to be identified as the basis of Staphylococcal virulence, and switching between commensal and pathogenic phenotypes is still unclear. The widely accepted Duke criteria provide high sensitivity and specificity for the diagnosis of IE where a series of major and minor clinical and pathologic criteria are implemented [12, 13]
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