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What virulence factors enable Staphylococcus aureus to cause blood stream infections?. Sadao Jinno 1 , Steven Seifried 2 , Matthew J. Bankowski 3 , and Alan Tice 1
Sadao Jinno1, Steven Seifried2, Matthew J. Bankowski3, and Alan Tice1
Department of Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 1; Department of Cell and Molecular Biology, University of Hawaii John A. Burns School of Medicine2; Diagnostic Laboratory Services, Inc. and The Queen’s and Kuakini Health Systems, Honolulu, Hawaii3;
Staphylococcus aureus (S. aureus) is a major cause of severe nosocomial and community-acquired infections.
S. aureus bloodstream infections (BSIs) have been reported to cause 30-day mortality of up to 29%.
Risk factors for BSIs
- intravascular catheters
- indwelling foreign body
- underlying medical conditions
Panton Valentine Leucocidine (PVL)
In a mouse mode, PVL+ strains produced necrotizing pneumonia
Toxic Shock Syndrome Toxin (TSST)-1
Cause toxic shock syndrome
Staphylococcal cassette chromosome mec (SCCmec)
Type II/III MRSA was associated with a longer length of stay
CC5 and CC30 are associated with hematogenous complications
Arginine Catabolic Mobile Element (ACME)
Associated with virulence and the ability to colonize humans
To identify the genes and virulence factors of S. aureus which facilitate or correlate with their ability to gain access to the blood stream
Comparison of S. aureusstrains isolated from BSIs with those from soft skin tissue infections (SSTI) in Hawaii
Spa type, the genes for PVL and mec A, TSST-1, SCC mec type and antimicrobial susceptibility.
The clinical isolates were selected from Diagnostic Laboratory service (DLS) and Clinical Laboratory Standards Institute
S. aureusstrains were obtained from the SAM culture collection database at the University of Hawaii JABSOM. It was begun in 2004 and currently consists of molecular biology studies from over 800 strains of staphylococcus.
Susceptibility tests were performed by using the Vitek system (bioMerieux Vitek Inc, Hazelwood, MO). All isolates were tested for susceptibility to oxacillin, clindamycin, erythromycin, gentamicin, levofloxacin, rifampin, trimethoprim-sulfamethoxazole (TMP-SMX), tetracycline, and vancomycin.
Oxacillin was used for methicillin susceptibility testing.
SAS software was used for statistical analysis. Frequency distribution of categorical potential risk factors was calculated for each group of SSTI and BSI.
the between-group-comparisons were made by means of Fisher's exact test.
A p value of 0.05 was considered statistically significant.
A total of 27 BSI isolates and 295 SSTI S. aureus isolates were identified. MRSA isolates accounted for 53.7% (173 out of 322).
*Values are numbers of isolates. Values in parentheses are percentages
There was no significant difference in SCC mec and Spa type between SSTI and BSI isolates.
PVL was not associated with BSIs
53% of SSTI and 42% of BSIs
TSST-1 was not associated with BSIs
1.7% of SSTI and 7.7% of BSIs
MRSA BSI isolates exhibited a significant resistance to clindamycin, tetracycline and levofloxacin compared with MRSA SSTI isolates (P <0.05).
A higher proportion of MRSA BSI isolates was resistant to gentamicin compared with MRSA SSTI isolates, almost reaching a statistical significance level (P = 0.056).
Both MRSA SSTI and BSI showed significant resistances to erythromycin (P=0.479).
No clinical information
Limited number of isolates
The differences we have found between blood and SSTI isolates suggest PVL, SCC mec, Spa type are not significant virulence factors for BSIs in Hawaii
TSST-1 may be associated with BSIs.
The correlation of bacteremia and some antibiotics susceptibility may be a useful clinical tool in evaluation and treating blood stream infections.
Further studies are needed with more specimens and clinical correlations.