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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

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what virulence factors enable staphylococcus aureus to cause blood stream infections

What virulence factors enable Staphylococcus aureus to cause blood stream infections?

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;

back ground
Back ground

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%.

BMJ. 2006;333:281.

risk factors for blood stream infections
Risk factors for Blood Stream Infections

Risk factors for BSIs

- intravascular catheters

- indwelling foreign body

- underlying medical conditions

correlations with virulence that have been reported
Correlations with virulence that have been reported

Panton Valentine Leucocidine (PVL)

In a mouse mode, PVL+ strains produced necrotizing pneumonia

Toxic Shock Syndrome Toxin (TSST)-1

Cause toxic shock syndrome

  • Science. 2007 Feb 23;315(5815):1130-3. Epub 2007 Jan 18.
correlations with virulence that have been reported1
Correlations with virulence that have been reported

Staphylococcal cassette chromosome mec (SCCmec)

Type II/III MRSA was associated with a longer length of stay

  • J Infect Dis. 2007;195:1678-1685.
correlations with virulence that has been reported
Correlations with virulence that has been reported

Spa typing

CC5 and CC30 are associated with hematogenous complications

Arginine Catabolic Mobile Element (ACME)

Associated with virulence and the ability to colonize humans

  • J Infect Dis. 2007 Sep 1;196(5):738-47.
  • Lancet. 2006 Mar 4;367(9512):705-6.
our objective bsis
Our Objective- BSIs

To identify the genes and virulence factors of S. aureus which facilitate or correlate with their ability to gain access to the blood stream

material and method
Material and method

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.

source of specimens
Source of specimens

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.

laboratory methods
Laboratory methods

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.

statistical methods
Statistical methods

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.

results
Results

A total of 27 BSI isolates and 295 SSTI S. aureus isolates were identified. MRSA isolates accounted for 53.7% (173 out of 322).

ssti vs bsi mssa and mrsa
SSTI vs BSI (MSSA and MRSA)

*Values are numbers of isolates. Values in parentheses are percentages

highlights
Highlights

There was no significant difference in SCC mec and Spa type between SSTI and BSI isolates.

highlights1
Highlights

PVL was not associated with BSIs

53% of SSTI and 42% of BSIs

p= 0.227

TSST-1 was not associated with BSIs

1.7% of SSTI and 7.7% of BSIs

p=0.109

highlights2
Highlights

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).

limitations
Limitations

Retrospective study

No clinical information

Limited number of isolates

conclusion
Conclusion

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.

conclusion1
Conclusion

The correlation of bacteremia and some antibiotics susceptibility may be a useful clinical tool in evaluation and treating blood stream infections.

slide25
Plan

Further studies are needed with more specimens and clinical correlations.