Title: What virulence factors enable Staphylococcus aureus to cause blood stream infections?
1What 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 Queens and Kuakini Health Systems,
Honolulu, Hawaii3
2Back 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. 2006333281.
3Risk factors for Blood Stream Infections
- Risk factors for BSIs
- - intravascular catheters
- - indwelling foreign body
- - underlying medical conditions
4Correlations 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 23315(5815)1130-3. Epub 2007
Jan 18.
5Correlations 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. 20071951678-1685 .
6Correlations 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 1196(5)738-47.
- Lancet. 2006 Mar 4367(9512)705-6.
7 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
8Material and method
- Comparison of S. aureus strains 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.
9Source of specimens
- The clinical isolates were selected from
Diagnostic Laboratory service (DLS) and Clinical
Laboratory Standards Institute - S. aureus strains 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.
10Laboratory 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.
11Statistical 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.
12Results
- A total of 27 BSI isolates and 295 SSTI S. aureus
isolates were identified. MRSA isolates accounted
for 53.7 (173 out of 322).
13SSTI vs BSI (MSSA and MRSA)
Characteristic SSTI BSI P-value
Inpatient 82(27.9) 22(81.5) lt0.001
MRSA 152(51.5) 22(81.5) 0.004
SCC mec type
Type?a 75(25.5) 11(40.7) 0.110
Type ? 20(6.8) 1(3.7) 1.000
Type ? 42(14) 6(22) 0.262
Mec A 38(12.9) 1(3.7) 0.441
Mec B 5(1.7) 1(3.7) 1.000
CCR1 2(0.7) 0(0) 1.000
CCR2 22(7.5) 2(7.4) 1.000
Values are numbers of isolates. Values in
parentheses are percentages
14SSTI vs BSI (MSSA and MRSA)
Characteristic SSTI BSI P-value
PVL 155(54.2) 11(40.7) 0.227
TSST-1 5 (1.7) 2 (7.4) 0.109
Spa type
CC8 145 (54.9) 12 (48) 0.691
CC2 39 (14.8) 6 (24) 0.240
CC12 16 (6.1) 0 (0) 0.379
CC85 11 (4.2) 2 (8) 0.229
15SSTI vs BSI (MRSA)
Characteristic SSTI (MRSA) BSI (MRSA) P-value
Inpatient 62(40.8) 19(86.4) lt0.001
SCC mec type
Type?a 74(48.7) 11(50.0) 1.000
Type ? 20(13.2) 1(4.5) 0.480
Type ? 31(20.4) 6(27.3) 0.577
Mec A 4(2.6) 1(4.5) 0.496
Mec B 2(1.3) 1(4.5) 0.335
CCR1 0(0) 0(0) 1.000
CCR2 12(7.9) 2(9.1) 0.692
16SSTI vs BSI (MRSA)
Characteristic SSTI (MRSA) BSI (MRSA) P-value
PVL 155(54.2) 11(40.7) 0.227
TSST-1 5 (1.7) 2 (7.4) 0.109
Spa type
CC8 106 (74.1) 10 (50.0) 0.030
CC2 22 (15.4) 6 (30.0) 0.131
CC12 9 (6.3) 0 (0) 0.605
CC85 2 (1.4) 0 (0) 1.000
17Antimicrobial Percentage of susceptible isolates (MSSA and MRSA ) Percentage of susceptible isolates (MSSA and MRSA ) P-value
Antimicrobial SSTI BSI P-value
Oxacillin 141 (48.6) 5 (21.7) 0.016
Levofloxacin 258 (87.1) 15 (57.1) 0.001
Clindamycin 250 (85.9) 14 (56.5) 0.001
Erythromycin 132 (45.2) 7 (26.1) 0.084
Gentamicin 293 (99.3) 24 (91.3) 0.028
Tetracycline 281 (95.5) 21 (78.3 ) 0.006
Rifampin 295 (100) 27 (100) 1.000
TMP-SMXa 292 (99.0) 27 (100) 1.000
Vancomycin 295 (100) 27 (100) 1.000
18Antimicrobial Percentage of susceptible isolates (Only MRSA) Percentage of susceptible isolates (Only MRSA) P-value
Antimicrobial SSTI (MRSA) BSI (MRSA) P-value
Levofloxacin 112(74.6) 7 (43.8) 0.017
Clindamycin 118(78.0) 8 (44.4) 0.004
Erythromycin 24(15.9) 11 (5.6) 0.479
Gentamicin 148 (98.7) 17 (88.9) 0.057
Tetracycline 139 (92.7) 14 (72.2) 0.016
Rifampin 150 (99.3) 20 (100) 1.000
TMP-SMX 149 (98.0) 20 (100) 1.000
Vancomycin 152 (100) 20 (100) 1.000
19Highlights
- There was no significant difference in SCC mec
and Spa type between SSTI and BSI isolates.
20Highlights
- 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
- p0.109
21Highlights
- MRSA BSI isolates exhibited a significant
resistance to clindamycin, tetracycline and
levofloxacin compared with MRSA SSTI isolates (P
lt0.05). - 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 (P0.479).
22Limitations
- Retrospective study
- No clinical information
- Limited number of isolates
23Conclusion
- 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.
24Conclusion
- The correlation of bacteremia and some
antibiotics susceptibility may be a useful
clinical tool in evaluation and treating blood
stream infections.
25Plan
- Further studies are needed with more specimens
and clinical correlations.