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Updated: Jul 9, 2026
Quantifying the Cytotoxicity of Staphylococcus aureus Against Human Polymorphonuclear Leukocytes
Published on: January 3, 2020
Increase of the USA300 clone among community-acquired methicillin-susceptible Staphylococcus aureus causing invasive
Michelle L McCaskill1, Edward O Mason, Sheldon L Kaplan
1Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA.
Background:
Methicillin-resistant Staphylococcus aureus (MRSA) USA300 is a predominant cause of community-acquired (CA) infection in the United States. We compared clinical characteristics of children with USA300 versus non-USA300 CA-methicillin-susceptible S. aureus (CA-MSSA) invasive infections at Texas Children's Hospital (TCH).
Methods:
Medical records were reviewed from children with invasive CA-MSSA infections at TCH between August 1, 2001 and September 30, 2006. Isolates were characterized by pulsed-field gel electrophoresis and polymerase chain reaction for Panton-Valentine leukocidin genes (pvl).
Results:
Invasive CA-MSSA infections increased from 14 in year 1 to 36 in year 5 (5-year total = 122 patients). Among the CA-MSSA isolates available for typing in the 5-year period, USA300 MSSA strains increased from 14% (2 of 14) to 35% (11 of 31) (P = 0.03). USA300 MSSA strains were more likely than non-USA300 MSSA strains to be nonsusceptible to erythromycin [66% (19 of 29) versus 28% (25 of 88); P < 0.01]. Osteomyelitis cases increased from 43% (6 of 14) in year 1 to 67% (24 of 36) in year 5. The majority of pvl(+) MSSA isolates were USA300 (71% (25 of 35); only 5% (4 of 82) of pvl(-) MSSA isolates were USA300. Patients with osteomyelitis caused by pvl isolates had significantly higher mean values for erythrocyte sedimentation rate at admission (P = 0.005) and erythrocyte sedimentation rate maximum value (P = 0.002), maximum C-reactive protein (P = 0.04), and absolute neutrophil count at presentation (P = 0.04) compared with patients whose isolates were pvl(-).
Conclusions:
USA300 accounted for a growing proportion of CA-MSSA isolates among children and was associated with increased numbers of invasive CA-MSSA infections at TCH, especially osteomyelitis. Associations were found in CA-MSSA osteomyelitis between pvl and increased concentrations of systemic inflammatory markers in patients.
Insights
Methicillin-susceptible Staphylococcus aureus (MSSA) USA300 strains are increasingly causing invasive infections in children, particularly osteomyelitis. These USA300 strains are linked to higher rates of erythromycin non-susceptibility and increased inflammatory markers.
Area of Science:
- Infectious Diseases
- Microbiology
- Pediatrics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) USA300 is a leading cause of community-acquired (CA) infections in the US.
- This study focuses on invasive CA-methicillin-susceptible S. aureus (CA-MSSA) infections in children at Texas Children's Hospital (TCH).
Purpose of the Study:
- To compare clinical characteristics of children with USA300 versus non-USA300 CA-MSSA invasive infections.
- To analyze trends in CA-MSSA infections and the prevalence of USA300 strains over a five-year period.
Main Methods:
- Retrospective review of medical records for pediatric CA-MSSA infections at TCH (August 2001-September 2006).
- Isolate characterization using pulsed-field gel electrophoresis and PCR for Panton-Valentine leukocidin (pvl) genes.
Main Results:
- Invasive CA-MSSA infections rose significantly, with USA300 MSSA strains increasing from 14% to 35% of typed isolates.
- USA300 MSSA strains showed higher rates of erythromycin non-susceptibility (66% vs. 28%).
- Osteomyelitis cases increased, and pvl-positive MSSA isolates, predominantly USA300, were associated with elevated inflammatory markers (ESR, CRP, ANC).
Conclusions:
- USA300 is a growing cause of invasive CA-MSSA infections in children, particularly osteomyelitis.
- Panton-Valentine leukocidin (pvl) presence in CA-MSSA osteomyelitis correlates with heightened systemic inflammation.
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