Authors: Copley LA, GaviriaAgudelo C, Wakeland W, Aroh C, Tareen N.
Children's Medical Center of Dallas, Dallas, Texas
Title: Variations in the Bacterial Genome of Methicillin-Resistant Staphylococcus Aureus Causing Pediatric Osteomyelitis Within a Community
Background: With the rising incidence of MRSA, there has been an increase in severity of illness among children with musculoskeletal infection. The majority of the MRSA organisms causing hematogenous osteomyelitis are of a single clone type, USA 300. It remains unknown whether there are underlying genetic differences among bacterial isolates that could play a role in the variability of the clinical spectrum of disease.
Hypothesis/Purpose: The aim of this study is to evaluate the genetic similarity among MRSA bacteria which have caused pediatric osteomyelitis in our community.
Methods: In 2010, children with confirmed culture positive osteomyelitis caused by MRSA were studied to assign a severity of illness score based on objective clinical and laboratory parameters. The bacterial isolates from these cases were subsequently analyzed with multi-locus sequence (MLST), multi-virulence locus sequence (MVLST), next generation sequence (NGS), and optical genetic sequencing (OpGen). Bacterial genetics were analyzed in comparison to USA 300 standards.
Results: Twelve children were studied and noted to have a broad range of clinical illness as demonstrated by severity of illness scores ranging from 0 to 9 with an average of 6.1. All twelve samples were gentically similar to the USA 300 clone type. MLST demonstrated that all samples were of single sequence type (ST8). MVLST identified genetic polymorphisms of only the HlgA gamma-hemolysin. OpGen demonstrated variability of a 19 kb insertion in two samples, a 12 kb insertion in one sample and a 40 kb deletion in two samples. NGS revealed 132 single nucleotide polymorphisms (an average of 11 per specimen) representing variations in 22 shared genes.
Discussion: The 2.8 million base pair genome of MRSA demonstrates substantial uniformity within a single community when considering clone type and seqeunce type. However, variations of indels, SNPs and the polymorphisms of the gamma-hemolysin may play a role in the variability in the clinical manifestations of disease. Gamma hemolysin is known to promote survival of MRSA in the bloodstream which normally contains insufficient free iron.
Conclusion: We have demonstrated bacterial genetic variability of the MRSA causing osteomyelitis within a single community which may play a role in the clinical variation in severity of illness in this disease process.