Necrotizing fasciitis and myositis caused by streptococcal flesh-eating bacteria

Spontaneous Necrotizing Fasciitis

Necrotizing soft tissue infections typically begin with direct inoculation of bacteria into the subcutaneous tissues. Here, we present a case with no such exposure, but with severe necrotizing fasciitis. We present a middle-aged man presented to the emergency department for a presumed allergic reaction after having initially sought care twice at an urgent care facility. The patient had swelling, but no tenderness of his right lateral chest and flank. Subsequent imaging showed extensive fluid in the fascial planes of the right chest wall requiring surgical debridement. Necrotizing fasciitis that is not treated with surgical debridement carries a mortality rate approaching 100%. This case highlights a potential atypical presentation as well as highlights the fact that the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score lacks sensitivity to rule out a necrotizing soft tissue infection, requiring surgical debridement for diagnosis.

Differential virulence gene expression of group A Streptococcus serotype M3 in response to co-culture with Moraxella catarrhalis

Streptococcus pyogenes (group A Streptococcus, GAS) and Moraxella catarrhalis are important colonizers and (opportunistic) pathogens of the human respiratory tract. However, current knowledge regarding colonization and pathogenic potential of these two pathogens is based on work involving single bacterial species, even though the interplay between respiratory bacterial species is increasingly important in niche occupation and the development of disease. Therefore, to further define and understand polymicrobial species interactions, we investigated whether gene expression (and hence virulence potential) of GAS would be affected upon co-culture with M. catarrhalis. For co-culture experiments, GAS and M. catarrhalis were cultured in Todd-Hewitt broth supplemented with 0.2% yeast extract (THY) at 37°C with 5% CO₂ aeration. Each strain was grown in triplicate so that triplicate experiments could be performed. Bacterial RNA was isolated, cDNA synthesized, and microarray transcriptome expression analysis performed. We observed significantly increased (≥4-fold) expression for genes playing a role in GAS virulence such as hyaluronan synthase (hasA), streptococcal mitogenic exotoxin Z (smeZ) and IgG endopeptidase (ideS). In contrast, significantly decreased (≥4-fold) expression was observed in genes involved in energy metabolism and in 12 conserved GAS two-component regulatory systems. This study provides the first evidence that M. catarrhalis increases GAS virulence gene expression during co-culture, and again shows the importance of polymicrobial infections in directing bacterial virulence.