Programme Hospitalier Recherche Clinique, Institut Pasteur, Inserm, French Public Health Agency.

A new member of the staphylococcal bi-component leucotoxins family, LukE (32 kDa) and LukD (34.3 kDa) has been characterized from Staphylococcus aureus strain Newman. LukE was 58^68% identical with the class S proteins, whereas LukD was 71^77% identical with the class F proteins of the family. A partial immunoreactivity with the various affinitypurified antibodies specific for the other proteins was observed. Immunoprecipitation assay and gene probing confirmed a 30% frequency among human clinical isolates, differing from the distribution of the other known leucotoxins (P 6 0.005). LukE+LukD was as effective as the Panton-Valentine leucocidin for inducing dermonecrosis when injected in the rabbit skin, but not hemolytic and poorly leucotoxic compared to other leucotoxins expressed by Staphylococcus aureus.z 1998 Federation of European Biochemical Societies.

Clinical symptoms of impetigo and staphylococcal scalded skin syndrome may not only be expressed as the splitting of cell layers within the epidermis but are often accompanied by some localized inflammation. Toxin patterns of Staphylococcus aureus isolates originating from patients with impetigo and also from those with other primary and secondary skin infections in a retrospective isolate collection in France and a prospective isolate collection in French Guiana revealed a significant association (75% of the cases studied) of impetigo with production of at least one of the epidermolysins A and B and the bicomponent leucotoxin LukE-LukD (P < 0.001). However, most of the isolates were able to produce one of the nonubiquitous enterotoxins. Pulsed-field gel electrophoresis (PFGE) of genomic DNA hydrolyzed with SmaI showed a polymorphism of the two groups of isolates despite the fact that endemic clones were suspected in French Guiana and France. The combination of toxin patterns with PFGE fingerprinting may provide further discrimination among isolates defined in a given cluster or a given pulsotype and account for a specific virulence. The new association of toxins with a clinical syndrome may reveal principles of the pathological process.

A competitive reverse transcription-PCR method was developed for the semiquantitation of the expression of genes encoding bicomponent leucotoxins of Staphylococcus aureus, e.g., Panton-Valentine leucocidin (lukPV), gamma-hemolysin (hlgA and hlgCB), and LukE-LukD (lukED). The optimization procedure included RNA preparation; reverse transcription; the use of various amounts of enzymes, antisense primer, and RNA; and the final amplification chain reaction. Reproducible results were obtained, with sensitivity for detection of cDNA within the range of 1 mRNA/10 4 CFU to 10 2 mRNA/CFU, depending on the gene. Both specific mRNAs were more significantly expressed at the late-exponential phase of growth. Expression was about 100-fold higher in yeast extract-Casamino Acids-pyruvate medium than in heart infusion medium. Expression of the widely distributed gamma-hemolysin locus in the NTCC 8178 strain was around 10-fold diminished compared with that in the ATCC 49775 strain. Because of the lower level of hlgA expression, the corresponding protein, which is generally not abundant in culture supernatant, should be investigated for its contribution to the leucotoxinassociated virulence. The agr, sar, and agr sar mutant strains revealed a great dependence with regard to leucotoxin expression on the global regulatory system in S. aureus, except that expression of hlgA was not affected in the agr mutant.Staphylococcal bicomponent leucotoxins are exotoxins consisting of two nonassociated but synergic class S (31 to 32 kDa) and class F (35 kDa) proteins. Among this family of toxins, the Panton-Valentine leucocidin (PVL) is encoded by two contiguous and cotranscribed genes, lukFPV and lukS-PV (31). Another locus encodes ␥-hemolysin and comprises three genes: the first two encode class S proteins (HlgA and HlgC), and the third one encodes a class F protein (HlgB). hlgA constitutes an upstream open reading frame, whereas hlgC and hlgB (hlgCB in this text) are cotranscribed (10). Another locus was recently characterized as two cotranscribed class S and class F proteinencoding genes, lukE and lukD (lukED in the text), respectively (16). Production of leucotoxins among Staphylococcus aureus strains was studied by radial gel immunoprecipitation (16, 30), but quantitation of leucotoxin expression by enzyme-linked immunosorbent assay remains difficult because of cross-reactivity due to sequence identity between class S components (55 to 72%) and class F components (71 to 79%), respectively (29). There may be S. aureus strains that produce ␥-hemolysin, PVL, and/or LukE-LukD.Leucotoxin production was associated with infections resulting in furuncles, community pneumonia, and some antibioticassociated diarrhea (11,15,24). These infection-related leucotoxins act as activators of human neutrophils before creating lytic pores sensitive to monovalent cations (34). The leucotoxins were shown to induce an important inflammatory response in vivo in rabbit skin and in rabbit vitreous humor (16,31,32). Therefore, to determine their respective roles in...

Background: Children are underrepresented in the COVID-19 pandemic and often experience milder disease than adolescents and adults. Reduced severity is possibly due to recent and more frequent seasonal human coronaviruses (HCoV) infections. We assessed the seroprevalence of SARS-CoV-2 and seasonal HCoV specific antibodies in a large cohort in north-eastern France.