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The injection of bacteria (Staphylococcus aureus, Stenotrophomonas maltophilia) or true fungi (Candida albicans, Candida tropicalis) that are pathogenic to humans into the silkworm hemolymph leads to death of the larvae within 2 days. Antibiotics used for clinical purposes have therapeutic effects on silkworms infected with these pathogens. The 50% effective doses obtained by injection into the silkworm hemolymph are consistent with those reported for mice. Injection of vancomycin and kanamycin into the silkworm hemolymph was effective, but oral administration was not. Chloramphenicol, which is effective by oral administration, appeared in the silkworm hemolymph soon after injection into the midgut, whereas vancomycin did not. Isolated midgut membranes were impermeable to vancomycin. Thus, the ineffectiveness of oral administration of vancomycin to silkworms is due to a lack of intestinal absorption.

SummarySilkworms are killed by injection of pathogenic bacteria, such as Staphylococcus aureus and Streptococcus pyogenes , into the haemolymph. Gene disruption mutants of S. aureus whose open reading frames were previously uncharacterized and that are conserved among bacteria were examined for their virulence in silkworms. Of these 100 genes, three genes named cvfA , cvfB , and cvfC were required for full virulence of S. aureus in silkworms. Haemolysin production was decreased in these mutants. The cvfA and cvfC mutants also had attenuated virulence in mice. S. pyogenes cvfA -disrupted mutants produced less exotoxin and had attenuated virulence in both silkworms and mice. These results indicate that the silkworm-infection model is useful for identifying bacterial virulence genes.

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The F region downstream of the mecI gene in the SCCmec element in hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) contains two bidirectionally overlapping open reading frames (ORFs), the fudoh ORF and the psm-mec ORF. The psm-mec ORF encodes a cytolysin, phenol-soluble modulin (PSM)-mec. Transformation of the F region into the Newman strain, which is a methicillin-sensitive S. aureus (MSSA) strain, or into the MW2 (USA400) and FRP3757 (USA300) strains, which are community-acquired MRSA (CA-MRSA) strains that lack the F region, attenuated their virulence in a mouse systemic infection model. Introducing the F region to these strains suppressed colony-spreading activity and PSMα production, and promoted biofilm formation. By producing mutations into the psm-mec ORF, we revealed that (i) both the transcription and translation products of the psm-mec ORF suppressed colony-spreading activity and promoted biofilm formation; and (ii) the transcription product of the psm-mec ORF, but not its translation product, decreased PSMα production. These findings suggest that both the psm-mec transcript, acting as a regulatory RNA, and the PSM-mec protein encoded by the gene on the mobile genetic element SCCmec regulate the virulence of Staphylococcus aureus.

Community acquired-methicillin resistant Staphylococcus aureus (CA-MRSA) is a socially problematic pathogen that infects healthy individuals, causing severe disease. CA-MRSA is more virulent than hospital associated-MRSA (HA-MRSA). The underlying mechanism for the high virulence of CA-MRSA is not known. The transcription product of the psm-mec gene, located in the mobile genetic element SCCmec of HA-MRSA, but not CA-MRSA, suppresses the expression of phenol-soluble modulin α (PSMα), a cytolytic toxin of S. aureus. Here we report that psm-mec RNA inhibits translation of the agrA gene encoding a positive transcription factor for the PSMα gene via specific binding to agrA mRNA. Furthermore, 25% of 325 clinical MRSA isolates had a mutation in the psm-mec promoter that attenuated transcription, and 9% of the strains had no psm-mec. In most of these psm-mec-mutated or psm-mec-deleted HA-MRSAs, PSMα expression was increased compared with strains carrying intact psm-mec, and some mutated strains produced high amounts of PSMα comparable with that of CA-MRSA. Deletion of psm-mec from HA-MRSA strains carrying intact psm-mec increased the expression of AgrA protein and PSMα, and virulence in mice. Thus, psm-mec RNA suppresses MRSA virulence via inhibition of agrA translation and the absence of psm-mec function in CA-MRSA causes its high virulence property.

Wild-type Staphylococcus aureus rapidly expands on the surface of soft agar plates. The rates of expansion and the shapes of the resultant giant colonies were distinct for different strains of laboratory stocks and clinical isolates. The colony spreading abilities did not correlate with the biofilm-forming abilities in these strains. Insertional disruption of the dltABCD operon, which functions at the step of D-alanine addition to teichoic acids, and of the tagO gene, which is responsible for the synthesis of wall teichoic acids, decreased the colony spreading ability. The results indicate that wall teichoic acids and D-alanylation of teichoic acids are required for colony spreading.In bacteria, motility is advantageous for the acquisition of nutrients. Many bacteria translocate by the propeller function of flagella (16,20). Although mycobacteria and streptococci do not have flagella, they can spread on solid surfaces via a mechanism called sliding (2,7,8,14). The sliding ability of these bacteria is provided by the expansive forces of a growing culture in combination with special surface properties of the cells resulting in reduced friction between the cell and its substrate (6, 7). In Mycobacterium smegmatis, glycopeptide lipids in the cell envelope are required for sliding (21,22). Bacillus subtilis and a nonflagellated mutant of this species have the sliding type of surface motility (11). In B. subtilis, surfactin secreted by the bacterium and extracellular potassium ions are required for the spreading (10). In addition, the gram-negative bacteria Escherichia coli, Vibrio cholerae, and Serratia marcescens have sliding ability that is independent of their flagella (3, 15). The biologic significance of the ability to slide and the sliding mechanism remains to be elucidated.Staphylococcus aureus is a nonflagellated gram-positive pathogen that causes various diseases, such as suppurative wound infections, meningitis, and sepsis. The recent emergence of methicillin-resistant S. aureus, which is resistant to a broad range of antibiotics, is the source of serious clinical problems. S. aureus forms a biofilm on medical devices, such as catheters left in the body. Biofilm formation is caused by the attachment of S. aureus to artificial surfaces and attenuates the effectiveness of antibiotics and antimicrobial peptides (4). Whether this bacterium can spread on a solid surface, however, is unknown. Staphylococcus epidermidis, a species closely related to S. aureus, has a spreading ability called darting, which has a speed of 6 m/min (7). In this report, we describe the ability of S. aureus to spread on soft agar surfaces at a speed of 100 m/min. The results of the present study indicate that wall teichoic acid and D-alanylation of teichoic acids are required for the colony spreading ability of S. aureus.S. aureus spreads rapidly on the surface of soft agar plates. Tryptic soy broth (Becton, Sparks, MD) supplemented with 0.24% agar (Nacalai Tesque, Inc., Kyoto, Japan) was autoclaved and poured into plates (diameter, 12 ...

Motility often plays a decisive role in the survival of species. Five systems of motility have been studied in depth: those propelled by bacterial flagella, eukaryotic actin polymerization and the eukaryotic motor proteins myosin, kinesin and dynein. However, many organisms exhibit surprisingly diverse motilities, and advances in genomics, molecular biology and imaging have showed that those motilities have inherently independent mechanisms. This makes defining the breadth of motility nontrivial, because novel motilities may be driven by unknown mechanisms. Here, we classify the known motilities based on the unique classes of movement-producing protein architectures.Based on this criterion, the current total of independent motility systems stands at 18 types. In this perspective, we discuss these modes of motility relative to the latest phylogenetic Tree of Life and propose a history of motility. During the ~4 billion years since the emergence of life, motility arose in Bacteria with flagella and pili, and in Archaea with archaella. Newer modes of motility became possible in Eukarya with changes to the cell envelope. Presence or absence of a peptidoglycan layer, the acquisition of robust membrane dynamics, the enlargement of cells and environmental opportunities likely provided the context for the (co)evolution of novel types of motility. K E Y W O R D S appendage, cytoskeleton, flagella, membrane remodeling, Mollicutes, motor protein, peptidoglycan, three domains | 9Genes to Cells MIYATA eT Al.