Listeriolysin O (LLO) and ActA are essential virulence determinants for Listeria monocytogenes pathogenesis. Transcription of actA and hly , encoding LLO, is regulated by PrfA and increases dramatically during intracellular infection. The 5 ¢ untranslated regions (5 ¢ UTRs) of actA and prfA have been shown to upregulate expression of their respective gene products. Here, we demonstrate that the...

Expression of the PrfA-controlled virulence gene hly (encoding the pore-forming cytolysin listeriolysin) is under negative regulation by readily metabolized carbon sources in Listeria monocytogenes. However, the hyperhemolytic strain NCTC 7973 exhibits deregulated hly expression in the presence of repressing sugars, raising the possibility that a defect in carbon source regulation is responsibl...

Listeria monocytogenes requires listeriolysin O (LLO) and ActA, the products of hly and actA, respectively, to establish a productive intracellular infection. LLO is essential for vacuolar lysis and entry into the cytosol, while ActA is required for bacterial spread to adjacent cells. We have used a transcriptional reporter gene system to compare the expression of actA and hly during intracellu...

Listeria monocytogenes insertion mutants defective in hemolysin production were generated using the conjugative transposons Tn916 and Tn1545. All of the nonhemolytic mutants (hly-) lacked a secreted 58-kD polypeptide, presumedly hemolysin, and were avirulent in a mouse model. An intracellular multiplication assay was established in monolayers of mouse bone marrow-derived macrophages, the J774 m...

Several genes involved in the lipopolysaccharide (LPS) biosynthetic pathway have been shown to affect the expression or activity of Escherichia coli hemolysin (Hly), a secreted cytotoxin that is the prototype of the RTX family of toxins. To further study this relationship, E. coli K-12 strains harboring mutations in the LPS biosynthetic genes rfaS, rfaQ, rfaJ, rfaP, and rfaC were transformed wi...

The gene coding for protein A (spa) of Staphylococcus aureus 8325-4 has been inactivated by substituting part of the spa coding sequence for a DNA fragment specifying resistance to ethidium bromide. The in vitro-constructed spa::EtBrr substitution mutation was introduced into the S. aureus chromosome by recombinational allele replacement. Southern blot hybridization showed that the in vitro-con...

Like all other Salmonella typhimurium strains examined, the smooth variants SF1397 (LT2) and 1366 and also their semi-rough and rough derivatives are non-haemolytic. Nevertheless, two haemolysin (Hly) plasmids of E. coli belonging to the inc groups incFIII,IV (pSU316) and incI2 (pHly152) were able to be introduced into these strains by conjugation and stably maintained. A considerable percentag...

We found that virulent hemolysin-producing (Hly+) Listeria monocytogenes strains inhibit antigen processing and presentation when added to macrophages in vitro. A virulent Hly- bacteria caused little or no inhibition. Live Hly+ bacteria inhibited presentation of both heat-killed L. monocytogenes and ovalbumin. Several observations indicate that hemolysin produced by intracellular bacteria was r...

The hemolytic Escherichia coli strain 536 (O6) propagates spontaneous hemolysin-negative mutants at relatively high rates (10(-3) to 10(-4)). One type of mutant (type I) lacks both secreted (external) and periplasmic (internal) hemolysin activity (Hlyex-/Hlyin-) and in addition shows no mannose-resistant hemagglutination (Mrh-), whereas the other type (type II) is Hlyex-/Hlyin+ and Mrh+. The ge...

Listeria monocytogenes is a bacterial pathogen that can invade the central nervous system (CNS), causing meningoencephalitis and brain abscesses. The diagnosis of CNS listeriosis, based on the isolation of the bacteria in the cerebrospinal fluid (CSF), can be difficult because of previous antibiotic treatment and a low number of bacteria in the CSF. To improve the sensitivity of microbiological...