Mechanisms of Bordetella pathogenesis.

Bordetella are Gram negative bacteria that cause respiratory tract infections in humans and animals. While at least five different species of Bordetella are known to exist, this review focuses on B. pertussis, B. bronchiseptica and B. parapertussis subspecies. In their virulent phase, all of these bacteria produce a nearly identical set of virulence factors which include adhesins such as filamentous hemagglutinin (FHA), fimbriae and pertactin, as well as toxins such as a bifunctional adenylate cyclase/hemolysin, dermonecrotic toxin, tracheal cytotoxin, a B. pertussis specific pertussis toxin and B. bronchiseptica specific type III secreted proteins. Expression of nearly all of these virulence factors is positively regulated by the products of the bvgAS locus. BvgA and BvgS comprise a two-component signal transduction system that mediates transition between at least three identifiable phases---a virulent (Bvg+) phase, an avirulent (Bvg-) phase and an intermediate (Bvg(i)) phase---in response to specific environmental signals. Bordetella colonize the ciliated respiratory mucosa, a surface designed to eliminate foreign particles, thereby making the adherence and persistence mechanisms of these bacteria crucial. The development of relevant animal models for B. bronchiseptica has enabled us to study Bordetella pathogenesis in the context of natural host-pathogen interactions. In addition, evolutionary studies across the various Bordetella species and detailed analysis of differential regulation of Bvg-activated/repressed genes has greatly enhanced our understanding of the mechanisms of Bordetella pathogenesis.

Phospholipid synthesis by Staphylococcus aureus during (Sub)Lethal attack by mammalian 14-kilodalton group IIA phospholipase A2.

Killing of gram-positive bacteria by mammalian group IIA phospholipases A2 (PLA2) requires the catalytic activity of the enzyme. However, nearly complete degradation of the phospholipids can occur with little effect on bacterial viability, suggesting that PLA2-treated bacteria can biosynthetically replace phospholipids that are lost due to PLA2 action. In the presence of albumin, phospholipid degradation products are quantitatively sequestered extracellularly. In the absence of albumin, the bacteria retain and substantially reutilize the phospholipid breakdown products and survive an otherwise lethal dose of PLA2. PLA2-treated bacteria also continue to incorporate sodium [2-(14)C]acetate into phospholipids, suggesting that the bacteria are attempting to repair the damaged membranes by de novo synthesis of phospholipids. To determine whether PLA2 action also triggers activation of bacterial lipolytic enzymes, the effects of nisin and PLA2 on the degradation of S. aureus lipids were compared. In contrast to nisin treatment, PLA2 treatment does not stimulate endogenous phospholipase activity in S. aureus. These findings show that S. aureus responds to PLA2 attack by continued phospholipid (re)synthesis by both de novo and salvage pathways. The fate of PLA2-treated S. aureus therefore appears to depend on the relative rates of phospholipid degradation and synthesis.

Cell-wall determinants of the bactericidal action of group IIA phospholipase A2 against Gram-positive bacteria.

We have shown previously that a group IIA phospholipase A2 (PLA2) is responsible for the potent bactericidal activity of inflammatory fluids against many Gram-positive bacteria. To exert its antibacterial activity, this PLA2 must first bind and traverse the bacterial cell wall to produce the extensive degradation of membrane phospholipids (PL) required for bacterial killing. In this study, we have examined the properties of the cell-wall that may determine the potency of group IIA PLA2 action. Inhibition of bacterial growth by nutrient deprivation or a bacteriostatic antibiotic reversibly increased bacterial resistance to PLA2-triggered PL degradation and killing. Conversely, pretreatment of Staphylococcus aureus or Enterococcus faecium with subinhibitory doses of beta-lactam antibiotics increased the rate and extent of PL degradation and/or bacterial killing after addition of PLA2. Isogenic wild-type (lyt+) and autolysis-deficient (lyt-) strains of S. aureus were equally sensitive to the phospholipolytic action of PLA2, but killing and lysis was much greater in the lyt+ strain. Thus, changes in cell-wall cross-linking and/or autolytic activity can modulate PLA2 action either by affecting enzyme access to membrane PL or by the coupling of massive PL degradation to autolysin-dependent killing and bacterial lysis or both. Taken together, these findings suggest that the bacterial envelope sites engaged in cell growth may represent preferential sites for the action and cytotoxic consequences of group IIA PLA2 attack against Gram-positive bacteria.