Improved Protection in a Rabbit Model of Community-Associated Methicillin-Resistant Staphylococcus aureus Necrotizing Pneumonia upon Neutralization of Leukocidins in Addition to Alpha-Hemolysin

Abstract

b Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), especially the USA300 pulsotype, is a frequent cause of skin and soft tissue infections and severe pneumonia. Despite appropriate antibiotic treatment, complications are common and pneumonia is associated with high mortality. S. aureus strains express multiple cytotoxins, including alpha-hemolysin (Hla) and up to five bicomponent leukocidins that specifically target phagocytic cells for lysis. CA-MRSA USA300 strains carry the genes for all six cytotoxins. Species specificity of the leukocidins greatly contributes to the ambiguity regarding their role in S. aureus pathogenesis. We performed a comparative analysis of the leukocidin susceptibility of human, rabbit, and mouse polymorphonuclear leukocytes (PMNs) to assess the translational value of mouse and rabbit S. aureus models. We found that mouse PMNs were largely resistant to LukSF-PV, HlgAB, and HlgCB and susceptible only to LukED, whereas rabbit and human PMNs were highly sensitive to all these cytotoxins. In the rabbit pneumonia model with a USA300 CA-MRSA strain, passive immunization with a previously identified human monoclonal antibody (MAb), Hla-F#5, which cross-neutralizes Hla, LukSF-PV, HlgAB, HlgCB, and LukED, provided full protection, whereas an Hla-specific MAb was only partially protective. In the mouse USA300 CA-MRSA pneumonia model, both types of antibodies demonstrated full protection, suggesting that Hla, but not leukocidin(s), is the principal virulence determinant in mice. As the rabbit recapitulates the high susceptibility to leukocidins characteristic of humans, this species represents a valuable model for assessing novel, cytotoxin-targeting anti-S. aureus therapeutic approaches.

Animal models of hospital-acquired pneumonia: current practices and future perspectives

“…Thus, in this review, the main characteristics of the most used P. aeruginosa pneumonia animal models for acute pneumonia, VAP and chronic pneumonia occurring in CF patients are summarized and compared ( Table 1). Several different species have been used to model human pneumonia including piglets (28)(29)(30), rodents (31)(32)(33), primates (34,35), sheep (36,37), dogs (38,39) and rabbits (40,41) and these models have proven instructive in studies of disease mechanisms and in antibiotic testing. Nonetheless, rodents have been the preferred choice in translational pulmonary research as they not only are in accordance with the 3R principles of animal experimentation (42) but also offer specific advantages such as the potential to validate key findings or elucidate distinct pathogenic steps in a wide range of developed transgenic rodent models that are available to the scientific community.…”

Targeting Alpha Toxin To Mitigate Its Lethal Toxicity in Ferret and Rabbit Models of Staphylococcus aureus Necrotizing Pneumonia

“…Consequently, it has been the focus of much research to better understand its role in pneumonia and its utility as a target for novel methods to treat or prevent S. aureus pneumonia (6)(7)(8)(9)(10). In fact, two anti-AT MAbs (MEDI4893 and AR-301) are currently in clinical development for the treatment or prevention of S. aureus pneumonia (11).…”

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

“…For example, LukAB is highly lytic to human phagocytes but only weakly toxic to murine cells due to species-specific differences in the LukAB receptor CD11b (60,63,64). Similarly, PVL and HlgCB do not bind murine C5aR1/2, the myeloid receptor for these toxins (65,66).…”

“…The species-specific disparity in receptor binding has likely led to an underestimation of the importance of these toxins for human disease. Notably, LukAB, PVL, and HlgCB are moderately toxic to leporine leukocytes, suggesting that rabbits may be a more appropriate model for assessing these human-evolved factors in vivo (63).…”