Before contacting host tissues, invading pathogens directly or indirectly interact with host microbiota, but the effects of such interactions on the initial stages of infection are poorly understood. Bordetella pertussis is highly infectious among humans but requires large doses to colonize rodents, unlike a closely related zoonotic pathogen, Bordetella bronchiseptica, raising important questions about the contributions of bacterial competition to initial colonization and host selection. We observed that <100 colony-forming units (CFU) of B. bronchiseptica efficiently infected mice and displaced culturable host microbiota, whereas 10 000 CFU of B. pertussis were required to colonize murine nasal cavities and did not displace host microorganisms. Bacteria isolated from murine nasal cavities but not those from the human lower respiratory tract limited B. pertussis growth in vitro, indicating that interspecies competition may limit B. pertussis colonization of mice. Further, a broad-spectrum antibiotic treatment delivered before B. pertussis inoculation reduced the infectious dose to <100 CFU, and reintroduction of single Staphylococcus or Klebsiella species was sufficient to inhibit B. pertussis colonization of antibiotic-treated mice. Together, these results reveal that resident microorganisms can prevent B. pertussis colonization and influence host specificity, and they provide rationale for manipulating microbiomes to create more-accurate animal models of infectious diseases.

Our results highlight discrepancies between whole-cell and acellular vaccination that could contribute to the increased incidence of B. pertussis infection since the transition to the use of acellular vaccination.

Type VI Secretion Systems (T6SSs) have been identified in numerous Gram-negative pathogens, but the lack of a natural host infection model has limited analysis of T6SS contributions to infection and pathogenesis. Here, we describe disruption of a gene within locus encoding a putative T6SS in Bordetella bronchiseptica strain RB50, a respiratory pathogen that circulates in a broad range of mammals, including humans, domestic animals, and mice. The 26 gene locus encoding the B. bronchiseptica T6SS contains apparent orthologs to all known core genes and possesses thirteen novel genes. By generating an in frame deletion of clpV, which encodes a putative ATPase required for some T6SS-dependent protein secretion, we observe that ClpV contributes to in vitro macrophage cytotoxicity while inducing several eukaryotic proteins associated with apoptosis. Additionally, ClpV is required for induction of IL-1β, IL-6, IL-17, and IL-10 production in J774 macrophages infected with RB50. During infections in wild type mice, we determined that ClpV contributes to altered cytokine production, increased pathology, delayed lower respiratory tract clearance, and long term nasal cavity persistence. Together, these results reveal a natural host infection system in which to interrogate T6SS contributions to immunomodulation and pathogenesis.

Pristinamycin displays unique antibacterial properties due to the synergy between its two components, pristinamycin I and pristinamycin II. Because this antibiotic is not water-soluble, its administration is restricted to the oral route, and its therapeutic potential is thereby limited. Novel water-soluble derivatives of the naturally-occurring antibiotic pristinamycin were obtained by modifications of its two major components. The modifications included regioselective and stereoselective substitution alpha to the carbonyl group in the 4-oxo-pipecolic acid residue of pristinamycin IA (PIA) and stereoselective conjugate addition to the double bond of the dehydroproline ring in pristinamycin IIA (PIIA). We report here the in-vitro and in-vivo activities of some representative water-soluble derivatives of pristinamycin IA and pristinamycin IIA against Staphylococcus aureus reference strains, sensitive or resistant to methicillin and/or macrolides.