Last data update: Apr 29, 2024. (Total: 46658 publications since 2009)
Records 1-10 (of 10 Records) |
Query Trace: Bearden SW [original query] |
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Yersinia pestis Δail Mutants Are Not Susceptible to Human Complement Bactericidal Activity in the Flea.
Kolodziejek AM , Bearden SW , Maes S , Montenieri JM , Gage KL , Hovde CJ , Minnich SA . Appl Environ Microbiol 2023 89 (2) e0124422 Ail confers serum resistance in humans and is a critical virulence factor of Y. pestis, the causative agent of plague. Here, the contribution of Ail for Y. pestis survival in the flea vector was examined. Rat or human but not mouse sera were bactericidal against a Y. pestis Δail mutant at 28°C in vitro. Complement components deposited rapidly on the Y. pestis surface as measured by immunofluorescent microscopy. Ail reduced the amount of active C3b on the Y. pestis surface. Human sera retained bactericidal activity against a Y. pestis Δail mutant in the presence of mouse sera. However, in the flea vector, the serum protective properties of Ail were not required. Flea colonization studies using murine sera and Y. pestis KIM6(+) wild type, a Δail mutant, and the Δail/ail(+) control showed no differences in bacterial prevalence or numbers during the early stage of flea colonization. Similarly, flea studies with human blood showed Ail was not required for serum resistance. Finally, a variant of Ail (Ail(F100V E108_S109insS)) from a human serum-sensitive Y. pestis subsp. microtus bv. Caucasica 1146 conferred resistance to human complement when expressed in the Y. pestis KIM6(+) Δail mutant. This indicated that Ail activity was somehow blocked, most likely by lipooligosaccharide, in this serum sensitive strain. IMPORTANCE This work contributes to our understanding of how highly virulent Y. pestis evolved from its innocuous enteric predecessor. Among identified virulence factors is the attachment invasion locus protein, Ail, that is required to protect Y. pestis from serum complement in all mammals tested except mice. Murine sera is not bactericidal. In this study, we asked, is bactericidal sera from humans active in Y. pestis colonized fleas? We found it was not. The importance of this observation is that it identifies a protective niche for the growth of serum sensitive and nonsensitive Y. pestis strains. |
LPS modification promotes maintenance of Yersinia pestis in fleas.
Aoyagi K , Brooks BD , Bearden SW , Montenieri JA , Gage KL , Fisher MA . Microbiology (Reading) 2014 161 628-38 Yersinia pestis, the causative agent of plague, can be transmitted by fleas in two different manners: by early phase transmission (EPT), which occurs shortly after flea infection, or by blocked fleas following long-term infection. Efficient flea-borne transmission is predicated upon the ability of Y. pestis to be maintained within the flea. Signature-tagged mutagenesis (STM) was used to identify genes required for Y. pestis maintenance in a genuine plague vector, Xenopsylla cheopis. The STM screen identified seven mutants that displayed markedly reduced fitness in fleas after four days, the time during which EPT occurs. Two of the mutants contained insertions in genes encoding glucose-1-phosphate uridylyltransferase (galU) and UDP-4-amino-4-deoxy-L-arabinose-oxoglutarate aminotransferase (arnB), which are involved in the modification of lipid A with aminoarabinose (Ara4N) and resistance to cationic antimicrobial peptides (CAMPs). These Y. pestis mutants were more susceptible to the CAMPs cecropin A and polymyxin B, and produced lipid A lacking Ara4N modifications. Surprisingly, an in-frame deletion of arnB retained modest levels of CAMP resistance and Ara4N modification, indicating the presence of compensatory factors. It was determined that WecE, an aminotransferase involved in biosynthesis of enterobacterial common antigen, plays a novel role in Y. pestis Ara4N modification by partially offsetting the loss of arnB. These results indicate that mechanisms of Ara4N modification of lipid A are more complex than previously thought, and these modifications, as well as several factors yet to be elucidated, play an important role in early survival and transmission of Y. pestis in the flea vector. |
Evaluation of the effect of host immune status on short-term Yersinia pestis infection in fleas with implications for the enzootic host model for maintenance of Y. pestis during interepizootic periods
Graham CB , Woods ME , Vetter SM , Petersen JM , Montenieri JA , Holmes JL , Maes SE , Bearden SW , Gage KL , Eisen RJ . J Med Entomol 2014 51 (5) 1079-1086 Plague, a primarily flea-borne disease caused by Yersinia pestis, is characterized by rapidly spreading epizootics separated by periods of quiescence. Little is known about how and where Y. pestis persists between epizootics. It is commonly proposed, however, that Y. pestis is maintained during interepizootic periods in enzootic cycles involving flea vectors and relatively resistant host populations. According to this model, while susceptible individuals serve as infectious sources for feeding fleas and subsequently die of infection, resistant hosts survive infection, develop antibodies to the plague bacterium, and continue to provide bloodmeals to infected fleas. For Y. pestis to persist under this scenario, fleas must remain infected after feeding on hosts carrying antibodies to Y. pestis. Studies of other vector-borne pathogens suggest that host immunity may negatively impact pathogen survival in the vector. Here, we report infection rates and bacterial loads for fleas (both Xenopsylla cheopis (Rothschild) and Oropsylla montana (Baker)) that consumed an infectious bloodmeal and subsequently fed on an immunized or age-matched naive mouse. We demonstrate that neither the proportion of infected fleas nor the bacterial loads in infected fleas were significantly lower within 3 d of feeding on immunized versus naive mice. Our findings thus provide support for one assumption underlying the enzootic host model of interepizootic maintenance of Y. pestis. |
Yersinia murine toxin is not required for early-phase transmission of Yersinia pestis by Oropsylla montana (siphonaptera: ceratophyllidae) or Xenopsylla cheopis (siphonaptera: pulicidae)
Johnson TL , Hinnebusch BJ , Boegler KA , Graham CB , MacMillian K , Montenieri JA , Bearden SW , Gage KL , Eisen RJ . Microbiology (Reading) 2014 160 2517-2525 Plague, caused by Yersinia pestis, is characterized by quiescent periods punctuated by rapidly spreading epizootics. The classical "blocked flea" paradigm, by which a blockage forms in the flea's proventriculus on average 1-2 weeks post infection, forces starving fleas to take multiple blood meals, thus increasing opportunities for transmission. Recently the importance of early-phase transmission (EPT), which occurs prior to blockage formation, has been emphasized during epizootics. While the physiological and molecular mechanisms of blocked flea transmission are well characterized, the pathogen-vector interactions have not been elucidated for EPT. Within the blocked flea model, Yersinia murine toxin (Ymt) has been shown to be important for facilitating colonization of the midgut within the flea. One proposed mechanism of EPT is the regurgitation of infectious material from the flea midgut during feeding. Such a mechanism would require bacteria to colonize and survive for at least brief periods in the midgut, a process that is mediated by Ymt. Two key bridging vectors of Y. pestis to humans, Oropsylla montana and Xenopsylla cheopis, were used in our study to test this hypothesis. Fleas were infected with a mutant strain of Y. pestis containing a nonfunctional ymt that was previously shown to be incapable of colonizing the midgut, and were then allowed to feed on SKH-1 mice 3 days post infection. Our results show that Ymt is not required for EPT by either flea species. |
Effects of low-temperature flea maintenance on the transmission of Yersinia pestis by Oropsylla montana
Williams SK , Schotthoeffer AM , Montenieri JA , Holmes JL , Vetter SM , Gage KL , Bearden SW . Vector Borne Zoonotic Dis 2013 13 (7) 468-78 Yersinia pestis, the causative agent of plague, is primarily a rodent-associated, flea-borne zoonosis maintained in sylvatic foci throughout western North America. Transmission to humans is mediated most commonly by the flea vector Oropsylla montana and occurs predominantly in the southwestern United States. With few exceptions, previous studies showed O. montana to be an inefficient vector at transmitting Y. pestis at ambient temperatures, particularly when such fleas were fed on susceptible hosts more than a few days after ingesting an infectious blood meal. We examined whether holding fleas at subambient temperatures affected the transmissibility of Y. pestis by this vector. An infectious blood meal containing a virulent Y. pestis strain (CO96-3188) was given to colony-reared O. montana fleas. Potentially infected fleas were maintained at different temperatures (6 degrees C, 10 degrees C, 15 degrees C, or 23 degrees C). Transmission efficiencies were tested by allowing up to 15 infectious fleas to feed on each of 7 naive CD-1 mice on days 1-4, 7, 10, 14, 17, and 21 postinfection (p.i.). Mice were monitored for signs of infection for 21 days after exposure to infectious fleas. Fleas held at 6 degrees C, 10 degrees C, and 15 degrees C were able to effectively transmit at every time point p.i. The percentage of transmission to naive mice by fleas maintained at low temperatures (46.0% at 6 degrees C, 71.4% at 10 degrees C, 66.7% at 15 degrees C) was higher than for fleas maintained at 23 degrees C (25.4%) and indicates that O. montana fleas efficiently transmit Y. pestis at low temperatures. Moreover, pooled percent per flea transmission efficiencies for flea cohorts maintained at temperatures of 10 degrees C and 15 degrees C (8.67% and 7.87%, respectively) showed a statistically significant difference in the pooled percent per flea transmission efficiency from fleas maintained at 23 degrees C (1.94%). This is the first comprehensive study to demonstrate efficient transmission of Y. pestis by O. montana fleas maintained at temperatures as low as 6 degrees C. Our findings further contribute to the understanding of plague ecology in temperate climates by providing support for the hypothesis that Y. pestis is able to overwinter within the flea gut and potentially cause infection during the following transmission season. The findings also might hold implications for explaining the focality of plague in tropical regions. |
Effects of temperature on the transmission of Yersinia pestis by the flea, Xenopsylla cheopis, in the late phase period
Schotthoefer AM , Bearden SW , Holmes JL , Vetter SM , Montenieri JA , Williams SK , Graham CB , Woods ME , Eisen RJ , Gage KL . Parasit Vectors 2011 4 191 BACKGROUND: Traditionally, efficient flea-borne transmission of Yersinia pestis, the causative agent of plague, was thought to be dependent on a process referred to as blockage in which biofilm-mediated growth of the bacteria physically blocks the flea gut, leading to the regurgitation of contaminated blood into the host. This process was previously shown to be temperature-regulated, with blockage failing at temperatures approaching 30 degrees C; however, the abilities of fleas to transmit infections at different temperatures had not been adequately assessed. We infected colony-reared fleas of Xenopsylla cheopis with a wild type strain of Y. pestis and maintained them at 10, 23, 27, or 30 degrees C. Naive mice were exposed to groups of infected fleas beginning on day 7 post-infection (p.i.), and every 3-4 days thereafter until day 14 p.i. for fleas held at 10 degrees C, or 28 days p.i. for fleas held at 23-30 degrees C. Transmission was confirmed using Y. pestis-specific antigen or antibody detection assays on mouse tissues. RESULTS: Although no statistically significant differences in per flea transmission efficiencies were detected between 23 and 30 degrees C, efficiencies were highest for fleas maintained at 23 degrees C and they began to decline at 27 and 30 degrees C by day 21 p.i. These declines coincided with declining median bacterial loads in fleas at 27 and 30 degrees C. Survival and feeding rates of fleas also varied by temperature to suggest fleas at 27 and 30 degrees C would be less likely to sustain transmission than fleas maintained at 23 degrees C. Fleas held at 10 degrees C transmitted Y. pestis infections, although flea survival was significantly reduced compared to that of uninfected fleas at this temperature. Median bacterial loads were significantly higher at 10 degrees C than at the other temperatures. CONCLUSIONS: Our results suggest that temperature does not significantly effect the per flea efficiency of Y. pestis transmission by X. cheopis, but that temperature is likely to influence the dynamics of Y. pestis flea-borne transmission, perhaps by affecting persistence of the bacteria in the flea gut or by influencing flea survival. Whether Y. pestis biofilm production is important for transmission at different temperatures remains unresolved, although our results support the hypothesis that blockage is not necessary for efficient transmission. |
Effects of temperature on early-phase transmission of Yersina pestis by the flea, Xenopsylla cheopis
Schotthoefer AM , Bearden SW , Vetter SM , Holmes J , Montenieri JA , Graham CB , Woods ME , Eisen RJ , Gage KL . J Med Entomol 2011 48 (2) 411-7 Sharp declines in human and animal cases of plague, caused by the bacterium Yersinia pestis (Yersin), have been observed when outbreaks coincide with hot weather. Failure of biofilm production, or blockage, to occur in the flea, as temperatures reach 30 degrees C has been suggested as an explanation for these declines. Recent work demonstrating efficient flea transmission during the first few days after fleas have taken an infectious blood meal, in the absence of blockage (e.g., early-phase transmission), however, has called this hypothesis into question. To explore the potential effects of temperature on early-phase transmission, we infected colony-reared Xenopsylla cheopis (Rothchild) fleas with a wild-type strain of plague bacteria using an artificial feeding system, and held groups of fleas at 10, 23, 27, and 30 degrees C. Naive Swiss Webster mice were exposed to fleas from each of these temperatures on days 1-4 postinfection, and monitored for signs of infection for 21 d. Temperature did not significantly influence the rates of transmission observed for fleas held at 23, 27, and 30 degrees C. Estimated per flea transmission efficiencies for these higher temperatures ranged from 2.32 to 4.96% (95% confidence interval [CI]: 0.96-8.74). In contrast, no transmission was observed in mice challenged by fleas held at 10 degrees C (per flea transmission efficiency estimates, 0-1.68%). These results suggest that declines in human and animal cases during hot weather are not related to changes in the abilities of X. cheopis fleas to transmit Y. pestis infections during the early-phase period. By contrast, transmission may be delayed or inhibited at low temperatures, indicating that epizootic spread of Y. pestis by X. cheopis via early-phase transmission is unlikely during colder periods of the year. |
Znu is the predominant zinc importer in Yersinia pestis during in vitro growth but is not essential for virulence
Desrosiers DC , Bearden SW , Mier I Jr , Abney J , Paulley JT , Fetherston JD , Salazar JC , Radolf JD , Perry RD . Infect Immun 2010 78 (12) 5163-77 Little is known about Zn homeostasis in Yersinia pestis, the plague bacillus. The Znu ABC transporter is essential for zinc (Zn) uptake and virulence in a number of bacterial pathogens. Bioinformatics analysis identified ZnuABC as the only apparent high-affinity Zn uptake system in Y. pestis. Mutation of znuACB caused a growth defect in Chelex-100-treated PMH2 growth medium, which was alleviated by supplementation with submicromolar concentrations of Zn. Use of transcriptional reporters confirmed that Zur mediated Zn-dependent repression and that it can repress gene expression in response to Zn even in the absence of Znu. Virulence testing in mouse models of bubonic and pneumonic plague found only a modest increase in survival in low-dose infections by the znuACB mutant. Previous studies of cluster 9 (C9) transporters suggested that Yfe, a well-characterized C9 importer for manganese (Mn) and iron in Y. pestis, might function as a second, high-affinity Zn uptake system. Isothermal titration calorimetry revealed that YfeA, the solute-binding protein component of Yfe, binds Mn and Zn with comparably high affinities (dissociation constants of 17.8 +/- 4.4 nM and 6.6 +/- 1.2 nM, respectively), although the complete Yfe transporter could not compensate for the loss of Znu in in vitro growth studies. Unexpectedly, overexpression of Yfe interfered with the znu mutant's ability to grow in low concentrations of Zn, while excess Zn interfered with the ability of Yfe to import iron at low concentrations; these results suggest that YfeA can bind Zn in the bacterial cell but that Yfe is incompetent for transport of the metal. In addition to Yfe, we have now eliminated MntH, FetMP, Efe, Feo, a substrate-binding protein, and a putative nickel transporter as the unidentified, secondary Zn transporter in Y. pestis. Unlike other bacterial pathogens, Y. pestis does not require Znu for high-level infectivity and virulence; instead, it appears to possess a novel class of transporter, which can satisfy the bacterium's Zn requirements under in vivo metal-limiting conditions. Our studies also underscore the need for bacterial cells to balance binding and transporter specificities within the periplasm in order to maintain transition metal homeostasis. |
Biofilm formation is not required for early-phase transmission of Yersinia pestis
Vetter SM , Eisen RJ , Schotthoefer AM , Monteneri JA , Holmes JL , Bobrov AG , Bearden SW , Perry RD , Gage KL . Microbiology (Reading) 2010 156 2216-2225 Our study investigated whether hms-mediated biofilm formation was necessary for early-phase transmission (EPT) of Yersinia pestis. In addition to the biofilm-dependent blockage model of plague transmission from flea to mammal, an EPT model of transmission, has been described where fleas transmit Y. pestis to a host up to 4 days post infection, which is insufficient time for blockages to form in flea foreguts. An artificial feeding system was used to feed Xenopsylla cheopis and Oropsylla montana rat blood spiked with either the parental Y. pestis strain KIM5(pCD1)+, two different biofilm-mutants (DeltahmsT , DeltahmsR), or a biofilm-overproducer mutant (DeltahmsP ). Infected fleas were then allowed to feed on naive Swiss Webster mice 1-4 days after infection and the mice were monitored for signs of infection up to three weeks post-exposure. The biofilm-defective mutants were transmitted from X. cheopis and O. montana as efficiently as the parent strain, whereas the transmission efficiency of fleas fed the biofilm-overproducer was significantly less than either the parent or biofilm-deficient strains. The bacterial loads in fleas infected with a biofilm-deficient strain harbored lower bacterial loads 4 days post infection when compared to fleas infected with the parent strain. Thus defects in biofilm formation did not prevent flea-borne transmission of Y. pestis in our EPT model and biofilm over-production inhibited efficient EPT, however biofilm may play a role in infection persistence in the flea. |
Recent findings regarding maintenance of enzootic variants of Yersinia pestis in sylvatic reservoirs and their significance in the evolution of epidemic plague
Bearden SW , Brubaker RR . Vector Borne Zoonotic Dis 2010 10 (1) 85-92 Despite the widespread presence of bubonic plague in sylvatic reservoirs throughout the world, the causative agent (Yersinia pestis) evolved in its present form within the last 20,000 years from enteropathogenic Yersinia pseudotuberculosis. Comparison of the genomes from the two species revealed that Y. pestis possesses only a few unique plasmid-encoded genes that contribute to acute disease, whereas this organism has lost about 13% of the chromosomal genes that remain active in Y. pseudotuberculosis. These losses reflect readily detectable additions, deletions, transpositions, inversions, and acquisition of about 70 insertion sequence (IS) inserts, none of which are likely to promote increased virulence. In contrast, major enzymes of intermediary metabolism, including glucose 6-phosphate dehydrogenase (Zwf ) and aspartase, are present but not catalytically functional due to the presence of missense mutations. The latter are generally not detectable by the technology of bioinformatics and, in the case of Y. pestis, result in radical changes in the metabolic flow of carbon. As an important consequence, plague bacilli exhibit a stringent low-calcium response characterized by conversion of L-glutamate (and metabolically related amino acids) to L-aspartate with secretion of the latter into supernatant fluid at 37 degrees C in culture media containing Na(+) but lacking added Ca(2+). This phenomenon also occurs in vivo and likely adversely affects the bioenergetics of host amino acid pools. Curiously, aspartase is functional in all tested enzootic (pestoides) strains of Y. pestis. These isolates are typically restricted to the ancient plague reservoirs of Central Asia and Africa and are fully virulent in members of the rodent Superfamily Muroidea but avirulent in guinea pigs and man. The implications of these findings for the distribution and ecology of Y. pestis could be significant. |
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