Bacterial Volatiles Attract Gravid Secondary Screwworms (Diptera: Calliphoridae).

Bovine blood inoculated and incubated with bacteria was tested to determine if secondary screwworm, Cochliomyia macellaria (F.), would be attracted to the incubated substrate for oviposition. Five species of bacteria, Klebsiella oxytoca (Flugge), Proteus mirabilis Hauser, Proteus vulgaris Hauser, Providencia rettgeri Hadley, Elkins and Caldwell, and Providencia stuartii Ewing, previously isolated from animal wounds infested by primary screwworms, Cochliomyia hominivorax (Coquerel), were used. Incubated substrates were tested in a two-choice cage bioassay to study landing response and oviposition by gravid C. macellaria. Significantly more flies landed on substrates containing P. mirabilis than on substrates with other species of bacteria. Klebsiella oxytoca-treated substrates attracted the least flies. Substrates containing bacteria incubated for 72 h attracted significantly more flies than those incubated for 24-, 48-, or 96-h period. In 3-h duration oviposition tests, substrates with P. rettgeri attracted significantly more flies to oviposit than the other four species. The most eggs were recorded when substrates treated with all five species of bacteria were offered for oviposition. It is likely that multiple active chemicals present in the volatiles from substrates treated with all five species result in greater response than those in a single species. At least 72-h incubation seems to be necessary to obtain the most active volatile chemicals. Results suggest that C. macellaria uses similar chemical cues as C. hominivorax from bacteria volatiles as oviposition attractant/stimulant.

Development of fatal intestinal inflammation in MyD88 deficient mice co-infected with helminth and bacterial enteropathogens.

Infections with intestinal helminth and bacterial pathogens, such as enteropathogenic Escherichia coli, continue to be a major global health threat for children. To determine whether and how an intestinal helminth parasite, Heligomosomoides polygyrus, might impact the TLR signaling pathway during the response to a bacterial enteropathogen, MyD88 knockout and wild-type C57BL/6 mice were infected with H. polygyrus, the bacterial enteropathogen Citrobacter rodentium, or both. We found that MyD88 knockout mice co-infected with H. polygyrus and C. rodentium developed more severe intestinal inflammation and elevated mortality compared to the wild-type mice. The enhanced susceptibility to C. rodentium, intestinal injury and mortality of the co-infected MyD88 knockout mice were found to be associated with markedly reduced intestinal phagocyte recruitment, decreased expression of the chemoattractant KC, and a significant increase in bacterial translocation. Moreover, the increase in bacterial infection and disease severity were found to be correlated with a significant downregulation of antimicrobial peptide expression in the intestinal tissue in co-infected MyD88 knockout mice. Our results suggest that the MyD88 signaling pathway plays a critical role for host defense and survival during helminth and enteric bacterial co-infection.

Helminth infection impairs autophagy-mediated killing of bacterial enteropathogens by macrophages.

Autophagy is an important mechanism used by macrophages to kill intracellular pathogens. The results reported in this study demonstrate that autophagy is also involved in the macrophage killing of the extracellular enteropathogen Citrobacter rodentium after phagocytosis. The process was significantly impaired in macrophages isolated from mice chronically infected with the helminth parasite Heligmosomoides polygyrus. The H. polygyrus-mediated inhibition of autophagy was Th2 dependent because it was not observed in macrophages isolated from helminth-infected STAT6-deficient mice. Moreover, autophagy of Citrobacter was inhibited by treating macrophages with IL-4 and IL-13. The effect of H. polygyrus on autophagy was associated with decreased expression and processing of L chain protein 3 (LC3), a key component of the autophagic machinery. The helminth-induced inhibition of LC3 expression and processing was STAT6 dependent and could be recapitulated by treatment of macrophages with IL-4 and IL-13. Knockdown of LC3 significantly inhibited autophagic killing of Citrobacter, attesting to the functional importance of the H. polygyrus-mediated downregulation of this process. These observations reveal a new aspect of the immunosuppressive effects of helminth infection and provide mechanistic insights into our earlier finding that H. polygyrus significantly worsens the in vivo course of Citrobacter infection.

Enhanced susceptibility of channel catfish to the bacterium Edwardsiella ictaluri after parasitism by Ichthyophthirius multifiliis.

Bacterium Edwardsiella ictaluri and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish. The objective of this study was to evaluate the susceptibility of channel catfish Ictalurus punctatus to E. ictaluri and determine bacterial loads in different fish organs after parasitism by Ich. Fish received the following treatments: (1) infected by I. multifiliis at 5000 theronts/fish and exposed to E. ictaluri; (2) infected by I. multifiliis alone; (3) exposed to E. ictaluri alone; and (4) non-infected control. E. ictaluri in fish organs were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEs/mg). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) higher mortality (91.7%) when exposed to E. ictaluri than non-parasitized fish (10%). The bacterial loads in fish infected by 5000 theronts/fish ranged from 6497 to 163,898 GEs/mg which was between 40 and 2000 fold higher than non-parasitized fish (49-141 GEs/mg). Ich infection enhanced the susceptibility of channel catfish to bacterial invasion and increased fish mortality.

Concurrent infection with an intestinal helminth parasite impairs host resistance to enteric Citrobacter rodentium and enhances Citrobacter-induced colitis in mice.

Infections with intestinal helminth and bacterial pathogens, such as enteropathogenic Escherichia coli, continue to be a major global health threat for children. To test the hypothesis that intestinal helminth infection may be a risk factor for enteric bacterial infection, a murine model was established by using the intestinal helminth Heligomosomoides polygyrus. To analyze the modulatory effect of a Th2-inducing helminth on the outcome of enteric bacterium Citrobacter rodentium infection, BALB/c and STAT 6 knockout (KO) mice were infected with H. polygyrus, C. rodentium, or both. We found that only BALB/c mice coinfected with H. polygyrus and C. rodentium displayed a marked morbidity and mortality. The enhanced susceptibility to C. rodentium and intestinal injury of coinfected BALB/c mice were shown to be associated with a significant increase in helminth-driven Th2 responses, mucosally and systemically, and correlated with a significant downregulation of protective gamma interferon and with a dramatic upregulation of the proinflammatory tumor necrosis factor alpha response. In addition, C. rodentium-associated colonic pathology in coinfected BALB/c mice was significantly enhanced, whereas bacterial burden was increased and clearance was delayed. In contrast, coinfection in STAT 6 KO mice failed to promote C. rodentium infection or to induce a more severe intestinal inflammation and tissue injury, demonstrating a mechanism by which helminth influences the development of host protective immunity and susceptibility to bacterial infections. We conclude that H. polygyrus coinfection can promote C. rodentium-associated disease and colitis through a STAT 6-mediated immune mechanism.

[Phenomenon of apoptosis in the survival of enterobacteria in the parasite-host system]. / Fenomen apoptoza v vyzhivanii énterobakterii v sisteme parazit-khoziain.

Data on the apoptosis phenomenon with enterobacteria used as a model are presented. One of the mechanisms regulating the vital activity of eukaryotic cells is, together with cell proliferation and differentiation, the phenomenon known as "apoptosis". This physiological process of the eukaryotic cells death is used by many parasites in parasite--host relationships in different epitopes. The system known to trigger programmed cell death, is the surface receptor Fas, the receptor of tumor necrosis factor (TNF alpha) activated by the corresponding FasL ligand and TNF alpha, which further triggers the cascade mechanisms of the execution program. In various representatives of enterobateria different proteins serve as Fas ligand, viz. protein IpaB in Shigella flexneri, SipB activating converting enzyme IL-1 beta, identical to capsase-1, in Salmonella spp., YopP in Yersinia spp. Still the mechanism triggering apoptosis in Yersinia spp. has some original features. In Escherichia coli alpha-hemolysin is the factor triggering the suicidal program, the triggering mechanism being mediated by an increase in intracellular calcium ions.