Response of Neisseria gonorrhoeae to Bdellovibrio species.

Bdellovibrio species are small, highly motile bacteria that are predators upon other bacteria in nature. Bdellovibrios attach to, penetrate, replicate within, and destroy prey that share the general characteristic of gram negativity. The lipopolysaccharide moiety of the cell membrane of target microorganisms appears to contain the principal receptor site for bdellovibrio attachment. Since gonococci also contain lipopolysaccharide that is similar in many respects to that contained within gram-negative rods, studies were conducted to determine the extent of gonococcal interaction with a variety of bdellovibrio species. Despite transient attachment, penetration of gonococci by bdellovibrios never occurred. Failure of bdellovibrio parasitization was unrelated to gonococcal species, colony type, piliation, penicillin susceptibility, or virulence as influenced by passage in embryonated eggs. In experiments involving mixtures of gonococci and more typical gram-negative bacillary prey, the latter were always attacked by bdellovibrios, whereas the former were ignored. Despite evidence for similarities between gonococcal and gram-negative bacillary lipopolysaccharides, resemblances do not extend to the point where gonococci are susceptible to bdellovibrio parasitization.     

Predator-prey model with disease infection in both populations

Chin-Kuei Hsiao Department of Applied Mathematics, National Chung Hsing University, Taichung, Taiwan Email: hsieh{at}mail.cmu.edu.tw Received on October 15, 2007. Revised on June 22, 2008. Accepted on July 2, 2008. A predator–prey model with disease infection in both populationsis proposed to account for the possibility of a contagious diseasecrossing species barrier from prey to predator. We obtain severalthreshold parameters from local analysis of various equilibriaof the proposed system as well as coupled conditions on thesethreshold parameters which determine the stability of theseequilibria. One of the coupled conditions, in the form of anecological threshold number for the predator–prey ecosystem,always determines the coexistence of predators and prey. Theother condition, in the form of a disease basic reproductionnumber, dictates whether the disease will become endemic inthe ecosystem. Under one combination of these coupled conditions,a highly infectious disease could drive the predators to extinctionwhen predators and prey would have coexisted without the disease.For another combination of the conditions, the predation ofthe more vulnerable infected prey could cause the disease tobe eradicated in the ecosystem, in some case even approachinga disease-free periodic solution, when the disease would haveotherwise remained endemic in the prey population in the absenceof predation. This indicates that the presence of disease inboth predators and prey could either promote or impair coexistence,and its precise impact needs to be explored specifically ineach particular situation. By considering disease infectionin both populations, our model also yields more complex dynamics,allowing for the possibility of bistability and periodic oscillation,in either disease-free or endemic states, in the ecosystem forwhich the conditions are obtained analytically and with thehelp of numerical simulations.     

Early exposure to odors changes later visual prey preferences in cuttlefish

Developmental studies have shown that environmental stimulation received by a developing sensory system can alter the developmental outcome of both that sensory system and other aspects of the nervous system. We investigated the ecologically relevant question of whether prior exposure to prey early in development within one sensory modality could influence later prey choice within a different sensory modality. Cuttlefish are visual predators; they can detect prey odors but attacks on prey cannot be elicited without visual stimulation. Cuttlefish eggs were exposed to the odor of shrimp (preferred prey), crabs (non-preferred prey), mollusks (non-prey), or a seawater control (no prey). Seven days after hatching, prey preferences were tested with a visual choice test between crabs and shrimp. Hatchlings exposed to crabs odors and the seawater control were significantly more likely to attack shrimp. Hatchlings exposed to mollusk odors showed no visual prey preference, while those exposed to shrimp preferentially attacked crabs. These results demonstrate a complex relationship between an early sensory exposure and later prey preference     

Non-lethal effects of predators on body growth and health state of juvenile lizards, Psammdromus algirus

Predation risk does not necessarily increase predation rates because prey may be able to behave differentially to cope with higher predation risk. However, antipredatory behaviors may be costly, leading to negative, although non-lethal, effects of predators on prey. We examined in outdoor enclosures whether an experimental increase in predation pressure, which did not increase direct mortality, but forced individuals to increase antipredatory behaviors, may have significant non-lethal effects on body growth and health state of juvenile lizards, Psammodromus algirus. Simulated persistent predator attacks resulted in slower rates of body size growth and body mass gain of juvenile lizards, which may greatly affect their future survival. However, juvenile lizards were able to maintain their initial body condition and immune response regardless of predation risk level. Moreover, our data suggested that experience of lizards with their home range “environment” might allow them to compensate the negative effects of temporal high predation risk on body condition when predation risk subsequently decreased. Finally, juvenile lizards with greater immune responses showed smaller increments in body size, but larger increments in body mass and body condition, at the end of the control treatment. In contrast, there was no relationship between immunity and growth after the experimental treatment.     

Keeping it together: absence of genetic variation and DNA incorporation by the predatory bacteria Micavibrio aeruginosavorus and Bdellovibrio bacteriovorus during predation

The use of predatory bacteria as a potential live therapeutic to control human infection is gaining increased attention. Earlier work with Micavibrio spp. and Bdellovibrio spp. has demonstrated the ability of these predators to control drug-resistant Gram-negative pathogens, Tier-1 select agents and biofilms. Additional studies also confirmed that introducing high doses of the predators into animals does not negatively impact animal well-being and might assist in reducing bacterial burden in vivo. The survival of predators requires extreme proximity to the prey cell, which might bring about horizontal transfer of genetic material, such as genes encoding for pathogenic genetic islands that would indirectly facilitate the spread of genetic material to other organisms. In this study, we examined the genetic makeup of several lab isolates of the predators Bdellovibriobacteriovorus and Micavibrioaeruginosavorus that were cultured repeatedly and stored over a course of 13 years. We also conducted controlled experiments in which the predators were sequentially co-cultured on Klebsiella pneumoniae followed by genetic analysis of the predator. In both cases, we saw little genetic variation and no evidence of horizontally transferred chromosomal DNA from the prey during predator–prey interaction. Culturing the predators repeatedly did not cause any change in predation efficacy.     

Impacts of Wolbachia infection on predator prey relationships: evaluating survival and horizontal transfer between wMelPop infected Aedes aegypti and its predators

The wMelPop strain of Wolbachia is currently being investigated for its potential use as a biological control agent to reduce the ability of Aedes aegypti (L.) mosquitoes to transmit dengue viruses. The survival of a potential wMelPop infected Ae. aegypti strain for field release is important as a higher susceptibility to predation in the wMelPop strain could result in difficulties in achieving fixation. We investigated immature and adult survival as a function of susceptibility to predation by six naturally occurring predator species; cyclopoid copepods, fish, predatory Toxorhynchites mosquito larvae and a salticid jumping spider. The trials indicated that wMelPop infected and uninfected Ae. aegypti larvae and adults were equally susceptible to predation to all six tested predators. In addition to evaluating any potential fitness costs to the infected host, we were unable to demonstrate horizontal transfer of wMelPop via consumption of infected Ae. aegypti larvae to the above predators. That susceptibility to predation was consistent across mosquito life stage, predator species and experimental venue is strong evidence that despite the neurotrophic and extensive nature of wMelPop infection, behavioral changes are not occurring, or at least not a determining factor in survival when exposed to a predator. Based on our results and the ecology of Wolbachia and mosquito predators, horizontal transfer of wMelPop from Ae. aegypti into naturally occurring predators is not cause for concern.     

The stability of internal equilibria in predator-prey models with breeding suppression

We present two models that represent the suppression of breedingby prey in response to short-term increases in predation pressure.For both of these models, we have been able to produce analyticconditions for the local stability of the interior steady state,in terms of the values of combinations of these parameters.Although our models are as simple as possible to capture theeffect of breeding suppression, the expressions for local stability,even in their simplest form, are complex. Thus, we come to theimportant conclusion that there is no simple and general rulefor the effect of the behaviours described here (anti-predatorybreeding suppression and prey switching by predators) on thestability of population dynamics. Rather, effects will be systemspecific. However, we hope that the results and methodologicalframework outlined here will provide a useful tool for othersto investigate the consequences for particular real systems.     

Survival of Aedes aegypti (Diptera: Culicidae) eggs in surface and subterranean breeding sites during the northern Queensland dry season

The effect of a protracted dry season on the viability of Ae. aegypti (L.) eggs was examined in Townsville, northern Queensland, Australia. Eggs were placed in several different surface and subterranean larval habitats; and after four dry season months, only 1-10% of eggs remained viable in the surface and subterranean sites, respectively. Low humidity and predation by Periplaneta americana (L.) were the major causes of egg mortality in eggs in surface sites. P. americana was the most significant cause of egg predation in subterranean breeding sites but fungi, especially Penicillium citrinum Thom, covered egg batches within 15 d. Mycotoxins produced by the spores of P. citrinum are believed to have killed embryonating eggs. The high mortality rate of Ae. aegypti eggs during the dry season suggests that this survival strategy is unlikely to contribute to rapid and successful recolonization of surface sites at the end of the wet season.     

Pathogenicity of Mycoplasma lipofaciens strain ML64, isolated from an egg of a Northern Goshawk (Accipiter gentilis), for chicken embryos.

Some Mycoplasma species are well-known avian pathogens and are of importance in poultry breeder flocks due to their pathogenic potential for embryos. Mycoplasmas are regularly detected in birds of prey, and a strain of Mycoplasma lipofaciens that was isolated from an egg of a Northern Goshawk (Accipiter gentilis) was examined for its pathogenicity in specific pathogen free chicken embryos since birds of prey eggs were not available for this purpose. The strain was found to be pathogenic, causing a high mortality as well as dwarfing, curled toes and infiltrations of heterophils in the liver, kidney, intestine and chorioallantoic membrane.     

Importance of prenatal nutrition to the development of a precocial chick

The developmental maturity of hatchling birds varies greatly across the altricial-precocial continuum and these differences are related to the relative proportions of yolk and albumen in a species' egg. In general, the more precocial the chick the greater the proportion of yolk in its egg. Egg composition can also vary within species with unknown consequences for the developing embryo. The present research sought to determine the importance of egg composition to avian development by experimentally removing 1, 2, 4, 8, 12, or 16% of the albumen from eggs of domestic fowl (Gallus gallus). Experimental chicks were paired to control chicks whose eggs were matched on the basis of original mass and laid by the same female but no albumen was removed from their eggs prior to incubation. Decreased levels of albumen significantly decreased chick size at hatch. Experimental subjects, however, had similar growth to controls after 20 days of ad-lib access to food, although sex differences between pairs indicated that the growth of females may be affected differentially by albumen removal. Righting responses were retarded in experimental subjects for the 2 and 4% albumen-removal groups. Egg composition can have important consequences for chick survival simply by influencing body size at hatch and it is suggested that the practice of using overall egg size as a measure of egg “quality” needs to be broadened by considering what is inside the egg as well. In addition, the unique opportunity presented by using an avian model to assess directly the specific influences of protein (albumen) and of fat (yolk) on growth and behavioral development is explored. © 1993 Wiley & sons. Inc.     

Oral ingestion of egg yolk immunoglobulin from hens immunized with an enterotoxigenic Escherichia coli strain prevents diarrhea in rabbits challenged with the same strain.

White Leghorn hens were immunized with enterotoxigenic Escherichia coli B16-4 with heat-labile enterotoxin and colonization factor antigen I in Freund's adjuvant. Specific antibodies were detected by an enzyme-linked immunosorbent assay in the serum after 8 days and in eggs after 10 days, with levels reaching peaks at 15 and 20 days after the first immunization, respectively. The protective effects of the egg yolk antibodies were tested in the rabbit reversible ileal tie model of diarrhea. Five control rabbits developed severe diarrhea within 72 h after inoculation with enterotoxigenic E. coli B16-4. Oral ingestion of egg yolks from immunized hens for 4 days prior to inoculation protected five rabbits from diarrhea after challenge with the same strain of E. coli. The rabbits showed no adverse effects from the ingestion of the egg yolks. Four rabbits fed control eggs were also afforded some protection in that three rabbits developed mild diarrhea and one rabbit remained entirely well. In vitro experiments showed that immunoglobulin from egg yolks interfered with the binding of E. coli to purified small bowel mucins; immunoglobulin from immunized hens reduced binding more than immunoglobulin from nonimmunized hens. These findings indicate that eggs from hens immunized with appropriate antigens have potential as a useful source of passive immunity.     

Lotka-Volterra equations with chemotaxis: walls, barriers and travelling waves

In this paper we consider a simple two species model for thegrowth of new blood vessels. The model is based upon the Lotka-Volterrasystem of predator and prey interaction, where we identify newlydeveloped capillary tips as the predator species and a chemoattractantwhich directs their motion as the prey. We extend the Lotka-Volterrasystem to include a one-dimensional spatial dependence, by allowingthe predators to migrate in a manner modelled on the phenomenonof chemotaxis. A feature of this model is its potential to supporttravelling wave solutions. We emphasize that in order to determinethe existence of such travelling waves it is essential thatthe global relationships of a number of phase plane featuresother than the equilibria be investigated.     

Interactions between Egg-eating Predator and Prey: The Effect of the Functional Response and of Age Structure

In this paper we analyse an age-structured predator-prey modelin which predators eat only very young prey. The model can beformulated as a system of three Volterra integral equationswith an implicitly defined non-linearity. An interpretationof the implicit relation is given. The linearized stabilityof the steady states is investigated. It turns out that concentrationof the predator on very young individuals is a stabilizing mechanism.Furthermore, it is seen that a compound parameter which is ameasure for the efficiency of the predator has a major influenceon the stability of the steady states. If the efficiency ofthe predator decreases the steady state can become unstableand oscillations will arise. Furthermore it is seen from themodel that the destabilizing effect of a juvenile period isstronger when it concerns the predator than when it concernsthe prey species. In an appendix it is shown that an egg-eatingpredator and an indiscriminately eating predator can coexistin a stable steady state while feeding on only one prey species.     

Association of Salmonella enterica serovar enteritidis yafD with resistance to chicken egg albumen

Salmonella enterica serovar Enteritidis is a major cause of food-borne diseases in industrialized countries. The incidence of S. enterica serovar Enteritidis infections has increased substantially in recent decades, and S. enterica serovar Enteritidis is now one of the leading serovars of Salmonella in the United States. A unique epidemiological characteristic of S. enterica serovar Enteritidis is its association with chicken shell eggs, since approximately 80% of all human gastrointestinal diseases can be traced to contaminated egg products. Eggs are contaminated when bacteria from reproductive tissues of infected hens are packaged into the eggs and persist inside the hostile egg albumen environment. Therefore, resistance to egg albumen is an important aspect in the transmission of S. enterica serovar Enteritidis. We identified a gene, yafD from S. enterica serovar Enteritidis, whose overexpression conferred upon S. enterica serovar Typhimurium enhanced resistance to egg albumen, while disruption of this gene in S. enterica serovar Enteritidis rendered the organism more susceptible to egg albumen. YafD is homologous to members of an exonuclease-endonuclease-phosphatase family, including some enzymes involved in DNA repair. Furthermore, we discovered that egg albumen has nuclease activities and uses both circular and linear DNA as substrates. We propose that YafD provides a survival advantage to S. enterica serovar Enteritidis in eggs by repairing DNA damage caused by egg albumen and that it may be one of the biologic determinants that contribute to the epidemiological association of S. enterica serovar Enteritidis with egg products.     

The production of eggs byEchinococcus multilocularis in the laboratory following in vivo and in vitro development

Adult worms ofEchinococcus multilocularis produced eggs in vitro following partial development in the definitive host for 20–21 days and maturation for 8 days in a monophasic or diphasic medium. The technique was shown to be reproducible with morphologically normal eggs produced in two separate experiments. The onset of egg production in vitro was identical to that in vivo although the number of eggs produced by each worm was less in vitro.Dedicated to Prof. J.D. Smyth, London     

Culex restuans (Diptera: Culicidae) oviposition behavior determined by larval habitat quality and quantity in southeastern Michigan

Oviposition is a critical stage in the mosquito lifecycle, and may determine population levels, distribution, biting behavior, and pathogen transmission. Knowledge of the oviposition behavior of Culex restuans Theobald has become particularly important with the emergence of West Nile virus (WNV) in North America. Laboratory and field studies have examined some factors that contribute to oviposition choice in Culex spp., but few studies have investigated responses to cues of future competition and breeding habitat availability in the field. We hypothesized that female Cx. restuans mosquitoes avoid laying eggs in habitats containing cues of larval competition, and that increased availability of larval habitat decreases egg density. To test these hypotheses, a series of field experiments were conducted in southeastern Michigan during summer 2002. We found that female mosquitoes prefer nutrient-enriched containers and decrease ovipositing in containers with conspecific larvae. In addition, greater habitat abundance decreased egg clutch density per container, although there was considerable aggregation of egg clutches. These results support our hypotheses and have potentially important implications for pathogen transmission by mosquitoes.     

Salmonella enteritidis colonization of the reproductive tract and forming and freshly laid eggs of chickens.

Salmonella enteritidis colonizes the tissues of the chicken ovary and oviduct, presumably contaminating eggs and thereby contributing to human outbreaks of salmonellosis. In this study, commercial adult laying hens were given an oral inoculation of 10(8) S. enteritidis organisms. Tissues from various organs, the intestines, and the reproductive tract, including freshly laid eggs, were collected daily for up to 40 days postinoculation (p.i.). Within 2 days p.i. S. enteritidis was detected by culture in pools of the spleen, liver, heart, and gallbladder tissues, in intestinal tissues of all infected birds, and in various sections of the ovary and oviduct. Detection of organisms by immunohistochemical staining was rare for most tissues in spite of their culture-positive status, suggesting a low level of tissue colonization. However, S. enteritidis could be detected by immunohistochemical staining in oviduct tissues associated with four forming eggs, indicating the possibility of a heavier colonization in the egg during its development. In two subsequent experiments, forming eggs taken from the oviduct with their associated tissue, were found to be culture positive for S. enteritidis at a rate of 27.1 and 31.4%, while freshly laid eggs in these experiments were culture positive at the rate of 0 and 0.6%. These observations suggest that while forming eggs are significantly colonized in the reproductive tract, factors within the eggs may control the pathogen before the eggs are laid. The data show that prior to egg deposition, forming eggs are subject to descending infections from colonized ovarian tissue, ascending infections from colonized vaginal and cloacal tissues, and lateral infections from colonized upper oviduct tissues. The data are consistent with an ascending infection of freshly laid eggs from the cloaca, as the incidence of positive eggs in experiments 1 and 3 coincided with heavily contaminated cloacal tissues (50.7 and 80%, respectively), while no positive eggs were detected in experiment 2 when cloacal colonization was low (8.3%). The data do not support the possibility of egg invasion by bacterial translocation from the peritoneal cavity.     

Intraguild predation among larval treehole mosquitoes, Aedes albopictus, Ae. aegypti, and Ae. triseriatus (Diptera: Culicidae), in laboratory microcosms.

We compared the tendency for 4th-instar larvae to prey on newly hatched larvae, and the vulnerability of those 1st instars to such predation for Aedes triseriatus (Say), Ae. aegypti (L.), and Ae. albopictus (Skuse), all container-breeding mosquitoes. The latter 2 species were introduced to North America and are now sympatric with Ae. triseriatus, a native species in eastern North America. The experiment also enabled the assessment of species-specific influences of food supplements and spatial heterogeneity on predatory behavior. Ae. triseriatus was substantially more predatory and less susceptible to attack than the other 2 species. These differences were amplified in food-deprived and spatially simple conditions, indicating that Ae. triseriatus predatory behavior may have important retarding effects on the colonization of occupied treehole habitats by Ae. albopictus. Ae. aegypti and Ae. albopictus were similar in imposing little (Ae. aegypti) or almost no (Ae. albopictus) predation on 1st instars and in being susceptible to predation by Ae. triseriatus. The general lack of species-specific differences between Ae. aegypti and Ae. albopictus indicates that interspecific predation is not a likely explanation for the rapid displacement of Ae. aegypti by Ae. albopictus in domestic containers in the southeastern United States.     

Behavioral differences of invasive container-dwelling mosquitoes to a native predator

Aquatic prey show behavioral modifications in the presence of predation-risk cues that alleviate their risk from predation. Aedes albopictus (Skuse), Aedes japonicus (Theobald), and Culex pipiens L. are invasive mosquitoes in North America, and their larvae are prey for the native mosquito predator, Toxorhynchites rutilus (Coquillett). Ae. albopictus and Ae. japonicus are recent invaders, whereas Cx. pipiens has been in the United States for >100 yr. In the presence of predation-risk cues from Tx. rutilus larvae, Cx. pipiens larvae increased the time spent resting at the surface (least risky behavior) more than the other prey species. Ae. japonicus larvae increased resting at the surface of the containers more than Ae. albopictus larvae in the presence of predation-risk cues. Cx. pipiens larvae spent more time motionless at the surface even in the absence of predation-risk cues when compared with the other species, indicating that Cx. pipiens larvae are the least vulnerable prey. As compared with the other prey species, Ae. albopictus larvae exhibited more high-risk behaviors both in the presence and absence of predation-risk cues, indicating that they are the most vulnerable prey. Ae. albopictus is the superior competitor; however, predation by Tx. rutilus larvae may prevent competitive exclusion by Ae. albopictus and promote coexistence among the three prey species.