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Ameba-associated microorganisms and diagnosis of nosocomial pneumonia.

To elucidate the role of ameba-associated microorganisms (AAMs) as etiologic agents of pneumonia, we screened for Legionella spp., Parachlamydia acanthamoeba, Afipia sp., Bosea spp., Bradyrhizobium spp., Mesorhizobium amorphae, Rasbo bacterium, Azorhizobium caulinodans, Acanthamoeba polyphaga mimivirus, and conventional microorganisms in 210 pneumonia patients in intensive-care units by using culture, polymerase chain reaction, and serologic testing. These resulted in 59 diagnoses in 40 patients. AAMs and non-AAMs were implicated in 10.5% of the patients. The infectious agents were identified in 15 patients: Acanthamoeba polyphaga mimivirus, 8; Legionella pneumophila, 3; L. anisa, 1; Parachlamydia sp., 1; Bosea massiliensis, L. worsleiensis, L. quinlivanii, and L. rubrilucens, 1; and M. amorphae and R. bacterium, 1. A. polyphaga mimivirus was the fourth most common etiologic agent, with a higher seroprevalence than noted in healthy controls. This finding suggested its clinical relevance. Therefore, AAM might cause nosocomial pneumonia and should be suspected when conventional microbiologic results are negative.

Acanthamoeba↗

Hygienic evaluation of terraria inhabited by amphibians and reptiles: cryptosporidia, free-living amebas, salmonella.

Amphibians and reptiles are popular pet animals in about 90.000 Austrian households despite their frequently debated capacity to transmit diseases associated with animal keeping. We studied the epidemiological significance of the triangle animal keeper, exotic pet animal, and feed mice by investigating the frequency of three intestinal infestations, caused by cryptosporidia, opportunistic free-living amebas and salmonella, in amphibians and reptiles living in a public vivarium. In addition to recording the first known occurrence of Naegleria australiensis in Austria, and of this species and of Acanthamoeba polyphaga in the feces of reptiles worldwide, we also detected a strong association between Salmonella subspecies I and captive reptiles and between S. sub-species III and free-living lizards. Thus, animal keeper, the exotic animals kept, and the feed mice may constitute an epidemiological pool for the interchange of these infectious agents. This new epidemiological situation may cause an increase of some opportunistic and exotic diseases such as reptile-borne salmonellosis. Despite the perceived benefits of keeping exotic animals in a household, the general public and especially those who have an immunodeficiency must be made aware of the danger of infectious diseases possibly being spread by their pets.

Amoeba↗

Analysis of microtubule arms and bridges in mitotic and interphase amebae of Dictyostelium discoideum.

We have analyzed transparencies of electron micrographs from ultrathin longitudinal sections through mitotic spindles of undifferentiated amebae of Dictyostelium discoideum for the presence of arms on microtubules (MTs) and bridges between them. We used the technique of microdensitometer scanning and computer-based model matching by cross-correlation and autocorrelation. We also determined that spindle MTs are composed of 13 protofilaments. Although regularly arranged lateral appendages are not a universal feature of MTs in these cells, both cross-correlation and autocorrelation analysis revealed that bridges between a kinetochore MT and its neighbor, and between MTs in the zone of overlap of the central spindle were significantly arranged on a 12-dimer superlattice. In addition, the autocorrelation analysis indicated a slight match with the 12-dimer model for neighboring non-kinetochore MTs. Although electron micrographs revealed putative arms on cytoplasmic and astral MTs, as well as bridges between central spindle MTs outside the zone of overlap, their arrangement did not match any of the models tested. Bridges between non-kinetochore MTs in the half-spindles possibly serve to reinforce the spindle scaffold. Bridges between kinetochore MTs and their neighbors may contribute to the mechanical stability of kinetochore fibers or they may be involved in poleward movements of the chromosomes. In the zone of overlap of the central spindle, the occurrence of frequent and regularly spaced bridges is consistent with models predicting that a sliding mechanism operates between MTs of opposite polarity in this region of the spindle to produce its elongation.

Analog-Digital Conversion↗

Naegleria fowleri in chick embryos. Effects of embryo age and incubation temperature, and the infectivity of embryo-derived amebae for mice.

Chick embryos were infected with Naegleria fowleri which was initially isolated from an ultimately fatal human case. Following inoculation of equivalent numbers of amebae on the chorioallantoic membrane, younger embryos died earlier than older embryos infected at the same time. Incubation of infected embryos at 32 degrees C prolonged survival only slightly in comparison with those at 37 degrees C. N. fowleri maintained for more than 25 serial passages in chick embryos retained infectivity for mice and the ability to convert to the biflagellate form in vitro.

Age Factors↗

[Studies on the viability of pathogenic amebae of the genus Naegleria in water of different sources (author's transl)].

Water specimens taken from the public water supply (A), a swimming-pool (B), and an inland lake (C) were infected with pathogenic amebae of the genus Naegleria (strain TY/Richmond). The specimens were stored at various temperatures for different periods. The water was then filtered and examined for naegleriae by animal inoculation. The results summarized in table 1 indicate that pathogenic naegleriae are viable at least for some weeks in warm tap and natural waters. Water from indoor swimming-pools however, may be a less suitable medium for the viability of pathogenic naegleriae.

Amoeba↗

Experimental infections with pathogenic free-living amebae in laboratory primate hosts: I (A) A study on susceptibility to Naegleria fowleri.

Studies were conducted on 27 Old World monkeys to determine their susceptibility to pathogenic strains (HB-1 and C-66) of Naegleria fowleri by intranasal, intravenous, or intrathecal inoculation of trophozoites. No clinically detectable disease resulted from either intranasal or intravenous inoculation, but 11 of 18 monkeys inoculated intrathecally succumed to acutely fatal meningoencephalitis, while the other 7 survived with no obvious permanent brain damage. Pathogenicity of N. fowleri appeared to be influenced by the strain virulence, growth phase, and cultural condition of the amebae, as well as age, immune competence, and other as yet unknown host factors.

Administration, Intranasal↗

Mechanisms of hyphal tip growth: tube dwelling amebae revisited.

Over 100 years ago, Reinhardt suggested that hyphal tip growth is comparable to ameboid movement inside a tube; the apical cytoplasm being protruded like a pseudopodium with the wall assembled on its surface. There are increasing data from hyphae which are explicable by this model. Fungi produce pseudopodia-like structures and their cytoplasm contains all of the major components implicated in pseudopodium production in animal cells. Most of these components are concentrated in hyphal tips and tip growth involves actin, a major component of pseudopodia. Together these data indicate that the essence of the ameboid model is still tenable. However, detailed mechanisms of tip growth remain too poorly known to provide definitive proof of the model and the behavior of the trailing cytoplasm indicates differences which are probably a response to the walled lifestyle.

Amoeba↗