Determination of acid phosphatase and leucine amino peptidase activity as an identification method for pathogenic Naegleria fowleri

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Differentiation of Naegleria fowleri and other Naegleriae by polymerase chain reaction and hybridization methods

In order to detect and identify Naegleria fowleri strains an assay based on the Polymerase Chain Reaction (PCR) was evaluated. The amplified DNA fragments were detected by gel electrophoresis and ethidium bromide staining, followed by Southern blot hybridization with an internal digoxigenin-labeled probe. A set of primers (B1B2) which flank a 678-bp region within a virulence-associated gene, allowed for the highly specific identification of N. fowleri, since Naegleriae (N. lovaniensis, N. australiensis, N. gruberi, N. andersoni and N. jadini) and other Protozoa did not react. These primers did not detect amplification products from various organisms: Gram-positive bacteria, Gram-negative bacteria, algae, yeasts and human DNA. Whereas a second set of primers (A1A2), which flank a different sequence, detected various Naegleriae and Acanthamoebae strains. After 40 amplification cycles, the limit of detection was a single cell (cyst or trophozoite). Thus, the PCR appears to be a rapid and powerful tool for identification and detection of N. fowleri.

Biology of Naegleria spp

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Partial purification and characterization of Naegleria fowleri beta-glucosidase

Naegleria fowleri cells, grown axenically, contain high levels of beta-D-glucosidase which catalyzes the hydrolysis of 4-methylumbelliferyl-beta-D-glucopyranoside (4MUGlc) (Km, 0.9 mM), octyl-beta-D-glucoside (Km, 0.17 mM), and p-nitrophenyl-beta-D-glucopyranoside at relative rates of 1.00, 2.88, and 1.16, respectively (substrate concentration, 3.0 mM). When the amebae are subjected to freeze-thawing, sonication, and centrifugation (100,000 g, 1 h), 85% of the beta-glucosidase activity appears in the supernatant fraction. The beta-glucosidase was purified 40-fold (34% yield) using a combination of chromatographic steps involving DE-52 cellulose, concanavalin A-Sepharose, and hydroxylapatite followed by isoelectric focusing. The predominant soluble beta-D-galactosidase activity in the Naegleria extract copurifies with the beta-D-glucosidase; the two activities have the same isoelectric point (pI, 6.9), similar heat stabilities, are both inhibited by lactobionic acid (Ki, 0.40 mM), and exhibit optima at pH 4.5, indicating that they are probably the same enzyme. The Naegleria beta-D-glucosidase has an apparent molecular weight of 66,000, a Stokes radius of 25 A, and a sedimentation coefficient of 4.2S. The beta-glucosidase is not inhibited by conduritol beta-epoxide or galactosylsphingosine but is completely inhibited by 1.25 mM bromo conduritol beta-epoxide. The latter compound, when present in the growth medium, inhibits the growth of the organism and profoundly alters its ultrastructure, the main effect being the apparent inhibition of cytokinesis and the generation of multinucleate cells. The issue of the role of the beta-glucosidase in the metabolism of the ameba and its possible role in pathogenic mechanisms are discussed.

Identification of Naegleria fowleri in fresh isolates of environmental amoebae using a staphylococcal coagglutination technique

A coagglutination test using Staphylococcus aureus Cowan strain 1 sensitized with specific antiserum successfully identified Naegleria fowleri in axenic and monoxenic culture by detection of a heat stable antigen released into the culture medium during growth. Strong coagglutination, visible to the naked eye, occurred within 30 sec when the sensitized reagent was mixed on a slide with medium from N. fowleri cultures. N. lovaniensis gave a weak cross-reaction which developed over one min clearly distinguishable from that of N.fowleri.N.gruberi and N. australiensis gave no reaction. The technique is proposed as part of a rapid and economical scheme for detecting N. fowleri in environmental samples very soon after primary isolation, with distinct advantages over conventional methods. Further development of the technique to detect other Naegleria spp. and the early diagnosis of primary amoebic meningoencephalitis are suggested as future applications.

Rapid identification of thermophilic Naegleria, including Naegleria fowleri using API ZYM system

The suitability of the API ZYM system for identifying thermophilic Naegleria species, based on enzyme presence and activity, was investigated. Replicate testing on strains of N fowleri, N lovaniensis, and N australiensis cultured in a monoxenic and an axenic medium showed that the system could provide a rapid and reproducible means of identifying the species soon after primary isolation. No single enzyme was found specific for any one species, but considerable differences were found in the patterns of activity of acid phosphatase and leucine arylamidase. When these were compared the species could be differentiated. Use of the system in conjunction with a simple culture method is proposed as a readily available means of monitoring environmental and public bathing sites to prevent primary amoebic meningoencephalitis.