There is an urgent need in aquaculture to develop microbial control strategies, since disease outbreaks are recognized as important constraints to aquaculture production and trade and since the development of antibiotic resistance has become a matter of growing concern. One of the alternatives to antimicrobials in disease control could be the use of probiotic bacteria as microbial control agents. This review describes the state of the art of probiotic research in the culture of fish, crustaceans, mollusks, and live food, with an evaluation of the results obtained so far. A new definition of probiotics, also applicable to aquatic environments, is proposed, and a detailed description is given of their possible modes of action, i.e., production of compounds that are inhibitory toward pathogens, competition with harmful microorganisms for nutrients and energy, competition with deleterious species for adhesion sites, enhancement of the immune response of the animal, improvement of water quality, and interaction with phytoplankton. A rationale is proposed for the multistep and multidisciplinary process required for the development of effective and safe probiotics for commercial application in aquaculture. Finally, directions for further research are discussed.

/pdf/probiotic-bacteria-as-biological-control-agents-in-4778jdx241.pdf

Probiotic Bacteria as Biological Control Agents in Aquaculture

Polyphasic taxonomy, a consensus approach to bacterial systematics.

Summary: Over the past decade, the genus Aeromonas has undergone a number of significant changes of practical importance to clinical microbiologists and scientists alike. In parallel with the molecular revolution in microbiology, several new species have been identified on a phylogenetic basis, and the genome of the type species, A. hydrophila ATCC 7966, has been sequenced. In addition to established disease associations, Aeromonas has been shown to be a significant cause of infections associated with natural disasters (hurricanes, tsunamis, and earthquakes) and has been linked to emerging or new illnesses, including near-drowning events, prostatitis, and hemolytic-uremic syndrome. Despite these achievements, issues still remain regarding the role that Aeromonas plays in bacterial gastroenteritis, the extent to which species identification should be attempted in the clinical laboratory, and laboratory reporting of test results from contaminated body sites containing aeromonads. This article provides an extensive review of these topics, in addition to others, such as taxonomic issues, microbial pathogenicity, and antimicrobial resistance markers.

The Genus Aeromonas: Taxonomy, Pathogenicity, and Infection

Summary: High-affinity iron acquisition is mediated by siderophore-dependent pathways in the majority of pathogenic and nonpathogenic bacteria and fungi. Considerable progress has been made in characterizing and understanding mechanisms of siderophore synthesis, secretion, iron scavenging, and siderophore-delivered iron uptake and its release. The regulation of siderophore pathways reveals multilayer networks at the transcriptional and posttranscriptional levels. Due to the key role of many siderophores during virulence, coevolution led to sophisticated strategies of siderophore neutralization by mammals and (re)utilization by bacterial pathogens. Surprisingly, hosts also developed essential siderophore-based iron delivery and cell conversion pathways, which are of interest for diagnostic and therapeutic studies. In the last decades, natural and synthetic compounds have gained attention as potential therapeutics for iron-dependent treatment of infections and further diseases. Promising results for pathogen inhibition were obtained with various siderophore-antibiotic conjugates acting as “Trojan horse” toxins and siderophore pathway inhibitors. In this article, general aspects of siderophore-mediated iron acquisition, recent findings regarding iron-related pathogen-host interactions, and current strategies for iron-dependent pathogen control will be reviewed. Further concepts including the inhibition of novel siderophore pathway targets are discussed.

/pdf/siderophore-based-iron-acquisition-and-pathogen-control-2r9qlb86av.pdf

Siderophore-Based Iron Acquisition and Pathogen Control

Carbon nanotubes are new members of carbon allotropes similar to fullerenes and graphite. Because of their unique electrical, mechanical, and thermal properties, carbon nanotubes are important for novel applications in the electronics, aerospace, and computer industries. Exposure to graphite and carbon materials has been associated with increased incidence of skin diseases, such as carbon fiber dermatitis, hyperkeratosis, and naevi. We investigated adverse effects of single-wall carbon nanotubes (SWCNT) using a cell culture of immortalized human epidermal keratinocytes (HaCaT). After 18 h of exposure of HaCaT to SWCNT, oxidative stress and cellular toxicity were indicated by formation of free radicals, accumulation of peroxidative products, antioxidant depletion, and loss of cell viability. Exposure to SWCNT also resulted in ultrastructural and morphological changes in cultured skin cells. These data indicate that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.

Exposure to Carbon Nanotube Material: Assessment of Nanotube Cytotoxicity using Human Keratinocyte Cells

Microbial metalloproteases and pathogenesis.

Under stress conditions, many species of bacteria enter into starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. Several human pathogenic bacteria have been reported to enter into the VBNC state under these conditions. The pathogenic VBNC bacteria cannot be grown using conventional culture media, although they continue to retain their viability and express their virulence. Though there have been debates on the VBNC concept in the past, several molecular studies have shown that not only can the VBNC state be induced under in vitro conditions but also that resuscitation from this state is possible under appropriate conditions. The most notable advance in resuscitating VBNC bacteria is the discovery of resuscitation-promoting factor (Rpf), which is a bacterial cytokines found in both Gram-positive and Gram-negative organisms. VBNC state is a survival strategy adopted by the bacteria, which has important implication in several fields, including environmental monitoring, food technology, and infectious disease management; and hence it is important to investigate the association of bacterial pathogens under VBNC state and the water/foodborne outbreaks. In this review, we describe various aspects of VBNC bacteria, which include their proteomic and genetic profiles under the VBNC state, conditions of resuscitation, methods of detection, antibiotic resistance, and observations on Rpf.

/pdf/current-perspectives-on-viable-but-non-culturable-vbnc-2pzp9lrq93.pdf

Current Perspectives on Viable but Non-Culturable (VBNC) Pathogenic Bacteria.

Seawater and organic material (live and/or dead matter deposited on any substratum submersed in seawater) were collected during the cool weather season from a coast of the Seto-Inland Sea, Japan, and analyzed to determine Vibrio parahaemolyticus densities and the occurrence of pathogenic strains, defined as those possessing tdh and/or trh genes by the polymerase chain reaction (PCR), using isolated DNA from enrichment culture of the samples. About 95% of the samples were positive for V. parahaemolyticus (with densities of 3 to >1400 cells per 100 ml water or 10 g organic samples) by the most-probable-number (MPN)-PCR technique with species-specific toxR primers, but only 40% were positive by the conventional MPN-culture technique (with densities ranging from 3 to 240 cells per 100 ml water or 10 g organics). Furthermore, the tdh and trh genes were positive in 55% and 20% of samples, respectively, by the MPN-PCR technique. No tdh and trh gene-positive strains were isolated by the conventional MPN-culture procedure. The difference in detection between the MPN-culture and the MPN-PCR techniques appeared to be significant and may be attributed to different detection sensitivities and other factors.

https://ousar.lib.okayama-u.ac.jp/files/public/0/7865/20160527180319820635/K002373.pdf

Environmental investigation of potentially pathogenic Vibrio parahaemolyticus in the Seto‐Inland Sea, Japan

A process monitoring/controlling system for the treatment of wastewater containing chromium(VI)

鉄 (イオン) はほとんどの生物の生存と増殖に不可欠な元素である。しかし, 宿主生体における鉄は大部分が結合型やヘム鉄として存在し, 細菌が自由に利用できる遊離鉄は極めて少ない。これは有害な活性酸素の生成防止と共に細菌感染症に対する非特異的生体防御機構の一つとなっている。それ故, 宿主生体中で増殖し得る病原菌は何らかの巧妙な鉄獲得系を保持している筈である。鉄欠乏下に発現する2つの鉄獲得系が明かにされている: 1) Fe3+に高親和性の輸送キレート剤, シデロフォア (siderophore, siderochrome とも呼ばれる) を産生し, トランスフェリンやラクトフェリンに結合している鉄を奪い取り, そのコンプレックスに特異的なレセプターを介して鉄を取り込む系; 2) トランスフェリン, ラクトフェリン, ヘムに結合している鉄をそれぞれに特異的なレセプターを介して直接利用する系。この能力は細菌の生体内増殖を可能にするので, 病原性 (強化) 因子の一つと考えられている。近年, 分子生物学的あるいは分子遺伝学的手法を用いて, これら鉄獲得系の発現調節機構や病原性強化における役割が個々の病原菌についてより詳細に解明されつつある。さらに, 鉄獲得に関与する遺伝子群と共に鉄獲得に直接関係のない病原因子遺伝子の発現も鉄欠乏に呼応して増加し, これに係わる統括的 (global) 調節因子の存在が明かにされた。病原菌の鉄獲得機構の解明は感染症防御のための新たな手段, 戦略を提供する可能性を秘めている。

Sumio Shinoda

Papers

Microbial metalloproteases and pathogenesis.

Current Perspectives on Viable but Non-Culturable (VBNC) Pathogenic Bacteria.

Environmental investigation of potentially pathogenic Vibrio parahaemolyticus in the Seto‐Inland Sea, Japan

A process monitoring/controlling system for the treatment of wastewater containing chromium(VI)

Iron uptake mechanisms of pathogenic bacteria