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.

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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.

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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

Mechanism of cellular membrane damage induced by melittin and mastoparan.

COVID-19 is a newly discovered infectious disease caused by the novel coronavirus The COVID-19 pandemic started at the end of December 2019 in Wuhan, China and spread rapidly across the world, especially in North and South America or Europe The number of infected cases in the developed countries in North America and Europe or South America is extremely high, whereas its number in the developing countries of Africa or Southeast Asia is not so high;therefore, the COVID-19 is different from the usual infectious disease outbreaks This article introduces the epidemiology of COVID-19, comparing with other historical infectious disease outbreaks

Epidemiology of the Novel Coronavirus Disease 2019 (COVID-19) and Several Remarkable Pandemics

The first recognized outbreaks of hemorrhagic colitis occurred in 1982 in the United State and its etiologic agent was identified to be Escherichia coli O157 : H7, a serotype not previously associated with diseases in humans. In Japan, isolates of the serotype O157 : H7 from contaminated drinking water were first implicated in an outbreak occurred in 1990 in a kindergarten of the Saitama Prefecture, and at least other 12 such outbreaks have been recorded in 1993-1995. In the year 1996, unprecedentedly large outbreaks and many sporadic cases of disease caused by E. coli O157 : H7 occurred in various parts of Japan, affecting more than 9000 people in total (11 deaths). In most cases, however, the ultimate source of the infection could not be traced. Although many different serotypes of E. coli, which are collectively referred to as enterohemorrhagic E. coli (EHEC), were found to cause bloody diarrhea, the serotype O157 : H7 has been recognized worldwide as the pathogen associated most frequently with serious complications known as hemolytic colitis and hemolytic uremic syndrome. E. coli O157 : H7 is characteristic of a low infectious dose, on the order of a few hundred organisms, which contributes to the spread of the infection in outbreak situations. Cattle are considered to be the major reservoir of EHEC including O157 : H7. EHEC strains produce at least two immunologically distinct cytotoxins that closely resemble the Shiga toxin produced by the Shigella dysenteriae type 1 strains. These toxins (called Shiga-like toxins or Vero toxins) appear to be responsible for causing many pathological effects associated with EHEC infections. However, how the toxins move from the intestinal tract lumen to the sites where they damage the kidney remains to be evaluated. Moreover, there are some doubts about the value of antibiotic therapy in such infections because of the observation that some antibiotics can increase the toxin expression in vitro and because of the concern that EHEC which are lysing due to their actions in the gastrointestinal tract lumen may actually release more toxin than do intact bacterial cells. Unique biochemical characteristics of E. coli O157 : H7-it ferments sorbitol very slowly and usually does not make β-glucuronidase- are used to differentiate this strain from other enteric E. coli strains. Alternative methods based on the detection of the toxins themselves by enzyme immunoassay are employed in parallel. This review describes the current understanding of the infectious disease caused by E. coli O157 : H7, with an emphasis on the main diagnostic tests and epidemiology for this serotype and the role of the toxins in pathogenesis.

Enterohemorrhagic Escherichia coli O157: H7 infection

Vibrio mimicus (Vm) haemagglutinins (HAs), such as an extracellular HA/protease (Vm-HA/protease) and a major outer membrane protein-HA (Vm-OMPHA), have been recognized as the putative adherence factors for the bacterium. However, the mechanism by which HAs coordinate the adherence function of the bacterium remains as yet unknown. We report herein the positive interaction between Vm-HA/protease and Vm-OMPHA resulting in significant enhancement of the haemagglutinating ability. In this interaction, no cleaved polypeptide was detected; however, limited proteolysis of Vm-OMPHA was confirmed by SDS-PAGE. The proteolytic activation of the native cell-associated Vm-OMPHA by limited proteolysis was also demonstrated in several V. mimicus strains. Proteolytic activation of OMPHA was also achieved with various proteases from bacterial and eukaryotic sources. These findings may indicate a novel coordination of V. mimicus HAs in the adherence of the bacterium.

Proteolytic activation of Vibrio mimicus (Vm) major outer membrane protein haemagglutinin (HA) with Vm-HA/protease: Implication for understanding bacterial adherence.

Vibrio mimicus, a human pathogen that causes gastroenteritis, produces an enterotoxic hemolysin as a virulence factor. The hemolysin is secreted extracellularly as an inactive protoxin and converted to a mature toxin through removal of the N-terminal propeptide, which comprises 151 amino acid residues. In this study, a novel protease having the trypsin-like substrate specificity was purified from the bacterial culture supernatant. The N-terminal amino acid sequence of the purified protein was identical with putative trypsin VMD27150 of V. mimicus strain VM573. The purified protease was found to cause maturation of the protoxin by cleavage of the Arg(151)-Ser(152) bond. Deletion of the protease gene resulted in increased amounts of the protoxin in the culture supernatant. In addition, expression of the hemolysin and protease genes was detected during the logarithmic growth phase. These findings indicate that the protease purified may mediate maturation of the hemolysin.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/1348-0421.12177

Sumio Shinoda

Papers

Mechanism of cellular membrane damage induced by melittin and mastoparan.

Epidemiology of the Novel Coronavirus Disease 2019 (COVID-19) and Several Remarkable Pandemics

Enterohemorrhagic Escherichia coli O157: H7 infection

Proteolytic activation of Vibrio mimicus (Vm) major outer membrane protein haemagglutinin (HA) with Vm-HA/protease: Implication for understanding bacterial adherence.

A novel extracellular protease of Vibrio mimicus that mediates maturation of an endogenous hemolysin