Salt Effects in Bacterial Growth : I. Preliminary Paper

New Evidence for the Role of Pituitary Adenylate Cyclase-Activating Polypeptide as an Antimicrobial Peptide in Teleost Fish

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed and conserved across species. We have previously shown that in teleost fish, PACAP not only possesses direct antimicrobial properties but also immunomodulatory effects against the bacterial pathogens Flavobacterium psychrophilum and Pseudomonas aeruginosa using in vitro and in vivo experiments. These previous results suggest PACAP can be used as an alternative to antibiotics to prevent and/or treat bacterial infections in the aquaculture industry. To accomplish this goal, more studies are needed to better understand the effect of PACAP on pathogens affecting fish in live infections. In the present study, the transcripts PACAP, PRP/PACAP, and VPAC2 receptor were examined in rainbow trout (Oncorhynchus mykiss) naturally infected with Yersinia ruckeri, which exhibited an increase in their expression in the spleen when compared to healthy fish. Synthetic Clarias gariepinus PACAP-38 has direct antimicrobial activity on Y. ruckeri and inhibits up to 60% of the bacterial growth when the peptide is at concentrations between 50 and 100 µM in TSB. The growth inhibition increased up to 90% in the presence of 12.5 µM of PACAP-38 when salt-free LB broth was used instead of TSB. It was also found to inhibit Y. ruckeri growth in a dose-dependent manner when the rainbow trout monocyte/macrophage-like cell line (RTS11) was pre-treated with lower concentrations of the peptide (0.02 and 0.1 µM) before going through infection. Differential gene expression was analyzed in this in vitro model. Overall, the results revealed new evidence to support the role of PACAP as an antimicrobial and immunomodulatory peptide treatment in teleosts.

Outer membrane protein N expressed in Gram-negative bacterial strain of Escherichia coli BL21 (DE3) Omp8 Rosetta strains under osmoregulation by salts, sugars, and pHs

This study presented the expression of the outer membrane protein N in E. coli BL21 (DE3) Omp8 Rosetta under its growth condition and by osmoregulation. The effects of osmotic stress caused by salts, sugars, or pH values on the survival of the target Gram-negative bacterial strain of E. coli BL21 (DE3) Omp8 Rosetta and OmpN expression remain unknown. Here, tryptone yeast extract with varied salts and concentrations was initially used to generate an LB broth medium. To show how salts and concentration affect bacterial growth, the optical density at 600 nm was measured. The findings supported the hypothesis that salts and concentrations control bacterial growth. Moreover, a Western blotting study revealed that OmpN overexpression was present in all tested salts after stimulation with both glucose and fructose after being treated individually with anti-OmpN and anti-histidine tag polyclonal antibodies on transferred nitrocellulose membrane containing crude OmpN. Following the presence of the plasmid pET21b(+)/ompN-BOR into E. coli BL21 (DE3) Omp8 Rosetta, which was expressed in the recombinant OmpN protein (BOR), OmpN expression was demonstrated for all monovalent cations as well as MgCl2. All of the tested salts, except for BaCl2, NaH2PO4, and KH2PO4, showed overexpression of recombinant BOR after Isopropyl β-D-1-thiogalactopyranoside (IPTG) induction. Using CH3COONa, both with and without IPTG induction, there was very little bacterial growth and no OmpN expression. With NaCl, a pH value of 7 was suitable for bacterial development, whereas KCl required a pH value of 8. According to this research, bacterial growth in addition to salts, sugars, and pH values influences how the OmpN protein is produced.

Understanding specific ion effects and the Hofmeister series

Specific ion effects (SIE), encompassing the Hofmeister Series, have been known for more than 130 years since Hofmeister and Lewith's foundational work. SIEs are ubiquitous and are observed across the medical, biological, chemical and industrial sciences. Nevertheless, no general predictive theory has yet been able to explain ion specificity across these fields; it remains impossible to predict when, how, and to what magnitude, a SIE will be observed. In part, this is due to the complexity of real systems in which ions, counterions, solvents and cosolutes all play varying roles, which give rise to anomalies and reversals in anticipated SIEs. Herein we review the historical explanations for SIE in water and the key ion properties that have been attributed to them. Systems where the Hofmeister series is perturbed or reversed are explored, as is the behaviour of ions at the liquid-vapour interface. We discuss SIEs in mixed electrolytes, nonaqueous solvents, and in highly concentrated electrolyte solutions - exciting frontiers in this field with particular relevance to biological and electrochemical applications. We conclude the perspective by summarising the challenges and opportunities facing this SIE research that highlight potential pathways towards a general predictive theory of SIE.

In vitro disinfection efficacy and clinical protective effects of common disinfectants against acute hepatopancreatic necrosis disease (AHPND)-causing Vibrio isolates in Pacific white shrimp Penaeus vannamei

Acute hepatopancreatic necrosis disease (AHPND) is one of the most significant bacterial diseases in global shrimp culture, causing severe economic losses. In the present study, we carried out in vitro antimicrobial tests to investigate the disinfection efficacy of 14 common disinfectants toward different AHPND-causing Vibrio spp., including eight isolates of V. parahaemolyticus, four isolates of V. campbellii, and one isolate of V. owensii. Polyhexamethylene biguanidine hydrochloride (PHMB) was revealed to possess the strongest inhibitory activity. Through analyzing and evaluating the results of antimicrobial tests and acute toxicity test, we selected PHMB and hydrogen peroxide (H₂O₂) for further clinical protection test. Clinical manifestations indicated that both PHMB (2 mg/L and 4 mg/L) and H₂O₂ (12 mg/L) could effectively protect juvenile Penaeus vannamei from the infection of V. parahaemolyticus isolate Vp362 at 10⁶ CFU/ml, and the survival rate was over 80%. When the bacterial concentration was reduced to 10⁵ CFU/ml, 10⁴ CFU/ml, and 10³ CFU/ml, the survival rate after treated by 1 mg/L PHMB was 64.44%, 93.33%, and 100%, respectively. According to the results, PHMB and H₂O₂ showed a lower toxicity while a better protection activity, particularly against a lower concentration of the pathogens. Therefore, these two disinfectants are proved to be promising disinfectants that can be applied to prevent and control AHPND in shrimp culture. Moreover, the methods of this study also provided valuable information for the prevention of other important bacterial diseases and suggested a reliable means for screening potential drugs in aquaculture.

The in-vitro antibacterial effects of organic salts, chemical disinfectants and antibiotics against pathogens of black disease in fairy shrimp of Thailand

The antibacterial effects of organic salts, chemical disinfectants and antibiotics were evaluated on cultures of Aeromonas hydrophila C03, Aeromonas sobria C26, A. sobria C29, Aeromonas caviae C24 and Acinetobacter sp. SH-94B, the pathogens that cause black disease found in fairy shrimps (Streptocephalus sirindhornae Sanoamuang et al. (2000) and Branchinella thailandensis Sanoamuang, Saengphan & Murugan) of Thailand. The minimal inhibitory concentrations (MICs) of organic salts (sodium chloride and potassium chloride) and antibiotics (oxytetracycline dihydrate, streptomycin sulphate, kanamycin monosulphate, chloramphenicol and ampicillin) were determined using the agar-dilution method. The effect of chemical disinfectants (sodium hypochlorite and chlorine dioxide) was evaluated by exposing bacteria to different concentrations of these chemicals for different periods of time. Interestingly, all strains were intrinsically resistant to 0.25-3% sodium chloride and potassium chloride. The effect of sodium hypochlorite was greater than that of chlorine dioxide, and 5-20 μg mL(-1) of sodium hypochlorite was sufficient to inhibit the growth of these bacteria, but the exposure time varied, depending on the bacterial species. Of the antibiotics tested, chloramphenicol and oxytetracycline dihydrate completely inhibited the selected strains. Chloramphenicol showed the highest antibacterial effect against all pathogenic species--the MIC and minimal bactericidal concentration (MBC) ranged from 0.8 to 3.1 μg mL(-1) from 3.1 to 6.25 μg mL(-1), respectively. To achieve control of black disease during cultivation of fairy shrimp, data derived from this study can be used as a basis for further toxicity tests in vivo.

STUDIES ON SALT ACTION : X. THE INFLUENCE OF ELECTROLYTES UPON THE VIABILITY AND ELECTROPHORETIC MIGRATION OF BACTERIUM COLI

1. The strain of Bacterium coli used in these experiments multiplies in distilled water at pH 6.0 and pH 8.0 and in Ringer-Locke solution at pH 6.0. Under all the other conditions studied the numbers decrease with the passage of time. 2. The electrophoretic charge of the cells is highest in distilled water at pH 6.0 and pH 8.0. Under all other conditions studied the velocity of migration is decreased, but the decrease is immediate and is not affected by more prolonged exposure. 3. A strongly acid solution (pH 2.0) causes a rapid death of the cells and a sharp decrease in electrophoretic charge, sometimes leading to complete reversal. 4. A strongly alkaline solution (pH 11.0) is almost as toxic as a strongly acid one, although in distilled water the organisms survive fairly well at this reaction. Electrophoretic charge, on the other hand, is only slightly reduced in such an alkaline medium. 5. In distilled water, reactions near the neutral point are about equally favorable to both viability and electrophoretic charge, pH 8.0 showing slightly greater multiplication and a slightly higher charge than pH 11.0. In the presence of salts, however, pH 8.0 is much less favorable to viability and somewhat more favorable to electrophoretic charge than is pH 6.0. 6. Sodium chloride solutions, in the concentrations studied, all proved somewhat toxic and all tended to depress electrophoretic charge. Very marked toxicity was, however, exhibited only in a concentration of .725 M strength or over and at pH 8.0, while electrophoretic migration velocity was only slightly decreased at a concentration of .0145 M strength. 7. Calcium chloride was more toxic than NaCl, showing very marked effects in .145 M strength at pH 8.0 and in 1.45 M strength at pH 6.0. It greatly depressed electrophoretic charge even in .0145 M concentration. 8. Ringer-Locke solution proved markedly stimulating to the growth of the bacteria at pH 6.0 while at pH 8.0 it was somewhat toxic, though less so than the solutions of pure salts. It depressed migration velocity at all pH values, being more effective than NaCl in this respect, but less effective than CaCl₂. 9. It would appear from these experiments that a balanced salt solution (Ringer-Locke's) may be distinctly favorable to bacterial viability in water at an optimum reaction while distinctly unfavorable in a slightly more alkaline solution. 10. Finally, while there is a certain parallelism between the influence of electrolytes upon viability and upon electrophoretic charge, the parallelism is not a close one and the two effects seem on the whole to follow entirely different laws.