The process of the attachment and growth of organisms on artificial solid surfaces is called biofouling. Biofouling organisms commonly undergo successive changes before a stable community is established. Microfouling organisms composed of bacteria, microalgae, and protozoa together with their exudates constitute the biofilm. Microfouling leads to macrofouling, which is the growth of larger fouling organisms. This problem has been recognized from decades ago; however, a long lasting and environmentally friendly antifouling strategy still eludes us. Among the prevailing preventive strategies, antifouling coatings based on organometallic or inorganic toxic species are used to protect ships and offshore platforms, while components of cooling water systems are protected by injecting biocides into the water column. A comprehensive account of the evolution of the biofouling community, factors controlling its formation, expenses incurred, and common antifouling strategies followed with their merits and demerits are described in this review.
The bactericidal activity of bis-quaternary ammonium compounds (bis-QACs) such as 4, 4'-(1, 6-hexamethylenedithio) bis (1-octylpyridinium bromide) (4DTBP-6, 8), which possess two quaternary ammonium cations in the molecule, is stronger than that of mono-QAC possessing one ammonium cation in the molecule. It is also reported that the bactericidal action of bis- QACs is less influenced by the molecular hydrophobicity of the drug or environmental conditions such as temperature or pH than that of mono-QAC. In order to clarify the mode of bactericidal action of a bis-QAC, 4DTBP-6, 8, against Escherichia coli, its bactericidal activity was kinetically elucidated compared with that of a mono-QAC, N-octylpyridinium bromide (P- 8). Though there was little difference in the dilution coefficient (n) of 4DTBP-6, 8 and P-8, the minimum effective concentration for the bactericidal action of 4DTBP-6, 8 was different from that of P-8. The rate constant (k) of the bactericidal action of 4DTBP-6, 8 was little influenced by the treatment temperature and the growth temperatures, and the Arrhenius plots of the k values showed a linearity. The apparent activation energy (Ea) for the bactericidal action of 4DTBP-6, 8 was 15.6kJ/mol. On the other hand, the k values of P-8 were extremely influenced by the treatment and growth temperatures, and the Arrhenius plots of the k values gave a broken line. The calculated Ea value was 99.8kJ/mol at a low temperature (10-30°C) and 40.6kJ /mol at a high temperature (30-40°C) Judging from these findings, it is clear that the mechanism of bactericidal action of bis-QAC is different from that of mono-QAC.
Phenylene-bis-quaternary ammonium compounds (Ph-bis-QACs), 4, 4'-(p-xylylenedithio) bis (1-alkylpyridinium iodide) s, N, N'-p-phenylenebis (1-alkyl-4-carbamoylpyridinium bromide) s and 4, 4'-(terephthaloylamino) bis (1-alkylpyridinium bromide) s composed of two pyridinium salt groups linked by a p-phenylene spacer chain were evaluated for their antimicrobial characteristics. We also compared the activities of these compounds with those of Methylene-bisquaternary ammonium compounds (M-bis-QACs), 4, 4% (1, 6-hexamethylenedithio) bis (1- alkylpyridinium iodide) s, N, N'-hexamethylenebis (4-carbamoyl-1-alkylpyridinium iodide) s and 4, 4% (tetramethylenedicarbonyldiamino) bis (1-alkylpyridinium iodide) s connected by a methylene spacer chain, and investigated the structure-activity relationship in a bis-QAC. Three Ph-bis-QACs exhibited a high and constant bactericidal activity with a carbon number from n = 8 to n =18, and a wide-ranging and effective antimicrobial activity against both bacteria and fungi. The antibacterial activities of Ph-bis-QACs were higher than those of M-bis-QACs by converting the methylene spacer chain of M-bis-QACs to a p-phenylene spacer chain. Moreover, while the activities of M-bis-QACs were influenced by the electron density of ammonium nitrogen, the activities of Ph-bis-QACs were not dependent on that. Therefore, these results suggested that the antibacterial activity of a bis-quaternary ammonium compound (bis- QAC) was strengthened more by decreasing the number of rotation axes in the spacer chain rather than changing the electron density of ammonium nitrogen and by increasing the rigid property of molecule structure, and that the steric structure of a bis-QAC is a significant factor influencing the antimicrobial activity of a bis-QAC.
The activities of three new quinolone compounds against vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) and their synergism with several commercially available antibiotics were investigated. Of the three novel new quinolone compounds tested, compound (1) was the most active against VRE and MRSA. Partial synergism was documented between compound (1) and the commercially available antibiotics such as ampicilin (ABPC), gentamicin (GM), minomycin (MINO), fosfomycin (FOM) and vancomycin hydrochloride (VCM) except in the case of ABPC and VCM against MRSA. Timekill analysis for compound (1) and the commercially available antibiotics such as ABPC, GM, MINO, FOM and VCM was performed by using one strain of VRE and one of MRSA. With the increase of the concentration of the added compound (1), the survival bacterial numbers decreased gradually. The above mentioned results suggested that compound (1) could reduce the daily administration dose of the commercially available antibiotics for the cure of nosocomial infection with its partial synergistic effect, and would have the possibility of reducing the occurrence of the nosocomial infections caused by VRE and/or MRSA.
A series of bis-quaternary ammonium compounds, 1, 4-dialky1-1, 4-dihydroxyethylpiperadinum diiodides (DAHP, bis-QACs), was immobilized on inorganic materials (glass beads and ferrite powder) using trimethoxysilane as a coupler to prepare the immobilized antimicrobial agents. GPA-n [with alkyl chain length (n) of 8 or 12 and a carrier of glass beads] and FPA-n [n =8, 12 and a carrier of ferrite] were developed. Their antimicrobial characteristics against Escherichia coil IFO 3301 or Staphylococcus aureus IFO 12732 were then investigated, and compared with those of [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC, mono-QACs) immobilized on inorganic materials. The antibacterial activity of the immobilized DAHP against E. coli IFO 3301 was 30 times higher than that of the immobilized TPOAC. GPA-12 and FPA-12 had a higher antimicrobial activity than GPA-8 and FPA-8, and exhibited wide spectra of antibacterial activity against six strains of gram-negative and five strains of gram-positive bacteria. The antibacterial activity was hardly influenced by environmentalpH but was significantly affected by temperature. A concomitant substance, peptone, had a distinct effect on the antibacterial activity of GPA-12 and FPA-12.
A new two-step enrichment method for the detection of Shigella sonnei in oysters and young corn was compared to the Bacteriological Analytical Manual (BAM) /Association of Analytical Communities (AOAC) method in a collaborative study.Twenty-one laboratories participated in the evaluation. Each laboratory used both methods for the detection of S. sonnei which had been inoculated into chilled or frozen oysters and young corn. The inoculum sizes for S. sonnet were 0, 14 and 140 cfu/25 g in oysters and 0, 18 and 180 cfu/25 g in young corn. Detection rates by PCR (invE and ipaH) and rates of S. sonnel colony appearance on three selective isolation agar media were compared. Statistical analyses were performed by the Welch test. The two methods gave detection rates of S. sonnei in 15/20 tests on oysters that were significantly different (p< 0.05). The new method showed superior detection rates for S. sonnei that had been inoculated into chilled and frozen oysters compared to the BAM / AOAC method with regard to the five detection items mentioned above. Both methods showed similar high detection rates for S. sonnel in chilled and frozen young corn. Based on these results, the new two-step enrichment method is recommended for the detection ofS. sonnei in food.