Bactericidal Activity Of Compounds Research Articles

How to Assess in vitro Probiotic Viability and the Correct Use of Neutralizing Agents.

Probiotic viability is generally determined by quantifying its resistance to simulated gastric juice or to simulated intestinal fluid in in vitro tests, which measure microbial survival after given periods of contact. The use of a neutralizing agent is needed to avoid a carry-over of gastric or intestinal juice into the culture media of the subsequent analysis and to avoid any antimicrobial effect extended over the defined period of contact of the test. Neutralization of gastric juice and intestinal juice are of the utmost importance to present data accurately. Failing to do so determines a carry-over of bactericidal activity to the plates used for the enumeration, which further reduces the number of surviving cells. Examples of such incorrect adaptation of the test are available in literature. The purpose of this perspective stems from the discovery that many studies do not adhere to internationally recognized standards, e.g., EN 1040:2005 (European Committee for Standardization [ECS], 2005), to evaluate the basic, bactericidal activity of compounds, especially for the neutralization step.

Tuning the bactericidal repertoire and potency of quinoline-based amphiphiles for enhanced killing of pathogenic bacteria

The overwhelming challenge posed by drug-resistant pathogenic bacteria underscores the need for potent bactericidal agents, which exhibit broad-spectrum activity and a mode of action that does not favor development of resistance. In the present study we report the synthesis and bactericidal activity of structurally diverse quinoline-based amphiphiles, having a fluorescent head group and varying hydrophobic chain length. A structure-guided bactericidal efficacy and broad-spectrum activity of the amphiphiles was apparent in screening experiments against a panel of common pathogenic bacteria. Structure–function studies by fluorescence-based assays revealed that the charge and hydrophobic chain length of amphiphiles were key structural determinants that radically boosted the bactericidal activity. The most potent amphiphile N-methyl 8-dodecoxy quinolinium iodide (compound 6) exhibited a dose-dependent bactericidal activity on target pathogens and could even inhibit the growth of a presumptive methicillin-resistant S. aureus (MRSA) strain. Fluorescence-based mechanistic studies and transmission electron microscope (TEM) analysis indicated that the initial binding of compound 6 to bacteria probably involved electrostatic interaction, whereas the hydrophobic chain of the amphiphile promoted membrane insertion, which culminated in large scale membrane disruption and loss in cell viability. Although the bactericidal activity of compound 6 was independent of bacterial transmembrane potential, interaction of the amphiphile with pathogenic bacteria resulted in rapid dissipation of membrane potential. Interestingly, compound 6 displayed high antimicrobial selectivity and did not affect the viability of human HT-29 cells. It is envisaged that the therapeutic regime of the bactericidal scaffold of compound 6 can be further expanded by rational structural design for generating potent bactericidal agents.

Involvement of cytoplasmic membrane damage in the copper (II)-dependent cytotoxicity of a novel naturally occurring tripyrrole

In the presence of a nonlethal concentration of Cu(II), washed Escherichia coli ATCC8739 cells were killed by a novel tripyrrole 1, isolated as a red pigment from the Serratia sp. Cell killing was accompanied by a depletion in the potassium pools of the cells due to the damage to the cytoplasmic membrane, without any detectable DNA damage as revealed by the transformed plasmid DNA and phage induction assay. This revealed that the bactericidal activity of compound 1 in the presence of Cu(II) results from membrane damage. Induction of endogenous catalase in the E. coli cells increased their resistance against the combination of compound 1 and Cu(II). Although compound 1 alone generated large amount of reactive oxygen species (ROS), it did not show any cell killing against E. coli in the absence of Cu(II). The Cu(II)-dependent bactericidal activity of compound 1 was suppressed by ethylenediaminetetraacetate, bathocuproine, catalase and superoxide disumutase (SOD), but not by dimethyl sulfoxide. These findings suggest that recycling redox reactions between Cu(II) and Cu(I), involving compound 1 and hydrogen peroxide on the cell surface, must be important in the mechanism of the killing. Compound 1 alone showed selective bactericidal activity against the gram positive bacterium, Bacillus cereus ATCC 6630, possibly due to its differential cellular transport.

Antibacterial Characteristics of N-Alkyl-2-alkylthiopyridinium and N-Alkyl-4-alkylthiopyridinium Salts.

N-Alkyl-2-alkylthiopyridinium (2TPX-n : X=I or Br, n=6-18) and N-alkyl-4-alkylthiopyridinium salts (4TPX-n), which have an electron-releasing group on the pyridine ring, were synthesized. Both 2TPBr-12 and 4TPBr-12 showed a wide and potent bactericidal spectrum of activity against Gram-negative bacteria (9 strains) and Gram-positive bacteria (3 strains), compared with N-dodecylpyridinium iodide (P-12) which has no substituents. The activity of these new compounds was not correlated with the hydrophobicity of the bacterial cell surface. This suggests that the bactericidal mechanism of 2TPBr-12 and 4TPBr-12 is different from that of P-12. The bactericidal and bacteriostatic activity of the new compounds against Escherichia coli K12 W3110 was closely influenced by their alkyl chain length. Since they have two hydrophobic alkyl chains in their structure, it seems that hydrophobic association between the molecule of 2TPX-n or 4TPX-n and medium components in the minimum inhibitory concentration measurement system caused the reduction in their apparent concentration. The bactericidal activity of these compounds was dependent on their bacterioclastic activity, and less dependent on their hydrophobicity (RM).