Bactericidal and Bacteriostatic Activity

The activity of antimicrobial drugs has also been described as being bacteriostatic or bactericidal, although this distinction depends on both the dmg concentration at the site 

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Nitrophenyl)benzofuran has shown high activity against Strophylococci, Pyocyaneae and E. coli test species of bacteria, while 3-(2-hydroxy-3,5-dichlorophenyl)-5,7-dichlorobenzofuran showed bactericidal and bacteriostatic activity against Staphylococcus aureus (67JPS1007). 

The Gellman laboratories later reported the chemical synthesis of a 17-mer based on the 12-helix forming trani-2-aminocyclopentanoic acids [64]. Charged amine fimctionalities in combination with neutral monomer units were incorporated into the oligomer to provide an amphiphilic secondary structure (Fig. 35). When tested for bactericidal and bacteriostatic activity against a vancomycin-resistant bacterial strain, this material exhibited activity similar to that of a known 23-mer... 

The PD of antimicrobial dmgs against microorganisms comprises three main aspects spectmm of activity, bactericidal and bacteriostatic activity, and the type of killing action (i.e., concentration-dependent, time-dependent, or co-dependent). Each of these is discussed below. Also described are the PD indices—minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)—and the mechanisms of action of antimicrobial drugs. 

The minimum inhibition concentrations for Dichlorophen in Table 43 enlighten the activity spectrum of the compound obviously there is a gap for Pseudo-monades. The efficacy against yeasts and fungi is, however, strong and equalized. The optimal pH for bactericidal activity is 5-6. At that pH Staphylococcus aureus is killed totally at 20°C within 10 min through 250 mg Dichlorophen/litre. However, in the presence of serum the bactericidal concentration of Dichlorophen is much higher (>1000 mg/litre). There is a big discrepancy between bactericidal and bacteriostatic activity the latter is especially distinctive at pH 8. 

Abbreviations of prominent use properties of the various classes of commercial surfactants are shown in Table 1. Antimicrobial activity includes germicidal, bactericidal, and bacteriostatic effects emolliency describes lubrication or a soft feel imparted to skin by surfactants a hair conditioner is a substantive surfactant appHed from aqueous solution to impart a lubricating or antistatic effect and opacifters are used to thicken hand-dishwashing products and cosmetic preparations to convey an appearance of high concentration and to retard solvent drainage from foam. 

Due to their excellent bactericidal and bacteriostatic properties and their general lack of serious side-effects (ref. 16) the B-lactam antibiotics still belong to the most favoured antibacterial drugs that are avaible. The research activities in the field of 6-lactam antibiotics including the chemical synthesis of 6-lactam antibiotics and related compounds, have increased up to now (ref. 16). 

A series of quatemized PUs were prepared by using different contents of the monomer A,A-bis(2-hydroxyethyl)isonicotinamide (BIN) dining the synthesis of PTMO-based PUs. The pyridine ring in BIN was then quatemized with different alkyl halides obtaining polymers with bactericidal activity against S. aureus and bacteriostatic activity against E. coli. 

Production of antagonistic compounds Several probiotics have been selected for their ability to produce compounds that are inhibitory towards the proliferation of (opportunistic) pathogens (Verschuere et al, 2000). In that way, they can be considered to be natural antibiotics. The bactericidal or bacteriostatic activity can mostly be ascribed to the production of bacteriocins, lysozymes, hydrogen peroxide, carbon dioxide or siderophores and/or the alteration in pH by the production of organic acids (Verschuere et al, 2000 Vine et al., 2006). TTie production of antagonistic compounds is a common trait for both marine and... 

Number and type of organism Bacteriostatic activity, ppm Bactericidal activity, log reduction... 

Dapsone, which was first proposed in 1941, possesses both bactericidal as weU as bacteriostatic activity with respect to Mycobacterium leprae and Mycobacterium tuberculosis. It is used to treat patients with herpetiform dermatitis. It is believed that the mechanism of its action consists of competitive inhibition of the enzyme dihydroprotease synthetase, which blocks synthesis of folic acid in microorganisms, allowing it to also be viewed as an analog of p-aminobenzoic acid. Synonyms of this drug are avosulfon, croysulfon and others. 

Methenamine (hexamethylenetetramine) is an aromatic acid that is hydrolyzed at an acid pH (<6) to liberate ammonia and the active alkylating agent formaldehyde, which denatures protein and is bactericidal. Methenamine is usually administered as a salt of either man-delic (Mandelamine) or hippuric Hiprex, Urex) acid. Not only do these acids acidify the urine, which is necessary to generate formaldehyde, but also, the resulting low urine pH is by itself bacteriostatic for some organisms. 

Isoniazid is bactericidal against actively growing M. tuberculosis and bacteriostatic against nonreplicating organisms. The minimal tuberculostatic inhibitory concentration (MIC) of isoniazid is 0.025 to 0.05 jig/mL. 

The bacteriostatic activity which is inhibition of growth and multiplication of bacteria and bactericidal activity, which is bacterial death, is induced by certain types of antibiotics. Cytotoxic action is selective for invading cancer cells and altering them without affecting the host cells. 

Trimethoprim, a trimethoxybenzylpyrimidine, selectively inhibits bacterial dihydrofolic acid reductase, which converts dihydrofolic acid to tetrahydrofolic acid, a step leading to the synthesis of purines and ultimately to DNA (Figure 46-2). Trimethoprim is about 50,000 times less efficient in inhibition of mammalian dihydrofolic acid reductase. Pyrimethamine, another benzylpyrimidine, selectively inhibits dihydrofolic acid reductase of protozoa compared with that of mammalian cells. As noted above, trimethoprim or pyrimethamine in combination with a sulfonamide blocks sequential steps in folate synthesis, resulting in marked enhancement (synergism) of the activity of both drugs. The combination often is bactericidal, compared with the bacteriostatic activity of a sulfonamide alone. 

Antibacterial agents may be classified as bacteriostatic or bactericidal (Table 51-3). For agents that are primarily bacteriostatic, inhibitory drug concentrations are much lower than bactericidal drug concentrations. In general, cell wall-active agents are bactericidal, and drugs that inhibit protein synthesis are bacteriostatic. 

Antimicrobial activity benzyl alcohol is bacteriostatic and is used as an antimicrobial preservative against Gram-positive bacteria, molds, fungi, and yeasts, although it possesses only modest bactericidal properties. Optimum activity occurs at pH below 5 little activity is shown above pH 8. Antimicrobial activity is reduced in the presence of nonionic surfactants, such as polysorbate 80. However, the reduction in activity is less than is the case with either hydroxybenzo-ate esters or quaternary ammonium compounds. The activity of benzyl alcohol may also be reduced by incompatibilities with some packaging materials, particularly polyethylene see Section 12. 

Dimethyl sulfoxide has been shown to have bactericidal, bacteriostatic, and fungistatic activity, although the concentration required is dependent on the organism present. 

Tetracyclines bind to the 305 ribosomal subunit and interfere with bacterial protein synthesis. They are bacteriostatic at normal therapeutic concentrations, but bactericidal at high concentrations. They enter bacteria by passive diffusion and an active carrier-mediated process. Mammalian cells do not possess the tetracycline transport mechanism. The tetracyclines are most active at acidic pH, which is of benefit in the treatment of abscesses. 

Certain strains of bacteria are resistant to the lytic properties of penicillins but remain. su.sccptible to their growth-inhibiting effects. Thus, the action of the antibiotic has been converted from bactericidal to bacteriostatic. This mechanism of resistance is termed tolerance and apparently results from impaired autolysin activity in the bacterium. 

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