Antimicrobial inoculum

To demonstrate that the mixture does not manifest antimicrobial activity, carry out the test as described previously up to the incubation step and add an inoculum of viable cells of the specified aerobic bacteria, anaerobic bacteria, and fungi. 

The criteria for evaluation of antimicrobial activity are given in Table 4 in teims of the log reduction in the number of viable microorganisms using as baseline the value obtained for the inoculum. No increase is dehned as not more than 0.5 log unit higher than the previous value obtained. 

The purpose of this example is to demonstrate the antimicrobial activity of the silver-based composition embodiments of the present invention on samples of beef flank steak inoculated on the exterior surface with a five strain cocktail of Salmonella species, or Escherichia coli 01 57 h7 at a high inoculum solution level (lxlO6 cfu/cm2) and separately at a low inoculum solution level (lxlO4 cfu/cm2) (cfu=colony forming unit). 

Irregular eyelid margins or function, irregular blinking, disturbed ocular surfece innervation, or abnormal tear film may compromise the epithelial surface. When an inoculum of sufficient quantity invades the conjimctiva, over-colonization by the infectious organism may result either from overwhelming normal flora or because the antimicrobial capabilities of the tear constituents have been exceeded. 

MIC is measured using standardized methods and a standardized inoculum size. In clinical cases, there may be sites of infection with only a few bacteria and other sites with many. Some bacteria grow and multiply very slowly at infection sites, while the laboratory incubator and optimal conditions encourage rapid growth and multiplication. Rapidly multiplying bacteria imder optimal test conditions are very sensitive to antimicrobial treatment. 

Fig. 11.2 Survival of Enterococcus faecalis exposed to a fluoroquinolone for 4 h at 37°C. Three initial bacterial concentrations were studied, 107cfu/ml ( ) 10 ctli/ml (A) and 105 cfu/ml (O). This clearly demonstrates a paradoxical effect (increasing antimicrobial concentrations past a critical level reveal decreased killing), and the effects of increased inoculum densities on subsequent killing (courtesy of Dr Z. Hashmi).

Antimicrobial activity was tested on standard strains of Enterococcus faecalis 4224, Staphylococcus aureus 3953 and 4223, Pseudomonas aeruginosa 3955 and Escherichia coli 3954, 3988 and 4225 (Czech Collection of Microorganisms, Brno). Microtiter wells containing serial twofold dilutions of samples are incolulated with a standard inoculum of the bacterium in question, the plates are incubated overnight, and the wells are then examined for the presence of bacterial growth. The lowest of each sample dilution series that prevents bacterial growth is considered to be the minimum inhibitory concentration (MIC) of the sample. 

Overnight culture of S. aureus was diluted 100-fold in fresh MH II Broth and used as inoculums for the antimicrobial screen. Working stocks (SOX) of LOPAC compounds and standard antibiotics were prepared in DMSO. Each well of the 96-well multiwell plate contained 245 pL of the inoculums and 5 pL of the 50X working stock. The multiwell plate was incubated at 37°C for 5 h. Culture samples were taken from each well and the BacTiter-Glo Assay was performed. The samples and concentrations are Wells 1-4 and 93-96, negative control of 2% DMSO, wells... 

The results of antimicrobial activities of polyester and polypropylene treated fabric with different bacteria are indicated in Tables 1-5. The inoculum was a nutrient broth culture containing 0.5x10, Ixio and 1.5 xlO /mL colony-forming units (CPU) of the bacterium. The results show that 1% and higher concentration of CTAB on both polyester and polypropylene fabrics reasonably inhibit the growth of E. coli at pH=7 and S. aureus and P. aeroginosa at pH=5.5 (pH=5.5 is the pH of body skin). This test can not be used for viscose nonwoven because of disturbing effect of adhesive used for fabric production. 

Figure 2.34 MBEC assay, (a) Biofilms form on the polyst5rene pegs of the MBEC device when planktonic bacteria adsorb to the surface. These bacteria become irreversibly attached and grow to form mature biofihns. Biofilms are encased in sUme, which is sometimes visible to the naked eye. Planktonic cells are also shed from the surface of biofilms, which serves as the inoculum for CA determinations, (b) The peg lid has 96 identical plastic pegs. This hd fits into a trough with channels designed to guide an inoculum across the surface of the pegs. The peg lid fits into a standard 96-well microplate as weU, which is used to set up serial dilutions of antimicrobials.

From the beginning, laboratory studies on the antibacterial properties of cefaclor pointed to an inherent chemical instability in solution and in neutral to alkaline bacteriological media. Test medium composition, pH, and inoculum density can significantly affect in vitro susceptibility assay results. For example, in both Mueller-Hinton broth and agar, chemical degradation of cefaclor is observed as a rapid loss of antimicrobial activity (50%) after 6 hr at 37°C (Preston, 1979). Special care is, therefore, recommended in the interpretation of in vitro test results. 

It has been well demonstrated that the antimiCTObial efficacy of plant-origin antimicrobials depends on several factors including the EO extraction method, the inoculum volume, growth phase, culture medium used, and intrinsic or extrinsic factors of the food such as pH, fat, protein, water content, antioxidants, preservatives, incubation time/temperature, packaging procedure, and physical structure (Tajkarimi et al. 2010).For example, in galangal flowers, oven-dried samples extracted with ethanol was more effective compared to the freeze-dried samples extracted with... 

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