Antimicrobial activity zone inhibition test

The analyst (farmer, veterinarian, laboratory scientist, or any other user) saturates a cotton tipped swab with sample tissue fluids, serum, urine, or feed extract. He then firmly places the saturated cotton swab on the surface of the appropriate growth medium previously surface streaked with the working dilution of the appropriate susceptible test organism. The test is then incubated at the proper temperature overnight and observed the next day for antimicrobial activity. If there is a zone of inhibition (no growth of the test organism) around the sample swab, the test is positive no inhibition indicates that antimicrobials are absent or below detectable levels in the sample tested. 

Newly synthesized compounds 22, 23, 25c-e, 26d and 29e were screened in vitro for their antimicrobial activities against Gram positive bacteria Staphylococcus aureus (NCTC-7447), Bacillus cereus (ATCC-14579) and Gram negative bacteria Serratia marcesens (IMRU-70) and Proteus merabitis (NTCC-289) using the paper disk diffusion method for the antibiotic sensitivity technique [60]. The tested compounds were dissolved in N,N-dimclhylformamidc (DMF) to obtain a 1 mg/mL solution. The inhibition zones of microbial growth produced by different compounds were measured in millimeters at the end of an incubation period of 48 h at 28 °C. DMF alone showed no inhibition zone. 

Bacterial sensitivity of each material was evaluated using the following assay - zone of inhibition of surface growth. The materials were tested against Streptococcus mutans and Enterococcus faecalis using assays that measured the diffusible inhibihon of bacterial growth on a blood-agar surface and estimated the antimicrobial activity. All procedures were performed under aseptic conditions. 

Fiber samples from the washing model were also tested for antibiotic release in a zone of inhibition assay. One cm pieces of polyester were washed for various times (with buffer changes as outlined previously), sterilized, and then plated on agar streaked with S. aureus (ATCC 29213). The zone of inhibition was measured after an overnight incubation. The control sample lost antimicrobial activity within 48 hours, while the pad/heat treated polyester continued to demonstrate anti-staphylococcal activity past 336 hours (Figure 10). 

The agar diffusion method (Kirby—Bauer) is also sometimes used for the evaluation of antibacterial activity of textiles. This is a relatively quick and easily executed semiquantitative method to determine antibacterial activity of diffusible antimicrobial agents on treated textile material. The bacteria are grown in nutrient broth medium and after appropriate dilution (e.g., lOOx) from the culture, test organisms are swabbed over the surface of agar plates. Ten-millimetre-diameter disks of the test fabric and control fabric are then gently pressed onto the surface of the plate. The plates are then incubated at 37 °C for 18—24 h. The antibacterial activity of the fabrics is demonstrated by the diameter of the zone of inhibition in comparison to the control textile sample. 

Knitted fabrics used for medical applications - such as in wound dressings - require a zone of inhibition. These may be studied using the AATCC 147 Parallel Streak Standard Method this is an appropriate semi quantitative method for evaluating the antibacterial activity of diffusible antimicrobial agents on treated fabrics. A test result for a fabric treated with the silver salt suspension and a control fabric is presented in Rg. 5.5, where the tested bacteria was Staphylococcus aureus. 

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