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Results

Field Samples

The results of total microbial populations are shown in Table 1. While microbes exist in the infill media the number was low compared to natural turfgrass field soils. It should be remembered that microbes tend to be present on most surfaces humans come in contact with and the simple presence of microbes should not be cause for concern. In fact, many products on the market claim to boost the microbial populations of natural turfgrass soils with higher microbial populations considered to be beneficial.

Table 1. Colony forming units (CFU) detected on R2A media per gram of crumb rubber.
Field ID#¹ Product CFU/g crumb rubber
#¹ H = sample collected from higher use area of field
L = sample collected from lower use area of field
* = sample collected from indoor field
1H 100% crumb rubber 20200
1L 100% crumb rubber 32667
2H Crumb rubber - Sand mix 3533
2L Crumb rubber - Sand mix 133
3H Crumb rubber - Sand mix 3467
3L Crumb rubber - Sand mix 13133
4H 100% crumb rubber 9467
4L 100% crumb rubber 30267
5H Crumb rubber - Sand mix 18867
5L Crumb rubber - Sand mix 8333
6H Crumb rubber - Sand mix 267
6L Crumb rubber - Sand mix 28333
7H Crumb rubber - Sand mix 4800
7L Crumb rubber - Sand mix 55333
8H Crumb rubber - Sand mix 4867
8L Crumb rubber - Sand mix 24133
9H 100% crumb rubber 9800
9L 100% crumb rubber 17867
10H* Crumb rubber - Sand mix 0
10L* Crumb rubber - Sand mix 67
11H Crumb rubber - Sand mix 33200
11L Crumb rubber - Sand mix 28000
12H 100% crumb rubber 333
12L 100% crumb rubber 800
13H 100% crumb rubber 267
13L 100% crumb rubber 67
14H 100% crumb rubber 8267
15H Crumb rubber - Sand mix 8600
15L Crumb rubber - Sand mix 3867
16H* Crumb rubber - Sand mix 200
16L* Crumb rubber - Sand mix 0
17H Crumb rubber - Sand mix 0
17L Crumb rubber - Sand mix 7267
18H 100% crumb rubber 5000
18L 100% crumb rubber 5533
19H Crumb rubber - Sand mix 53067
19L Crumb rubber - Sand mix 80000
20H Crumb rubber - Sand mix 54333
20L Crumb rubber - Sand mix 8867
Native soil (silt loam) 259500
Sand based soil 309500

Pile fiber samples were also collected from several fields. CFUs for fiber samples range from 200-2933 CFUs per fiber sample (2 fibers approximately 1 cm long) indicating that the fibers alone generally exhibited lower microbial populations compared to the infill.

Microbial colonies isolated from field samples generally included both fungi and bacteria. Some fields had predominantly one organism type while other fields contained a variety of organisms. In order to positively identify the presence of S. aureus, three procedures were used. No colonies isolated from any crumb rubber or fiber samples tested positive for S. aureus via selective media, gram stain or latex agglutination tests.

Other Surfaces

Surfaces other than athletic playing surfaces were tested for the presence of microbes and S. aureus. These surfaces are not granulated and thus the results are listed in Table 2 as total colony number as opposed to CFU per gram of granulated material.

Table 2. Number of colonies per swab detected on R2A media from various sources in public spaces and an athletic training facility.
Source Colony number
*Sampled immediately after use
Public areas
Computer mouse >600
Elavator button 155
Outside door handle 80
Computer keyboard 33
Athletic training facility
Cold pool 24
Blocking pads* 130
Sauna 536
Football* 142
Weight equipment 1* 62
Weight equipment 2* 414
Towel hamper 103
Stretching table 14
Used towels* 29
Trash can for drink cups 205
Table 3. Surfaces that tested positive (+) for S. aureus colonies per swab detected.
Source Colony number
*Sampled immediately after use
Public areas
Human hands +
Human faces +
Computer mouse -
Elavator button -
Outside door handle -
Computer keyboard -
Athletic training facility
Natural turfgrass playing field -
Synthetic turf playing field -
Cold pool -
Blocking pads* +
Sauna -
Football* -
Weight equipment 1* +
Weight equipment 2* +
Towel hamper -
Stretching table +
Used towels* +
Trash can for drink cups -

Microbial colonies isolated from surfaces included a mixture of fungi and bacteria. Colonies from the trash can were predominantly fungi. While not specifically identified, all colonies from the sauna swab appeared to be the same. S. aureus was positively identified from several samples including towels, blocking pads, weight equipment, and the stretching table. In addition, S. aureus was positively identified from every facial and hand swabs tested.