Elucidation of bacteria found in car interiors and strategies to reduce the presence of potential pathogens

Abstract

The human microbiome is influenced by a number of factors, including environmental exposure to microbes. Because many humans spend a large amount of time in built environments, it can be expected that the microbial ecology of these environments will influence the human microbiome. In an attempt to further understand the microbial ecology of built environments, the microbiota of car interiors was analyzed using culture dependent and culture independent methods. While it was found that the number and type of bacteria varied widely among the cars and sites tested, Staphylococcus and Propionibacterium were nearly always the dominant genera found at the locations sampled. Because Staphylococcus is of particular concern to human health, the characteristics of this genus found in car interiors were investigated. Staphylococcus epidermidis, S. aureus, and S. warnerii were the most prevalent staphylococcal species found, and 22.6% of S. aureus strains isolated from shared community vehicles were resistant to methicillin. The reduction in the prevalence of pathogenic bacteria in cars by using silver-based antimicrobial surface coatings was also evaluated. Coatings containing 5% silver ion additives were applied to steering wheels, placed in cars for five months and were found to eliminate the presence of culturable pathogenic bacteria recovered from these sites relative to controls. Together, these results provide new insight into the microbiota found in an important built environment, the automobile, and potential strategies for controlling the presence of human pathogens.

Figure 1.

Analysis of CFUs present at different car interior locations. (A) Image of a typical car interior with swab sampling sites labels. Swabs of 6.5 × 6.5 cm area were collected from (A) steering wheel, (B) radio volume knob, (C) gear shifter, (D) center console, (E) door latch, (F) door lock, (G) door lock control, (H) door handle, (I) window control, (J) cruise control button, and (K) interior steering wheel. (B) Number of CFUs isolated from swab locations A–K from 18 different cars. ns = not sampled.

Figure 2.

Analysis of car interior plastics treated with antimicrobial formulations for the ability to resist S. aureus surface colonization. Hard plastic surfaces (A) or soft plastic surfaces (B) that were either untreated (control) or sprayed with the indicated antimicrobial formulations were exposed to 6 × 10⁵ CFUs of S. aureus and the number of CFUs present after 24 h was determined. Error bars show the SE of the mean; *p < 0.005 vs 24 h control.

Figure 3.

Analysis of artificially weathered car interior plastics treated with antimicrobial formulations for the ability to resist S. aureus surface colonization. Hard plastic surfaces (A) or soft plastic surfaces (B) that were either untreated (control) or sprayed with indicated antimicrobial formulations were artificially weathered then incubated with upto 6 × 10⁵ CFUs S. aureus. The number of CFUs present after 24 h was determined. Black bars are unweathered surfaces, gray bars were exposed to 2,500 kJ m⁻², and white bars were exposed to 5,000 kJ m⁻². Error bars the SE of the mean; *p < 0.005 vs the comparable 24 h control.

Figure 4.

Analysis of CFUs present on production steering wheels vs silver treated steering wheels. (A) Locations of swabbing at hard trim piece locations (T1–3) or soft exterior locations (S1–5). (B) Number of CFUs isolated from swab locations from trim (T) or exterior steering wheel locations (S) from production (Pro) vs silver coated (Ag) steering wheels. *p < 0.005 vs the comparable production piece; **p < 0.05 vs the comparable production piece.