Bacterial Reductions Following Rinses with Listerine or Listerine Zero

To compare the new alcohol-free Listerine Zero to traditional Listerine for ability to reduce oral bacteria, including halitosis-causing anaerobic bacteria (H₂S producers), and mutans streptococci (MS). 

Method:

Prior to any morning oral hygiene, a baseline sample of unstimulated saliva was collected. Subjects then rinsed with Listerine Zero or Listerine for 30 seconds.  After 10 minutes, another sample was collected.  Subjects were provided supplies to rinse before bedtime and collect a saliva sample the next morning prior to oral hygiene.  After at least two weeks, the subjects repeated the protocol with the opposite rinse.  Samples were cultured on Columbia Blood Agar, MSKB Agar, and OHO Agar medium with .2g/l lead, incubated, and colony forming units enumerated.  A paired-samples t-test and the Wilcoxon signed-rank were used to determine significant differences between bacterial counts at baseline and 10 minutes and between baseline and overnight. 

Result:

Rinsing with Listerine or Listerine Zero significantly reduced total bacteria, MS, and H₂S producers in the 10 minute post-rinse saliva sample, and significantly reduced the number of MS in the overnight sample.  In addition, the Listerine Zero rinse significantly reduced H₂S producers in the overnight sample.  When comparing the rinses for each subject, the reductions in total bacteria in the overnight sample were significantly greater for Listerine Zero than for Listerine.  The range of reductions at 10 minutes post-rinse varied greatly between subjects following a rinse with Listerine, whereas most subjects showed approximately a one log reduction in total bacteria following the rinse with Listerine Zero. 

Conclusion:

Within the limits of our protocol, Listerine could not be distinguished from Listerine Zero in total bacterial reductions 10 minutes post-rinse.  However, Listerine Zero out-performed Listerine in the total bacterial overnight post-rinse reductions.  Listerine Zero appears to be an effective alternative for consumers who wish to avoid daily alcohol exposure.