Table 5.

Effect of ultrasonication on the size of microbial aggregates in cultures of biofilms as determined by microscopic observation

Aggregate length (μm)No. of aggregates/μl after sonication treatment ofa:
None70% for 1 min70% for 2 min70% for 3 min90% for 1 min
5.0–7.251.2 (47.3)48.0 (16.0)18.7 (8.3)20.0 (8.0)20.0 (11.5)
7.3–9.930.4 (17.6)10.7 (6.1)6.7 (2.3)c 10.7 (4.6)5.3 (3.0)c
10–2920.0 (8.0)2.7 (1.2)c ND5.3 (5.3)c 1.3 (1.2)c
30–494.0 (2.8)NDND1.3 (2.3)ND
50–693.2 (3.3)NDNDNDND
110–1300.8 (1.8)NDNDNDND
Total109.6 (69.7)61.3 (27.2)25.3 (9.2)c 37.3 (12.2)c 26.7 (16.6)c
  • a Values represent the mean number of aggregates per microliter observed in three (sonication treatment) or five (control) aliquots. Values in parentheses are the standard deviations associated with each mean.

  • b ND, no aggregates were detected. The detection threshold was 0.8 aggregate per μl.

  • c Values are significantly different (P ≤ 0.05) from the corresponding value for the control. Since sonication had a significant effect on the variance of aggregate concentration among treatments (Bartlett’s test; P ≤ 0.05), a nonparametric test was used to determine the effect of sonication on the mean number of aggregates. Significant differences indicated here are based on pairwise comparisons obtained by using rank sums from the Kruskal-Wallis single-factor analysis of variance test for data with tied ranks. Values of q for the pairwise test were compared with the critical values of q as described by Zar (17).