TABLE 4.

Filtration efficiency of Isopore polycarbonate filters in the presence of microbial aggregates and other particles^a

Isolate	Concn of isolate (CFU/ml)b	Particle source	Concn of total bacteria in particle source (CFU/ml)e	% Recoveryf
P. fluorescens PF130A	1.93 × 106	Leaf washingc	0	93
	5.06 × 105	Leaf washing	2.03 × 106	101
	4.76 × 105	Leaf washing	7.47 × 105	96
	4.16 × 104	Leaf washing	7.47 × 105	113
	5.16 × 103	Leaf washing	7.47 × 105	98
	7.60 × 105	Biofilm cultured	8.40 × 103	97
P. putida MC1-100	1.01 × 106	Biofilm culture	4.54 × 105	93
H. alvei MC1-057	3.75 × 105	Biofilm culture	5.78 × 104	90
C. aquaticum MC1-108	1.24 × 106	Biofilm culture	4.11 × 105	94

^aEfficiency is expressed as the percentage of cells of rifampin-resistant strains of pure-culture, prefiltered bacteria that pass across filters in mixed suspensions containing biofilms and other particles. 

^bMean concentration of prefiltered, pure-culture isolates, determined on rifampin-containing medium, in mixtures containing biofilms or other particles. 

^cSuspensions were obtained by washing leaves of broad-leaf endive in sterile buffer. The frequency of naturally occurring rifampin-resistant bacteria was <10⁻² for these washings. 

^dSuspensions were obtained as described in the text. The frequency of naturally occurring rifampin-resistant bacteria was <2 × 10⁻⁴ for these cultures. 

^eMean concentrations of total bacteria from leaf washings or biofilm cultures in the mixtures containing pure-culture suspensions. 

^fPercent rifampin-resistant CFU recovered from the mixtures. These values are the means of four to eight independent filtrations for each mixture.