TABLE 4.

Pneumococcal titers from biofilms and biofilm effluents after vortex mixing and subsequent titration in the presence and absence of B. cereus β-lactamase^a

Antibiotic concn (mg/liter)	Pneumococcal titer after exposure to:
	Benzylpenicillin				Amoxicillin
	BHI		BHI with β-lactamase		BHI		BHI with β-lactamase
	Biofilm	Effluent	Biofilm	Effluent	Biofilm	Effluent	Biofilm	Effluent
16.0	11.95	8.44	11.81	7.04	10.32	5.25	10.23	5.04
4.0	13.43	9.28	13.56	8.68	10.27	6.06	10.49	6.34
1.0	14.41	9.36	14.39	9.53	14.43	9.46	14.36	9.59
0.25	14.51	10.30	14.50	10.17	14.60	9.47	14.64	9.43
0.064	14.59	10.44	14.55	10.34	14.49	9.20	14.27	9.20
0.016	14.56	10.70	14.41	10.68	ND	ND	ND	ND

^aIndividual biofilms were inoculated with mixtures of S. pneumoniae serotype 19 and β-lactamase-positive M. catarrhalis and, after 24 h, were exposed to a single concentration of an antibiotic for 18 h; effluent was then collected for 15 min. Individual biofilms were sacrificed in BHI or BHI containing 10⁴ mU of B. cereus β-lactamase per ml. Titrations of the biofilm and effluent were then performed in the absence or presence of the B. cereus enzyme. Titers in biofilm (log₁₀) are expressed as recoverable CFU per biofilm; titers in effluent are expressed as CFU per milliliter. ND, not done.