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Antimicrobial Agents and Chemotherapy, October 1998, p. 2521-2526, Vol. 42, No. 10
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Interaction of Streptococcus pneumoniae and Moraxella catarrhalis: Investigation of the Indirect Pathogenic Role of beta -Lactamase-Producing Moraxellae by Use of a Continuous-Culture Biofilm System

R. K. Budhani and J. K. Struthers*

Department of Medical Microbiology, Manchester Royal Infirmary and the University of Manchester, Manchester M13 9WL, United Kingdom

Received 19 December 1997/Returned for modification 1 April 1998/Accepted 13 July 1998

The majority of clinical isolates of Moraxella catarrhalis produce beta -lactamase. The role of this enzyme in the phenomenon of indirect pathogenicity, in which a true pathogen such as Streptococcus pneumoniae is protected from the action of certain beta -lactam antibiotics, is well recognized. By using a simple continuous-culture biofilm system, it has been shown that the pneumococcus attains high titers in excess of 1012 CFU/biofilm; furthermore, the penicillin-sensitive pneumococcus used remained susceptible to a range of beta -lactam antibiotics in these biofilms (R. K. Budhani and J. K. Struthers, J. Antimicrob. Chemother. 40:601-602, 1997). This system was used to characterize the antibiotic susceptibility of this isolate when grown with beta -lactamase-negative or -positive moraxellae. When grown with beta -lactamase-producing moraxellae in the presence of either benzylpenicillin or amoxicillin, the pneumococcus was protected in the range of the antibiotic concentrations to which it would be considered resistant. With amoxicillin-clavulanic acid the titers of the two organisms collapsed at the antibiotic concentration at which moraxellae became susceptible. The levels of beta -lactamase activity in cell-free supernatants of broth culture, in biofilm, and in biofilm effluent revealed distinct differences in this activity; levels in biofilm were significantly lower than those in broth culture supernatants. The system appears suitable for studying organisms under antibiotic stress and for investigating the interactions of bacteria under such conditions.

* Corresponding author. Present address: Public Health Laboratory Service, Coventry and Warwickshire Hospital, Stoney Stanton Rd., Coventry, CV1 4FH, United Kingdom. Phone: 44(1203) 844122. Fax: 44(1203)220081. E-mail: jkstruthers{at}covphl.globalnet.co.uk.

Antimicrobial Agents and Chemotherapy, October 1998, p. 2521-2526, Vol. 42, No. 10
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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