beta-Lactamase-producing Moraxella catarrhalis may prevent the emergence of penicillin-resistant Streptococcus pneumoniae in children with recurrent acute otitis media

Antibiotic resistance in pathogens causing acute otitis media in Finnish children

INTRODUCTION

Microbiology and susceptibility of middle ear pathogens in children change over time and antibiotic resistance is increasing globally. For the clinicians it is important to be up to date about the resistance situation when considering antibiotic treatment in acute otitis media (AOM). In this study we analysed the resistance profile of AOM pathogens in out-patient children in Finland.

METHODS AND MATERIALS

A total of 41 culture positive middle ear fluid (MEF) samples were analysed for bacteria and the presence of antibiotic resistant strains. The samples were obtained from children aged six - 39 months who participated in the otitis media trial during one year period.

RESULTS

The most common pathogen was Haemophilus influenzae 17 (40%), followed by Streptococcus pneumoniae in 15 (35%) and Moraxella catarrhalis in 8 (19%). Other pathogens were detected in 3 (7%) of cases. Antibiotic resistance or diminished sensitivity was seen in 63% of the detected bacteria and 28% of pathogens produced beta-lactamase.

CONCLUSIONS

Antibiotic resistant bacterial strains causing AOM have increased in Finland. Nevertheless, most of the pathogens (72%) were sensitive to amoxicillin, which is still recommended as the first line antibiotic in the treatment of AOM.

Beta-lactamase-producing nontypeable Haemophilus influenzae fails to protect Streptococcus pneumoniae from amoxicillin during experimental acute otitis media

Acute otitis media (AOM) is the most common reason for outpatient antimicrobial therapy. Mixed infections pose a potential problem, since the first-line drug used for the treatment of AOM, amoxicillin, can be neutralized by beta-lactamase-producing pathogens of the upper respiratory tract. To study the effects of a 5-day course of amoxicillin on a mixed middle ear infection, rats were challenged with Streptococcus pneumoniae alone or in combination with beta-lactamase-producing nontypeable Haemophilus influenzae. Amoxicillin was introduced at the clinical peak of the infection. Local and systemic changes were monitored by otomicroscopy, bacterial culture, and analysis of histological changes and the expression of the transforming growth factor beta (TGF-beta) gene. beta-Lactamase-producing H. influenzae did not demonstrate an ability to protect S. pneumoniae. Amoxicillin eradicated the pneumococci in all treated animals but increased to some degree the ability of H. influenzae to persist at the site of infection. Thus, only an insignificant acceleration of the resolution of the AOM caused by a mixture of pathogens was observed during treatment. Moderate to major morphological changes could not be avoided by treatment of the mixed infections, but a slight downregulation of TGF-beta expression was observed. In contrast to infections caused by a single pathogen, the mixed infections induced white plaques in the tympanic membrane at a remarkably high frequency independent of treatment. These experimental findings constitute support for further studies of antimicrobial drugs and AOM caused by bacteria with and without mechanisms of antibiotic resistance.