Current patterns and evolution of antibiotic resistance among bacterial pathogens involved in acute otitis media

Penicillin resistance among Streptococcus pneumoniae is becoming a global problem. Different evolutionary phases in the development of resistance can be differentiated according to the local distribution of bacterial strains with different levels of penicillin resistance: susceptible, early phase, low-level resistance phase, multipopulational phase, high-level resistance phase and very high-level resistance phase. These phases evolve in different periods (cryptic, penetration period, evolutionary period and stationary period) which describe the presumed natural history of the resistant organisms. The selective effect of the antibiotic usage depends on the amount and type of the drug, and also on the evolutionary period dominating the geographic area where the antibiotic is used. Macrolide resistance is also a growing problem, probably proportional to the amount of drug used. In the case of beta-lactams, 'more is different' strategies may be useful to control clinically low-level resistant strains with aminopenicillins, and could slow the evolution to higher rates of resistance in some areas; nevertheless, surveillance of the evolution of high-level resistance is mandatory. In Haemophilus influenzae, the proportion of beta-lactamase-positive strains is also very high, frequently over 25% of cases; in all cases the combination amoxycillin---clavulanate restores the susceptible phenotype. In this case, surveillance should be focused on the increase in non-beta-lactamase-mediated penicillin resistance and fluoroquinolone resistance, or in the potential evolution towards extended-spectrum beta-lactamases.