Antimicrobial resistance in respiratory pathogens isolated in Brazil during 1999-2000

The in vitro antimicrobial susceptibility of the respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis to commonly tested and prescribed agents was investigated during 1999-2000 and compared with results obtained during a previous 1997-1998 study. Of 448 isolates of S. pneumoniae collected and tested in 1999-2000, 77.2% were susceptible, 19.9% were intermediate, and 2.9% were resistant to penicillin, demonstrating that there were no major changes in susceptibility to penicillin from 1997-1998 (77.1% susceptible, 18.7% intermediate, 4.2% resistant). All S. pneumoniae isolates from 1999-2000 were susceptible to levofloxacin and vancomycin, and >90% were susceptible to the b-lactams (amoxicillin-clavulanate, ceftriaxone, and cefuroxime) and macrolides (azithromycin and clarithromycin), showing that susceptibility to these agents also remained unchanged since 1997-1998. The most notable increase in resistance between the two studies was demonstrated by trimethoprim-sulfamethoxazole, which increased from 23.4% to 38.6%. Penicillin resistance correlated with resistance to b-lactams, macrolides, and trimethoprim-sulfamethoxazole in both studies. In H. influenzae, the prevalence of b-lactamase-producing isolates remained unchanged (10.6% in 1999-2000; 11.0% in 1997-1998). All H. influenzae isolates were susceptible to levofloxacin, ceftriaxone, cefuroxime, and azithromycin, and showed no change between the two studies. Trimethoprim-sulfamethoxazole resistance was present in 40.1% of isolates in 1999-2000, and in 45.2% in 1997-1998. In M. catarrhalis, the prevalence of b-lactamase-producing isolates was unchanged (97.9% in 1999-2000; 98.0% in 1997-1998). The most active agents against M. catarrhalis were azithromycin (MIC90, <0.03 mg/ml) and levofloxacin (MIC90, 0.03 mg/ml). Overall, these results suggest that, in Brazil, between 1999-2000 and 1997-1998, there have been no significant changes in the susceptibility of respiratory pathogens to any of the commonly tested and prescribed agents with the exception of trimethoprim-sulfamethoxazole for S. pneumoniae.