Antimicrobial susceptibility patterns and ␤-lactam resistance mechanisms of 544 Haemophilus influenzae isolates through the nationwide Acute Respiratory Infections Surveillance (ARIS) network in Korea during 2005 and 2006 were determined. Resistance to ampicillin was 58.5%, followed by resistance to cefuroxime (23.3%), clarithromycin (18.7%), cefaclor (17.0%), amoxicillin-clavulanate (10.4%), and chloramphenicol (8.1%). Levofloxacin and cefotaxime were the most active agents tested in this study. ␤-Lactamase production (52.4%) was the main mechanism of ampicillin resistance, affecting 96.1% of TEM-1-type ␤-lactamase. According to their ␤-lactam resistance mechanisms, all isolates were classified into the following groups: ␤-lactamase-negative, ampicillin-sensitive (BLNAS) strains (n ‫؍‬ 224; 41.5%); ␤-lactamase-positive, ampicillin-resistant (BLPAR) strains (n ‫؍‬ 255; 47.2%); ␤-lactamase-negative, ampicillin-resistant (BLNAR) strains (n ‫؍‬ 33; 6.1%); and ␤-lactamase-positive, amoxicillin-clavulanate-resistant (BLPACR) strains (n ‫؍‬ 28; 5.2%). Among the BLNAR and BLPACR strains, there were various patterns of multiple-amino-acid substitutions in penicillin-binding protein 3. Particularly, among BLNAR, group III isolates, which had three simultaneous substitutions (Met377Ile, Ser385Thr, and Leu389Phe), were identified for the first time in Korea. Three group III strains displayed the highest MIC of cefotaxime (1 to 2 g/ml). The results indicate the importance of monitoring a changing situation pertaining to the increase and spread of BLNAR and BLPACR strains of H. influenzae for appropriate antibiotic therapy for patients with respiratory tract infections in Korea.

A longitudinal analysis was carried out of the colonization by four potential respiratory pathogens -Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus -in 165 healthy children (aged 3-7 years) attending three kindergartens and 417 healthy children (aged 7-10 years) attending an elementary school in Seoul, Korea, by four consecutive examinations over 1 year. The prevalence of nasal carriers of one or more of four bacteria was found to be higher in younger children (¡7 years) (mean 68.6 %) than that in older children (mean 46.8 %). The mean rates of nasal carriage of Strep. pneumoniae, H. influenzae, M. catarrhalis and Staph. aureus were 16.8, 18.9, 20.2 and 18.2 %, respectively. Colonization by Strep. pneumoniae, H. influenzae and M. catarrhalis was higher in pre-school children (28.6, 32.4 and 35.0 %, respectively) than in school children (12.2, 13.6 and 14.3 %, respectively). Carriage trends differed with age, with Strep. pneumoniae, H. influenzae and M. catarrhalis colonization decreasing with age but Staph. aureus colonization increasing. Positive associations of co-occurrence between Strep. pneumoniae, H. influenzae and M. catarrhalis were evident, with a significant negative association evident between Staph. aureus and the other three bacteria. A better understanding of the colonization and interaction of potential respiratory pathogens may be important for predicting changes in bacterial ecology and for designing control strategies that target bacterial colonization in upper respiratory tract infections.

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