Prevalence of β-lactamase-negative ampicillin-resistant haemophilus influenzae isolated from patients of a teaching hospital in Thailand.

The aim of this study was to investigate the prevalence of b-lactamase-negative ampicillinresistant (BLNAR) Haemophilus influenzae isolated from patients of a teaching hospital in Thailand. Eighty-eight isolates of H. influenzae were collected between September 2005 and March 2008. All isolates were identified and characterized for biotypes and capsular types. The b-lactamase production of these isolates was examined, and their susceptibility to the following 12 antimicrobial agents was determined: ampicillin (AMP), amoxicillin-clavulanate (AMC), cefotaxime (CTX), cefuroxime (CXM), meropenem (MEM), clarithromycin (CLR), telithromycin (TEL), tetracycline (TET), ciprofloxacin (CIP), levofloxacin (LEV), trimethoprim-sulfamethoxazole (SXT), and chloramphenicol (CHL). Of the 88 H. influenzae isolates, 69 (78.4z), 13 (14.8z), 4 (4.5z), and 2 (2.3z) were from the respiratory tract, pus, the genital tract, and blood, respectively. Half of the isolates were biotype II (44 isolates, 50z). The other half comprised biotypes I (23 isolates, 26.1z), III (15 isolates, 17.1z), and IV (6 isolates, 6.8z). All isolates were capsular non-typeable, except for 2 isolates that were type f. Antimicrobial susceptibility showed that all isolates were susceptible to AMC, CTX, MEM, TEL, CIP, and LEV (100z), whereas 96.6z, 94.3z, 80.7z, 68.2z, 50.0z, and 44.3z were susceptible to CXM, CLR, CHL, TET, AMP, and SXT, respectively. The b-lactamase-production rate of H. influenzae isolates was 40.9z, and the prevalence of BLNAR was 18.2z.