Antimicrobial susceptibility of Haemophilus influenzae strains isolated from the urethra of men with acute urethritis and/or epididymitis

We determined minimum inhibitory concentrations (MICs) of 41 antimicrobial agents for 73 clinical strains of Haemophilus influenzae isolated from the urethra of men with acute urethritis and/or epididymitis and examined the strains for the production of β-lactamase. We also compared their antimicrobial susceptibilities with those of H. influenzae strains from respiratory tract or otorhinolaryngological infections that were reported in Japan. The proportion of β-lactamase-nonproducing ampicillin-resistant strains from acute urethritis and/or epididymitis appeared to be lower, but that of β-lactamase-producing ampicillin-resistant strains appeared to be higher, compared with those from respiratory tract or otorhinolaryngological infections. However, their antimicrobial susceptibilities to a variety of other antimicrobial agents would be similar to those from respiratory tract or otorhinolaryngological infections. Almost all of the strains of H. influenzae from acute urethritis and/or epididymitis were susceptible to the agents, including ceftriaxone, quinolones, macrolides, and tetracyclines, commonly prescribed for treatment of acute urethritis based on the MIC breakpoints recommended by the Clinical and Laboratory Standards Institute. Ceftriaxone and quinolones could be effective on H. influenzae-induced urethritis. However, azithromycin treatment failures were reported in acute urethritis caused by H. influenzae strains considered susceptible to azithromycin. Further studies will be needed to determine MIC breakpoints of antimicrobial agents, which are recommended for treatment of urogenital infections, for H. influenzae strains causing these infections. Nevertheless, this study provides useful data regarding antimicrobial susceptibilities of H. influenzae strains isolated from the urogenital tract, which have rarely been studied.