Antimicrobial Agents and Chemotherapy, August 1999, p. 1901-1908, Vol. 43, No. 8
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Pathology, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, Ohio 44106,1 and Department of Pathology, Hershey Medical Center, Hershey, Pennsylvania 170332
Received 20 August 1998/Returned for modification 31 January 1999/Accepted 25 May 1999
The susceptibilities of Streptococcus pneumoniae (1,476 strains) and untypeable Haemophilus influenzae (1,676 strains) to various oral
-lactam, macrolide-azalide, and
fluoroquinolone antimicrobial agents were determined by broth
microdilution. Organisms were isolated from specimens obtained from
outpatients in six geographic regions of the United States. MIC data
were interpreted according to pharmacodynamically derived breakpoints
applicable to the oral agents tested. Among H. influenzae
strains, 41.6% were
-lactamase positive. Virtually all H. influenzae strains were susceptible to amoxicillin-clavulanate
(98%), cefixime (100%), and ciprofloxacin (100%), while 78% were
susceptible to cefuroxime, 57% were susceptible to amoxicillin, 14%
were susceptible to cefprozil, 9% were susceptible to loracarbef, 2%
were susceptible to cefaclor, and 0% were susceptible to azithromycin
and clarithromycin. Among S. pneumoniae isolates, 49.6%
were penicillin susceptible, 17.9% were intermediate, and 32.5% were
penicillin resistant, with penicillin MICs for 50 and 90% of the
isolates tested of 0.12 and 4 µg/ml, respectively. Overall, 94% of
S. pneumoniae isolates were susceptible to amoxicillin and
amoxicillin-clavulanate, 69% were susceptible to azithromycin and
clarithromycin, 63% were susceptible to cefprozil and cefuroxime, 52%
were susceptible to cefixime, 22% were susceptible to cefaclor, and
11% were susceptible to loracarbef. Although ciprofloxacin has
marginal activity against S. pneumoniae, no high-level
fluoroquinolone-resistant strains were found. Significant cross-resistance was found between penicillin and macrolides-azalides among S. pneumoniae isolates, with 5% of the
penicillin-susceptible strains being macrolide-azalide resistant,
compared with 37% of the intermediate isolates and 66% of the
resistant isolates. Resistance was highest in S. pneumoniae
isolates from patients younger than 10 years of age, middle ear and
paranasal sinus specimens, and the southern half of the United States.
With the continuing rise in resistance, judicious use of oral
antimicrobial agents is necessary in all age groups.
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