Naslov
Effect of inoculum size on the antibiotic susceptibilities of ß-lactamase positive isolates of Moraxella catarrhalis

Autori
Bedenić, Branka ; Vraneš, Jasmina

Izvornik
Medicinski glasnik Ljekarske komore Zeničko-dobojskog kantona (1840-0132) 2 (2005), 2; 60-63

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Moraxella catarrhalis; beta-lactamases; inoculum effect; penicillins; cephalosporins

Sažetak
It is well known that bacteria producing beta-lactamases in general show marked inoculum effect in susceptibility testing. The aim of this study is to determine the effect of inoculum size on the susceptibility of beta-lactamase positive strains of M. catarrhalis to oral beta-lactam and non beta-lactam antibiotics. MICs of antibiotics were determined by a twofold microdilution technique with two different inoculum sizes were tested: 5x 105 CFU/ml -standard inoculum and 5 x107 CFU/ml -high inoculum.The highest increase ( 4 fold) was observed with penicillins alone (amoxycillin and ampicillin) or combined with inhibitor and ceftibuten, followed by older cephalosporins, erithromycine and chloramphenicol ( 2 fold) . Tetracycline did not show a significant increase in MIC when higher the inoculum size was applied. In spite of the increase in MIC with high inoculum all strains were still susceptible to amoxycillin combined with clavulanate. MICs of cephalosporins were also below the resistance breakpoint for most of the strains at the higher inoculum. According to that, we can conclude that therapeutic implication of the inoculum effect were not significant. These data suggest that that high inocula should be used to determine MICs of ampicillin and amoxycillin for M. catarrhalis but that this precaution is unnecessary with the cephalosporins tested or with amoxycillin/clavulanate.

Izvorni jezik
Engleski

Znanstvena područja
Temeljne medicinske znanosti, Kliničke medicinske znanosti

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