Comparative In- Vitro Activity of Fourteen Antibiotics Against Clinical Isolates of Enterococci

Summary

The in-vitto antibacterial activities of fourteen antimicrobial agents, including ampicillin, amikacin, Augmentin, ceftazidime, cefotaxime, ceftriaxone, ciprofloxacin, erythromycin, gentamicin, penicillin G, piperacillin, rifampicin, streptomycin and vancomycin, were compared against 195 enterococcal strains isolated from clinical specimens received at the King Abdulaziz University Hospital in Saudi Arabia. The antibacterial susceptibility was determined by the minimal inhibitory concentration (MIC) using an agar dilution method. Ampicillin, Augmentin and vancomycin exhibited the greatest activity, inhibiting 90% of the tested strains (MIC90) at 2 μg/ml, followed by penicillin G and piperacillin with MIC90 of 4 μg/ml. Erythromycin, third generation cephalosporins, aminoglycosides and rifampicin, on the other hand, had poor activity against enterococci with MIC90s well above the obtainable serum concentrations. The clinical implications of resistance to aminoglycosides and the alternative antimicrobial therapy in serious entrococcal infections are discussed in the text.     

In- Vitro Activity of Ampicillin/Sulbactam and Other Antibiotics against Clinical Isolates of Haemophilus sp. and Branhamella catarrhalis

Summary

The ampicillin/sulbactam combination is one of several such drug combinations of a beta-lactam and suicide inhibitor having a wide spectrum of activity.

These characteristics induced us to evaluate the in vitro activity of this combination towards 54 strains of Haemophilus sp. (38 beta-lactamase producers) and 20 strains of Branhamella catarrhalis (16 beta-lactamase producers).

All strains were isolated from sputum, sinusal aspiration and tympanocentesis.

In the case of Haemophilus sp beta-lactamase producers, minimal inhibitory concentrations of ampicillin were reduced 8 times by the use of the inhibitor; good results were also obtained for B. catarrhalis.

Haemophilus influenzae, B. catarrhalis together with Streptococcus pneumoniae are recognized as the major pathogens involved in upper respiratory tract infections. The increasing frequency of beta-lactamase producing strains has impaired the use of aminopenicillins.

The combination of an inhibitor and beta-lactam restore the activity of the latter, suggesting that this combination can serve as first choice in therapy.