In- Vitro Activity of Ciprofloxacin and Sixteen Other Antimicrobial Agents against Blood Culture Isolates

Summary

The in-vitro antibacterial activities of seventeen antimicrobial agents including ampicillin, amikacin, Augmentin, aztreonam, cefazolin, cefuroxime, cefotaxime, ceftizoxime, ceftriaxone, ciprofloxacin, cloxacillin, erythromycin, gentamicin, penicillin G, piperacillin and vancomycin were compared against 100 Gram-negative and Gram-positive strains isolated from blood culture specimens received at the King Abdulaziz University Hospital (KAUH), in Jeddah, Saudi Arabia.

The antibacterial susceptibility was determined by the minimal inhibitory concentration (MIC), using an agar dilution method. Ciprofloxacin exhibited the greatest activity, inhibiting 90% of the tested strains (MIC₉₀) at a concentration ranging from < 0.015-0.5 mg/L. Against cloxacillin resistant or susceptible strains of Staphylococcus aureus and coagulase-negative staphylococci, ciprofloxacin had similar activity with MIC₉₀, of 0.2 mg/L. Salmonella typhi and salmonella species which were resistant to ampicillin and augmentin remained sensitive to ciprofloxacin (Mid₉₀ < 0.015-0.125) mg/L.). Against gentamicin sensitive and resistant Pseudomonas aeruginosa and Pseudomonas species, ciprofloxacin MIC₉₀ was 0.5 and 1 mg/L respectively. Aminoglycosides, third generation cephalosporins, aztreonam and antipseudomonal penicillins, on the other hand, showed high MIC₉₀ well above the obtainable serum concentrations against Enterobacteriaceae and Pseudomonas species.     

Comparative In- Vitro Activity of Piperacillin and Piperacillin Plus Tazobactam Towards Beta-Lactamase Producing Clinical Isolates

Summary

The authors evaluated the in-vitro antibacterial activity of piperacillin alone and of piperacillin combined with tazobactam, a new beta-lactamase inhibitor, on 398 clinical isolates, both Gram-positive and Gram-negative. The piperacillin/tazobactam combination was evaluated in the fixed ratio 8:1. The vast majority of the microorganisms tested had reduced susceptibility to piperacillin (minimum inhibitory concentration (MIC) range 0.12— > 256 mg/1) due to beta-lactamase production.

The following results were obtained: against Haemophilus influenzae, tazobactam was effective in reducing the MICs of piperacillin by 512 fold. The activity of piperacillin/tazobactam was lower against Pseudomonas sp., while some activity was demonstrated against some strains of Klebsiella. Good activity was seen not only against methicillin-susceptible (MS) staphylococci but also against some methicillin-resistant (MR) strains. In the latter, the combination of piperacillin/tazobactam was active only if the strains showed beta-lactamase production. These findings are interesting above all in regard to the synergistic effect demonstrated against MR beta-lactamase producing staphylococci and the Klebsiella-Enterobacter-Serratia (KES) group.     

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.     

Comparative In Vitro Activity of Sparfloxacin (AT 4140, RP 64206 - SPFX) Against 275 Multiresistant Clinical Isolates

The in-vitto activity of sparfloxacin was compared with that of pefloxacin, ofloxacin, ciprofloxacin, imipenem, ceftazidime, gentamicin and amikacin against 275 multiresistant nosocomial clinical isolates. They consisted of Pseudomonas aetuginosa (37), Entetobacter cloacae (42), Acinetobactet anitratus (60), Klebsiella pneumoniae (37) and Staphylococcus sp (99). Minimum inhibitory concentrations (MIC₉₀) and geometric mean MICs for sparfloxacin were as follows (mg/1): P. aeruginosa 128 - 23.7, E. cloacae 1 - 0.13, A. anitratus 2 - 0.14, K. pneumoniae 1 - 0.08, MRSA 16 - 0.98, MSSA 0.12 - 0.03, MRSE 0.25 - 0.12 and MSSE 0.12 - 0.05. It is concluded that sparfloxacin was the most potent agent against staphylococci and A. anitratus including strains resistant to the other quinolones while ciprofloxacin was the most potent agent against P. aeruginosa, E. cloacae and K. pneumoniae.