Susceptibility of Staphylococcus aureus and Staphylococcus epidermidis to 65 Antibiotics

Abstract

The susceptibilities of 36 recent isolates of Staphylococcus aureus and 35 recent isolates ofStaphylococcus epidermidis were determined against each of 65 antimicrobial agents and against two of them in combination. Rifampin was the most active of all the agents tested against both S. aureus and S. epidermidis. Among the penicillins, cloxacillin, dicloxacillin, and nafcillin were most active, although benzylpenicillin and phenoxymethyl penicillin were more active against susceptible strains. Cephaloridine was the most active of the cephalosporins, and sisomicin was the most active aminoglycoside. Minocycline was more active than the other tetracycline analogues tested. Among the macrolide-lincomycin compounds in clinical use, clindamycin was more active, and lincomycin was less active than erythromycin. The synergy of trimethoprimsulfamethoxazole was more striking against S. aureus than against S. epidermidis. The median minimal inhibitory concentrations of the penicillins, cephalosporins, and aminoglycosides were lower against S. aureus, whereas the minimal inhibitory concentrations of the tetracyclines were lower against S. epidermidis.A large number of new natural and semisynthetic antibiotics with anti-staphylococcal activity have been introduced recently. This study was performed to compare their activities with those of other compounds that have been available for several or more years. The desirability of having comparative data on the same organisms from one laboratory, obtained by a uniform method, is obvious.Tests were performed on both Staphylococcus aureus and Staphylococcus epidermidis for the purpose of observing possible differences, and also to obtain information that would be potentially useful in clinical medicine. MATERIALS AND METHODSSixty-five antimicrobial preparations and two of them in combination (trimethoprim plus sulfamethoxazole in a ratio of 1:16; this was selected for convenience of making dilutions for the test -a ratio of 1:20, which has been suggested as the trimethoprim/sulfamethoxazole ratio in blood, might have been used, but no great differences in results were anticipated by using 1:16) were tested for antibacterial activity against 36 strains of S. aureus and 35 strains of S. epidermidis (in several instances, only 12 strains of S. aureus and 12 or 32 strains of S. epidermidis were tested). The antimi- Tables 1 through 3; also shown in these tables are the abbreviations for each compound, as used in the figures.The organisms tested were all recent clinical isolates at Boston City Hospital, provided by A. Kathleen Daly and Alice McDonald, and identified on the basis of colonial morphology, Gram stain, coagulase reaction, and mannitol fermentation tests. The susceptibility testing was done by the agar dilution method using Mueller-Hinton agar and the inocula replicator of Steers et al. (8), using as inoculum 10-3 dilutions of overnight cultures. Plates were read for inhibition of growth after 18 h of incubation at 37 C and compared with a refrigerated, inoculated control (fo...

Efficacy of High Doses of Levofloxacin in Experimental Foreign-Body Infection by Methicillin-Susceptible Staphylococcus aureus

“…Rifampin never achieved a bactericidal effect in either phase. While rifampin has usually been considered an antistaphylococcal bactericidal agent (28,35,41), some authors have reported results consistent with our own (3, 9, 17). In contrast, levofloxacin reached a potent killing rate in the log phase and it also showed bactericidal activity in the stationary phase, although higher concentrations than those for the exponential phase were required.…”

Use of a Heavy Inoculum in the In Vitro Evaluation of the Anti-Staphylococcal Activity of 19 Cephalosporins

“…However, most of the standard in vitro studies have shown little or no difference in the anti-staphylococcal activity of those newest cephalosporins in comparison with other cephalosporins that have been available for several years or more (5,15,17). Previous studies (3,14) have already established a certain correlation between the susceptibility of various cephalosporins to staphylococcal ,B-lactamase and the magnitude of the effect of the inoculum size when those same cephalosporins were tested against large and small inocula of staphylococci.…”

“…However, most of the standard in vitro studies have shown little or no difference in the anti-staphylococcal activity of those newest cephalosporins in comparison with other cephalosporins that have been available for several years or more (5,15,17 …”

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm

“…The treatment of extremity trauma can be complicated by polymicrobial infections and systemic antibiotic treatment that can be toxic to organ systems [6,11,13,35,56,58]. Localized antimicrobial drug delivery systems, including biomaterial carrier matrices and coatings on implants, have become a focus to combat biofilm formation and infection for both preventive and treatment strategies [1,7,13,27,29,43,49,63,64].…”

“…The five coating-type groups (12 catheters in six mice) included uncoated wires; uncoated wires with codelivery of antibiotic solution (1 lg/mL vancomycin; 16 lg/mL amikacin); phosphatidylcholine-only coated; AV-combination coated; and A-coated. Amikacin was chosen as a single high-dose antibiotic because of its activity against S aureus as well as Gram-negative bacteria [58]. Two catheters from the same experimental group were implanted into the dorsa of each mouse bilaterally, one each on the right and left side of the spine, and then inoculated with a polymicrobial mixture of 10 5 CFUs of S aureus (UAMS-1) and 10 4 CFUs of P aeruginosa (Schroeter) Migula (ATCC 1 27317 TM , Manassas, VA, USA) directly into the lumen of the catheter.…”