Antibiotic Susceptibility Tests with Fastidious and Nonfastidious Bacterial Reference Strains: Effects of Aerobic versus Hypercapnic Incubation

Abstract

Representative antimicrobial drugs were examined under aerobic and hypercapnic (3 and 5% v/v CO₂) incubation with the Bauer-Kirby agar disk diffusion, a broth microdilution method, and the agar dilution procedure against nonfastidious, standard ATCC quality control strains and against two Β-hemolytic streptococcal, two pneumococcal, and three Haemophilus influenzae ATCC strains. It was found that an atmosphere of 3-5% CO₂ merely antagonized amikacin, gentamicin, and netilmicin; the activity of penicillin G was antagonized only against Staphylococcus aureus ATCC 29213 in broth media, but not against any of the other strains. The activity of teicoplanin, and less so that of vancomycin, was enhanced only against S. aureus strain ATCC 25923, but not against the other strains. It was concluded that susceptibility tests, excluding aminoglycoside antibiotics, of Β-hemolytic streptococci, pneumococci, and H. influenzae and H. parainfluenzae should be incubated under 3% (candle jar or incubator) or 5% CO₂ (incubator) so as to ensure optimal growth of capnephilic strains and thus avoid potentially misleading large inhibition zones or deceptively low minimal inhibitory concentrations.

Antimicrobial activity of methyl australate from Ganoderma australe

“…Likely, the increase of lipophilicity, due to the methylation of the carboxyl group, facilitate the transport of this substance through outer membrane of the Gram-negative cell, once it is formed by lipoproteins, lipopolysaccharides, and phospholipids. The values found in the microrganisms-test for the reference compounds, tetracycline, ampicillin and fl uconazol, were in accordance with those reported in the literature (Pfaller et al, 1995;Traub;Leonhard, 1995).…”

Antibacterial activity of orsellinates

“…This phenomenon corresponds to increased lipophilicity of the molecule, wich permits penetration into cell membranes (9). The MIC values of these two compounds are equivalent to those described in the literature for a great number of commercial antibiotics used in clinical treatments (8,10,11). E. coli was not sensitive to the substances tested.…”

Antagonism of Teicoplanin and Vancomycin Activity by Chocolatized Mueller-Hinton Agar

“…Disk susceptibility tests were carried out according to the method of Bauer et al [4]; the diameters of the inhibition zones were interpreted using the latest NCCLS criteria [5], The agar dilution method [2] served to determine the minimal inhibitory concentra tions (MICs) of the two glycopeptide antibiotics. The bacterial suspensions in saline (turbidity = McFarland Values are the diameters (mm) of inhibition zones.1 = Intermediate disk susceptibility; R = resistance (disk); ND = not done.…”

“…Recent investigations regarding the inhibi tory activities of several antimicrobial drugs against diverse fastidious and nonfastidious bacteria on/in various media disclosed that chocolatized (80°C, 13 min) Mueller-Hinton agar (CHOC-MHA), which contained 5% (vol/vol) defibrinated sheep blood, antago nized the glycopeptide antibiotics teicoplanin and vancomycin against enterococci, pneu mococci, staphylococci, and streptococci [1,2], Very recently, Jensen ct al. [3] observed that 5% (vol/vol) horse blood in various me dia antagonized teicoplanin and vancomycin; however, chocolatized media were not inves tigated.…”