Determination of the ID50 values of antibacterial agents in agar

The Virulence Index: A Metric for Quantitative Analysis of Phage Virulence

Background: One of the main challenges in developing phage therapy and manufacturing phage products is the reliable evaluation of their efficacy, performance, and quality. Since phage virulence is intrinsically difficult to fully capture, researchers have turned to rapid but partially inadequate methods for its evaluation. Materials and Methods: This study demonstrates a standardized quantitative method to assess phage virulence based on three parameters: the virulence index (V_P )-quantifying the virulence of a phage against a host, the local virulence (v_i )-assessing killing potential at given multiplicities of infection (MOIs), and MV₅₀ -the MOI at which the phage achieves 50% of its maximum theoretical virulence. This was shown through comparative analysis of the virulence of phages T4, T5, and T7. Results: Under the conditions tested, phage T7 displayed the highest virulence, followed by phage T4 and, finally, by phage T5. The impact of parameters such as temperature and medium composition on virulence was shown for each phage. The use of the method to evaluate the virulence of combinations of phages-for example, for cocktail formulation-is also shown with phages T5 and T7. Conclusions: The method presented provides a platform for high-throughput quantitative assessment of phage virulence and quality control of phage products. It can also be applied to phage screening, evaluation of phage strains, phage mutants, infection conditions and/or the susceptibility of host strains, and the formulation of phage cocktails.

Characterization of Enterococcus faecium mutants resistant to mundticin KS, a class IIa bacteriocin

The emergence and spread of mutants resistant to bacteriocins would threaten the safety of using bacteriocins as food preservatives. To determine the physiological characteristics of resistant mutants, mutants ofEnterococcus faeciumresistant to mundticin KS, a class IIa bacteriocin, were isolated. Two types of mutant were found that had different sensitivities to other antimicrobial agents such as nisin (class I) and kanamycin. Both mutants were resistant to mundticin KS even in the absence of Mg2+ions. The composition of unsaturated fatty acids in the resistant mutants was significantly increased in the presence of mundticin KS. The composition of the phospholipids in the two resistant mutants also differed from those in the wild-type strain. The putative zwitterionic amino-containing phospholipid in both mutants significantly increased, whereas amounts of phosphatidylglycerol and cardiolipin decreased. These changes in membrane structure may influence resistance of enterococci to class IIa and class I bacteriocins.

Cefroxadine (CGP-9000), an orally active cephalosporin

Cefroxadine (GCP-9000; CXD), 7 beta[D-2-amino-2-(1,4-cyclohexadienyl)-acetamido]-3-methoxy-ceph-3-em-carboxylic acid, is a new orally active cephalosporin derivative. The spectrum of antibacterial activity of CXD is identical with that of cephalexin (CEX), but CXD was twofold more effective than CEX against Escherichia coli and Klebsiella pneumoniae, CXD was as stable to penicillinase as CEX, but it was hydrolyzed by cephalosporinase, with a relative rate of hydrolysis similar to that of CEX. The affinities of CXD and CEX to penicillin-binding proteins of E. coli were estimated; the affinity of CXD to penicillin-binding protein 1Bs was higher than that of CEX. Consistent with this, CXD had more intensive lytic activity than CEX. In vivo antibacterial activities of CXD and CEX were compared using systemic infections of mice with E. coli and K. pneumoniae; CXD was consistently more active than CEX.

In vitro antibacterial activity of AM-715, a new nalidixic acid analog

AM-715 [1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid] is a new nalidixic acid analog. AM-715 has a broad spectrum of antibacterial activity against gram-positive and gram-negative bacteria. The antibacterial activity of AM-715 was greater than those of pipemidic acid and nalidixic acid. AM-715 had higher antibacterial activity against Pseudomonas aeruginosa than did gentamicin. Most nalidixic acid-resistant bacteria were susceptible to AM-715, and cross-resistance was not observed between AM-715 and various antibiotics. The minimal concentration of AM-715 required to inhibit the growth of 75% of the total number of clinical isolates was as follows: Escherichia coli, 0.04 mug/ml; Klebsiella pneumoniae, 0.1 mug/ml; Serratia marcescens, 0.88 mug/ml; Enterobacter spp., 0.076 mug/ml; Staphylococcus aureus, 1.10 mug/ml; P. aeruginosa, 0.38 mug/ml; and nalidixic acid-resistant strains of gram-negative bacteria, 0.62 mug/ml. AM-715 at minimal inhibitory concentrations or at slightly higher concentrations had bactericidal activity against various species of bacteria. The effect of inoculum sizes on minimal inhibitory concentrations and minimal bactericidal concentrations of AM-715 against gram-negative bacteria was smaller than on those of pipemidic acid and nalidixic acid. The dose-response curve of AM-715 indicated a steep gradient, and the 50% inhibited doses of AM-715 were 0.014 mug/ml against E. coli ML4707 and 0.21 mug/ml against P. aeruginosa NC-5.