Selective synthetic growth medium “Acinetobacter phenylalanine agar” for isolation and identification of Acinetobacter calcoaceticus — Acinetobacter baumannii complex species

The aim of the study was to carry out clinical and microbiological testing of selective growth medium Acinetobacter phenylalanine agar to isolate and identify bacterial species belonging to the Acinetobacter calcoaceticus — Acinetobacter baumannii complex (ACB complex). For this, 400 samples of clinical material (wound discharge, blood, urine, bronchoalveolar lavage) were examined in 2018 in the Clinical and Bacteriological Laboratory of the Military Medical Academy by using routine assays (seeding on blood agar growth medium, pure culture isolation and identification by using biochemical assays as well as VITEK 2 microbial identification system, bioMerieux) and plating together with growth medium Acinetobacter phenylalanine agar selective to Acinetobacter spp. owing to L-phenylalanine as a sole nitrogen and carbon source additional selected with trimethoprim. ACB complex Acinetobacters were identified 18–24 hours later after incubation at 37°C by emergence of typical colonies on selective medium. Control tests for cytochrome oxidase as well as oxidative/fermentation (OF)-glucose test by using peroxide-hydrogen microvolume method (for 1 h) allowed to rapidly distinguish ACB complex Acinetobacters from other bacteria as well as from Acinetobacter spp. unable to glucose oxidation. Next, species identity for all isolated Acinetobacter strains was established by using matrix-activated laser desorption/ionization with time-of-flight mass spectrometry (MALDI-TOF MS). It was found that by using novel vs. routine assay Acinetobacter spps. were isolated in 26 (18 samples — in monoculture, 8 — in association with Pseudomonas aeruginosa or Klebsiella pneumoniae subsp. pneumoniae with tiny associate colonies) vs. 20 (7 — in monoculture, 13 — in association with Pseudomonas aeruginosa, Klebsiella, Escherichia, Citrobacter, Providencia, Staphylococcus, Enterococcus, C. albicans). Using MALDI-TOF MS method revealed that 25 out of 26 Acinetobacter strains isolated on selective growth medium belonged to the ACB complex (A. baumannii — 23, A. pittii — 2), whereas one strain (A. baylyi) did not belong to ACB complex. Hence, the diagnostic specificity of the Acinetobacter phenylalanine agar synthetic growth medium for isolation and identification of the A. calcoaceticus — A. baumannii complex species comprised 96.2%, with diagnostic sensitivity exceeding that one for routine assay by 25%. Use of selective growth medium accelerates research by allowing to isolate and identify ACB complex Acinetobacter spp. 18–24 h later after plating clinical material. Selectivity of growth medium was potentially stable, as its major trophic selection factor did not depend on acquired bacterial antibiotic resistance, which is also suitable as a synthetic growth medium for standardized studies.

Characterization of the biocontrol activity of Debaryomyces hansenii in the control of Penicillium digitatum on grapefruit

Interactions between Debaryomyces hansenii and Penicillium digitatum were studied in culture and on fruit to better characterize the observed biological control of green mold on grapefruit by the yeast. The antagonist did not produce antibiotic substances in culture and was ineffective in protecting against the disease when killed by heat or chemicals. Incidence of green mold was dependent upon the concentration of both the pathogen spores and the antagonist yeast cells. Control of green mold was most effective at 109 cfu/mL of D. hansenii. The role of available nutrients in the biological control activity of D. hansenii was assessed. Significant inhibition of spore germination and hyphal growth of P. digitatum in culture was achieved by the addition of the yeast cells to a minimal synthetic growth medium. Inhibition of P. digitatum by the antagonist in culture and on the fruit peel could be overcome by the addition of exogenous nutrients. Our results indicate that competition for nutrients may play a role in the biocontrol of P. digitatum by D. hansenii on grapefruit.Key words: biological control, Penicillium digitatum, Debaryomyces hansenii, grapefruit.

Variations du contenu lipidique occasionnées par la carence en pyridoxine du milieu nutritif de Ceratocystis ulmi

Pyridoxin deficiency of the synthetic growth medium results on four of the five strains of the studied Ceratocystis ulmi in an increase (6.9 to 18.8%) of the lipid content of the mycelium. This increase mainly affects the neutral lipid fraction. The analysis of fatty acids shows a significative decrease, both in the neutral and the polar lipid fraction, of the polyunsaturated fatty acid content, and in some cases the total disappearance of the linolenic acid.

An improved synthetic growth medium for Halobacterium cutirubrum

A synthetic medium is described in which Halobacterium cutirubrum grows as well as in complex media.

Adenosine-induced bacteriostasis in Micrococcus sodonensis

In a synthetic growth medium at a concentration of 1.0 mM, adenosine had a marked bacteriostatic effect on the growth of Micrococcus sodonensis. With the exceptions of hypoxanthine and inosine, which were slightly inhibitory, other purine bases and ribonucleosides did not inhibit the growth of the organism. When incubation of adenosine-supplemented cultures was prolonged, the organism was able to recover from the growth inhibition after a period of time which varied directly with the initial adenosine concentrations. Chromatographic analysis of the supernatants of those cultures revealed that exogenous adenosine concentrations declined steadily and the termination of the inhibited phase of growth correlated with the exhaustion of exogenous adenosine.It was observed that de novo biosynthesis of thiamine was inhibited in adenosine-supplemented cultures and that this inhibition was also relieved upon the exhaustion of exogenous adenosine. Bacteriostasis could be prevented by including either thiamine or its pyrimidine precursor (B1-pyrimidine) in adenosine-supplemented cultures and it was concluded that the observed growth inhibition reflected a depletion of the intracellular thiamine pool resulting from an adenosine-associated inhibition of B1-pyrimidine biosynthesis.