Mechanism of Antibacterial Antibiotic Sensitivity in Pythium ultimum

Abstract

The unusual sensitivity of a Pythium ultimum isolate to three inhibitors of prokaryote protein synthesis [tetracycline (TET), chloramphenicol (CAM), erythromycin (ERY)] was investigated. TET inhibited growth in shake culture by 40 yo at 10 ,ug ml-I and 99 yo at 100 pg ml-l within 5 h (one doubling period). CAM inhibited growth by 40 yo at 500 pg ml-l and 70°,, at I mg ml-l. Cycloheximide (CHI), a eukaryote protein synthesis inhibitor, blocked growth completely at 1 pg ml-l. These agents reduced incorporation of leucine and phenylalanine into protein by 40 to 50 yo (100 pg TET ml-l, 500 pg CAM ml-l) or 93 0;(1 pg CHI ml-l) within 20 min. This rapid inhibitory effect could not be attributed to impaired mitochondrial energy generation. TET inhibition increased to 90 yo by 60 min, but CAM inhibition did not change for 5 h. TET inhibited both the transport and protein synthetic (cytoplasmic) components of amino acid incorporation, but CAM impaired only the transport activity. CHI blocked protein synthesis, but did not inhibit transport detectably. In contrast to these results, growth inhibition by ERY did not increase with dose (4004 inhibition at 10 to 500 pg ml-l), and ERY at 500 pg ml-l inhibited neither amino acid transport nor protein synthesis in 5 h. The results indicate that the sensitivity of P. ultimum to these prokaryote inhibitors reflects unusual permeability properties, which account for impaired transport (CAM, TET) and allow access of the drugs to sensitive intracellular sites, the cytoplasmic (TET) and mitochondrial (ERY) protein synthetic systems.

In Vitro Susceptibility of Pythium insidiosum to Macrolides and Tetracycline Antibiotics

“…This is the first description of the inhibitory action of macrolides and tetracycline antibiotics against P. insidiosum isolated from animal pythiosis cases. The mechanism of action of these classes of antibiotics against P. insidiosum should be similar to that described for Pythium ultimum, i.e., reduced incorporation of amino acids into proteins, inhibition of protein synthesis, and inhibition of amino acid transport (17).…”

“…Although the mechanism of action of these drugs on eukaryotic organisms is not completely understood, the main mechanisms described include the inhibition of protein synthesis (14,17) and selective inhibition of both mitochondrial and plastid activity (12) and intracellular calcium release (22). However, there have been no susceptibility studies using these classes of antibiotics against P. insidiosum.…”

“…The inability of the genus Pythium to synthesize ergosterol explains the difficulties of antifungal therapy because ergosterol is the target of action for the majority of antifungal agents (19). Interestingly, previous studies have shown that Pythium ultimum and Pythium debaryanum are quite sensitive to the 70S ribosome-active antibiotics, such as tetracyclines and erythromycin (16,17).…”

In Vitro Susceptibility of Pythium insidiosum Isolates to Aminoglycoside Antibiotics and Tigecycline

“…Members of the genus Pythium are known to be susceptible to some antibiotics of the tetracycline, macrolide, aminoglycoside, and amphenicol classes (5,6,8,12). McMeekin and Mendoza (9) reported that streptomycin may have a stimulatory or inhibitory effect on P. insidiosum depending on the culture conditions, and Loreto et al (7) described an in vitro inhibitory activity of minocycline against P. insidiosum.…”

“…The absence of ergosterol in the cell wall of this oomycete restrains the treatment of pythiosis with antifungal therapy due to the fact that most antifungal drugs act by inhibiting the synthesis of ergosterol. Radical surgery and immunotherapy are among the best therapeutic options, but the improved cure rates are directly associated with early diagnosis of pythiosis (14).Members of the genus Pythium are known to be susceptible to some antibiotics of the tetracycline, macrolide, aminoglycoside, and amphenicol classes (5,6,8,12). McMeekin and Mendoza (9) reported that streptomycin may have a stimulatory or inhibitory effect on P. insidiosum depending on the culture conditions, and Loreto et al (7) described an in vitro inhibitory activity of minocycline against P. insidiosum.…”