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soluble low-molecular-weight thiazoline derivatives containing a 2-hdroxyphenylthiazolinyl-thiazolidine scaffold. Pyoverdines and pyochelines are reported to
enhance antibacterial activity of antimicrobial drugs if administered in the form of
a complex. Pyoverdin-ampicillin conjugates and pyochelin-gallium conjugates
were shown to have better antimicrobial activity against Pseudomonas aeruginosa
when compared to activity of the drugs alone.
Polyketides Pseudomonas produces many secondary metabolites of biological
importance using the polyketide pathway with the help of the enzyme polyketide
synthase. Mupirocin, pyoluteorin and 2,4-diacetylphloroglucinol are examples of
polyketide antimicrobials produced by Pseudomonas. Pseudomonic acids are a
group of closely related antibiotics with a 17-carbon skeleton in their structure.
Pseudomonic acid A–E are produced by P.s fluorescens. Pseudomonic acid A is also
called mupirocin (Fig. 12.7a), which shows activity against gram-positive organisms, especially against superficial infections caused by S. aureus. The antibiotic is
also active against some gram-negative bacteria like Haemophilus influenzae and
Neisseria gonorrhoeae but is much less active against most gram-negative bacilli
anaerobes. Mupirocin shows bacteriostatic effect at low concentrations and is bactericidal at high concentrations. Mupirocin exerts its antibacterial activity by binding to the isoleucine tRNA synthetase thereby inhibiting protein synthesis.
Pyoluteorin (Fig. 12.7b) is an antifungal compound containing a biochlorinated pyrrole linked to a resorcinol moiety produced by certain strains of P. flurescens.
Pylouteorin can effectively inhibit phytopathogenic fungi, including the plant
pathogen Pythium ultimum, and suppress plant diseases caused by this fungus. 2,
4-Diacetylphloroglucinol (DAPG) is a polyketide produced by P. fluorescens both
in vitro and in the rhizosphere of wheat. Apart from its activity as a biocontrol
agent, DAPG shows broad-spectrum antifungal and antibacterial effects. It causes
membrane damage to the phytopathogenic Pythium spp. and is particularly inhibitive of the zoospores of these fungi (de Souza et al. 2003).
Modified Lipopeptides Lipodepsinonapeptides are a class of phytotoxins which are
composed of a polar head and a hydrophobic 3-hydroxy fatty acid chain.
Syringomycin (Fig. 12.7c) is a representative compound of this group produced by
most strains of P. syringae. Three types of syringomycins are produced that differ
only by the length of the fatty acid moiety: decanoic acid (syringomycin A1),
dodecanoic acid (syringomycin E) and tetradecanoic acid (syringomycin G).
Syringotoxins and syringostatins are lipodepsinonapeptides produced by P. syringae isolated from citrus and lilac hosts, respectively. Pseudomycin is isolated from
saprophytic P. syringae inhabiting barley. Syringomycin and other lipodepsinonapeptides show fungicidal activity against a broad spectrum of filamentous fungi
such as Geotrichum candidum and yeasts such as Rhodotorula pilimanae. The antifungal properties of syringomycins were sought to be exploited against clinically
relevant fungi like Candida and postharvest fungal pathogens of citrus fruit such as
12 Antimicrobials from Microbes
soluble low-molecular-weight thiazoline derivatives containing a 2-hdroxyphenylthiazolinyl-thiazolidine scaffold. Pyoverdines and pyochelines are reported to
enhance antibacterial activity of antimicrobial drugs if administered in the form of
a complex. Pyoverdin-ampicillin conjugates and pyochelin-gallium conjugates
were shown to have better antimicrobial activity against Pseudomonas aeruginosa
when compared to activity of the drugs alone.
Polyketides Pseudomonas produces many secondary metabolites of biological
importance using the polyketide pathway with the help of the enzyme polyketide
synthase. Mupirocin, pyoluteorin and 2,4-diacetylphloroglucinol are examples of
polyketide antimicrobials produced by Pseudomonas. Pseudomonic acids are a
group of closely related antibiotics with a 17-carbon skeleton in their structure.
Pseudomonic acid A–E are produced by P.s fluorescens. Pseudomonic acid A is also
called mupirocin (Fig. 12.7a), which shows activity against gram-positive organisms, especially against superficial infections caused by S. aureus. The antibiotic is
also active against some gram-negative bacteria like Haemophilus influenzae and
Neisseria gonorrhoeae but is much less active against most gram-negative bacilli
anaerobes. Mupirocin shows bacteriostatic effect at low concentrations and is bactericidal at high concentrations. Mupirocin exerts its antibacterial activity by binding to the isoleucine tRNA synthetase thereby inhibiting protein synthesis.
Pyoluteorin (Fig. 12.7b) is an antifungal compound containing a biochlorinated pyrrole linked to a resorcinol moiety produced by certain strains of P. flurescens.
Pylouteorin can effectively inhibit phytopathogenic fungi, including the plant
pathogen Pythium ultimum, and suppress plant diseases caused by this fungus. 2,
4-Diacetylphloroglucinol (DAPG) is a polyketide produced by P. fluorescens both
in vitro and in the rhizosphere of wheat. Apart from its activity as a biocontrol
agent, DAPG shows broad-spectrum antifungal and antibacterial effects. It causes
membrane damage to the phytopathogenic Pythium spp. and is particularly inhibitive of the zoospores of these fungi (de Souza et al. 2003).
Modified Lipopeptides Lipodepsinonapeptides are a class of phytotoxins which are
composed of a polar head and a hydrophobic 3-hydroxy fatty acid chain.
Syringomycin (Fig. 12.7c) is a representative compound of this group produced by
most strains of P. syringae. Three types of syringomycins are produced that differ
only by the length of the fatty acid moiety: decanoic acid (syringomycin A1),
dodecanoic acid (syringomycin E) and tetradecanoic acid (syringomycin G).
Syringotoxins and syringostatins are lipodepsinonapeptides produced by P. syringae isolated from citrus and lilac hosts, respectively. Pseudomycin is isolated from
saprophytic P. syringae inhabiting barley. Syringomycin and other lipodepsinonapeptides show fungicidal activity against a broad spectrum of filamentous fungi
such as Geotrichum candidum and yeasts such as Rhodotorula pilimanae. The antifungal properties of syringomycins were sought to be exploited against clinically
relevant fungi like Candida and postharvest fungal pathogens of citrus fruit such as
12 Antimicrobials from Microbes