Microbiology - Volume 136, Issue 6, 1990

Several inhibitors of ornithine and arginine decarboxylases reduced growth of the fungus Botrytis cinerea cultured on Czapek Dox agar. Of these, the most effective were difluoromethylornithine (DFMO), dehydromonofluoro-methylornithine, difluoromethylarginine and dehydromonofluoromethylarginine. The growth inhibition due to 1 mm-DFMO could be partially reversed with 1 μm-putrescine. Other compounds causing significant reversal of DFMO-mediated growth inhibition included diaminopentane (cadaverine), diaminoheptane, spermidine, 7,7-difluorospermidine, spermine, bis(2-aminoethyl)amine, 2-hydroxy-1,3-diaminopropane, monoacetylputrescine, butenediamine and aminoguanidine. Some compounds, which were relatively innocuous by themselves, increased growth inhibition due to DFMO. Notably effective compounds were methylacetylenicputrescine, aminooxyaminopropane, butynediamine, 2,2-difluoroputrescine, diacetylputrescine, methylglyoxal bis(guanylhydrazone), streptomycin, certain methylated amines, and cyclohexylamine and related compounds. Growth inhibition due to a homologous series of diguanidines [NH2C(=NH)NH(CH2) x NHC(=NH)NH2] was also tested. These were especially effective when x = 12, and when x = 5 or 6. In general, the results suggest that amino-acid-based inhibitors of ornithine decarboxylase have a greater permeability than amine-based inhibitors.

Four, NAD-independent, clinical isolates of Haemophilus parainfluenzae were recovered from a genital ulcer, a purulent skin lesion, a sputum specimen and a throat swab respectively. With the exception of NAD requirement, the strains exhibited the biochemical characteristics of H. parainfluenzae biotype II. The genetic relationship between these isolates and a standard strain of H. parainfluenzae was determined by testing transforming activities of two chromosomal markers, streptomycin resistance and nalidixic acid resistance. The clinical isolates were efficient donors and recipients in transformation. In addition, we demonstrated transfer of the genes conferring NAD independence to typical, NAD-requiring H. parainfluenzae and Haemophilus influenzae strains.

While wild-type Escherichia coli K12 cannot grow with l-serine as carbon source, two types of mutants with altered methionine metabolism can. The first type, metJ mutants, in which the methionine biosynthetic enzymes are expressed constitutively, are able to grow with l-serine as carbon source. Furthermore, a plasmid carrying the metC gene confers ability to grow on l-serine. These observations suggest that in these mutants, l-serine deamination may be a result of a side-reaction of the metC gene product, cystathionine β-lyase: The second type is exemplified by two newly isolated strains carrying mutations mapping between 89·6 and 90 min. These mutants use l-serine as carbon source, and also require methionine for growth with glucose at 37°C and above. The phenotypes of the new mutants resemble those of both met and his constitutive mutants in some respects, but have been differentiated from both of them.

Escherichia coli strain H.I.8 (O128:B12) produces low levels of a Shiga-like toxin (SLT) which we have called SLTIIva because of its close relationship with SLTIIv. The Vero cell cytotoxicity of SLTIIva is neutralized by antisera against SLTII and SLTIIv but not by antisera against SLTI. These data indicate that the SLT of strain H.I.8 is a member of the SLTII family. Since SLTIIva shares with SLTIIv the property of having low cytotoxicity to HeLa cells compared with Vero cells, it is appropriate to consider both toxins as variants of SLTII. SLTIIva differs from SLTIIv in that it is more heat-stable. Further, SLTIIv-producing strains of E. coli have only been isolated from pigs while the SLTIIva-producing E. coli strain examined in this study was isolated from a human infant with diarrhoea. The genes for this SLT were cloned from a cosmid library of total cellular DNA by screening recombinants for Vero cell toxicity and with a DNA probe derived from SLTIIv structural genes. Nucleotide sequence analysis was performed on a 2·0 kb AvaII-HincII fragment which encodes the toxin gene. The nucleotide sequence data confirm the close relationship between SLTIIva and SLTIIv: they have 98% nucleotide sequence homology in the B subunit gene and 70·6% homology in the A subunit gene. Comparison of DNA sequences indicated that SLTIIva was most closely related to SLTIIv, closely related to SLTII and less closely related to SLTI.

Low concentrations (41 μm) of Hinosan (Edifenphos) inhibited hyphal extension and decreased the hyphal growth unit length and phosphatidylcholine content of Fusarium graminearum A3/5, but had no effect on specific growth rate. Thus, at low concentrations, Hinosan acted as a paramorphogen, increasing hyphal branching, but not inhibiting growth. The colony radial growth rate and specific growth rate of F. graminearum were significantly decreased at Hinosan concentrations of 82 μm and 492 μm, respectively.