Pectobacterium wasabiae has a narrow host range, having previously only been associated with Japanese horseradish. However, recent characterisation of Pectobacterium causing soft rotting in New Zealand has identified putative P. wasabiae isolates pathogenic to potato. In this study, phylogenetic reconstruction of acnA and mdh DNA sequences and fluorescent amplified fragment length polymorphisms (fAFLP) were used to confirm the identity of the putative P. wasabiae isolates. Both methods clustered the potato isolates closely with the type strain for P. wasabiae, ICMP9121, and also differentiated them from other plant pathogenic enterobacteria. PCR, DNA hybridisation and hypersensitive response (HR) assays were subsequently used to investigate the presence in P. wasabiae of the type III secretion system (T3SS) as well as other virulence factors known to be involved in development of disease by enterobacteria. Although all P. wasabiae strains appeared to elicit a type III-dependent HR in tobacco, genes associated with the T3SS and the putative virulence factors HecB and DspE could not be detected. Thus, genetic characterisation of P. wasabiae confirmed that it is a naturally occurring pathogen on potato, which does not possess the same suite of virulence factors that are involved in the pathogenicity of other enterobacteria on this host.

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bListeriosis is caused by the food-borne pathogen Listeria monocytogenes, which can be found in seafood and processing plants. To evaluate the risk to human health associated with seafood production in New Zealand, multi-virulence-locus sequence typing (MVLST) was used to define the sequence types (STs) of 31 L. monocytogenes isolates collected from seafood-processing plants, 15 from processed foods, and 6 from human listeriosis cases. The STs of these isolates were then compared with those from a collection of seafood isolates and epidemic strains from overseas. A total of 17 STs from New Zealand clustered into two lineages: seafood-related isolates in lineages I and II and all human isolates in lineage II. None of the New Zealand STs matched previously described STs from other countries. Isolates (belonging to ST01-N and ST03-N) from mussels and their processing environments, however, were identical to those of sporadic listeriosis cases in New Zealand. ST03-N isolates (16 from mussel-processing environments, 2 from humans, and 1 from a mussel) contained an inlA premature stop codon (PMSC) mutation. Therefore, the levels of invasiveness of 22 isolates from ST03-N and the three other common STs were compared using human intestinal epithelial Caco-2 cell lines. STs carrying inlA PMSCs, including ST03-N isolates associated with clinical cases, had a low invasion phenotype. The close relatedness of some clinical and environmental strains, as revealed by identical MVLST profiles, suggests that local and persistent environmental strains in seafood-processing environments pose a potential health risk. Furthermore, a PMSC in inlA does not appear to give L. monocytogenes a noninvasive profile.

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A real-time quantitative PCR assay targeting a 16S-23S intergenic spacer region sequence was devised to measure the sizes of populations of Lactobacillus salivarius present in ileal digesta collected from broiler chickens. This species has been associated with deconjugation of bile salts in the small bowel and reduced broiler productivity. The assay was tested as a means of monitoring the sizes of L. salivarius populations from broilers fed diets with different compositions, maintained at different stocking densities, or given the antimicrobial drugs bacitracin and monensin in the feed. Stocking densities did not influence the numbers of L. salivarius cells in the ileum. A diet containing meat and bone meal reduced the size of the L. salivarius population relative to that of chickens given the control diet, as did administration of bacitracin and monensin in the feed. These changes in the target bacterial population were associated with improved broiler weight gain.

Bacterial blotch of Agaricus bisporus has typically been identified as being caused by either Pseudomonas tolaasii (brown blotch) or Pseudomonas gingeri (ginger blotch). To address the relatedness of pseudomonads able to induce blotch, a pilot study was initiated in which pseudomonads were selectively isolated from mushroom farms throughout New Zealand. Thirty-three pseudomonad isolates were identified as being capable of causing different degrees of discoloration (separable into nine categories) of A. bisporus tissue in a bioassay. These isolates were also identified as unique using repetitive extragenic palindromic PCR and biochemical analysis. Relationships between these 33 blotch-causing organisms (BCO) and a further 22 selected pseudomonad species were inferred by phylogenetic analyses of near-full-length 16S rRNA gene nucleotide sequences. The 33 BCO isolates were observed to be distributed throughout the Pseudomonas fluorescens intrageneric cluster. These results show that in addition to known BCO (P. tolaasii, P. gingeri, and Pseudomonas reactans), a number of diverse pseudomonad species also have the ability to cause blotch diseases with various discolorations. Furthermore, observation of ginger blotch discoloration of A. bisporus being independently caused by many different pseudomonad species impacts on the homogeneity and classification of the previously described P. gingeri.The genus Pseudomonas (sensu stricto) comprises a taxon of metabolically versatile organisms that are ubiquitous in soil and water and play an important role as plant, animal, and human pathogens (37). Microbial diversity in mushroom farms has previously been reported, with pseudomonads accounting for 10% of bacteria in compost and sometimes more than 50% of bacteria in casing soils (48).Discoloration of Agaricus bisporus caused by pathogenic pseudomonads, the so-called blotch diseases, are well documented. Pseudomonas tolaasii contamination results in sunken, dark brown lesions (35, 55); Pseudomonas reactans causes mild dark purple to light brown discoloration and a slight surface depression that becomes deeper and darker with age (59); while the pale yellowish red discoloration that develops into a reddish ginger-colored discoloration (ginger blotch disease) is characteristic of Pseudomonas gingeri (60).Of the blotch-causing pseudomonads, the best characterized is P. tolaasii. P. tolaasii enters the mushroom farm in peat and limestone used in the casing process (63), and, once present, P. tolaasii is able to attach to mycelial surfaces of developing A. bisporus (40, 42). Temperature and relative humidity have been suggested as important environmental conditions that influence the pathogenicity of P. tolaasii within the mushroom farm (50). A minimal application of 2.7 ϫ 10 6 to 10 8 CFU ⅐ ml Ϫ1 of P. tolaasii was reported as the threshold for inducing disease (34), although other thresholds have been proposed (31,44,62). Pathogenic P. tolaasii isolates synthesize a lowmolecular-weight extracellular toxin, tolaasin, that is the p...

Two field trials were conducted to investigate different herbage grasses and cereals for their susceptibility to the disease take-all, for their impact on concentrations of the pathogen, Gaeumannomyces graminis var. tritici (Ggt), in soil and for their effect on development of take-all in a subsequent wheat crop. In the herbage grass trial, Bromus willdenowii was highly susceptible to Ggt, produced the greatest post-senescence Ggt concentrations in soil and highest incidence of take-all in following wheat crop. Lolium perenne, Lolium multiflorum and Festuca arundinacea supported low Ggt soil concentrations and fallow the least. The relationship between susceptibility to Ggt and post-senescence concentrations in soil differed between pasture grasses and cereals. In a trial in which Ggt was added to half the plots and where wheat, barley, triticale, rye or fallow were compared, the susceptibility of the cereals to take-all was not clearly linked to post-harvest soil Ggt concentrations. In particular, triticale and rye had low and negligible take-all infection respectively, but greater postharvest soil Ggt concentrations than barley or wheat. This indicates that low Ggt concentrations on roots may build up during crop senescence on some cereals. Soil Ggt concentrations were greater following harvest in inoculated plots sown to cereals, but in the second year there was more take-all in the previously noninoculated than inoculated plots. Thus, the grass and cereal species differed in susceptibility to take-all, in their impact on Ggt multiplication and in associated take-all severity in following wheat crop.

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