Marek Bartoszewicz

The members of the Bacillus cereus group are commonly present contaminants of fresh and heat-treated milk.

To determine the level of milk contamination by Bacillus cereus sensu lato, 44 samples were collected from a dairy farm and two independent dairies in northeastern Poland. A total of 680 B. cereus sensu lato isolates were recovered. Based on spore counts, their highest level in milk was found during the spring and summer months. Although significant variations in chromosomal DNA polymorphisms among B. cereus sensu lato isolates were noted based on repetitive element sequence polymorphism (rep-PCR) and pulse-field gel electrophoresis (PFGE), indistinguishable B. cereus isolates were observed in all sampling points and locations. Both B. cereus sensu stricto/Bacillus weihenstephanensis and Bacillus thuringiensis cultured from milk harbored nheA, hblA, and cytK in, respectively, 80%, 55%, and 60% of the isolates. With respect to Bacillus mycoides/Bacillus pseudomycoides, 30% and 70% of theses isolates harbored, respectively, nheA and hblA. The presence of cytK was not detected in any isolate. Our data show the occurrence of potentially toxic B. cereus s.l. in both raw and heat-treated milk, thus emphasizing the requirement for precautions that prevent spore germination and vegetative proliferation by keeping the milk at low temperatures during all steps of production and dispensation to the consumers.

Natural isolates of Bacillus thuringiensis display genetic and psychrotrophic properties characteristic of Bacillus weihenstephanensis

Aim:  To determine the potential of Bacillus thuringiensis, known primarily for its entomopathogenicity, to be a psychrotolerant contaminant of stored products.

Diversity of thermal ecotypes and potential pathotypes of Bacillus thuringiensis soil isolates

Ecological diversification of Bacillus thuringiensis soil isolates was examined to determine whether bacteria adapted to grow at low temperature and/or potentially pathogenic correspond to genetically distinct lineages. Altogether, nine phylogenetic lineages were found among bacilli originating from North-Eastern Poland (n = 24) and Lithuania (n = 25) using multi-locus sequence typing. This clustering was chiefly confirmed by pulsed-field gel electrophoresis. One third of the bacilli were found to be psychrotolerant, which strongly supports the hypothesis of the existence of thermal ecotypes among B. thuringiensis. PCR screening was also performed to detect potential enterotoxin genes and Bacillus anthracis pXO1- and pXO2-like replicons. The cytK-positive isolates (22%) were significantly associated with two phylogenetic lineages (potential CytK pathotypes), whereas there was no correlation between phylogenetic grouping and the presence of the potential tripartite enterotoxin pathotypes (86% of strains). A statistically significant association between phylogenetic lineages and ecologic properties was found with regard to the cry1-positive Lithuanian isolates, while the cry genes in Polish isolates and the pXO1- and pXO2 replicon-like elements showed scattered distribution across phylogenetic lineages. Our results support the hypothesis that B. thuringiensis comprises strains belonging to different phylogenetic lineages, which exhibit specific ecological properties.

Comparison of lipid profiles of Malassezia pachydermatis strains isolated from dogs with otitis externa and without clinical symptoms of disease

Malassezia pachydermatis can cause infections of the skin and mucous membranes, especially in animals. It becomes a problem also in medicine. It is considered that metabolic disorders as well as hormonal and immunological status of the host promote diseases caused by M. pachydermatis. Here we consider whether specific features of fungi could also favour infections. We checked whether there are differences in lipid profiles between strains obtained from dogs with otitis externa and strains obtained from healthy dogs. Lipid profiles were determined using thin layer chromatography and gas chromatography–mass spectrometry. All analyses were carried out on 32 strains derived from dogs with otitis externa and 31 strains isolated from dogs without symptoms of disease. The results show that strains isolated from dogs without symptoms of otitis externa are characterised by a higher content of fatty acids. They contain significantly more behenic and lignoceric acids on medium without addition of lipids, and more oleic acid and total monounsaturated fatty acids on medium with lipids supplementation. These strains have also a higher content of esters of ergosterol and triglycerides. Data obtained show differences which may be specific features of M. pachydermatis‐specific strains related to the ability of infection, which could be not directly related of the host condition.

Genetic relationships and population structure of Malassezia pachydermatis strains isolated from dogs with otitis externa and healthy dogs

ABSTRACT Malassezia pachydermatis causes infections of the skin and mucous membranes, especially in animals. It is commonly accepted that symptom manifestation depends on the physiological status of the host (different metabolic, hormonal, and immunological disorders). However, it should be considered whether distinct strains of M. pachydermatis could have different pathogenic potential and maintain opposite relations with the host, such as commensalism or parasitism. The scope of this study was to explore the population structure, genetic diversity, and phylogenetic relationships of M. pachydermatis strains isolated from dogs with clinical symptoms of otitis externa and from healthy dogs in order to investigate their relationships and evolutionary history. For all tests, a group of 30 strains derived from dogs with otitis externa and 34 strains from healthy dogs were used. The level of genetic diversity was initially assessed by polymerase chain reaction (PCR)-based random amplification of polymorphic DNA (RAPD-PCR), whereas evolutionary history was assessed by comparison of the nucleotide sequences of the internal transcribed spacer ITS1 region of nuclear rDNA. RAPD-PCR fingerprinting revealed a high level of genetic polymorphism in both tested groups (85% of unique profiles), but clinical isolates usually grouped together with other strains from otitis externa cases. Sequencing analysis identified 17 distinct genotypes with 59 polymorphic sites within both populations; however, putatively virulent strains were more closely related, indicating a probable correlation between the genotype and the virulence potential. Therefore, the hypothesis that M. pachydermatis virulence depends solely on the host’s properties should be reconsidered including evolutionary and epidemiological data.

Spores and vegetative cells of phenotypically and genetically diverse Bacillus cereus sensu lato are common bacteria in fresh water of northeastern Poland

Gram-positive rods Bacillus cereus sensu lato (sl) are common in natural habitats and food products. It is believed that they are restricted to spores; however, their ecology in aquatic habitats is still poorly investigated. Thus, the aim of the study was to assess the rain-dependent fluctuations in the concentration of B. cereus sl vegetative cells and spores, with evaluation of their phylogenetic and population structure in relation to the toxicity and psychrotolerance. We proved that vegetative cells of B. cereus sl are widely distributed in fresh water of rivers and lakes, being as common as spores. Moreover, heavy rain has a huge impact on their concentration in undisturbed environments. The diversity of B. cereus sl reflects the multiple sources of bacteria and the differences between their distinct environments. Next, their diverse genetic structure and phenotypes better fit their ecological properties than their taxonomic affiliation.