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Archives of Microbiology (v.193, #11)

Epidemiology and molecular mechanism of integron-mediated antibiotic resistance in Shigella by Xing Ke; Bing Gu; Shiyang Pan; Mingqing Tong (pp. 767-774).

Integrons are gene capture and expression systems that are characterized by the presence of an integrase gene. This encodes an integrase, a recombined site, and a promoter. They are able to capture gene cassettes from the environment and incorporate them using site-specific recombination. The role of integrons and gene cassettes in the dissemination of multidrug resistance in Gram-negative bacteria is significant. In Shigella species, antimicrobial resistance is often associated with the presence of class 1 and class 2 integrons that contain resistance gene cassettes. Multiple and complex expression regulation mechanisms involving mobile genetic elements in integrons have been developed in the evolution of Shigella strains. Knowledge of the epidemiology and molecular mechanisms of antimicrobial resistance in this important pathogen is essential for the implementation of intervention strategies. This review was conducted to introduce the structures and functions of integrons in Shigella species and mechanisms that control integron-mediated events linked to antibiotic resistance.

Keywords: Shigella ; Integron; Antimicrobial resistance; Gene cassettes

Factors affecting survival of Listeria monocytogenes and Listeria innocua in soil samples by Heather P. McLaughlin; Pat G. Casey; Jeni Cotter; Cormac G. M. Gahan; Colin Hill (pp. 775-785).

We investigated the ability of several strains of L. monocytogenes and Listeria innocua strains to survive in local soil samples in vitro. Survival of three L. monocytogenes strains, EGDe, CD83, and CD1038, and three L. innocua strains, CLIP, FH2117, FH2152, was monitored in soil samples by direct enumeration of colony-forming units on selective agar. The study did not demonstrate any species-specific difference in soil survival, and all Listeria strains exhibited a marked decline in numbers over time. Bioluminescence imaging approaches to detect lux-tagged strains in soil proved largely ineffective, most likely due to the reduced metabolic activity of strains in this environment. We investigated the influence of specific factors including the presence of a background microbiota, growth temperature, moisture and strain motility upon persistence in this environment. A sequenced L. monocytogenes strain, EGDe, was capable of active growth in sterile soil yet exhibited a decline in the presence of the normal soil microbiota. Furthermore, greater survival was seen at lower incubation temperatures in normal soil. Finally, we demonstrated a direct correlation between motility and survival of L. monocytogenes in soil with highly motile L. monocytogenes strains exhibiting greater soil survival than non-motile mutants.

Keywords: Listeria; Soil; Motility; Virulence; Metal

Osmotic stress response in C. glutamicum: impact of channel- and transporter-mediated potassium accumulation by Ines Ochrombel; Markus Becker; Reinhard Krämer; Kay Marin (pp. 787-796).

Potassium accumulation is an essential aspect of bacterial response to diverse stress situations; consequently its uptake plays a pivotal role. Here, we show that the Gram-positive soil bacterium Corynebacterium glutamicum which is employed for the large-scale industrial production of amino acids requires potassium under conditions of ionic and non-ionic osmotic stress. Besides the accumulation of high concentrations of potassium contributing significantly to the osmotic potential of the cytoplasm, we demonstrate that glutamate is not the counter ion for potassium under these conditions. Interestingly, potassium is required for the activation of osmotic stress-dependent expression of the genes betP and proP. The Kup-type potassium transport system which is present in C. glutamicum in addition to the potassium channel CglK does not contribute to potassium uptake at conditions of hyperosmotic stress. Furthermore, we established a secondary carrier of the KtrAB type from C. jeikeium in C. glutamicum thus providing an experimental comparison of channel- and carrier-mediated potassium uptake under osmotic stress. While at low potassium availability, the presence of the KtrAB transporter improves both potassium accumulation and growth of C. glutamicum upon osmotic stress, at proper potassium supply, the channel CglK is sufficient.

Keywords: CglK; KtrAB; Gene expression; C. jeikeium

Survival of thermophilic and hyperthermophilic microorganisms after exposure to UV-C, ionizing radiation and desiccation by Kristina Beblo; Thierry Douki; Gottfried Schmalz; Reinhard Rachel; Reinhard Wirth; Harald Huber; Günther Reitz; Petra Rettberg (pp. 797-809).

In this study, we investigated the ability of several (hyper-) thermophilic Archaea and phylogenetically deep-branching thermophilic Bacteria to survive high fluences of monochromatic UV-C (254 nm) and high doses of ionizing radiation, respectively. Nine out of fourteen tested microorganisms showed a surprisingly high tolerance against ionizing radiation, and two species (Aquifex pyrophilus and Ignicoccus hospitalis) were even able to survive 20 kGy. Therefore, these species had a comparable survivability after exposure to ionizing radiation such as Deinococcus radiodurans. In contrast, there was nearly no difference in survival of the tested strains after exposure to UV-C under anoxic conditions. If the cells had been dried in advance of UV-C irradiation, they were more sensitive to UV-C radiation compared with cells irradiated in liquid suspension; this effect could be reversed by the addition of protective material like sulfidic ores before irradiation. By exposure to UV-C, photoproducts were formed in the DNA of irradiated Archaea and Bacteria. The distribution of the main photoproducts was species specific, but the amount of the photoproducts was only partly dependent on the applied fluence. Overall, our results show that tolerance to radiation seems to be a common phenomenon among thermophilic and hyperthermophilic microorganisms.

Keywords: Radiation; UV-C; Ionizing; Survival; Hyperthermophilic; Desiccation

In vitro and in vivo pathogenicity of Salmonella enteritidis clinical strains isolated from North America by Devendra H. Shah; Xiaohui Zhou; Tarek Addwebi; Margaret A. Davis; Douglas R. Call (pp. 811-821).

Salmonella enteritidis is a leading cause of food-borne gastroenteritis worldwide. In this study, 48 strains of S. enteritidis isolated from clinical cases of salmonellosis in North America were tested for their virulence-associated traits including cell invasiveness, biofilm, motility, presence of a virulence plasmid, and virulence in orally challenged mice. The majority of strains exhibited high invasiveness (n = 45), whereas only few strains (n = 3) exhibited low invasiveness. All low-invasive strains (100%, 3/3) were biofilm negative, whereas the distribution of biofilm positive and negative phenotypes among high-invasive strains was 53.4% (24/45) and 46.6% (21/45), respectively. The in vitro cell invasiveness was not associated with biofilm formation (Fisher’s exact test, P = 0.23) or the presence of a spvB gene, a marker for the virulence-associated plasmid (Fisher’s exact test, P = 1). There was no correlation between cell invasiveness and motility (Spearman’s rank test, r = −0.15; P = 0.27). Virulence testing in orally challenged mice revealed that the low-invasive strains were as virulent as high-invasive strains, indicating that in vitro cell invasiveness did not correlate with in vivo virulence. In conclusion, we show that despite phenotypic diversity among clinical strains of S. enteritidis, the majority of strains are highly invasive in vitro and in vivo.

Keywords: Salmonella enteritidis ; Motility; Biofilm; Virulence

Growth phase-dependent UV-C resistance of Bacillus subtilis: data from a short-term evolution experiment by Marko Wassmann; Ralf Moeller; Günther Reitz; Petra Rettberg (pp. 823-832).

After 700 generations of a short-term evolution experiment with Bacillus subtilis 168, two strains were isolated, the UV-adapted strain MW01 and the UV-unexposed control strain DE69, and chosen for UV-C radiation resistance studies with respect to growth phase. The ancestral strain from the evolution experiment was used as reference for comparative purposes. Cells of the UV-adapted strain showed significant differences in their physiology (growth behavior, doubling time, cell density, and sporulation capacity) and were more resistant to UV in all monitored stages. These findings implicate the evolution to an increased UV radioresistance was not limited to a specific growth phase and led to reduced growth dynamics, compared with those obtained from the ancestral and the control strain.

Keywords: Bacillus subtilis ; Experimental evolution; UV resistance; Growth phase; Stress response

Adhesion and biofilm formation of Mycoplasma pneumoniae on an abiotic surface by Jonathan D. Kornspan; Mark Tarshis; Shlomo Rottem (pp. 833-836).

We demonstrated that when M. pneumoniae was grown on an abiotic surface of either glass or polystyrene with a serum-containing medium, the bacteria adhered to the surface and formed highly differentiated volcano-like biofilm structures. As adherence to the surface and/or biofilm formation was totally inhibited by anti-P1 polyclonal monospecific antibodies, we suggest that the adherence of M. pneumoniae to the abiotic surface and/or biofilm formation is associated with P1, the major tip organelle protein of this organism. Furthermore, adherence and/or biofilm formation was markedly inhibited by treating the serum component of the growth medium with neuraminidase or by growing the bacteria in the presence of sialyllactose, suggesting that the initial step in the adherence to and/or biofilm formation by M. pneumoniae on an abiotic surface is the interaction of the bacterium through its tip organelle with sialic acid residues of serum glycoproteins.

Keywords: Mycoplasma pneumoniae ; Biofilm; P1-protein; Sialic acid

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Archives of Microbiology (v.193, #11)

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Archives of Microbiology (v.193, #11)