Serum survival and plasmid possession by strains of Salmonella enteritidis, Salm. typhimurium and Salm. virchow

Strains of Salmonella enteritidis, Salm. typhimurium and Salm. virchow , carrying different numbers of plasmids, were examined for the ability to multiply in sera. Viable counts were performed to monitor the kinetics of growth of bacteria when in human, chicken and turkey sera. The presence of plasmids in Salm. enteritidis, Salm. typhimurium and Salm. virchow reduced considerably the ability of strains of these serotypes to multiply in serum. SDS-PAGE was used to show that growth of Salm. enteritidis in serum did not involve changes in outer membrane proteins or lipopolysaccharide. It was concluded that the carriage of plasmids may be disadvantageous for the survival in serum of certain common salmonella serotypes.     

Oligonucleotide probes specific for the genus Salmonella and for Salm. typhimurium

The Crystal Enteric/Nonfermenter (E/NF) identification kit (Becton Dickinson Microbiology Systems, USA) was evaluated using water-derived bacterial isolates and results compared to those obtained by the API 20E system (BioMérieux, UK). Both the E/NF and 20E systems correctly identified 93% of the Enterobacteriaceae reference cultures. Both systems agreed in the identification of 64·9% of environmental isolates. The E/NF system gave a positive identification to 88·0% of isolates and the 20E to 79·5% of isolates. The principal tests which gave differing reactions between the two systems were arginine dihydrolase, lysine decarboxylase, urease and citrate utilization.     

A rat model of infection by Salmonella typhimurium or Salm. enteritidis

Salmonellosis in the rat has many similarities with the disease in humans, with the ileum thought to be the main site of colonization/invasion in both species. Thus, the rat may be a useful way to study the mechanism of infection by these pathogenic bacteria. A series of infection trials carried out with Hooded Lister rats showed that a salmonella infection persisted for an extended period of time and that salmonellae bind to the small intestinal epithelium as early as 4 h after intragastric intubation. Reinfection from the large intestine may not therefore initially play a significant role in the salmonella infection process. The rat model may therefore provide a means to test in vivo interventionist strategies, designed to block binding of the pathogens in the gastrointestinal tract.     

Survival of Salmonella enteritidis PT4 and Salm. typhimurium Swindon in aerosols

A.S. McDERMID AND M.S. LEVER. 1996. Small particle aerosols of plate-grown Salmonella enteritidis and Salm. typhimurium were generated and maintained within a rotating drum at 75% relative humidity and 24°C for 2 h. Plate-grown organisms were found to be more aerosol-stable than broth-grown organisms. Differences were observed between the two species; plate-grown Salm. typhimurium retained 100% viability after 2 h compared to approximately 70% for plate-grown Salm. enteritidis . A large proportion of cells of both serotypes remained viable in aerosols after 2 h, confirming the potential for airborne transmission for these organisms, e.g. within henhouses and during food     

Effect of Water Activity on Heat Survival of Staphylococcus aureus, Salmonella typhimurium and Salm. senftenberg

The viability of Staphylococcus aureus heated at 55° in phosphate buffer was determined on recovery media of different water activity ( a_w ) levels. The basal recovery medium, tryptone–soya agar ( a_w 0.997) was adjusted to lower a_w levels by the addition of NaCl, glycerol or sucrose. Maximum survival occurred at a_w 0.997. Viability was reduced to 1/10 of the maximum at a_w 0.98 when a_w , was controlled by sucrose or NaCl but not until a_w 0.93 with glycerol. To eliminate effects such as incomplete mixing or post-heating dilution and in order to use conditions comparable to those occurring in foods, a solid medium heating/recovery method was also used. This involved heating, by immersion, of surface-inoculated agar plates and recovery of survivors in situ . Heat resistance studies could thus only be carried out at a_w levels permitting growth on the heating/recovery medium. Staphylococcus aureus, Salmonella typhimurium and Salm. senftenberg 775W were heated at 55° and recovered in situ on tryptone-soya agar adjusted to lower a_w levels as above. Maximum survival of Staph. aureus occurred at a higher a_w with glycerol ( a_w 0.965) than with NaCl (0.92) or sucrose (0.90). The maximum survival of both Salm. typhimurium and Staph. aureus heated at 55° occurred at the same a_w (0.965) with glycerol. This maximum was not affected by the duration of heating. As a contrast, heat resistance of Salm. senftenberg 775W was virtually unaffected by reduction in the a_w of the heating/recovery medium.     

禽大肠杆菌、肠炎、鼠伤寒、鸡白痢及鸡伤寒沙门菌多重PCR方法的建立及应用

【背景】大肠杆菌病和沙门菌病是最常见的家禽细菌性疾病,给养禽业造成严重经济损失。另外,禽大肠杆菌和沙门菌也是重要的人畜共患病原菌,可通过禽类及其产品传播给人类,对人类健康造成严重威胁。加强禽大肠杆菌和沙门菌的快速鉴别检测,对养禽业和公共卫生都具有重要意义。【目的】建立禽大肠杆菌、肠炎沙门菌、鼠伤寒沙门菌、鸡白痢沙门菌和鸡伤寒沙门菌的多重PCR检测方法。【方法】通过比较分析确定禽致病性大肠杆菌、肠炎沙门菌、鼠伤寒沙门菌、鸡白痢沙门菌和鸡伤寒沙门菌的特异靶标基因,设计5对特异性引物,通过条件优化建立多重PCR方法,分析该多重PCR方法的特异性、敏感性及可靠性。【结果】该方法能特异性地鉴定禽致病性大肠杆菌、肠炎沙门菌、鼠伤寒沙门菌、鸡白痢沙门菌和鸡伤寒沙门菌,每个PCR反应的最低检出限分别为103 CFU细菌和100 pg基因组DNA。临床分离菌株检测显示,多重PCR与传统血清学方法结果一致。【结论】建立的多重PCR方法能够快速鉴别禽致病性大肠杆菌和不同血清型沙门菌,对禽大肠杆菌病和沙门菌病的流行病学调查及临床检测具有重要意义。     

沙门菌、大肠杆菌和金黄色葡萄球菌的多重PCR检测

根据沙门菌invA基因、大肠杆菌phoA基因和金黄色葡萄球菌nuc基因序列,设计3对特异性引物进行多重PCR并对反应条件进行优化。结果表明3对引物能特异地扩增出284bp、622bp、484bp的目的条带;最佳反应条件为沙门菌、大肠杆菌、金黄色葡萄球菌的引物浓度分别为40nmol／L、40nmol／L、80nmol／L,Mg^2＋浓度2．4mmol／L,dNTP浓度2001μmol／L,Taq DNA聚合酶1.5u,退火温度55．0℃-57．4℃之间;在此条件下多重PCR同时检测DNA的敏感性分别是10．2pg、10．2pg、102．0pg,检测时间4h。建立的多重PCR是一种敏感、特异、准确、快速的方法,为同时检测食品中沙门菌、大肠杆菌和金黄色葡萄球菌奠定了基础。     

Interactions of High-Affinity Cationic Blockers with the Translocation Pores of B. anthracis,C. botulinum,and C. perfringens Binary Toxins

Cationic β-cyclodextrin derivatives were recently introduced as highly effective, potentially universal blockers of three binary bacterial toxins: anthrax toxin of Bacillus anthracis, C2 toxin of Clostridium botulinum, and iota toxin of Clostridium perfringens. The binary toxins are made of two separate components: the enzymatic A component, which acts on certain intracellular targets, and the binding/translocation B component, which forms oligomeric channels in the target cell membrane. Here we studied the voltage and salt dependence of the rate constants of binding and dissociation reactions of two structurally different β-cyclodextrins (AmPrβCD and AMBnTβCD) in the PA₆₃, C2IIa, and Ib channels (B components of anthrax, C2, and iota toxins, respectively). With all three channels, the blocker carrying extra hydrophobic aromatic groups on the thio-alkyl linkers of positively charged amino groups, AMBnTβCD, demonstrated significantly stronger binding compared with AmPrβCD. This effect is seen as an increased residence time of the blocker in the channels, whereas the time between blockages characterizing the binding reaction on-rate stays practically unchanged. Surprisingly, the voltage sensitivity, expressed as a slope of the logarithm of the blocker residence time as a function of voltage, turned out to be practically the same for all six cases studied, suggesting structural similarities among the three channels. Also, the more-effective AMBnTβCD blocker shows weaker salt dependence of the binding and dissociation rate constants compared with AmPrβCD. By estimating the relative contributions of the applied transmembrane field, long-range Coulomb, and salt-concentration-independent, short-range forces, we found that the latter represent the leading interaction, which accounts for the high efficiency of blockage. In a search for the putative groups in the channel lumen that are responsible for the short-range forces, we performed measurements with the F427A mutant of PA₆₃, which lacks the functionally important phenylalanine clamp. We found that the on-rates of the blockage were virtually conserved, but the residence times and, correspondingly, the binding constants dropped by more than an order of magnitude, which also reduced the difference between the efficiencies of the two blockers.