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Differential Maintenance of the M184V Substitution in the Reverse Transcriptase of Human Immunodeficiency Virus Type 1 by Various Nucleoside Antiretroviral Agents in Tissue Culture. Marco Petrella, 2004.The M184V substitution in human immunodeficiency virus type 1 reverse transcriptase (RT) is rapidly selected in tissue culture following serial passage of wild-type virus in the presence of increasing concentrations of lamivudine (3TC) . M184V is also associated with several alterations of RT enzymatic function in vitro that may adversely affect viral fitness or replication capacity, which creates a potential rationale for its maintenance once it has been selected by antiviral chemotherapy . However, the relative effectiveness of nucleoside RT inhibitors that are structurally unrelated to 3TC in selecting and/or maintaining M184V has not been investigated . In the present study, we have studied the abilities of a variety of drugs, i.e., zalcitabine (ddC), didanosine (ddI), abacavir (ABC), and the novel nucleoside SPD754, in addition to 3TC, to maintain the presence of M184V in tissue culture and have shown that SPD754, ABC, and 3TC are able to preserve M184V in mixed dual infections consisting of wild-type viruses and clinical isolates which contained the M184V mutation . Moreover, M184V could also be maintained in these cultures when a subtherapeutic concentration of 3TC (i.e., 0.05 µM) was used . In contrast, neither ddI nor ddC was able to maintain M184V to the same extent as the other drugs after 10 weeks of tissue culture in mixtures of wild-type viruses and isolates containing M184V in different proportions . Activities of Dicationic Compounds against Trichomonas vaginalis. Andrea L. Crowell, 2004.We evaluated 44 novel cationic compounds for activity against metronidazole-sensitive and -resistant Trichomonas vaginalis isolates . Six compounds in three different structural classes demonstrated 50% inhibitory concentrations as low as 1 µM against both sensitive and resistant isolates, suggesting a mode of action independent of parasite biochemical pathways that confer resistance to 5-nitroimidazoles . Rectal Administration of Escherichia coli O157:H7: Novel Model for Colonization of Ruminants. Haiqing Sheng, 2004.Escherichia coli O157:H7 causes hemorrhagic colitis and life-threatening complications . Because healthy cattle are reservoirs for the bacterium, ruminant infection models have applications in analyzing the relationship between cattle and this human pathogen and in testing interventions to reduce or prevent bovine colonization with this bacterium . Current approaches often do not reliably mimic natural, long-term bovine colonization with E . coli O157:H7 in older calves and adult animals (ages that enter our food chain) . Based on the recent identification of the bovine rectoanal junction mucosa as a site of E . coli O157:H7 colonization, we developed a novel rectal swab administration colonization model . We compared this method with oral dosing and direct contact transmission (Trojan) methods . E . coli O157:H7 carriage status was determined by fecal or rectoanal mucosa swab culture . High (  1010 CFU) and low (107 CFU) oral doses of E . coli O157:H7 in sheep and cattle resulted in variable infection with the bacterium . Some animals became colonized with the bacteria and remained culture positive for several weeks, and some animals did not become colonized and rapidly cleared the bacteria in a few days . Pen mates of E . coli O157:H7 culture-positive Trojan cattle had a low infection rate and variable colonization status . However, rectal swab administration of E . coli O157:H7 to cattle resulted in consistent long-term colonization in all animals . The surprising ease with which long-term infections resulted from a single application of bacteria to the rectoanal mucosa also strongly supported this location as a site of E . coli O157:H7 colonization in cattle .
Plasmid DNA Supercoiling and Gyrase Activity in Escherichia coli Wild-Type and rpoS Stationary-Phase Cells. Yazmid Reyes-Domínguez, 2003.Stationary-phase cells displayed a distribution of relaxed plasmids and had the ability to recover plasmid supercoiling as soon as nutrients became available . Preexisting gyrase molecules in these cells were responsible for this recovery . Stationary-phase rpoS cells showed a bimodal distribution of plasmids and failed to supercoil plasmids after the addition of nutrients, suggesting that rpoS plays a role in the regulation of plasmid topology during the stationary phase .
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