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ASM Articles in the Spotlight. The ASM journals Eukaryotic Cell, Infection and Immunity, and the Journal of Virology highlight current articles of interest in their Spotlight sections:  


Plague Pathogenicity Details Dissected

The caf genes of Yersinia pestis, the plague agent, were thought to be important for virulence. They encode a capsule that shields Y. pestis from host phagocytes, and may interfere with defensive signaling within the host. Nonetheless, they are not required for full virulence following artificial injection of cultured bacteria. Florent Sebbane, an INSERM researcher based at the Institut Pasteur de Lille, France, and his collaborators from the Rocky Mountain Laboratories–NIH constructed a caf-negative Y. pestis and found it to be as virulent as the wild type when injected into animals. The team then fed blood infected with either wild-type or mutant Y. pestis to fleas, which then had a go at experimental mice. Under these more natural circumstances, the mutant was less virulent than the wild type, but Sebbane notes that “this decrease in virulence can be compensated for by a high flea burden.” The data “highlight the importance of studying Y. pestis pathogenesis in the natural context of arthropod-borne transmission,” says Sebbane. More comprehensive surveillance is needed for atypical strains in plague foci, as are supplementary diagnostic procedures. Sebbane hopes to characterize the biological role of caf/F1 in flea bite transmission, “but it will not be trivial.”

Sebbane, C. Jarrett, D. Gardner, D. Long, and B. J. Hinnebusch. 2009. The Yersinia pestis caf1M1A1
fimbrial capsule operon promotes transmission by flea bite in a mouse model of bubonic plague. Infect. Immun. 77: 1222–1229.)

Novel pH-Dependent Factor Promoting Cryptococcus Virulence

Cryptococcus neoformans causes cryptococcosis worldwide, especially in immunocompromised individuals. “It’s been estimated that C. neoformans is responsible for more mortalities than tuberculosis in sub-Saharan Africa due to the high incidence of HIV infections there,” says Alexander Idnurm of the University of Missouri-Kansas City. As with many eukaryotic pathogens, performing mutant screens to identify new virulence determinants is a challenge. Idnurm et al. used insertional mutagenesis and incorporated unique signature tags, enabling pools of strains to be screened directly in amouse model. One gene required for virulence that emerged was ENA1. Ena1 homologs function as salt pumps in other fungi. Interestingly, in C. neoformans the only identified phenotype for ena1 mutants in vitro is sensitivity to alkaline pH. Thus, Ena1 either plays a role in host niches where the pH is higher than physiological levels or has other novel functions. The signature-tagged mutant collection holds promise for identifying many new determinants of cryptococcal interaction with its hosts. Future analysis of Ena1 in this and other pathogens should result in new insights into fungal pathogenesis.

(A. Idnurm, F.J. Walton, A. Floyd, J.L. Reedy, and J. Heitman. 2009. Identification of ENA1 as a virulence gene of the human pathogenic fungus Cryptococcus neoformans
through signature-tagged insertional mutagenesis. Eukaryot. Cell 8:315–326.)

Drug Susceptibility Classification Schemes May Need Upgrading

Guidelines for susceptibility to antibiotics are general rules, and may only be valid when they have incorporated the relationship of pharmacokinetics (PK, what the body does to the drug) and pharmacodynamics (PD, what the drug does to the body). One variable used to generate the classifications of “susceptible,” “intermediate,” or “resistant,” the minimum inhibitory concentration (MIC), may be a better predictor of patient outcomes when PK/PD is considered. Marc H. Scheetz of Northwestern Memorial Hospital, Chicago, et al. showed that this is the case for levofloxacin, which served as a proxy for fluoroquinolones, generally. “Among all patients that had a bloodstream infection with a levofloxacin-susceptible gram-negative organism, we found increased length of infection and hospital stay after the infection when the infecting organism had a high MIC and was compared to similar patients with a low MIC,” says Scheetz. “This study provides the first clinical evidence, to our knowledge, that a reconsideration of the classification scheme for fluoroquinolones may be necessary.”

(R. Fife, M.H. Scheetz, J.M. Feinglass, M.J. Postelnick, and K.K. Scarsi. 2009. Effect of differences in MIC values on clinical outcomes in patients with bloodstream infections caused by gram-negative organisms treated with levofloxacin. Antimicrob. Agents Chemother. 53:1074–1079.)

Anti-Smallpox Strategy Works in Mice

More than 35 years have elapsed since the smallpox vaccination program ended, leaving an entire generation without immunity. Threats remain, of reintroduction either through germ warfare or via natural recombination such as the monkeypox outbreak in 2003, creating an urgent need for therapeutics. Variola virus, which causes smallpox, monkeypox virus, and the vaccinia virus are large complexDNAviruses that hijack the host factors such as the tyrosine kinases JAK2 and EGF receptor in order to replicate. Chulbul M. Ahmed, Rea Dabelic, and colleagues in Howard M. Johnson’s laboratory at the University of Florida, Gainesville, constructed small-molecule mimetics of a cellular regulatory protein, SOCS-1, which inhibits these enzymes, preventing viruses from hijacking the cellular replication machinery. “These SOCS-1 mimetics protected mice against lethal vaccinia virus infection,” says Ahmed. “Thus, we demonstrated that an endogenous cellular regulator of poxviruses has the potential to treat viral diseases such as those caused by smallpox virus.”

(C. M. Ahmed, R. Dabelic, L. W. Waiboci, L. D. Jager, L. L. Heron, and H. M. Johnson. 2009. SOCS-1 mimetics protect mice against lethal poxvirus infection: identification of a novel endogenous antiviral system. J. Virol. 83:1402–1415.)

A New Killer Toxin Shows Similarities to Ubiquitin
 De Ingeniis

The yeast Pichia anomala secretes a killer toxin, Pikt, that has robust antimicrobial activity against the yeasts Dekkera/Brettanomyces which create major problems for the wine industry. Ilaria Mannazzu of the Universita` degli Studi di Sassari, Italy, et al. show that Pikt bears many similarities to ubiquitin, including molecular mass, N-terminal sequence, chromatographic behavior, and cross-reaction with specific anti-ubiquitin antibodies. “Since ubiquitin is a small protein whose main function is to target proteins for intracellular degradation, our results were at the same time intriguing and unexpected,” says Mannazzu. “The antimicrobial activity of a secreted ubiquitin-like protein is a novel topic, which deserves further investigation. We believe that Pikt might represent a useful tool to shed light on the antifungal activity of ubiquitin-like proteins.” Differences though, include that unlike ubiquitin, Pikt was completely hydrolyzed by protease XIV and partially hydrolyzed by pepsin. Mannazzu says that “due to Pikt’s great potential as a natural antimicrobial for wine aging and storage, we are planning to further investigate its mechanism of action.”

(J. De Ingeniis, N. Raffaelli, M. Ciani, and I. Mannazzu. 2009. Pichia anomala
DBVPG 3003 secretes a ubiquitin-like protein that has antimicrobial activity. Appl. Environ. Microbiol. 75:1129–1134.)