American Society of Microbiology 101st General Meeting. 20-24 May 2001, Orlando, FL, USA

The application of sophisticated molecular biology, genetics and genomics has made possible the advanced analyses of microbial genes, the topology of DNA and chromosomes, and insight into the regulation of gene expression during all stages of the life cycle of microbes, both in vitro and in vivo. The struggle to control contagious pathogens continues world wide amidst resistance emergence to many classes of antimicrobial agents. Many hospital, research and community labs are applying themselves to a more thorough understanding of the molecular basis of this resistance. New drugs which improve on predecessor agents were presented. The following classes of antimicrobial agents were represented: quinolones, cephems, macrolides and natural products. New target opportunities against both lethal (essential) gene targets and virulence targets were presented throughout the conference. In addition, increasing attention to the involvement of microbial life forms in immune function and dysfunction were described in numerous presentations.

100th American society for microbiology annual meeting

The 100th ASM Annual Meeting, attended by approximately 10,000 delegates, continued the trend of concentrating on bacteria and antibacterial therapy, mixed with genomics and a diverse number of additional topics. Of the various marketable drug classes, the quinolones received attention with respect to susceptibility studies and several drug comparison studies. New marketable drugs were also of interest, especially given the reservoirs of resistance presented by several speakers. Drugs in development include the antibacterial daptomycin and protegrins and the antifungal lipodepsinonapeptides and echinocandins, to name a few. It is still unclear whether or not antibiotic treatment regimens for Chlamydia pneumonia will he necessary, as association of this bacteria with several chronic diseases, such as atherosclerosis and asthma, was discussed. The development of novel antibiotics was highlighted and the potential role that microbial genomics technology could play was a recurring theme. In fact, a number of symposia treated the increasingly popular topic of genomics in a variety of themes, including phenotyping arrays, transcriptional profiling, proteomics, expression profiling, genome sequencing, target areas or essentiality of genes via gene knockout systems, the role of genomics in pharmaceutical development and fungal genomics. Similarly, genomics plays a role in developing a deeper appreciation for classical areas of interest in microbial physiology, such as gene regulation, cell division, fatty acid biosynthesis, DNA replication and cell signalling. Even in the bio-inorganic field of study in microbial metabolite activation, genomics plays a role. The sequencing of the large gene clusters of the auxiliary proteins necessary to synthesise or activate the metallo-proteins provided insights into the mechanisms of activation of these microbial enzymes, including the genes for the nif gene cluster in Azotobacter vinelandii, the urease from Kiebsiella aerogenes and the three hydrogenases in Ralstonia eutropha.

Comparison of the D-glutamate-adding enzymes from selected gram-positive and gram-negative bacteria

The biochemical properties of the D-glutamate-adding enzymes (MurD) from Escherichia coli, Haemophilus influenzae, Enterococcus faecalis, and Staphylococcus aureus were investigated to detect any differences in the activity of this enzyme between gram-positive and gram-negative bacteria. The genes (murD) that encode these enzymes were cloned into pMAL-c2 fusion vector and overexpressed as maltose-binding protein-MurD fusion proteins. Each fusion protein was purified to homogeneity by affinity to amylose resin. Proteolytic treatments of the fusion proteins with factor Xa regenerated the individual MurD proteins. It was found that these fusion proteins retain D-glutamate-adding activity and have Km and Vmax values similar to those of the regenerated MurDs, except for the H. influenzae enzyme. Substrate inhibition by UDP-N-acetylmuramyl-L-alanine, the acceptor substrate, was observed at concentrations greater than 15 and 30 microM for E. coli and H. influenzae MurD, respectively. Such substrate inhibition was not observed with the E. faecalis and S. aureus enzymes, up to a substrate concentration of 1 to 2 mM. In addition, the two MurDs of gram-negative origin were shown to require monocations such as NH4+ and/or K+, but not Na+, for optimal activity, while anions such as Cl- and SO4(2-) had no effect on the enzyme activities. The activities of the two MurDs of gram-positive origin, on the other hand, were not affected by any of the ions tested. All four enzymes required Mg2+ for the ligase activity and exhibited optimal activities around pH 8. These differences observed between the gram-positive and gram-negative MurDs indicated that the two gram-negative bacteria may apply a more stringent regulation of cell wall biosynthesis at the early stage of peptidoglycan biosynthesis pathway than do the two gram-positive bacteria. Therefore, the MurD-catalyzed reaction may constitute a fine-tuning step necessary for the gram-negative bacteria to optimally maintain its relatively thin yet essential cell wall structure during all stages of growth.

Insertional inactivation of a gene which controls expression of vancomycin resistance on plasmid pHKK100

Expression of inducible high level vancomycin resistance (Vmr) in enterococci appears to require other plasmid-encoded genes in addition to the previously described structural genes vanA and vanH. Tn917 mutagenesis was used to identify such a region in the Vmr plasmid pHKK100. Insertional inactivation of a 693-bp open reading frame upstream from vanH resulted in complete loss of Vmr. This putative 26,642-Da protein has been designated VanR.

Plasmodium falciparum: In vitro characterization and human infectivity of a cloned line

The culture-adapted NF54 isolate of Plasmodium falciparum was subjected in vitro to three sequential limiting dilution titrations and the resulting clone was given the designation CVD1. DNA sequence analysis of the gene encoding the circumsporozoite (CS) protein revealed differences between CVD1 and the published NF54 CS gene. CVD1 had 1191 bp, 397 amino acids, and 42 repeat units while NF54 had 1218 bp, 405 amino acids, and 44 repeat units. The CVD1 clone was more sensitive to chloroquine than was the parental line, in vitro. Anopheles stephensi mosquitoes were infected equally by the cloned and uncloned parasites. Volunteers were readily infected by NF54 and CVD1 following infectious mosquito bites. The availability of a well-characterized, chloroquine-sensitive clone which safety infects humans should facilitate performance of experimental challenge studies to assess vaccine efficacy.