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ß-Lactamase-Producing Nontypeable Haemophilus influenzae Fails To Protect Streptococcus pneumoniae from Amoxicillin during Experimental Acute Otitis Media. Eva Westman, 2004.Acute otitis media (AOM) is the most common reason for outpatient antimicrobial therapy . Mixed infections pose a potential problem, since the first-line drug used for the treatment of AOM, amoxicillin, can be neutralized by ß-lactamase-producing pathogens of the upper respiratory tract . To study the effects of a 5-day course of amoxicillin on a mixed middle ear infection, rats were challenged with Streptococcus pneumoniae alone or in combination with ß-lactamase-producing nontypeable Haemophilus influenzae . Amoxicillin was introduced at the clinical peak of the infection . Local and systemic changes were monitored by otomicroscopy, bacterial culture, and analysis of histological changes and the expression of the transforming growth factor beta (TGF-ß) gene . ß-Lactamase-producing H . influenzae did not demonstrate an ability to protect S . pneumoniae . Amoxicillin eradicated the pneumococci in all treated animals but increased to some degree the ability of H . influenzae to persist at the site of infection . Thus, only an insignificant acceleration of the resolution of the AOM caused by a mixture of pathogens was observed during treatment . Moderate to major morphological changes could not be avoided by treatment of the mixed infections, but a slight downregulation of TGF-ß expression was observed . In contrast to infections caused by a single pathogen, the mixed infections induced white plaques in the tympanic membrane at a remarkably high frequency independent of treatment . These experimental findings constitute support for further studies of antimicrobial drugs and AOM caused by bacteria with and without mechanisms of antibiotic resistance . hetL Overexpression Stimulates Heterocyst Formation in Anabaena sp . Strain PCC 7120. Duan Liu, 2002.The cyanobacterium Anabaena sp . strain PCC 7120 forms single heterocysts about every 10 to 15 vegetative cells along filaments . PatS is thought to be a peptide intercellular signal made by developing heterocysts that prevents neighboring cells from differentiating . Overexpression of the patS gene suppresses heterocyst formation . The hetL gene (all3740) was isolated in a genetic screen to identify genes involved in PatS signaling . Extracopy hetL allowed heterocyst formation in a patS overexpression strain . hetL overexpression from a heterologous promoter in wild-type Anabaena PCC 7120 induced multiple-contiguous heterocysts (Mch) in nitrate-containing medium . The predicted HetL protein is composed almost entirely of pentapeptide repeats with a consensus of A(D/N)L*X, where * is a polar amino acid . Thirty Anabaena PCC 7120 genes contain this repeat motif . A synthetic pentapeptide corresponding to the last 5 amino acids of PatS, which suppresses heterocyst formation in the wild type, did not suppress heterocyst formation in a hetL overexpression strain, indicating that HetL overexpression is affecting heterocyst regulation downstream of PatS production . The transcription regulator NtcA is required for the initiation of heterocyst formation . hetL overexpression allowed the initiation of heterocyst development in an ntcA-null mutant, but differentiation was incomplete . hetR and hetC mutations that block heterocyst development are epistatic to hetL overexpression . A hetL-null mutant showed normal heterocyst development and diazotrophic growth, which could indicate that it is not normally involved in regulating development, that it normally plays a nonessential accessory role, or perhaps that its loss is compensated by cross talk or redundancy with other pentapeptide repeat proteins . Carbon Starvation Can Induce Energy Deprivation and Loss of Fermentative Capacity in Saccharomyces cerevisiae. Elisabeth Thomsson, 2003.Seven different strains of Saccharomyces cerevisiae were tested for the ability to maintain their fermentative capacity during 24 h of carbon or nitrogen starvation . Starvation was imposed by transferring cells, exponentially growing in anaerobic batch cultures, to a defined growth medium lacking either a carbon or a nitrogen source . After 24 h of starvation, fermentative capacity was determined by addition of glucose and measurement of the resulting ethanol production rate . The results showed that 24 h of nitrogen starvation reduced the fermentative capacity by 70 to 95%, depending on the strain . Carbon starvation, on the other hand, provoked an almost complete loss of fermentative capacity in all of the strains tested . The absence of ethanol production following carbon starvation occurred even though the cells possessed a substantial glucose transport capacity . In fact, similar uptake capacities were recorded irrespective of whether the cells had been subjected to carbon or nitrogen starvation . Instead, the loss of fermentative capacity observed in carbon-starved cells was almost surely a result of energy deprivation . Carbon starvation drastically reduced the ATP content of the cells to values well below 0.1 µmol/g, while nitrogen-starved cells still contained approximately 6 µmol/g after 24 h of treatment . Addition of a small amount of glucose (0.1 g/liter at a cell density of 1.0 g/liter) at the initiation of starvation or use of stationary-phase instead of log-phase cells enabled the cells to preserve their fermentative capacity also during carbon starvation . The prerequisites for successful adaptation to starvation conditions are probably gradual nutrient depletion and access to energy during the adaptation period . Molecular Analysis of the rfb O Antigen Gene Cluster of Salmonella enterica Serogroup O:6,14 and Development of a Serogroup-Specific PCR Assay. Collette Fitzgerald, 2003.The Kauffmann-White scheme for serotyping Salmonella recognizes 46 somatic (O) antigen groups, which together with detection of the flagellar (H) antigens form the basis for serotype identification . Although serotyping has become an invaluable typing method for epidemiological investigations of Salmonella, it does have some practical limitations . We have been characterizing the genes required for O and H antigen biosynthesis with the goal of developing a DNA-based system for the determination of serotype in Salmonella. The majority of the enzymes involved in O antigen biosynthesis are encoded by the rfb gene cluster . We report the sequencing of the rfb region from S . enterica serotype Sundsvall (serogroup O:6,14) . The S . enterica serotype Sundsvall rfb region is 8.4 kb in length and comprises six open reading frames . When compared with other previously characterized rfb regions, the serogroup O:6,14 sequence is most related to serogroup C1 . On the basis of DNA sequence similarity, we identified two genes from the mannose biosynthetic pathway, two mannosyl transferase genes, the O unit flippase gene and, possibly, the O antigen polymerase . The whole cluster is derived from a low-G+C-content organism . Comparative sequencing of an additional serogroup O:6,14 isolate (S . enterica serotype Carrau) revealed a highly homologous sequence, suggesting that O antigen factors O:24 and O:25 (additional O factors associated with serogroup O:6,14) are encoded outside the rfb gene cluster . We developed a serogroup O:6,14-specific PCR assay based on a region of the putative wzx (O antigen flippase) gene . This provides the basis for a sensitive and specific test for the rapid identification of Salmonella serogroup O:6,14 .
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