Regulation ofSerratia marcescens is a Gram-negative enterobacterium that has become an important opportunistic pathogen, largely due to its high degree of natural antibiotic resistance. One factor contributing to this natural antibiotic resistance is reduced outer membrane permeability, which is controlled in part by OmpC and OmpF porin proteins. OmpF expression is regulated by micF, an RNA transcript encoded upstream of the ompC gene, which hybridizes with the ompF transcript to inhibit its translation. Regulation of S. marcescens porin gene expression, as well as that of micF, was investigated using b-galactosidase reporter gene fusions in response to 5, 8 and 10 % sucrose, 1, 5 and 8 mM salicylate, and different pH and temperature values. b-Galactosidase activity assays revealed that a lower growth temperature (28 6C), a more basic pH (pH 8), and an absence of sucrose and salicylate induce the transcription of the ompF gene, whereas the induction of ompC is stimulated at a higher growth temperature (42 6C), acidic pH (pH 6), and maximum concentrations of sucrose (10 %) and salicylate (8 mM). In addition, when multiple conditions were tested, temperature had the predominant effect, followed by pH. In this study, it was found that the MicF regulatory mechanism does not play a role in the osmoregulation of the ompF and ompC genes, whereas MicF does repress OmpF expression in the presence of salicylate and high growth temperature, and under low pH conditions. INTRODUCTIONSerratia marcescens is a Gram-negative enteric bacterium that has become an important opportunistic pathogen associated with a number of life-threatening diseases and nosocomial infections. In the last two decades, S. marcescens has gained much attention due to a high incidence of antibiotic resistance. b-Lactam resistance in this organism is due in part to b-lactamase enzymes (Sanders & Sanders, 1992); however, a reduction in the levels of outer membrane porins is also responsible for altering resistance levels by decreasing the outer membrane permeability (Gutmann et al., 1984).Our group has characterized two S. marcescens porins, OmpC and OmpF (Hutsul & Worobec, 1997), with molecular masses of 40 and 41 kDa, respectively. These porins are non-specific protein channels that serve to take in nutrients and antibiotics, such as b-lactams, and export waste products. OmpF is believed to have a slightly larger pore diameter, resulting in a faster rate of diffusion through OmpF than through OmpC. The structural genes for both OmpF and OmpC have been cloned and sequenced. S. marcescens OmpC and OmpF are 71 % and 68 % similar to Escherichia coli OmpC and OmpF, respectively, at the amino acid level (Hutsul & Worobec, 1997).The production of E. coli OmpF and OmpC is regulated by many environmental factors, such as osmotic pressure, temperature and pH. Production of the appropriate outer membrane porin is required for survival of the organism under widely differing conditions (Csonka, 1989). For example, in the human gut, where concentrations of both nutri...

Estrogen receptor α (ERα) activity is regulated by phosphorylation at several sites. Recently several antibodies specific for individual phosphorylated sites within ERα have became available. Such antibodies potentially provide invaluable tools to gain insight into the relevance in vivo of phosphorylated ERα in human breast tumors. However, validation of these antibodies for immunohistochemistry in particular is necessary in the first instance. In this study we have investigated the usefulness of several antibodies generated to specific phosphorylated sites within ERα for immunohistochemistry of formalin-fixed, paraffin-embedded human breast cancer biopsy samples. As well, these data demonstrate for the first time, the detection of multiple phosphorylated ERα forms in breast cancer (P-S104/106-ERα, P-S118-ERα, P-S167-ERα, P-S282-ERα, P-S294-ERα, P-T311-ERα, and P-S559-ERα) suggesting the possibility that profiling of phosphorylated ERα isoforms might be useful in selecting subgroups of breast cancer patients that would benefit from endocrine therapy.

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Serratia marcescens is a prominent opportunistic nosocomial pathogen resistant to several classes of antibiotics. The major mechanism for fluoroquinolone resistance in various Gram-negative pathogens is active efflux. Our group previously identified SdeAB, a resistance-nodulation-cell division (RND) efflux pump complex, and a TolC-like outer-membrane protein (HasF), which together mediate energy-dependent fluoroquinolone efflux. In addition, a regulatory protein-encoding gene in the upstream region of sdeAB was identified (sdeR) and found to be 40 % homologous to MarA, an Escherichia coli transcriptional regulator. To provide conclusive evidence as to the role of these components in S. marcescens, sdeB, hasF and sdeR deletion mutants were constructed. Suicide vectors were created and introduced via triparental mating into S. marcescens UOC-67 (wild-type) and, for sdeB and hasF, T-861 (clinical isolate). We have analysed these genetically altered strains using minimal inhibitory concentration (MIC) assays for a wide range of compounds (fluoroquinolones, SDS, novobiocin, ethidium bromide and chloramphenicol). Intracellular accumulation of a variety of fluoroquinolones was measured fluorospectroscopically. The sdeB, hasF and sdeR knockout strains were consistently more susceptible to antibiotics than the parent strains, with the sdeB/hasF double knockout strain showing the highest susceptibility. A marked increase in fluoroquinolone (ciprofloxacin) accumulation was observed for strains deficient in either the sdeB or hasF genes when compared to the parental strains, with the highest ciprofloxacin accumulation observed for the sdeB/hasF double knockout. Antibiotic accumulation assays for the sdeB knockout mutant strains performed in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP), a proton-motive-force inhibitor, demonstrated that SdeAB-mediated efflux is proton-motive-force dependent. Due to the comparable susceptibility of the sdeB and the hasF individual knockouts, we conclude that S. marcescens HasF is the sole outer-membrane component of the SdeAB pump. In addition, MIC data for sdeR-deficient and overexpressing strains confirm that SdeR is an activator of sdeAB and acts to enhance the overall multidrug resistance of S. marcescens.

Serratia marcescens is an important nosocomial agent having high antibiotic resistance. A major mechanism for S. marcescens antibiotic resistance is active efflux. To ascertain the substrate specificity of the S. marcescens SdeCDE efflux pump, we constructed pump gene deletion mutants. sdeCDE knockout strains showed no change in antibiotic susceptibility in comparison with the parental strains for any of the substrates, with the exception of novobiocin. In addition, novobiocin was the only antibiotic to be accumulated by sdeCDE-deficient strains. Based on the substrates used in our study, we conclude that SdeCDE is a Resistance-Nodulation-Cell Division family pump with limited substrate specificity.