During hypoxia, tumor suppressor p53 overexpression may be associated with HIF1A-dependent pathway to initiate apoptosis. Moreover, p53-independent pathway may also induce apoptosis through the Bcl-2 pathway.  However, overexpression of HIF1A is cancer- and individual-specific, and depends on the accompanying genetic alternations and levels of pro- and anti-apoptotic factors present. One study on epithelial ovarian cancer shows HIF1A and nonfunctional tumor suppressor p53 is correlated with low levels of tumor cell apoptosis and poor prognosis.  Further, early-stage esophageal cancer patients with demonstrated overexpression of HIF1 and absence of BCL2 expression also failed photodynamic therapy.  Studies of glioblastoma multiforme show striking similarity between HIF1A protein expression pattern and that of VEGF gene transcription level.
Table 2. Generation times for some common bacteria under optimal conditions of growth. Bacterium Medium Generation Time (minutes) Escherichia coli Glucose-salts 17 Bacillus megaterium Sucrose-salts 25 Streptococcus lactis Milk 26 Streptococcus lactis Lactose broth 48 Staphylococcus aureus Heart infusion broth 27-30 Lactobacillus acidophilus Milk 66-87 Rhizobium japonicum Mannitol-salts-yeast extract 344-461 Mycobacterium tuberculosis Synthetic 792-932 Treponema pallidum Rabbit testes 1980
In keeping with its role as an agent of opportunistic infection, S. marcescens was traditionally associated with low intrinsic pathogenicity. Whilst almost all isolates produce extracellular products such as DNase, chitinase, lecithinase, lipase, gelatinase and siderophores, it appears that in S. marcescens , these products do not act as potent virulence factors ( 5 ). Nevertheless, ongoing studies indicate that S. marcescens may produce other invasive factors. Almost all isolates of S. marcescens secrete a pore-forming haemolysin, ShIA, that is associated with cell cytotoxicity and the release of inflammatory mediators. This cytotoxin is thought to assist in tissue penetration ( 43 ) and may be linked to the expression of an extensive host invasive pathogenic pathway involving bacterial swarming and quorum sensing ( 58 , 61 ). S. marcescens isolates have also been shown to engage in cell signaling mechanisms involved in biofilm production ( 97 ). If future studies confirm the pathogenic role of biofilm in S. marcescens , this may correlate with other characteristics of this opportunistic pathogen including adherence, colonization and antimicrobial resistance.