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blue Which of the following statements about biofilms is/are true. none false In a single species biofilm, the interior environment is uniform throughout. No, Nutrient utilization, waste product excretion, and diffusion limitation result in the formation a wide variety of micro-niches, even in a single species biofilm. Oxygen concentrations, for example, rapidly drop to very low levels just inside the outer layer of the biofilm. true Biofilms can often continue to grow at nutrient concentrations too limited to support planktonic cell growth. Yes, The biofilm matrix can adsorb and concentrate nutrients from the bulk fluid even when they are at very low concentrations as in municipal water supplies. true In biofilms there is often metabolic cooperation (syntrophism) in which the metabolic waste product of one organism becomes the nutrient source for another. Yes, The lactic acid produced by streptococci growing in the oral cavity may be used by veillonellae as a nutrient source. false The environment of the biofilm matrix is not conducive to lateral gene transfer mechanisms such as transformation or conjugation. No, Lateral gene transfer in the form of transformation and conjugation has been demonstrated to occur at higher efficiency in biofilms than in planktonic culture. Which of these is/are responsible for the metabolic heterogeneity of multi-species biofilms? none true Diffusion limitation in which materials from outside the biofilm (e.g. Oxygen) may be at higher concentration near the surface of the biofilm than in the interior. Yes, Oxygen concentrations and those of other materials that are used up by the living members of the biofilm exhibit sharp concentration gradients. true Competition for nutrients by several members of a biofilm community may result in complex distribution of some materials. Yes, If several members of a biofilm are competing for the same nutrient, local concentrations may be quite variable. true Waste materials of some biofilm organisms may either stimulate or inhibit the growth of other organisms within the biofilm. Yes, Lactate produced by Streptococcus, for example, is a nutrient for Veillonella. true A metabolic intermediate produced by one organism may become inhibitory to that organism unless another organism in the biofilm removes it. Yes, Hydrogen ions produced by the S-organism which is a component of the mutualistic pair of organisms called Methanobacillus omelianskii is inhibitory to that organisms unless removed by its partner Methanobacterium strain MOH. Which of the following hypotheses is/are believed to be at least partially responsible for the resistance of biofilms to antimicrobials? none true The antibiotic does not penetrate the biofilm matrix well so that cells away from the biofilm surface will not be as readily affected. Yes, Although most antibiotics penetrate biofilms readily, some, which have high molecular weight or are hydrophobic may not penetrate well. true Some biofilms produce compounds like penicillinase or catalase, which are capable of destroying the antimicrobial (penicillin or hydrogen peroxide), thus reducing their local concentrations below effective levels. B. Yes, Some biofilm component organisms are known to be able to degrade certain antimicrobials like Penicillin and hydrogen peroxide. true Some cells within the biofilm are metabolically inactive (quiescent). Cells, which are not metabolically active, have few points of attack and therefore are not particularly susceptible to antimicrobials. Yes, Metabolically inactive cells are less susceptible to antimicrobics a than actively growing ones. true Cell-Cell signaling in the biofilm may induce certain genes that control the production of efflux pumps which can pump the antimicrobial out of the cell fast enough to prevent their toxic effect. D. Yes, The acyl-homoserine lactones active in cell-cell signaling may accumulate rapidly in biofilms turning on genes for efflux pumps as well as many other properties. Biofilms have a reputation as being resistant to many “threats” the environment may hold for bacterial cells. Which of the following are biofilms particularly resistant to? none true Antibiotics Yes, Biofilms possess a number of mechanisms, which make them quite resistant to most antibiotics. true Predation by protozoa and phagocytic white blood cells Yes, The slimy biofilm matrix is quite difficult for protozoa and white blood cells to penetrate. They may graze the surface, but cells at depth in the biofilm are not destroyed. false X-rays No, Biofilms are not a barrier to X-rays. true Antibodies Yes, Antibodies are relatively high molecular weight proteins and do not penetrate the biofilm matrix readily. From the “point of view of a bacterium”, which of these are advantages of being part of a biofilm. none true A biofilm matrix concentrates nutrients from the bulk fluid in which nutrients a re often quite dilute. Yes, Biofilms have been shown to concentrate nutrients from dilute media. true A biofilm is often quite resistant to chemical disinfectants and antibiotics. Yes, For a variety of reasons, biofilms may be as much as 1000 times more resistant to antimicrobials than planktonic cells. true The matrix of a biofilm permits the horizontal transfer of genes from one organisms to another. Yes, Lateral or horizontal gene transfer takes place at a higher frequency in biofilms than in planktonic culture. true Cells in a biofilm are quite resistant to predation by protozoa or phagocytic white blood cells. Yes, Protozoa and white blood cells may remove bacterial cells from the surface of biofilms, but are not effective in removing the biofilm entirely.