Microflix activity immunology infection and initial response

8 Virtually all the microbial traits you have read about in earlier chapters are controlled or influenced by heredity. The inherited characteristics of microbes include shape, structural features, metabolism, ability to move, and interactions with other organisms. Individual organisms transmit these characteristics to their offspring through genes.

The development of antibiotic resistance in microorganisms is often carried on plasmids such as those in the photo, which are readily transferred between bacterial cells. They are responsible for the emergence of methicillin-resistant Staphylococcus aureus and the recent emergence of carbapenem- resistant Klebsiella pneumoniae. The emergence of vancomycin- resistant S. aureus (VRSA) poses a serious threat to patient care. In this chapter you will see how VRSA acquired this characteristic.

Emerging diseases provide another reason why it is important to understand genetics. New diseases are the results of genetic changes in some existing organism; for example, E. coli O157:H7 acquired the genes for Shiga toxin from Shigella.

Currently, microbiologists are using genetics to study unculturable microbes and the relationship between hosts and microbes.

The Big Picture on pages 206–207 highlights key principles of genetics that are explained in greater detail throughout the chapter.

In the Clinic As a nurse at a U.S. military hospital, you treat service members injured in the recent Middle East conflicts. You notice that wounds infected by Acinetobacter baumannii are not responding to antibiotics. The Centers for Disease Control and Prevention reports that the antibiotic- resistance genes found in A. baumannii are the same as those in Pseudomonas, Salmonella, and Escherichia. Cephalosporin-resistance genes are on the chromosome, tetracycline resistance is encoded by a plasmid, and streptomycin resistance is associated with a transposon. Can you suggest mechanisms by which Acinetobacter acquired this resistance?

Hint: Read about genetic recombination on pages 229–235.

Microbial Genetics

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▶ Plasmids exist in cells separate from chromosomes.

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CHAPTER 8 Microbial Genetics 205

Structure and Function of the Genetic Material LEARNING OBJECTIVES

8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics.

8-2 Describe how DNA serves as genetic information.

8-3 Describe the process of DNA replication.

8-4 Describe protein synthesis, including transcription, RNA processing, and translation.

8-5 Compare protein synthesis in prokaryotes and eukaryotes.

Genetics is the science of heredity. It includes the study of genes: how they carry information, how they replicate and pass to sub- sequent generations of cells or between organisms, and how the expression of their information within an organism determines its characteristics. The genetic information in a cell is called the genome. A cell’s genome includes its chromosomes and plas- mids. Chromosomes are structures containing DNA that physi- cally carry hereditary information; the chromosomes contain the genes. Genes are segments of DNA (except in some viruses, in which they are made of RNA) that code for functional prod- ucts. Usually these products are proteins, but they can also be RNAs (ribosomal RNA, transfer RNA, or microRNA).