Bauman Microbiology Chapter 20 Critical Thinking Answers p. 570. Investigations of Mycobacterium tuberculosis have clearly demonstrated that this pathogen can be transmitted among airline passengers; however, as of 2002, no cases of in-flight transmissions of meningococci have been reported to the CDC. What are some possible explanations for the lack of documented cases of in-flight transmission of N. meningitidis ? M. tuberculosis has mycolic acid in its cell wall which makes it resistant to drying, so it can survive being suspended in aerosols for a long enough period of time to be transmitted through aircraft air systems. The Gram-negative Neisseria do not tolerate dry conditions, and so may not survive long enough to be transmitted in-flight. In addition, the Neisseria are fastidious pathogens that cannot long survive being outside the host without extensive nutrient supplementation. p. 574. Resistance to antimicrobial agents is more commonly seen in hospital-acquired infections with enteric bacteria than in community-based infections with the same species. Explain why this is so. In the hospital environment antimicrobial agents are pervasive, providing essentially constant selective pressure for microorganisms to develop resistance, and non-resistant strains will not survive long. In the community setting where antimicrobials are less extensively used, there are better opportunities for non-resistant strains to survive. p. 583. Haemophilus influenzae was so named because researchers isolated the organism from flu patients. Specifically, how could a proper application of Koch’s postulates have prevented this misnomer? If the researchers had established that the bacterium was sometimes but not always present (Koch’s first postulate) in flu cases, they would probably not have misnamed the organism.
Bauman Chapter 21 Answers to Critical Thinking Questions p. 597 Mycoplasma pneumoniae , like many pathogenic bacteria, is resistant to penicillin; however, unlike most resistant species, Mycoplasma does not synthesize beta-lactamase. Explain why Mycoplasma is resistant to penicillin. Penicillin blocks synthesis of bacterial cell walls. Mycoplasma pneumoniae has no cell wall, so penicillin has no affect on M. pneumoniae. p. 598 Why do pediatricians refrain from using tetracycline to treat mycoplasmal infections in children? Tetracycline interferes with development of bones and teeth and so should not be given to pregnant women or to children who are still growing bones or teeth. p. 599 Why do most cases of Rocky Mountain spotted fever occur in May, June, and July? The tick vectors of Rocky Mountain Spotted Fever are most active in the late spring and early summer, so most people are fed on by the ticks in these three months. p. 602 Explain the etymology of the names of the diseases caused by Ehrlichia . Both disease names refer to the cells that are infected and killed by the two species: human monocytic ehrlichiosis is caused by Ehrlichia chaffeensis, which infects and kills monocytes, while the disease caused by Ehrlichia equi , which infects neutrophils, a type of granulocyte, is known as human granulocytic ehrlichiosis. p. 605 Why is either erythromycin or sulfonamide substituted for doxycycline in treatment of chlamydial infections in children?