Production of exotoxin A and several proteolytic enzymes and hemolysins are factors that contribute ...

A
Although P. aeruginosa is an environmental inhabitant, it is also a successful opportunistic pa-thogen. Factors that contribute to pathogenicity include the production of exotoxin A, which kills host cells by inhibiting protein synthesis, and the production of several proteolytic enzymes and hemolysins that destroy cells and tissue. On the bacterial cell surface, pili may mediate attachment to host cells. Some strains produce alginate, a polysaccharide polymer that inhibits phagocytosis and contributes to infection potential in patients with cystic fibrosis.

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A
In the clinical setting, Pseudomonas aeruginosa is the most commonly encountered gram-negative species that is not a member of the Enterobacteriaceae family. This organism survives in various environments in nature, as well as in homes and hospitals (see Table 21-1). Because of the ubiquitous nature of P. aeruginosa, transmission of this organism to humans can occur in a variety of ways.

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B
S. maltophilia is notoriously resistant to most currently available antimicrobial agents, leaving trimethoprim-sulfamethoxazole as the primary drug of choice for infections caused by this spe-cies. Although a few other agents, such as minocycline, ticarcillin and clavulanic acid, and chlo-ramphenicol, often exhibit in vitro activity, clinical experience with these agents is not extensive. Therefore, trimethoprim-sulfamethoxazole remains the drug of choice.

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C
Acinetobacter spp. are plump coccobacilli that tend to resist alcohol decolorization. The Borde-tella spp. are coccobacilli or short rods. S. maltophilia, P. oryzihabitans, and P. luteola are short-to-mediumsized straight rods.

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D
Enterobacteriaceae inhabit a wide variety of niches that include the human gastrointestinal tract, the gastrointestinal tract of other animals, and various environmental sites. Some are agents of zoonosis, causing infections in animal populations. Just as the reservoirs for these organisms vary, so do their modes of transmission to humans.

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