hypersecretion of electrolytes and water in the large intestine, leading to profuse watery diarrhea and dehydration.
V. parahaemolyticusis also a cause of gastrointestinal disease in humans, whereasV. vulnificuscauses serious and
potentially life-threatening cellulitis (infection of the skin and deeper tissues) and blood-borne infections. Another
representative of Vibrionales,Aliivibrio fischeri, engages in a symbiotic relationship with squid. The squid provides
nutrients for the bacteria to grow and the bacteria produce bioluminescence that protects the squid from predators
(Figure 4.8).
Figure 4.8 (a)Aliivibrio fischeriis a bioluminescent bacterium. (b)A. fischericolonizes and lives in a mutualistic
relationship with the Hawaiian bobtail squid (Euprymna scolopes). (credit b: modification of work by Margaret McFall-
Ngai)
The genusLegionellaalso belongs to the Gammaproteobacteria.L. pneumophila,the pathogen responsible for
Legionnaires disease, is an aquatic bacterium that tends to inhabit pools of warm water, such as those found in
the tanks of air conditioning units in large buildings (Figure 4.9). Because the bacteria can spread in aerosols,
outbreaks of Legionnaires disease often affect residents of a building in which the water has become contaminated
withLegionella.Infact,thesebacteriaderivetheirnamefromthefirstknownoutbreakofLegionnairesdisease,which
occurred in a hotel hosting an American Legion veterans’ association convention in Philadelphia in 1976.
Figure 4.9 (a)Legionella pneumophila, the causative agent of Legionnaires disease, thrives in warm water. (b)
Outbreaks of Legionnaires disease often originate in the air conditioning units of large buildings when water in or near
the system becomes contaminated withL. pneumophila.
Enterobacteriaceae is a large family ofenteric(intestinal) bacteria belonging to the Gammaproteobacteria. They
are facultative anaerobes and are able to ferment carbohydrates. Within this family, microbiologists recognize two
distinct categories. The first category is called the coliforms, after its prototypical bacterium species,Escherichia coli.
Coliforms are able to ferment lactose completely (i.e., with the production of acid and gas). The second category,
noncoliforms, either cannot ferment lactose or can only ferment it incompletely (producing either acid or gas, but not
152 Chapter 4 | Prokaryotic Diversity
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