Aeromonas Clinical Manifestations Quiz

Study Notes

Plesiomonas shigelloides: facultatively anaerobic, Gram-negative rod that is oxidase- and catalase-positive, ferments glucose.
Found in aquatic environments, limited by a minimum growth temperature of 8°C.
Causes gastroenteritis, especially from consuming uncooked shellfish; can lead to extraintestinal infections like meningitis and septicemia.
Laboratory Diagnosis: Isolated using nonselective and enteric-selective media (e.g., HE agar); indole-positive, methyl-red-positive, reduces nitrates, and ferments glucose, maltose, and trehalose.
Antimicrobial Susceptibility: Susceptible to cephalosporins, trimethoprim–sulfamethoxazole, imipenem, and quinolones.

Strictly aerobic, catalase-positive, oxidase-positive, and Gram-negative bacilli with respiratory metabolism.
Commonly associated with pulmonary infections in cystic fibrosis patients and severe infections in burn and trauma patients.
Motility through polar flagella; capable of forming acids and reducing nitrates.

Found in aquatic environments, associated with intestinal and extraintestinal diseases.
Some strains produce enterotoxins, hemolysin, and a cytopathic factor.
Laboratory Diagnosis: Isolation of a fermenting, oxidase-positive, Gram-negative bacillus should raise suspicion for Aeromonas spp.
Antimicrobial Susceptibility: Susceptible to quinolones, aminoglycosides, carbapenems, and trimethoprim–sulfamethoxazole; produces β-lactamase conferring resistance to penicillins and first-generation cephalosporins.

Small, motile, non-spore-forming, Gram-negative bacilli that are microaerophilic (optimal growth in 5-10% O2).
C. jejuni: Most common cause of bacterial enteritis in the U.S., linked to improperly cooked poultry; diarrhea may be bloody and self-limited, lasting up to a week.
Can result in extraintestinal infections and is a recognized antecedent of Guillain–Barré syndrome.

Endotoxins: Composed of lipid and polysaccharide, elicit symptoms like fever, chills, and DIC; includes K1 antigen related to neonatal meningitis.
K. pneumoniae Capsule: Inhibits phagocytosis; Vi antigen of Salmonella serotype Typhi impairs intracellular killing.
Laboratory Diagnosis: Eosin methylene blue (EMB) and MacConkey's agar differentiate lactose fermenters; XLD and HE agar are selective for Salmonella and Shigella.
Antimicrobial Susceptibility: E. coli and P. mirabilis are susceptible to ampicillin; various species exhibit resistance to first-generation cephalosporins.