Disease caused by Enterobacteriaceae: Klebsiella, Enterobacter, Serratia, Proteus, Providencia, Citrobacter.

Question 1

Klebsiella infections

Answer 1

Klebsiella species, especially Klebsiella pneumoniae, are known for causing a variety of infections, including pneumonia (often in immunocompromised patients), urinary tract infections (UTIs), and liver abscesses. K. pneumoniae produces a thick capsule, which helps evade phagocytosis. The bacteria can also cause nosocomial infections, including bloodstream infections. Diagnosis is based on isolation from clinical samples (e.g., sputum, urine) and identification of the characteristic mucoid colonies on MacConkey agar. Treatment typically involves broad-spectrum antibiotics such as cephalosporins or carbapenems, depending on antibiotic susceptibility.

Question 2

Enterobacter infections

Answer 2

Enterobacter species, such as Enterobacter cloacae and Enterobacter aerogenes, are opportunistic pathogens that can cause UTIs, pneumonia, and bloodstream infections, particularly in hospitalized patients with weakened immune systems. These organisms can produce extended-spectrum beta-lactamases (ESBLs), leading to resistance to beta-lactam antibiotics. Diagnosis involves isolation from clinical specimens, and treatment may require the use of carbapenems or other antibiotics based on sensitivity testing.

Question 3

Serratia infections

Answer 3

Serratia species, particularly Serratia marcescens, are associated with nosocomial infections, including UTIs, pneumonia, and bloodstream infections. S. marcescens is often identified by its red pigment, prodigiosin, which may appear in culture media. The bacteria produce a range of virulence factors, including DNases and lipases, which contribute to tissue invasion. Treatment may involve antibiotics such as imipenem or meropenem, but resistance to multiple drugs is common, so susceptibility testing is essential.

Question 4

Proteus infections

Answer 4

Proteus species, especially Proteus mirabilis, are frequently implicated in UTIs, particularly in patients with urinary catheterization or structural abnormalities. These bacteria are urease producers, leading to the formation of kidney stones (struvite stones). In addition to UTIs, Proteus can cause wound infections, sepsis, and pneumonia. The bacteria are known for their swarming motility on agar. Diagnosis is based on culture and urease testing. Treatment typically includes cephalosporins, aminoglycosides, or carbapenems, depending on susceptibility.

Question 5

Providencia infections

Answer 5

Providencia species, such as Providencia stuartii, are associated with UTIs, wound infections, and bloodstream infections, particularly in immunocompromised patients. These bacteria are resistant to many antibiotics due to the production of beta-lactamases and other resistance mechanisms. Diagnosis involves culture and identification through biochemical testing. Treatment options are limited and depend on antimicrobial susceptibility testing, with carbapenems and aminoglycosides often being effective.

Question 6

Citrobacter infections

Answer 6

Citrobacter species, including Citrobacter freundii, are opportunistic pathogens that can cause UTIs, respiratory infections, and neonatal meningitis. They are known to produce beta-lactamases and can be resistant to multiple drugs. C. freundii is often implicated in infections in immunocompromised patients, such as those undergoing chemotherapy or organ transplantation. Diagnosis is based on culture from clinical samples, and treatment typically involves beta-lactam agents (with resistance considerations) or carbapenems for more resistant strains.