What are the characteristics of the family Enterobacteriaceae (Enteric Bacteria), a group of Gram-negative, facultatively anaerobic, rod-shaped bacteria?

From the Guidelines

Enterobacteriaceae is a large family of gram-negative bacteria characterized by their rod-shaped morphology and inability to form spores, and they are increasingly developing antimicrobial resistance, particularly through production of extended-spectrum beta-lactamases (ESBLs) and carbapenemases, making infections difficult to treat and representing a significant public health concern worldwide. These facultative anaerobes can grow with or without oxygen and are found widely in soil, water, plants, and the intestinal tracts of humans and animals 1. They typically measure 1-5 μm in length and possess peritrichous flagella for motility, though some genera are non-motile. Enterobacteriaceae ferment glucose, reduce nitrates to nitrites, and are oxidase-negative and catalase-positive. Their cell wall contains lipopolysaccharide (LPS), which contributes to their pathogenicity by triggering inflammatory responses. Many members produce important virulence factors including adhesins, invasins, toxins, and capsules that enhance their ability to cause disease. The family includes numerous clinically significant pathogens such as Escherichia coli, Salmonella, Shigella, Klebsiella, Proteus, Enterobacter, Serratia, and Yersinia. These organisms cause a wide range of infections including urinary tract infections, pneumonia, septicemia, meningitis, and gastrointestinal diseases. Some of the key characteristics of Enterobacteriaceae include:

• Rod-shaped morphology
• Inability to form spores
• Facultative anaerobes
• Presence of peritrichous flagella for motility
• Ability to ferment glucose and reduce nitrates to nitrites
• Oxidase-negative and catalase-positive
• Presence of lipopolysaccharide (LPS) in their cell wall
• Production of virulence factors such as adhesins, invasins, toxins, and capsules
• Ability to cause a wide range of infections The increasing development of antimicrobial resistance among Enterobacteriaceae is a significant public health concern, with the production of ESBLs and carbapenemases being a major contributor to this problem 1. This has led to a need for new and effective treatment options, including the use of carbapenem-sparing regimens and the development of new antibiotics such as ceftazidime/avibactam and ceftolozane/tazobactam 1. Overall, Enterobacteriaceae are an important family of bacteria that play a significant role in human disease, and their increasing resistance to antimicrobial agents is a major public health concern.

From the Research

Characteristics of Family Enterobacteriaceae

• Enterobacteriaceae are a family of Gram-negative bacteria that are common causes of both community-acquired and hospital-acquired infections, including urinary tract infections (UTIs), pneumonia, and sepsis 2, 3, 4, 5.
• These organisms can acquire genes that encode for multiple antibiotic resistance mechanisms, including extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, and carbapenemases 2, 3, 6.
• The production of β-lactamase enzymes is a primary mechanism of resistance to β-lactams in Enterobacteriaceae, with carbapenem-resistant Enterobacteriaceae (CRE) being a major concern due to their high morbidity and mortality rates, especially in immunocompromised patients 3.
• Enterobacteriaceae that produce ESBLs and AmpC β-lactamases are increasingly recognized as important causes of community-acquired infections, including UTIs and bloodstream infections 6.
• The clinical features and treatment outcomes of patients with bacteremic UTIs caused by multidrug-resistant (MDR) Enterobacteriaceae are compared to those with non-MDR Enterobacteriaceae, with MDR pathogens being independently associated with severe sepsis or septic shock at presentation 4.
• The use of empiric antibiotic therapy for patients with UTIs presented with severe sepsis and/or septic shock should be broad-spectrum to effectively cover MDR Enterobacteriaceae 4.
• The cost of antibiotics is a small component of total costs in the treatment of Enterobacteriaceae infections, but each extra day of inadequate treatment adds significant costs to hospital costs 5.

Resistance Mechanisms

• ESBLs are a type of β-lactamase enzyme that confers resistance to extended-spectrum cephalosporins 2, 6.
• AmpC β-lactamases are another type of β-lactamase enzyme that confers resistance to cephalosporins and other β-lactam antibiotics 2, 6.
• Carbapenemases are enzymes that confer resistance to carbapenems, a class of broad-spectrum β-lactam antibiotics 3.
• The production of these enzymes is often plasmid-mediated, allowing for the horizontal transfer of resistance genes between bacteria 6.

Clinical Implications

• The increasing prevalence of MDR Enterobacteriaceae highlights the need for judicious use of antibiotics and the implementation of antimicrobial stewardship principles 2.
• The use of broad-spectrum empiric antibiotic therapy should be considered in patients with severe sepsis or septic shock, especially if a patient has recently traveled to a high-risk area 4, 6.
• The treatment of CRE infections is often challenging, and combination therapy may be preferred over monotherapy due to its broad-spectrum coverage and synergistic effects 3.