What are examples of Gram-negative bacilli?

Examples of Gram-Negative Bacilli

Gram-negative bacilli include Escherichia coli, Klebsiella species, Pseudomonas aeruginosa, Enterobacter species, Proteus species, Acinetobacter species, and Serratia species, which are major causes of hospital-acquired infections and can develop significant antimicrobial resistance. 1

Common Gram-Negative Bacilli by Family

Enterobacteriaceae

• Escherichia coli - frequently isolated from urinary tract infections and a common cause of bacteremia 1, 2
• Klebsiella species (including K. pneumoniae and K. oxytoca) - important pathogens in respiratory and urinary tract infections 1
• Enterobacter species - commonly associated with healthcare-associated infections 1
• Proteus species (including P. mirabilis and P. vulgaris) - often found in urinary tract infections 1
• Serratia marcescens - can cause pneumonia and bloodstream infections 1, 3
• Citrobacter species - can cause various nosocomial infections 1
• Salmonella species - have predilection for vascular tissue with translocation from the gastrointestinal tract 2

Non-Fermenters

• Pseudomonas aeruginosa - prominent cause of infection, especially in immunocompromised hosts and patients with cystic fibrosis 1
• Acinetobacter species (particularly A. baumannii) - increasingly important nosocomial pathogen with high rates of antibiotic resistance 1
• Stenotrophomonas maltophilia - often resistant to many antibiotics including carbapenems 4
• Burkholderia cepacia - particularly problematic in patients with cystic fibrosis 4

Other Gram-Negative Bacilli

• Haemophilus influenzae - respiratory pathogen 1
• Legionella pneumophila - cause of atypical pneumonia 5
• Moraxella catarrhalis - respiratory pathogen 5

Clinical Significance

Common Sites of Infection

• Urinary tract - Gram-negative bacilli are the leading cause of urinary tract infections and subsequent bacteremia 2
• Respiratory tract - particularly in hospitalized patients or those with underlying lung disease 2, 3
• Intra-abdominal infections - second most common source of gram-negative bacteremia 2
• Skin and soft tissue - especially in immunocompromised hosts 2
• Bloodstream - can lead to sepsis and high mortality 6, 7

Risk Factors for Gram-Negative Infections

• Hospitalization, especially in intensive care units 1
• Immunocompromised status (neutropenia, chemotherapy) 1, 2
• Recent antibiotic therapy 1
• Invasive procedures or devices 2
• Advanced age 6
• Residence in long-term care facilities 1

Antimicrobial Resistance

• Carbapenem-resistant Gram-negative bacilli (CRGNB) include carbapenem-resistant Enterobacteriales (CRE), carbapenem-resistant Acinetobacter baumannii (CRAB), and carbapenem-resistant Pseudomonas aeruginosa (CRPA) 1
• Extended-spectrum β-lactamases (ESBLs) production is common among Enterobacteriales 1
• Multidrug-resistant (MDR) strains are increasingly prevalent, limiting treatment options 1
• P. aeruginosa has intrinsic resistance to many antimicrobials through multiple efflux pumps 1

Treatment Considerations

• Empiric antibiotic therapy should be administered promptly to neutropenic patients at the onset of fever 1
• For carbapenem-resistant infections, newer agents or combination therapy may be required 1
• Imipenem is active against many Gram-negative bacilli including Acinetobacter spp., Citrobacter spp., Enterobacter spp., E. coli, Klebsiella spp., Proteus species, P. aeruginosa, and Serratia spp. 4
• Fluoroquinolones like ciprofloxacin and levofloxacin have activity against many Gram-negative organisms but resistance is increasing 8, 5

Special Populations

• In neutropenic patients, common Gram-negative pathogens include E. coli, Klebsiella species, Enterobacter species, and P. aeruginosa 1, 2
• In elderly nursing home residents, S. aureus, enteric gram-negative rods, and Pseudomonas species are common causes of pneumonia 1
• Diabetic foot infections often involve mixed flora including Gram-negative bacilli 1

Understanding the common Gram-negative bacilli and their resistance patterns is essential for appropriate empiric antibiotic selection and effective treatment of infections.