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Gram-negative Bacterial Infection


Gram-negative bacteria are a specific type of bacteria with unique characteristics. Like most bacteria, they can cause infections throughout the body. Common infection sites include the lungs, urinary tract, bloodstream, nervous system, and soft tissues. Surgical wounds can also become infected with gram-negative bacteria.
Common gram-negative bacteria and the infections they cause include:
  • Escherichia coli (E. coli)—food poisoning, urinary tract infections, gastroenteritis, and newborn meningitis
  • Pseudomonas aeruginosa—lung and urinary tract infections
  • Klebsiella—meningitis, and lung, urinary tract, and bloodstream infections
  • Acinetobacter baumannii—several types of infections in wounded soldiers
  • Neisseria gonorrhoeae— gonorrhea , a sexually transmitted disease
  • Enterobacteriaceae—urinary tract, lung, and bloodstream infections, and food poisoning (includes carbapenem-resistant Enterobacteriaceae, which are very resistant to antibiotics)
Development of Pneumonia in the Air Sacs of the Lungs
pneumonia lung fluid
Copyright © Nucleus Medical Media, Inc.


Bacteria are normally found throughout the body including on the skin and in the intestines. When kept in balance, bacteria can help the body work normally. However, an imbalance of the bacteria or passing of bacteria to areas where there are no bacteria, can lead to an infection. An infection will develop if large amounts of bacteria are present, the bacteria are aggressive, or the immune system is weakened.
Common ways for bacteria to pass to vulnerable parts of the body include:
  • Use of medical devices that pass into the body, such as IV or urinary catheters
  • Open wounds
  • Contact with someone who has or has been exposed to gram-negative bacteria

Risk Factors

Hospitalization is the most common risk factor for gram-negative bacterial infections. The longer the stay in the hospital, the higher the risk of infection.
Other factors that increase the risk of a bacterial infection include:


Symptoms will depend on the location of the infection. Fever is a common sign of infection.


You will be asked about your symptoms and medical history. A physical exam will be done.
A bacterial infection may be suspected based on the symptoms.
A sample of fluids may be taken from the suspected area. The sample will be examined in the lab to identify the specific type of bacteria that is causing the infection. Samples may be taken through:
  • Blood tests and culture
  • Urine tests and culture
  • Sputum samples
  • Stool samples
  • Lumbar puncture —to test the cerebrospinal fluid that protects the brain and spinal cord
  • Cultures of abscesses, skin lesions, soft tissues, wounds, or other areas where an infection is suspected
These tests may not always be done. They may only be done for severe infections or infections that are not responding to treatment.


Bacterial infections may first be treated with antibiotics that are effective against a wide range of infections. The specific type of antibiotic may be changed if the infection is not responding to the first antibiotic. It also takes time to get the results of a bacterial test because the bacteria need to grow in the lab. Your doctor may change the antibiotic you are given if the test shows that a gram-negative bacteria is causing the infection.
Gram-negative bacterial cells are protected by strong walls. These walls can make it difficult for many antibiotics to fight the bacteria. Gram-negative bacteria may also have other defenses against antibiotic treatment such as:
  • Extended spectrum beta-lactamase (ESBL)—a chemical produced by bacteria that can stop certain antibiotics from working well
  • Genetic material obtained from other bacteria to help them resist antibiotics
Because gram-negative bacteria can learn to resist antibiotics, current commonly used antibiotics may not work. Some of these infections may respond to older types of antibiotics that are rarely used today. It is unlikely that the bacteria have been exposed to these older antibiotics which means there is little chance the bacteria has developed a resistance. Unfortunately, older antibiotics are more toxic than current medications and can cause serious side effects. Research is being done to try to find better antibiotic options for these infections.
If left untreated, gram-negative bacteria can cause serious health complications and death.


Gram-negative bacteria are most commonly spread during hand-to-hand contact in a medical care setting. During a hospital stay staff will take steps to reduce your chance of infection such as:
  • Washing their hands repeatedly
  • Wearing gloves when needed
  • Keeping incisions or wounds covered
  • Protecting medical equipment such as catheters or ventilators and limiting use or length of use
Steps you can take to reduce your chances of infection during a hospital stay include:
  • Washing your hands often and reminding visitors and healthcare providers to do the same
  • Not allowing others to touch your incisions or any medical equipment attached to your body
  • Asking why and how long you will need invasive equipment, such as catheters or intubation
The use of antibiotics when not medically necessary or improper use of antibiotics is increasing the amount of antibiotic-resistant bacteria. Medical professionals are being encouraged to make careful decisions before recommending antibiotics. Patients can also ask their doctor why antibiotics are recommended for specific infections.


Centers for Disease Control and Prevention
IDSA—Infectious Diseases Society of America


Infection Prevention and Control Canada
Public Health Agency of Canada


Antibiotic resistance threats in the United States, 2013. Centers for Disease Control and Prevention website. Available at: Accessed December 11, 2017.
Bacteremia with gram-negative bacilli. EBSCO DynaMed Plus website. Available at: . Updated November 6, 2015. Accessed December 11, 2017.
Bacterial meningitis in adults. EBSCO DynaMed Plus website. Available at: . Updated September 26, 2017. Accessed December 11, 2017.
Carbapenem-resistant Enterobacteriaceae (CRE). EBSCO DynaMed Plus website. Available at: . Updated August 28, 2017. Accessed December 11, 2017.
Extended spectrum beta-lactamases (ESBLs). EBSCO DynaMed Plus website. Available at: . Updated November 7, 2017. Accessed December 11, 2017.
Gram-negative bacteria. National Institute of Allergy and Infectious Diseases website. Available at: Updated July 11, 2016. Accessed December 11, 2017.
Gram-negative bacteria and who can get them. Safe Care Campaign website. Available at: Accessed December 11, 2017.
Gram-negative bacteria infections in healthcare settings. Centers for Disease Control and Prevention website. Available at: Updated January 17, 2011. Accessed December 11, 2017.
Kaye KS, Pogue JM. Infections caused by resistant gram-negative bacteria: epidemiology and management. Pharmacotherapy. 2015;35(10):949-962.

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