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Nasogastric Tubes May Harbor Pathogens

Kate Traynor

A small study conducted in Israel suggests that nasogastric tubes could be an important source of Pseudomonas aeruginosa infection among elderly residents of long-term care facilities.

According to a report in the August issue of Emerging Infectious Diseases, P. aeruginosa was cultured from the throats of 18 out of 53 long-term care facility residents who had been fed for at least two weeks through a nasogastric tube. In contrast, the organism was not present in tongue swabs obtained from a similar group of 50 patients who lived in the same wards as the tube-fed patients but were fed without the device.

An analysis of samples taken from four of the P. aeruginosa-colonized patients confirmed that the organism was part of a biofilm growing on the polyvinyl chloride nasogastric tubes.

Biofilms form when communities of microorganisms, like P. aeruginosa, adhere to a wet environmental surface and produce a slimy, sticky polysaccharide substance. Microorganisms that are part of a biofilm tend to be much more resistant to antimicrobials than freely suspended, or planktonic, microorganisms.

According to the report's authors, biofilms on nasogastric tubes "probably play a major role in the persistence of [P. aeruginosa's] colonization of the oropharynges of these patients and interfere with [the organism's] eradication by antibiotics."

In the current study, P. aeruginosa isolates obtained from the tube-fed patients' throats were less susceptible to amikacin than a reference sample of P. aeruginosa cultured from sputum samples obtained from residents of the same facility during the year before the study took place. P. aeruginosa isolates from the two groups had similar degrees of resistance to tazobactam–piperacillin, ceftazidime, and imipenem.

The authors noted that the transfer of tube-fed patients to hospitals or other health care facilities could possibly spread P. aeruginosa, including resistant isolates, to other patients.

According to the report, the study took place in four skilled-nursing wards at a 158-bed "geriatric hospital." Residents of this type of facility require close medical supervision for conditions such as severe bed sores, advanced cancer, and hemodynamic instability.

The average age of patients was 78 years for tube-fed patients and 81 years for those in the control group—a difference that was not significant. Other medical and demographic characteristics, such as a diagnosis of dementia, stroke, or diabetes mellitus, and the presence of residual teeth, were similar in the two groups.

Patients who had advanced cancer and those who had undergone antimicrobial therapy within two weeks before the study began were ineligible to participate. Also excluded were patients who had received chemotherapy or radiotherapy to the neck.

Overall, nearly two-thirds of the tube-fed patients were found to be colonized by at least one species of gram-negative bacteria, including P. aeruginosa. Although none of the patients in the control group harbored this organism, 8 percent were colonized by another type of gram-negative bacterium.

The authors speculated that the inability of tube-fed patients to chew and swallow inhibits the "mechanical clearance" of the mouth, producing an environment that is ripe for bacterial colonization by P. aeruginosa and other gram-negative bacteria.