Wednesday, 7 May 2008

Alcohol hand rubs increase growth of Acinetobacter

Edwards, J., Patel, G. & Wareham, D.W. (2007). Low concentrations of commercial alcohol hand rubs facilitate growth of and secretion of extracellular proteins by multidrug-resistant strains of Acinetobacter baumannii. J Med Microbial 56, 1595–1599.

The medical profession continues to be haunted by serious bacterial infections acquired within hospitals. If the bacteria can survive antibiotics, as in the so-called multidrug-resistant strains, treatment can be very difficult. The classic measure of good hand hygiene can reduce infection rates by 10–50 %, so hospitals have introduced ways for staff to clean their hands frequently without suffering from chapped skin. These include using alcohol-based hand rubs (ABHRs) dispensed from a pump adjacent to patients’ beds. These are solutions of ethanol or isopropanol, often in combination with an antiseptic and moisturiser which are less irritating to skin than soap.

Although studies have shown that ABHRs reduce infection rates, they are not effective against all bacteria. One example is the spores of Clostridium difficile that can cause very serious gastrointestinal infections. Now, Justin Edwards, Greta Patel and David Wareham from Barts and The London NHS Trust and the MRC Clincal Sciences Centre of Imperial College London have found evidence that low concentrations of ABHRs enhance in vitro growth of Acinetobacter baumannii, an opportunistic pathogen of critically ill patients.

A. baumannii has emerged in recent years as an important cause of ventilatorassociated pneumonia and blood infections in patients with burns, immunosuppression and critical illness. Many strains also turn out to be resistant to many antibiotics so that treatment is extremely difficult. The bacteria have a remarkable ability to persist on surfaces in the hospital environment and are spread by the hands of hospital staff so that hand hygiene is the key factor in preventing these infections.

The researchers therefore tested whether low concentrations of commercially available ABHRs could affect the growth of multidrug-resistant A. baumannii. Depending on the growth medium, the presence of 0.01–1 % ABHR resulted in increased growth of A. baumannii. In contrast, a hand-cleaning product that was free of alcohol and relied on strong detergents to kill bacteria did not support the growth of A. baumannii at all.

The researchers then investigated the proteins secreted by A. baumannii as it grew because previous work has shown that low concentrations of ethanol increase the virulence as well as the numbers of A. baumannii. They discovered that oomph was a major secreted protein, along with another protein with an unknown role. OmpA is well known and may help the cells take up ethanol as a food source when other nutrients are in short supply. It may also help the bacterial cells sense each other and form films on surfaces.

The findings of this paper are certainly interesting, but their clinical significance remains unclear. However, if low concentrations of ABHRs do indeed exist in the clinical environment, this work may have implications for those hospitals currently experiencing outbreaks of A. baumannii.