Hospital air is a potential route of transmission of beta-lactam–resistant bacteria (BLRB), which are important causative agents of nosocomial infections, according to research published in the American Journal of Infection Control.

Dr. Mahnaz Nikaeen of the department of environmental health engineering at Isfahan (Iran) University of Medical Sciences, and his coauthors collected and tested 64 air samples from four hospital wards to determine the prevalence of airborne BLRB in different teaching hospitals, to evaluate the frequency of five common beta-lactamase–encoding genes in isolated resistant bacteria, and to identify the most predominant BLRB by 16s rRNA gene sequencing. The sampling locations in each hospital included operating rooms, ICUs, surgery wards, and internal medicine wards.

The investigators detected airborne bacteria by using culture plates with and without beta-lactams.

The prevalence of BLRB in the air samples ranged between 3% and 34%, Dr. Nikaeen said. Oxacillin-resistant bacteria had the highest prevalence, followed by ceftazidime- and cefazolin-resistant bacteria. Acinetobacter spp, Acinetobacter baumannii, and Staphylococcus spp were the most predominant BLRB.

Gene sequencing revealed that the frequency of beta-lactamase–encoding genes in isolated BLRB ranged between 0% and 47%, with the highest and lowest detection for OXA-23, commonly found in Acinetobacter spp, and CTX-m-32, a gene prevalent in extended-spectrum beta-lactamase–producing Enterobacteriaceae, respectively. MecA, a genetic element found in methicillin-resistant Staphylococcus spp, had a relatively high frequency in surgery wards and operating rooms, whereas the frequency of blaTEM, another common extended-spectrum beta-lactamase produced by Enterobacteriaceae, was higher in intensive care units and internal medicine wards. OXA-51, a chromosomally located intrinsic gene in A. baumannii, was detected in four wards.

“Isolation of beta-lactam–resistant Staphylococcus spp and A. baumannii as the most predominant BLRB indicated the potential role of airborne bacteria in dissemination of nosocomial infections,” Dr. Nikaeen and his coauthors said. “The results confirm the necessity for application of effective control measures that significantly decrease the exposure of high-risk patients to potentially airborne nosocomial infections.”

The authors reported having no conflicts.

Read the complete study in the American Journal of Infection Control ( doi:10.1016/j.ajic.2016.01.041).

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