Antibiotic-resistant bacteria from air samples collected in nursing homes

Introduction: Antibiotic resistance is currently a worldwide public health problem that can include diverse mechanisms and bacterial species. The understanding and monitoring of such phenomena is essential to avoid further dissemination. The main aim of this study was the characterization of antibiotic resistance mechanisms in bacterial strains collected in air samples from nursing homes and compare them with clinical samples isolated from the same geographic area. Materials and methods: Air samples were collected from bedrooms, living rooms and outdoor of 4 nursing homes located in Lisbon, Portugal. Screening of antimicrobial susceptibility of 18 Gram-negative (5 Acinetobacter spp., 1 Klebsiella oxytoca, 4 Pantoea spp., 7 Pseudomonas spp., 1 Sphingomonas paucimobilis) and 12 Gram-positive (3 Micrococcus luteus, 3 Staphylococcus spp.) isolates was performed by disk diffusion method. Different antibiotic resistant genes were searched by PCR. PFGE was used to evaluate clonality between K. oxytoca isolated from the air environment and other strains from clinical origin. Results and discussion: The majority of strains were susceptible to all antibiotics tested. Among beta-lactam antibiotics, reduced susceptibility to cefoxitin was detected in Staphylococcus capitis, through expression of the mecA gene, and to ampicillin, piperacillin and piperacillin-tazobactam in 1 K. oxytoca expressing a blaOXY-5-type beta-lactamase. Nonsusceptibility to meropenem and piperacillin-tazobactam was observed in 2 Pseudomonas putida however no antibiotic resistance gene was detected. Regarding quinolones, non-susceptibility was found in 1 S S. capitis, 2 Staphylococcus haemolyticus, and 1 K. oxytoca. The molecular characterization of the mecA-positive S. capitis from the nursing homes and from a hospital within the same region suggests a potential dissemination of strains between these two environments. The genetic relatedness of K. oxytoca from nursing homes (n=1) and clinical isolates (n=9) recovered within the same region, allowed to conclude that they were not genetically related. Conclusions: Globally, nursing homes environments may act as complementary reservoirs of antibiotic resistant bacteria and antibiotic resistance genes. Thus, a better understanding of the antibiotic resistance mechanisms and dissemination pathways in other reservoirs than human is essential to control its emergence and spread.