Prevalence and diversity of bacteria and clinically relevant antibiotic resistance genes in human residences

Alatawi, E 2019, Prevalence and diversity of bacteria and clinically relevant antibiotic resistance genes in human residences, Doctor of Philosophy (PhD), Science, RMIT University.

Document type: Thesis
Collection: Theses

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Title Prevalence and diversity of bacteria and clinically relevant antibiotic resistance genes in human residences
Author(s) Alatawi, E
Year 2019
Abstract Human health can be positively or negatively affected by indoor microbiomes. with direct links found between indoor bacteria and outbreaks  of infectious disease. Additionally, these indoor bacteria may harbour antibiotic resistance genes (ARGs). Several environments, including indoor environments such as hospitals have been found to be potential reservoirs of antibiotic resistance genes. The emergence and spread of antibiotic resistance genes in environmental and pathogenic bacteria increases the risks to human health as these bacteria can be transmitted to humans through skin contact, inhalation and ingestion. Since people spend the majority of their lives indoors, they are constantly exposed to a diverse community of indoor bacteria. To better understand and evaluate the potential beneficial and/or adverse health impacts of bacterial communities that surround us and that are present in our homes, it is increasingly important to study these bacterial communities and their associated antibiotic resistances.

In this research project a total of 132 residential samples were obtained from four habitats (dust, kitchen surfaces, bathroom surfaces and drinking water samples) from eleven human residences and were used to investigate the variation in the structure, diversity and composition of bacterial communities within and between different houses and residential habitats, applying 16S ribosomal RNA gene next generation sequencing (NGS). Subsequently, Polymerase Chain Reaction (PCR) and quantitative real-time (Q-PCR) were used to determine the prevalence, distribution and abundance of 12 antibiotic resistance genes in human residences, namely: tetM and tetB, ermB, ampC, vanA, mecA, aac(6')-Ie-aph(2"), sulII, catII, dfrA1, mcr-1 and blaNDM-1 encoding resistance to tetracycline, erythromycin, ampicillin, vancomycin, methicillin, aminoglycoside, sulfonamide, chloramphenicol, trimethoprim, colistin and carbapenem, respectively. The four most frequently detected antibiotic resistance genes namely: tetM, ermB, sulII and ampC genes were then sequenced using amplicon-based next generation sequencing to describe the diversity of these antibiotic resistance genes and to identify their likely bacterial taxonomic origins within human residences.

The structure, diversity and composition of bacterial communities was found to vary within and between different habitats in the human residences. These bacterial communities were found to be habitat-specific rather than house-specific. Nevertheless, within each residential habitat, samples clustered largely with respect to their house of origin. In addition, the residential dust showed the highest diversity whereas drinking water was found to be the least diverse habitat in human residences. Numbers of bacterial taxa identified ranged from 867±38 operational taxonomic units (OTU) in dust to 73±7 OTU in drinking water. Bacterial communities in human residences were primarily related to those  from soil and human-related bacteria in dust, from soil, human skin, food and water in kitchen surface samples, and the bacteria in bathroom surface samples were mostly associated with those from either human skin or from water. The most abundant genera identified in this study included Acinetobacter and Pseudomonas (related to those from soil), Enhydrobacter, Chryseobacterium, Staphylococcus, Streptococcus and Corynebacterium (related to those from human body), Lactobacillus, Lactococcus and Bacillus (related to those from food) and Sphingomonas and Methylobacterium (related to those from water samples). Furthermore, in this study, potentially pathogenic bacteria have been detected in all residential habitats and houses which represent a major public health risk in our homes.

Eight clinically relevant antibiotic resistance genes (namely: tetM, tetB, ermB, ampC, sulII, catII, mcr-1 and blaNDM-1) were detected in the 11 houses and with different frequencies and abundances within and between different human residences. The most commonly detected antibiotic resistance genes in human residences were tetM (75%) and ermB (55%) genes. Moreover, antibiotic resistance genes such as blaNDM-1 and mcr-1 genes, which confer resistance to the antibiotics of last resort carbapenem and colistin, were detected with frequencies of 30% and 25%, respectively. The bathroom surfaces harboured the highest proportion (37%) of antibiotic resistance genes compared to dust (28%), kitchen surfaces (27%) and drinking water (11%). The ampC gene, which encodes ß-lactam resistance, was found in drinking water with a very high relative abundance. In this study, a number of factors such as occupancy intensity and cleaning behaviours showed a possible influence on both diversity of bacterial communities and frequency of detection of antibiotic resistance genes. The diversity of antibiotic resistance genes was found to vary within and between different habitats in the human residences. Furthermore, antibiotic resistance genes were related to those from human-associated bacteria including those in potentially pathogenic bacteria such as Staphylococcus aureus, Streptococcus pneumoniae and Acinetobacter baumannii. The association between antibiotic resistance genes identified in this study and those on mobile elements suggests horizontal gene transfer (HGT) of these ARGs between bacteria within residential habitats. Multiple resistance genes related to those from potential pathogenic bacteria such as Escherichia coli and Klebsiella pneumoniae were detected. Novel sequence variants were identified for the ampC gene. This research shows that human residences are a reservoir for antibiotic resistance genes. Overall, this research demonstrates that the home microbiome and antibiotic resistome will be a key driver for public health in human residences.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Science
Subjects Microbiology not elsewhere classified
Keyword(s) Residential microbiomes
Human residences
Antibiotic resistance genes
Bacterial communities
Bacterial diversity
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Created: Fri, 15 Nov 2019, 09:38:34 EST by Adam Rivett
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