The bacteriology of fallen leaves (Phylloplane) from council parks and green spaces in Northern Ireland: Clinical significance for at risk people living with cystic fibrosis (CF).

Authors

Beverley Cherie Millar, Aliyu Ibrahim Dabai, Jonathan Stirling, Alan Murphy, Laura Jenkins, Juluri R Rao, John E Moore

Published in

The Ulster medical journal. Volume 95. Issue 2. Pages 54-65. Epub Oct 19, 2026.

Abstract

People living with cystic fibrosis (CF) may suffer from chronic respiratory infections due to acquired environmental organisms, ultimately leading in increased morbidity and mortality. Consequently, parents of children living with CF frequently ask their CF healthcare professional about sources and potential routes of transmission of environmental organisms to their child. This allows parents to make an informed decision regarding risk assessment/risk management of outdoor/ nature-based activities. Mitigations can then be put in place to help minimise or absolutely avoid exposure of the child to these sources, thereby helping to reduce/eliminate the potential for acquisition of a respiratory infection with such environmental organisms.Northern Ireland enjoys 96,470 hectares of green spaces along with just under 2,000 miles of off-road trials. To date, there has not been any scientific reports on the microbiology of fallen leaves, which children enjoy playing with during Autumn time. The aim of this study was therefore to examine the microbiology of fallen leaves from multiple public parks and green spaces in Northern Ireland, collected at Autumn time and to correlate these organisms with the microbiology from the Northern Ireland CF paediatric population, of shared bacterial genera and species, in order to ascertain the relative clinical importance of organisms identified from leaf litter to the CF paediatric population.
Fallen leaves were collected from 22 public parks and greenspace sites in Northern Ireland during the Autumn 2023, which represented all 11 Council areas in Northern Ireland, with two sites per council area being sampled. Total viable counts (TVCs) were performed on each leaf litter and all organisms cultured were identified molecularly using 16S rRNA PCR and gene sequencing techniques. Direct antimicrobial susceptibility testing (DAST) of bacteria isolated from fallen leaves was determined for six antibiotics (four antibiotic classes), including the aminoglycosides, gentamicin; the fluoroquinolones, ciprofloxacin; the betalactams, ampicillin, piperacillin-tazobactam and meropenem, as well as the potentiated sulphonamides, cotrimoxazole (sulphamethoxazole & trimethoprim). Routine service microbiological records of respiratory specimens from 183 paediatric individuals with cystic fibrosis attending the Northern Ireland Paediatric Cystic Fibrosis Centre, Royal Belfast Hospital for Sick Children, Belfast Health and Social Care Trust, Belfast, were compared anonymously with organisms isolated from leaf litter. Comparisons were recorded at both genus and species levels.
The mean TVC was log 7.35 ± 0.57/g leaves (standard deviation) and ± 0.12 (standard error of mean). The median TVC was log 7.23/g leaves. Patrician Villas Play Park, Strabane had the lowest count (log 6.49/g leaves) and Wallace Park, Lisburn had the highest count (log 9.38/g leaves). Fifteen bacterial genera and 17 species were identified in this study, comprising 11 Gram negative and 4 Gram positive genera, including Aeromonas sp., Arthrobacter koreensis, Arthrobacter sp., Bacillus sp., Buttiauxella agrestis, Buttiauxella sp., Carnobacterium divergens, Citrobacter sp., Citrobacter werkmanii, Enterobacter cloacae, Enterobacter sp., Lelliottia amnigena, Pectobacterium atrosepticum, Pectobacterium sp. Pseudomonas fluorescens, Pseudomonas fragi, Pseudomonas seleniipraecipitans, Pseudomonas spp., Pseudomonas veronii, Rahnella victoriana, Serratia fonticola, Serratia proteamaculans, Serratia spp., Sporosarcina contaminans, Stenotrophomonas rhizophila, Stenotrophomonas sp. and Yersinia kristensenii. Pseudomonas aeruginosa was not isolated from leaves collected from any site. Eight bacterial genera were shared between children living with CF and leaf litter and included: Aeromonas, Citrobacter, Enterobacter, Pseudomonas, Rahnella, Serratia, Stenotrophomonas and Yersinia. Only four species were shared between children living with CF and leaf litter, including: Enterobacter cloacae, Pseudomonas fluorescens, Pseudomonas fragi and Pseudomonas veronii. Bacterial organisms isolated from leaves from all sites were resistant to ampicillin (100%), but were fully sensitive to ciprofloxacin (100%), piperacillin-tazobactam (100%) and gentamicin (100%). Regarding meropenem and cotrimoxazole, resistance to these antibiotics was 45.5% and 4.5%, respectively.
Fallen leaves isolated from public parks and green spaces in Northern Ireland were shown to harbour a diverse variety of bacteria, some of which have been isolated from respiratory specimens from children living with CF. None of these bacteria including the co-isolated species represented clinically significant respiratory pathogens of the CF lung and were regarded as transient colonisers of the CF lung. Pseudomonas aeruginosa was not identified in this study originating from fallen leaves. When deciding on the relative risk of children living with CF playing with leaves, parents of children living with CF need to make an informed decision, balancing the sensory exploration of nature through interaction with leaves, as well as physical, emotional and social benefits gained from nature play, with the relative risk of exposure to environmental organisms.

PMID:
42893267
Bibliographic data and abstract were imported from PubMed on 18 Oct 2026.

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