Aerobiology

Michael L. Muilenberg,Harriet A. Burge

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351468077
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Conservation & Protection
• Index: Biological Sciences

Aerobiology is the study of airborne particles that have an impact on humans and other organisms. Every day, we are exposed to airborne particles, including "natural" particles such as pollen, bacteria, and fungi, and "unnatural" particles, such as asbestos fibers and noxious chemicals. Aerobiology highlights the current interests in this field, primarily the ecology and distribution of airborne particles and their effects on health.

Chapter 1

MICROBIAL EMISSIONS FROM COMPOSTS AND ASSOCIATED RISKS – TRIALS AND TRIBULATIONS OF AN OCCUPATIONAL AEROBIOLOGIST

John Lacey
Pauline A.M. Williamson
Brian Crook

CONTENTS

I.	Abstract
II.	Introduction
III.	Materials and Methods
IV.	Mushroom Composts
	A.	Job Category A: Compost Preparation
	B.	Job Category A: Spawning
	C.	Job Category B: Cookout
	D.	Job Category C: Growing Houses
V.	Domestic Waste Compost
	A.	Precomposting Processing
	B.	Dismantling the Pile
	C.	Postcomposting Processing
VI.	Problems of Sampling Occupational Environments
VII.	Suggestions for Future Study
Acknowledgments
References

I. ABSTRACT

Composting is used to produce substrates suitable for mushroom cultivation or to aid in the disposal of domestic waste. Handling such composts can cause the release of microorganisms in large numbers and present hazards to workers, especially of hypersensitivity pneumonitis and aspergillosis. On mushroom farms, up to 10⁸ actinomycete spores (mostly Thermomonospora spp.) and bacteria/m³ air can be released when compost is disturbed, especially during spawning. During our studies, Saccharopolyspora (Faenia) rectivirgula and Thermoactinomyces spp., sometimes implicated in mushroom worker’s lung, were usually few. Talaromyces, Scytalidium spp., and Aspergillus fumigatus were the predominant fungi, each numbering up to 6.5 × 10³/m³ air. Personal samplers showed that workers were heavily exposed during spawning. Up to 10⁸ actinomycetes and bacteria/m³ were also released into the air when composted domestic waste was handled. The most abundant species differed with composting conditions but Saccharomonospora, Thermoactinomyces, Thermomonospora, Saccharopolyspora, and Streptomyces were all abundant in some samples. A. fumigatus and Penicillium spp. tended to be more numerous in composted domestic waste than in mushroom composts (up to 2.7 × 10⁶ spores/m³). The study of occupational lung disease among workers handling composts is complicated by many problems, including overloading of samplers due to the high spore concentrations, intermittent sources, identification of organisms that might be implicated, poor growth and antigen production in culture, disease diagnosis, and risk assessment. These problems are discussed and suggestions made for future study.

II. INTRODUCTION

Composting provides an example of occupational exposure to bacteria and actinomycete and fungal spores that illustrates many of the problems that beset the occupational aerobiologist. Composting is an exothermic process in which organic substrates are subjected to microbial degradation. Microbial activity leads to the production of heat, with temperatures up to 70°C or more, through the energy released by respiration. Mushroom and domestic waste composts differ in their substrates and in the control of temperature. Microorganisms are released into the air when compost piles are formed or dismantled, when compost is moved, especially where it falls from one conveyor to another, when mushroom spawn is added and during pre- and post-compost processing of domestic waste. The nature of the airborne microflora depends on the existing contamination of the starting materials, microbial development between disposal and composting and, subsequently, development during composting. Allergen-producing organisms, especially when present in large numbers. can present a hazard to the health of exposed workers, through occupational asthma or extrinsic allergic alveolitis (hypersensitivity pneumonitis).¹ Infection rarely occurs.

This chapter describes approaches to the problems of sampling large concentrations of spores, identification of microorganisms and their antigens, disease diagnosis and risk assessment, and makes suggestions for further work.

III. MATERIALS AND METHODS

The samplers we have used at mushroom and domestic waste composting sites (although not all discussed in detail in this chapter) have included cascade impactors, collecting on non-nutrient surfaces (20 1/min, up to 2 min).² Andersen culture plate cascade impactors (Graseby Andersen, Smyrna. GA) (25 1/min. 5–60 s),³ multi-stage liquid impingers (55 1/min, up to 30 min),⁴ Millipore^® (Millipore Corp., Bedford, MA) or Nuclepore^® (Corning Costar Corp., Cambridge, MA) personal filtration aerosol monitors (with 0.8 μm diameter pores; 2 1/min, up to 3 h),⁵ high-volume filtration air samplers (650 1/min, up to 30 min), large-volume electrostatic sampler (Sci-Med Environmental Systems, Eden Prairie. MN) (600 1/min, up to 30 min) and a Royco^® particle counter (Pacific Scientific. Marlow, U.K.) (0.28 or 2.8 I min for 30 or 60 s every 2 or 5 min). Isolation media and temperatures used have included:

• For fungi: (1) 2%( malt extract (Oxoid^®. Unipath Ltd., Basingstoke. Hampshire. U.K.) agar + penicillin (20 IU/ml) + streptomycin (40 units/ml)⁶ (25 and 37°C): (2) dichloran rose bengal chlortetracycline agar (Oxoid) (25 and 37°C)

• For total bacteria and actinomycetes: (1) nutrient agar (Oxoid^®. half-strength) + actidione (100 μg/ml)⁶ (25 and 40°C); (2) tryptone soya agar (Oxoid, half-strength) + actidione (100 μg/ml) (37°C): (3) tryptone soya agar (Oxoid. half-strength) + 0.4% casein hydrolysate agar (TSC) + actidione (100 μg/ml)⁶ (55°C)

• For Gram-negative bacteria: violet red bile glucose agar (Oxoid) (37°C)

• For streptococci: KF Streptococcal agar (Oxoid) (37°C)

• For Salmonella: Sample from multi-stage liquid impinger incubated in Rappaport’s medium at 43°C for 8 h then plated on modified xylose lysine (XLD) and Brilliant green agars

• For Thermomonospora spp.: TSC + rifampicin (5 μg/l) + actidione (100 μg/ml) (55°C)⁷

• For S. rectivirgula: modified hippurate agar (NaCl, 20.0 g; MgSO₄.7H₂O, 0.2 g: NH₄H₂,PO₄, 1.0 g: sodium hippurate (hippuric acid. Na salt), 3.0 g: K₂HPO₄, 1.0 g; agar, 24.0 g; phenol red, 5.0 ml; distilled water, 1000 ml) + actidione (100 μg/ml) (HAX) (55°C)

• For Thermoacrinomyces spp: Czapek yeast casein agar (Czapek agar, Oxoid, 45.4 g; yeast extract, 5 g; casein hydrolysate, 2 g; water, 1000 ml) + tyrosine (0.3%) + novobiocin (25 μg/ml) (55°C)⁸

Samples using Andersen samplers together with each medium/incubation temperature combination and, where possible, with personal filtration samplers were collected in triplicate at each site and stated concentrations are the means of these determinations. Unless stated otherwise, spore/cell concentrations are from Andersen sampler plates, corrected for multiple deposition of particles at deposition sites using the table from Andersen,³ or from personal filtration samplers, after resuspension, dilution, and plating following the methods of Palmgren et al.⁵

IV. MUSHROOM COMPOSTS

Mushroom compost is usually made from horse manure, wetted straw, gypsum, and a nitrogenous supplement, often poultry manure, which is stacked for 7- 10 days with regular turning in long piles that heat to 75–80°C (Phase 1). In Phase 2, the partially composted material is placed in large chambers (tunnels) and is heated to about 60°C with hot, humidified air for 3–10 days. Some thermophilic actinomycetes grow during Phase 1 but most develop during Phase 2 to form a visible white weft on the compos.⁹ After cooling, the compost is mixed with spawn and placed in growing houses in trays or on continuous shelves. The fruiting bodies are picked by hand (cropping). After cropping is complete, the compost is pasteurized with steam (cookout) and removed from the trays or shelves for disposal. To evaluate worker exposure, general environmental samples were collected using Andersen and other samplers in each area (only Andersen sampler results are presented here), and personal filtration aerosol monitors were fitted on representative workers and operated for periods up to 3 h, depending on shift and break patterns. To simplify interpretation of exposure measurements, workers were placed in different job categories depending on the nature of their exposure to compost. Job category A included workers who prepared the compost and added the mushroom spawn; Job category B included workers who only handled the compost after cropping was complete and were responsible for pasteurization of the compost and emptying boxes; Job category C, the largest category, included all who picked mushrooms.

A. JOB CATEGORY A: COMPOST PREPARATION

Straw bales for composting often released many spores when opened (straw blending; Figure 1). On one farm, bales were fed into a machine with a co...