Water as a Source of Indoor Air Contamination with Potentially Pathogenic Aeromonas hydrophila in Aquaculture

Abstract

Human activities influence the presence of potentially pathogenic bacteria in indoor air. The aim of this study was to determine the effect of the experimental rearing of European grayling and European perch in a recirculating aquaculture system on the contamination of indoor air with potentially pathogenic Aeromonas hydrophila (PPAH) and the resulting health risks to humans. The PPAH counts, their resistance to seven antibiotics, and the multiple antibiotic resistance (MAR) index were determined in samples of indoor air and water from rearing tanks. The PPAH counts were highest in the laboratory bioaerosol where two fish species were reared. The calculated indoor/outdoor ratio (I/O > 1) demonstrated that tank water was the internal source of PPAH emissions. The unconstrained PCA revealed strong positive relationships (p ≤ 0.05) between the PPAH counts in the indoor air and water samples. Most of the PPAH strains isolated from laboratory air were resistant to tetracycline, cefotaxime, and erythromycin, and 26-82% of the isolates exhibited multiple drug resistance. The values of the MAR index were similar in samples of laboratory air and water (0.23-0.34 and 0.24-0.36, respectively). Agglomerative clustering revealed two clusters of strains isolated from laboratory air and tank water. The results of this study indicate that aquaculture can be a source of indoor air contamination with PPAH.

Keywords: MAR index; aquaculture laboratory; indoor air; potentially pathogenic Aeromonas hydrophila.

Figure 1

Indoor air and water sampling sites in the building of the Aquaculture and Ecological Engineering Center of the University of Warmia and Mazury in Olsztyn (Poland). Lab—laboratory; CAEG—control (outdoor) air sampled during the European grayling experiment; CAEP—control (outdoor) air sampled during the European perch experiment; LAEG—laboratory air sampled during the European grayling experiment; LAEP—laboratory air sampled during the European perch experiment; HAEG—hallway air sampled during the European grayling experiment; HAEP—hallway air sampled during the European perch experiment; WEG—water sampled from rearing tanks during the European grayling experiment; WEP—water sampled from rearing tanks during the European perch experiment; RT—rearing tank; M—microstrainer; TF—trickling filter; UV—UV lamp.

Figure 2

PCA biplot of the correlations (p ≤ 0.05) between the counts of potentially pathogenic Aeromonas hydrophila (PPAH) in the samples of indoor air and water collected during the European grayling (LAEG, HAEG, CAEG, and WEG) and European perch (LAEP, HAEP, CAEP, and WEP) experiments. Yellow lines denote the bacterial counts in the samples of laboratory air (LAEG and LAEP); grey lines denote the bacterial counts in the samples of hallway air (HAEG and HAEP); green lines denote the bacterial counts in the control samples of outdoor air (CAEG and CAEP); blue lines denote the bacterial counts in the water samples (WEG and WEP); and black lines denote the physical parameters: R—relative humidity (solid line) and T—temperature (dashed line).

Figure 3

Differences in the proportion of potentially pathogenic Aeromonas hydrophila (PPAH) in the total counts of mesophilic Aeromonas hydrophila (TCMAH) in the samples of indoor (LAEG, HAEG, LAEP, and HAEP) and outdoor (CAEG and CAEP) air collected during the rearing experiments involving (a) European grayling, and (b) European perch, determined by the two-tailed test. CAEG—control (outdoor) air during the European grayling experiment; CAEP—control (outdoor) air during the European perch experiment; LAEG—laboratory air during the European grayling experiment; LAEP—laboratory air during the European perch experiment; HAEG—hallway air during the European grayling experiment; and HAEP—hallway air during the European perch experiment. Error bars denote the minimum/maximum values. The red plus sign denotes the mean value.

Figure 4

Antibiotic resistance profile of potentially pathogenic Aeromonas hydrophila (PPAH) strains isolated from the indoor air (LAEG, HAEG, LAEP, and HAEP), outdoor air (CAEG and CAEP), and water (WEG and WEP) during the fish rearing experiments in RAS. CAEG—control (outdoor) air during the European grayling experiment; CAEP—control (outdoor) air during the European perch experiment; LAEG—laboratory air during the European grayling experiment; LAEP—laboratory air during the European perch experiment; HAEG—hallway air during the European grayling experiment; HAEP—hallway air during the European perch experiment; WEG—water collected from rearing tanks stocked with European grayling; WEP—water collected from rearing tanks stocked with European perch. The number of isolated strains is given in brackets. Red squares with the letter “R” denote antibiotic resistance.

Figure 5

Antibiotic resistance of potentially pathogenic Aeromonas hydrophila (PPAH) strains isolated from the samples of indoor air (LAEG, HAEG, LAEP, and HAEP), outdoor air (CAEG and CAEP), and water (WEG and WEP) during the rearing experiments involving European grayling and European perch. The red plus sign denotes the MAR index.

Figure 6

Similarities between the indoor air and water sampling sites based on the counts of potentially pathogenic Aeromonas hydrophila (PPAH) resistant to cefotaxime (CTX), cotrimoxazole (SXT), gentamicin (CN), tetracycline (TE), erythromycin (E), norfloxacin (NOR), and chloramphenicol (C). CAEP and CAEP—control samples of outdoor air collected during the European grayling and European perch experiments, respectively; LAEG and LAEP—samples of laboratory air collected during the European grayling and European perch experiments, respectively; HAEG and HAEP—samples of hallway air collected during the European grayling and European perch experiments, respectively; WEG and WEP—samples of tank water collected during the European grayling and European perch experiments, respectively.