rather than “antibiotics.” Antibiotics revolutionized medicine in the twentieth century. However, their effectiveness and easy access have also led to their overuse,
prompting bacteria to develop resistance. This has led to widespread problems and
prompted the World Health Organization (WHO) to classify antibiotic resistance as a
“serious threat is no longer a prediction for the future, it is happening right now in
every region of the world and has the potential to affect anyone, of any age, in any
country.”
The appearance of drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), is a problem resulting from the diversity and abuse of
antibiotics, and multiple-drug-resistant bacteria, called “super resistant bacteria,”
began appearing in 2010, quickly becoming a major societal problem. Antibiotics
are used not only in medical care but also in stock raising (i.e., ranching) and the
aquaculture business, particularly when mixed with bait and supplied in nurseries.
Not only are antibiotics discharged as excrement, but they are also excreted from bait
directly into the environment and may have a great impact on aquatic ecosystems.
Therefore, it is important to understand the influences of antibiotics, including the
appearance of drug-resistant bacteria, on aquatic ecosystems.
7.6.1 Oxytetracycline
The antibacterial spectrum is wide, and the antibiotic Oxytetracycline (OTC) is used in
the marine products industry, most commonly including aquaculture, and resistant
bacteria have been confirmed in the outdoors. However, there has been no ecosystem
impact assessment of OTC reported. The test results of oxytetracycline were compared
with 43 ecological influence tests (42 single-species examinations and a large-scale
outdoor mesocosm). The LOEC of the large-scale outdoor microcosm was estimated
to be 100 μg/L, whereas the m-NOEC of the microcosm test was 70 μg/L, and it was
demonstrated that the microcosm test is sufficiently applicable for use as an OECD
test. Additionally, it succeeded in determining the relative community metabolism
(RCM) (i.e., the metabolic activity of the community), and a difference was observed
in the metabolic activity as a result of exposure to OTC. It was also shown that the
microcosm test was able to reflect the mechanisms of the antibiotic influence. Furthermore, because RCM changed with changes in the community structure, what a
near menstruation state could reproduce was suggested by impossible natural ecosystem in the conventional test method, which did not include community structure, and
was able to show the superiority of the microcosm test for this assessment.
Resistant bacteria appeared in the microcosm by adding the antibiotic OTC. The
shape of the bacterial colony cultured in the control system in a PY nutrient medium
was different from the form of the bacterial colony cultured in the nutrient medium
and which had OTC, clearly to become 25 mg/L to PY nutrient medium. The colony
pro-control was whitish as a whole, and the border of the colony was not clear. Two
colonies, which greatly varied in shape, appeared in the system with the addition of
7 mg/L of OTC. The first colony was generally light yellow and viscous, and the
second colony was white, and the border exhibited clear granulation. Because the
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K. Murakami et al.
prompting bacteria to develop resistance. This has led to widespread problems and
prompted the World Health Organization (WHO) to classify antibiotic resistance as a
“serious threat is no longer a prediction for the future, it is happening right now in
every region of the world and has the potential to affect anyone, of any age, in any
country.”
The appearance of drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), is a problem resulting from the diversity and abuse of
antibiotics, and multiple-drug-resistant bacteria, called “super resistant bacteria,”
began appearing in 2010, quickly becoming a major societal problem. Antibiotics
are used not only in medical care but also in stock raising (i.e., ranching) and the
aquaculture business, particularly when mixed with bait and supplied in nurseries.
Not only are antibiotics discharged as excrement, but they are also excreted from bait
directly into the environment and may have a great impact on aquatic ecosystems.
Therefore, it is important to understand the influences of antibiotics, including the
appearance of drug-resistant bacteria, on aquatic ecosystems.
7.6.1 Oxytetracycline
The antibacterial spectrum is wide, and the antibiotic Oxytetracycline (OTC) is used in
the marine products industry, most commonly including aquaculture, and resistant
bacteria have been confirmed in the outdoors. However, there has been no ecosystem
impact assessment of OTC reported. The test results of oxytetracycline were compared
with 43 ecological influence tests (42 single-species examinations and a large-scale
outdoor mesocosm). The LOEC of the large-scale outdoor microcosm was estimated
to be 100 μg/L, whereas the m-NOEC of the microcosm test was 70 μg/L, and it was
demonstrated that the microcosm test is sufficiently applicable for use as an OECD
test. Additionally, it succeeded in determining the relative community metabolism
(RCM) (i.e., the metabolic activity of the community), and a difference was observed
in the metabolic activity as a result of exposure to OTC. It was also shown that the
microcosm test was able to reflect the mechanisms of the antibiotic influence. Furthermore, because RCM changed with changes in the community structure, what a
near menstruation state could reproduce was suggested by impossible natural ecosystem in the conventional test method, which did not include community structure, and
was able to show the superiority of the microcosm test for this assessment.
Resistant bacteria appeared in the microcosm by adding the antibiotic OTC. The
shape of the bacterial colony cultured in the control system in a PY nutrient medium
was different from the form of the bacterial colony cultured in the nutrient medium
and which had OTC, clearly to become 25 mg/L to PY nutrient medium. The colony
pro-control was whitish as a whole, and the border of the colony was not clear. Two
colonies, which greatly varied in shape, appeared in the system with the addition of
7 mg/L of OTC. The first colony was generally light yellow and viscous, and the
second colony was white, and the border exhibited clear granulation. Because the
106
K. Murakami et al.