Identification and characterization of
Serratia nematophila
and
Acinetobacter guillouiae
from putrid-skin disease lesions in farmed Chinese spiny frog (
Quasipaa spinosa
)
Authors: Guo Ling , Jin Xiyu , Yang Dan , Wei Li , Chen Jie , Lin Zhihua , Ma Li 
Published: December 2024

Serratia
and
Acinetobacter
are recognized as significant opportunistic pathogens affecting aquatic animals and humans. However, their infections in amphibians are poorly documented, and their pathogenicity to the Chinese spiny frog (
Quasipaa spinosa
) remains unexplored. This study investigated an outbreak of putrid-skin disease among
Q. spinosa
on a farm in Lishui City, Zhejiang Province, China. Two pathogenic strains, GL-XJ7 and GL-XJ11, were isolated from disease lesions and identified as
Serratia nematophila
and
Acinetobacter guillouiae
, respectively, through morphological, physiological, biochemical, and molecular analyses including 16S rDNA sequencing and phylogenetic tree construction. Experimental infections revealed median lethal concentrations (LD
50
) over 72 h of 3.98×10
7
CFU/mL for
S. nematophila
strain GL-XJ7 and 3.16 × 10
6
CFU/mL for
A. guillouiae
strain GL-XJ11. Infected frogs exhibited symptoms consistent with natural infections, including reduced vitality, skin shedding, and ulceration. Histopathological examinations demonstrated that both strains induced hepatocellular damage, nuclear alterations, muscular atrophy, myofibrillar degeneration, and intestinal necrosis. Antibiotic susceptibility tests showed that
S. nematophila
strain GL-XJ7 was highly susceptible to ceftazidime and gentamicin, while
A. guillouiae
strain GL-XJ11 exhibited high susceptibilities to tetracycline, ceftazidime, and gentamicin. Both strains demonstrated resistance to penicillin, ampicillin, bacitracin, and clindamycin. This study provides the first description of natural
S. nematophila
strain GL-XJ7 and
A. guillouiae
strain GL-XJ11 infections and their pathogenesis in
Q. spinosa
, highlighting potential risks to other animals and human health. These findings establish a theoretical foundation for the clinical management and prevention of putrid-skin disease in artificially bred frogs.

IMPORTANCE

Frogs are among the most widely distributed amphibians globally. The Chinese spiny frog (
Quasipaa spinosa
) is a unique amphibious species endemic to China and holds significant economic value in aquaculture. Effective disease prevention and control are crucial for the sustainable development of frog breeding industries and the conservation of genetic resources. In this study, we investigated a putrid-skin disease outbreak at a frog farm in Lishui City, Zhejiang Province, Eastern China. We isolated and identified the causative pathogenic bacteria and analyzed their pathogenicity through artificial infection experiments and histopathological examinations. This research provides the first data on the pathogenic characteristics of
Serratia nematophila
and
Acinetobacter guillouiae
in
Q. spinosa
. Furthermore, we assessed the antibiotic susceptibility of these two pathogens, revealing their multidrug resistance. Our findings offer a scientific foundation for the accurate diagnosis and control of putrid-skin disease in frogs, contributing to the preservation of
Q. spinosa
genetic resources.