No abstract

As an important zoonotic pathogen, Staphylococcus aureus has led to serious mastitis and endometritis in infected dairy cows. In this study, a total of 164 strains of S. aureus were isolated from dairy cows in Xinjiang Province, China, and subjected to assays to determine drug susceptibility and biofilm (BF) formation ability. Enterotoxin-related genes were detected, and the transcription levels of genes related to BF formation were determined by using reverse transcription-quantitative polymerase chain reaction. Moreover, the pathogenicity of isolates with different BF formation abilities was determined by measuring their hemolysis activity, half lethal dose (LD50) and organ bacterial load. The results showed that 86.0% of S. aureus isolates could form BF. Among them, 42.1% of the strains had weak BF formation ability, and most strains with a strong BF formation ability were ica gene carriers. The S. aureus isolates displayed multidrug resistance and their drug resistance was positively correlated with their BF formation ability. Moreover, 96.3% of the S. aureus isolates carried enterotoxin genes. Among them, the detection rates of the novel enterotoxin genes were higher than those of conventional enterotoxin genes. Furthermore, isolates with a strong BF formation ability had higher LD50 but lower hemolysis ability and organ bacterial load than those of the isolates with weak or no BF ability. However, isolates without BF ability produced more severe pathological changes than those of isolates with strong BF formation ability. These findings suggest that higher BF ability and presence of novel enterotoxin genes are important characteristics of S. aureus isolates from dairy cows in Xinjiang Province, China, and such isolates may pose potential threats to food safety.

The ribonuclease III (RNase III) is an important enzyme system that regulates non-coding RNA (ncRNA) levels. In this study, LM-ΔrncS gene deletion strain was investigated by gene overlap extension PCR (SOE-PCR) and homologous recombination techniques. The environmental stress response, biofilm formation and virulence were determined and compared between the deletion strain LM-ΔrncS and the parental strain LM EGD-e. When compared with LM EGD-e, the adaptability of LM-ΔrncS was significantly reduced (P<0.05) under the stress of 30°C/42°C, pH 9, 5% NaCl, 3.8% ethanol and 0.1% H2O2. Biofilm formation ability of LM-ΔrncS was significantly lower (P<0.05) than that of LM EGD-e. In LM-ΔrncS, the transcription levels of ncRNA SreA and SbrA genes were significantly decreased (P<0.05). The adhesion rate and invasion rate of LM-ΔrncS in RAW264.7 cells were significantly lower (P<0.01) than those of LM EGD-e, and the survival and proliferation of LM-ΔrncS in RAW264.7 cells were also significantly decreased (P<0.05). Moreover, the transcription levels of InlA, hly, prfA and SigmaB gene were significantly lower (P<0.05) than those of LM EGD-e. LD50 of LD-ΔrncS in BALB/c mice was increased by 1.49 logarithmic orders, and the survival time of the mice was significantly prolonged when compared with LM EGD-e. In addition, the bacterial load in the liver and spleen was markedly decreased, and its pathological damage was also reduced. This study confirmed that RNase III RncS is involved in the regulation of environmental stress response, biofilm formation and virulence in LMd.