Identity and virulence properties of Aeromonas isolates from healthy Northern snakehead (Channa argus) in China.

Members of the genus Aeromonas are opportunistic pathogen of a variety of aquatic animals that exhibits multidrug resistance, phenotypes, virulence genes and virulence. The present study described the species distribution and the potential pathogenicity of Aeromonas isolated from healthy Northern snakehead (Channa argus) in China. Molecular identification revealed that A. veronii biovar veronii (69/167; 41·3%) and A. hydrophila (41/167; 24·6%) were the most common species found in Northern snakehead intestine based on sequencing of the 16S rRNA gene and DNA gyrase subunit B protein. The distribution of seven virulence factors including aer (84·4%), act (80·8%), ser (40·1%), Aha (27·5%), lip (23·4%), exu (15·0%) and LuxS (12·6%) were determined exclusively in Aeromonas isolates. All the seven virulence genes were present in 9·6% (16/167), among which 11 strains were identified as A. veronii biovar veronii. For the strains harbouring seven virulence genes, the 50% lethal doses (LD50 ) of isolates were lower compared to the isolates carrying two virulence genes. The challenge tests revealed that isolate W31 had the lowest lethal dose, causing 50% mortality at 4·5 × 103 colony-forming units (CFU) per ml. Furthermore, histopathology of Northern snakehead infected with Aeromonas strains showed necrosis and congestion in liver, spleen and kidney and also damage to the intestine. This study confirms that the Aeromonas strains isolated from healthy Northern snakehead may be a cause of concern for public health. SIGNIFICANCE AND IMPACT OF THE STUDY: Aeromonas species are widely distributed in aquatic environments and have considerable virulence potential. The aim of this study was to identify Aeromonas strains isolated from healthy Northern snakehead, and to investigate if Aeromonas species isolated from healthy fish potential pathogenicity with special reference to virulence and epidemiology studies.

Effects of arsenic on the biofilm formations of arsenite-oxidizing bacteria.

Arsenite-oxidizing bacteria (AOB) play a key role in the biogeochemical cycle of arsenic in the environment, and are used for the bioremediation of As contaminated groundwater; however, it is not yet known about how arsenic affects biofilm formations of AOB, and how biofilm formations affect bacterial arsenite-oxidizing activities. To address these issues, we isolated seven novel AOB strains from the arsenic-contaminated soils. They can completely oxidize 1.0 mM As(III) in 22-60 h. Their arsenite oxidase sequences show 43-99% identities to those of other known AOB. Strains Cug1, Cug2, Cug3, Cug4, and Cug6 are able to form biofilms with thickness of 15-95 µm, whereas Cug8 and Cug9 cannot form biofilms. It is interesting to see that arsenite inhibited the biofilm formations of heterotrophic AOB strains, but promoted the biofilm formations of autotrophic strains in a concentration-dependent manner. The arsenite-oxidizing rates of Cug1 and Cug4 biofilms are 31.6% and 27.6% lower than those of their suspension cultures, whereas the biofilm activities of other strains are similar to those of their suspension cultures. The biofilm formation significantly promoted the bacterial resistance to arsenic. This work is the first report on the complex correlations among environmental arsenic, bacterial biofilm formations and bacterial arsenite-oxidizing activities. The data highlight the diverse lifestyle of different AOB under arsenic stress, and provide essential knowledge for the screening of efficient AOB strains used for constructions of bioreactors.

Prominent contribution of Th1, Th17, and Tregs to the host response during M. neoaurum infection.

Nontuberculous mycobacteria are ubiquitous in outside environment and animals. As for nontuberculous mycobacteria infection, there is only limited information in humans regarding infection and the subsequent immune response, especially for Mycobacterium neoaurum. Here, haematoxylin-eosin and Ziehl-Neelsen staining were used to observe pathological changes and detect acid-fast bacilli in organ samples in mouse model. Flow cytometry and quantitative real-time polymerase chain reaction were performed to analyze the contribution of Th1, Th17 and Tregs to the host immune response. M. neoaurum caused chronic infection in mice, resulting in infiltrates with large aggregates of inflammatory cells, especially macrophages, in lung tissues. Our results indicated that 72% of CD4+ T cells appeared in the early days of infection, which was followed by a decrease to 47% by day 32, and then a rise to 76% by day 56. Moreover, we found higher frequency of IFN-g-producing CD4+ T cells and elevated mRNA expression of the transcription factor T-bet in the lungs; however, we observed lower mRNA expression of the transcription factor RORgt and lower frequency of IL-17-producing CD4+ T cells. A transient relative decrease in the number of Treg cells was observed in the lungs; however, the number of Tregs did not change significantly between the first and last day following infection. Thus, M. neoaurum causes chronic infection in C57BL/6 mice, with Th1, Th17, and Tregs playing a prominent role in the host response. The present study may lay the basis for further studies on the mechanisms underlying infection with nontuberculous mycobacteria.

Seroprevalence and associated risk factors of Toxoplasma gondii infection in psychiatric patients: a case-control study in eastern China.

In recent years, the effect of Toxoplasma gondii infection on the cerebrum and neuropsychiatric patients has been increasingly highlighted. However, there is limited information about the epidemiology of T. gondii infection in psychiatric patients in Shandong province, eastern China. Therefore, through a case-control study, 445 patients hospitalized for diacrisis or treatment in Weihai, eastern China, and 445 control subjects from the general population of the same region matched by gender, age, and residence were examined with enzyme-linked immunoassays for the presence of IgG and IgM antibodies to T. gondii and associated sociodemographic and behavioural characteristics in a population of psychiatric patients. Seroprevalence of IgG antibodies to T. gondii in psychiatric patients (77/445, 17·30%) was significantly higher than in control subjects (55/445, 12·36%) (P = 0·038). Fourteen (3·15%) psychiatric patients and 10 (2·25%) control subjects had IgM antibodies to T. gondii (P = 0·408). Multivariate analysis using logic regression showed that T. gondii infection was associated with cats at home and consumption of raw/undercooked meat in psychiatric patients. Considering that most psychiatric patients usually have lower cognitive functioning and additional transmission routes related to their inappropriate behaviours that could enhance the risk of infection, psychiatric patients should be considered as a specific group of T. gondii infection.

Chlamydia psittaci exposure in pet birds.

Chlamydia psittaci is a zoonotic pathogen with a wide range of avian hosts and may be transmitted to humans and cause severe disease. To assess the risk of psittacosis posed by pet birds, the seroprevalence of Chlamydia psittaci antibodies in 360 Eurasian siskins (Carduelis spinus), 289 oriental skylarks (Alauda arvensis) and 36 black-tailed grosbeaks (Coccothraustes migratorius) in Gansu province, north-western China was detected by an indirect haemagglutination assay. Twenty-seven out of 289 (9.34 %) Alauda arvensis, 45 out of 360 (12.50 %) Carduelis spinus and 2 out of 36 (5.56 %) Coccothraustes migratorius were positive for Chlamydia psittaci infection at a cut-off dilution of 1 : 16. The prevalence of Chlamydia psittaci was higher in Carduelis spinus (12.5 %) than in Alauda arvensis (9.34 %) and Coccothraustes migratorius (5.56 %); however, the differences were not statistically significant (P>0.05). Statistical analysis indicated that Chlamydia psittaci seroprevalence in adult pet birds (12.4 %, 67/540) was significantly higher than that in juvenile pet birds (4.83 %, 7/145) (P<0.01). There was no statistical difference in Chlamydia psittaci seroprevalence between male (12.4 %) and female (8.27 %) birds. To our knowledge, this is the first report indicating the seroprevalence of Chlamydia psittaci exposure in pet birds in China. Our results indicate that close contact with pet birds poses the risk of zoonotic transmission of Chlamydia psittaci.

Seroprevalence of Chlamydia psittaci infection in market-sold adult chickens, ducks and pigeons in north-western China.

Chlamydia psittaci, the agent of psittacosis in humans, infects a wide range of avian species. To assess the risk of psittacosis posed by domestic birds in the urban environment, the prevalence of C. psittaci antibodies in 413 chickens (Gallus domesticus; 305 caged and 108 free-range), 334 ducks (Anas spp.; 111 caged and 223 free-range) and 312 pigeons (Columba livia) in Lanzhou, north-western China, was detected using the indirect haemagglutination assay. The specific antibodies were found in sera of 55 (13.32 %) chickens, 130 (38.92 %) ducks and 97 (31.09 %) pigeons. Statistical analysis showed that the seroprevalence of C. psittaci infection in chickens was significantly lower than that in ducks and pigeons (P<0.05). The C. psittaci seroprevalence in caged and free-range chickens was 7.54 % and 29.63 %, respectively, and the difference was statistically significant (P<0.05). The C. psittaci seroprevalence in caged and free-range ducks was 26.13 % and 45.29 %, respectively (P<0.05). To our knowledge, this is the first study indicating the presence of C. psittaci infection in market-sold chickens, ducks and pigeons in north-western China. Close contact with these birds is associated with a risk of zoonotic transmission of C. psittaci. Public education should be implemented to reduce the risk of avian to human transmission of such a pathogenic agent.