Characterization,Virulence And Resistance Of Aeromonas Isolated From Patients With Infectious Diarrhea In Zhejiang Province

Background and ObjectiveDiarrhea is an essential public health problem in the world,mostly caused by contaminated food and water.Infectious diarrhea is a symptom of infection caused by various bacteria,viruses or parasites,commonly occurring in developing countries.China is one of the countries with a high burden of infectious diarrhea.In 2017,1471990 cases of infectious diarrhea were reported in China,in which 1284644 cases were Class C infectious diseases(infectious diarrhea other than cholera,bacillary and amebic dysentery,typhoid and paratyphoid),far more than Class A and B intestinal infectious disease,so detection of other pathogens is necessary.However,the diarrheagenic pathogens detected in domestic clinical laboratories are mainly pathogenic bacteria of Class A and B infectious disease such as Vibrio cholerae,Salmonella spp.and Shigella spp.,and the detection of other pathogens is ignored.Species of Aeromonas are facultative anaerobic,gram-negative,rod-shaped bacteria that are widely distributed in nature,especially in the water environment.Since 1961,when the first strain was isolated from human feces,aeromonads have been incriminated as agents of diarrhea.The lack of attention to Aeromonas leads to the lack of the data on prevalence,virulence factors and drug resistance of Aeromonas in domestic.Zhejiang province,located in coastal area,has a long coastline and abundant water resources,and in summer,the warm and humid climate is conducive to the growth of Aeromonas,all of which increase the potential risk of infection.This study collected stool specimens of patients with acute diarrhea,in 5 hospitals of Zhejiang province from January 2010 to December 2017,for the identification of pathogens,to clarify the prevalence of Aeromonas and provide data for performing routine clinical testing more scientifically;carried out genetic testing to specify the virulence characteristics of Aeromonas,laying the foundation for study of the pathogenesis of Aeromonas;through susceptibility testing to understand the characteristics of antimicrobial resistance of Aeromonas,so as to guide clinical treatments.MethodsFrom January 2010 to December 2017,we collected stool specimens of patients with acute diarrhea in 5 hospitals in Zhejiang province.The isolations and identifications of bacterial pathogens were carried out by the standard testing procedures and MALDI-TOF MS.The detection of virulence genes and drug susceptibility test were carried out on Aeromonas strains by PCR and Kirby-Bauer disk agar diffusion method,respectively.The clinical information of every case was collected to analyze the clinical characteristics of Aeromonas-associated diarrhea.Results1.From January 2010 to December 2017,we collected a total of 25853 cases of acute diarrhea,in which bacterial pathogens in the top three were diarrheagenic Escherichia coli(23.03%),Vibrio parahaemolyticus(7.05%),and Aeromonas(5.10%).2.Among 8747 cases in which the culture and identification of Aeromonas were carried out,there was no gender difference in the prevalence of Aeromonas(P>0.05).The differences in the prevalence of Aeromonas between age groups were significant(P<0.001),and the elderly people aged 60 and over has the highest proportion(6.70%).The differences in the prevalence of Aeromonas in different seasons was also significant(P<0.001),and the highest proportion(6.02%)of Aeromonas occurred in summer.3.The proportion of Aeromonas singly isolated cases was 67.66%,whose clinical presentations were abdominal pain(58.3%),vomiting(19.3%)and fever(12.9%).Mushy stool(45.83%)was the most common,followed by liquid stool(29.69%).Aeromonas combined with other pathogens were isolated in 32.34%of cases.And Aeromonas was mostly combined with diarrheagenic Escherichia coli(40 cases,11.98%),Vibrio parahaemolyticus(27 cases,8.08%)and Plesiomonas shigelloides(16 cases,4.79%).4.688 Aeromonas strains were isolated from 636 stool specimens of Aeromonas-positive cases,including 587 strains singly isolated,92 strains isolated from 46 stools,and 9 strains isolated from 3 stools.587 strains singly isolated included 9 species,mainly Aeromonas veronii(194 strains,28.20%)and Aeromonas caviae(182 strains,26.45%).5.Of 688 Aeromonas strains,97.5%carried at least one virulence gene.The most prevalent virulence genes in Aeromonas were gcaT,fla,alt,acg,ela,act and lip(>37%),while aexT,lafA,tapA,ompAⅡ,ahp and aopH were the least frequently detected(<8%).There were differences in the prevalence of most virulence genes among A.hydrophila,A.caviae and A.veronii(P<0.05).6.The sensitivity of Aeromonas to antimicrobials was more than 79%,other than cefoxitin(63.37%),tetracycline(61.63%)and imipenem(60.47%);the resistance rates of Aeromonas isolates to 17 drugs were less than 27%;and the sensitivity(>85%),the intermediate sensitivity(<10%)and the resistance(<5%)to quinolone drugs,first-line drugs for the treatment of diarrhea,were ideal.There were differences in the susceptibility to most drugs among A.hydrophila,A.caviae and A.veronii(P<0.05).Conclusions1.Aeromonas is the third most prevalent bacterial pathogen of acute diarrhea and should be considered in the detection of pathogens in patients with diarrhea during the summer and autumn.2.Among different species of Aeromonas,there are differences in the distribution of virulence genes and the drug resistance,so they should be treated differently in clinical.3.Aeromonas are sensitive to quinolone drugs and can be the first choice in clinical practice.