Identification of enteroinvasive Escherichia coli and Shigella strains in pediatric patients by an IpaC-specific enzyme-linked immunosorbent assay

Molecular assessment of antimicrobial resistance and virulence in multi drug resistant ESBL-producing Escherichia coli and Klebsiella pneumoniae from food fishes, Assam, India

The present study investigated the prevalence of Extended-Spectrum Beta Lactamase (ESBL) -producing E. coli and K. pneumoniae from the food fishes in retail markets in Assam, India. A total of 54 ESBL-producing E. coli and 12 K. pneumoniae isolates were recovered from 79 fish samples and were analyzed for antimicrobial resistance genes (ARGs) and virulence genes. E. coli isolates were categorized as multi drug resistant with resistance up to 12 different antibiotics with multiple antibiotic resistances (MAR) index ranging from 0.26 to 0.63. In E. coli, 100% resistance to cefotaxime along with 6% resistance to ceftazidime (third-generation cephalosporins) was observed. Moreover, 85% of the E. coli isolates were resistant to cefepime, a fourth-generation cephalosporin. K. pneumoniae showed resistance to 11 different antibiotics with MAR index value ranging from 0.21 to 0.57. All K. pneumoniae isolates showed 100% resistance to cefotaxime, 67% resistance to ceftazidime and 75% resistance to cefepime. Molecular characterization of ARGs revealed the presence of CTX-M group 1(CTX-M-15) in almost all E. coli isolates (98%, n = 53) and 100% in K. pneumoniae. A combination of uniplex and multiplex PCRs revealed fewer ARGs in E. coli isolates, with each isolate carrying 3 to 5 genes (tetA, dfrA1, sul1, sul2, qnrB, qnrS, aac(6')-Ib-cr). Majority of the E. coli were assigned to low-virulence phylogroup B1 and A while 8% of them belonged to pathogenic phylogroup D. 31 unique genetic profiles were identified for E. coli isolates by Pulsed-Field Gel Electrophoresis (PFGE) typing. K. pneumoniae isolates were highly diverse with 11 unique genetic profiles and a substantial ARG profile (bla_TEM, bla_SHV, bla_OXA-1-like, tetA, strA, strB, dfrA1, sul1, sul2, qnrB, qnrS, aac(6')-Ib-cr, oqxA, oqxB). The frequency of ARGs ranged between 4 and 11. All K. pneumoniae isolates belonged to capsular serotype with wzi gene. Virulence gene iutA was prominent in all isolates while ybtS and kfu were confirmed in two isolates. Our findings raise concerns that fishes bought for consumption may serve as potential reservoirs of AMR genes and pose serious threat to public health. The study emphasizes the need for extensive surveillance of resistant strains in aquaculture and related settings, their in-depth analysis of population structure and transmission dynamics.

Relationship among Shigella spp. and enteroinvasive Escherichia coli (EIEC) and their differentiation

Shigellosis produces inflammatory reactions and ulceration on the intestinal epithelium followed by bloody or mucoid diarrhea. It is caused by enteroinvasive E. coli (EIEC) as well as any species of the genus Shigella, namely, S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. This current species designation of Shigella does not specify genetic similarity. Shigella spp. could be easily differentiated from E. coli, but difficulties observed for the EIEC-Shigella differentiation as both show similar biochemical traits and can cause dysentery using the same mode of invasion. Sequencing of multiple housekeeping genes indicates that Shigella has derived on several different occasions via acquisition of the transferable forms of ancestral virulence plasmids within commensal E. coli and form a Shigella-EIEC pathovar. EIEC showed lower expression of virulence genes compared to Shigella, hence EIEC produce less severe disease than Shigella spp. Conventional microbiological techniques often lead to confusing results concerning the discrimination between EIEC and Shigella spp. The lactose permease gene (lacY) is present in all E. coli strains but absent in Shigella spp., whereas β-glucuronidase gene (uidA) is present in both E. coli and Shigella spp. Thus uidA gene and lacY gene based duplex real-time PCR assay could be used for easy identification and differentiation of Shigella spp. from E. coli and in particular EIEC.

Escherichia coliserogroup O2 and O28ac O-antigen gene cluster sequences and detection of pathogenicE. coliO2 and O28ac by PCR

The O-antigen gene clusters of Escherichia coli serogroups O2 and O28ac were sequenced, and PCR assays were developed to identify strains belonging to these 2 serogroups. Sixteen and 8 open reading frames were mapped to these loci in E. coli O2:H4 U 9-41 and E. coli O28ac:H25 96-3286, respectively. The wzx (O-antigen flippase) and wzy (O-antigen polymerase) genes in the E. coli O2 and O28ac O-antigen gene clusters were selected as targets for PCR assays for their identification. PCR assays targeting the wzx and wzy genes were specific for these serogroups, with one exception. Escherichia coli serogroup O42 strains gave positive results with wzx and wzy PCR assays targeting E. coli O28ac, and antiserum raised against O42 cross-reacted with serogroup O28ac strains. The O-antigen gene cluster of a strain of E. coli serogroup O42 was sequenced, and there were only 3 nt differences between the O-antigen gene clusters of the O28ac and O42 strains. Multiplex PCR assays targeting the O2 wzx gene, the stx1, stx2, hly, eae, and saa genes, and the O28ac wzx, ial, ipaC, and ipaH genes were developed for detecting Shiga toxin-producing E. coli O2 strains and enteroinvasive E. coli O28ac strains, respectively. The O2 and O28ac wzx and wzy genes can be used as diagnostic markers in PCR assays for rapid identification of these serogroups as an alternative to serotyping, and the multiplex PCR assays targeting serogroup-specific genes in combination with virulence genes can be used to identify and to detect pathogenic serogroup O2 and O28ac strains.

Comparison of media for the selective culture of enteroinvasive Escherichia coli

MacConkey, eosine-methylene blue, deoxycholate-citrate, salmonella-shigella, and xylose-lysine-deoxycholate agars were compared for their ability to support the growth and to facilitate the recovery of enteroinvasive Escherichia coli strains from artificially contaminated as well as from clinical faecal samples. When grown as pure cultures, the 78 enteroinvasive Escherichia coli strains, as a group, exhibited the same growth characteristics as did Shigella isolates ( n=59), i.e. both organisms grew more weakly than did Salmonella strains ( n=22) on the various selective plates but 4- to 10-fold better than normal Escherichia coli isolates ( n=53). Xylose-lysine-deoxycholate and deoxycholate-citrate plates were more effective in recovering enteroinvasive Escherichia coli from faecal samples than was salmonella-shigella agar. Likewise, xylose-lysine-deoxycholate agar, similar to the differentiating MacConkey and eosine-methylene blue agars, was less inhibitory for defined "sensitive" strains than were the selective media tested. Preincubating clinical faecal samples in selenite F or in gram-negative broth did not influence the recovery of enteroinvasive Escherichia coli significantly. These data show that the use of xylose-lysine-deoxycholate, in combination with MacConkey or eosine-methylene blue agar, provides the best chance for recovery of enteroinvasive Escherichia coli when randomly selecting colonies from faecal cultures for subsequent molecular or immunological identification assays.

A colony blot immune assay to identify enteroinvasive Escherichia coli and Shigella in stool samples

Using an IpaC protein-specific monoclonal antibody a colony blot immune assay was developed for the identification of enteroinvasive Escherichia coli (EIEC) and Shigella in fecal specimens, and was evaluated in a field study. By screening the entire culture plates the colony blot assay was significantly more sensitive than the investigation of 16 randomly selected colonies from artificially contaminated fecal specimens. Among the 165 stool samples from 121 patients with diarrhea the immune assay detected IpaC expressing colonies in 16 out of the 17 specimens positive with a Shigella-, and EIEC-specific polymerase chain reaction targeting the ipaH gene. Guided by the colony blots, Shigella was isolated from 12, while EIEC from four of the samples. The IpaC-specific colony blot immune assay is a simple screening method to detect EIEC in stool samples for laboratories not equipped with molecular techniques.

A colony blot immunoassay to detect enteroinvasive Escherichia coli and Shigella in water samples

AIMS

The aim of the study was to develop a colony blot immunoassay to detect Shigella and enteroinvasive Escherichia coli (EIEC) in water.

METHODS AND RESULTS

Spiked samples were filtered through nitrocellulose membranes. Colony prints on the filters were tested with a monoclonal antibody specific to IpaC, an antigen coded by the invasion plasmid of Shigella and EIEC. Invasive pathogens could be successfully detected with the technique, even in the presence of a large number of non-pathogenic bacterial cells. The method was significantly more sensitive in identifying pathogen-containing samples then the traditional culture-based approach.

CONCLUSION

The IpaC-specific colony blot immunoassay is an inexpensive method for identifying the aetiological agents of bacillary dysentery in water samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

The technique could be particularly useful in detecting enteroinvasive E. coli which often remains undetected by bio- and serotyping.

Diarrheagenic Escherichia coli

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler's diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (entero-pathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.