Virulence Characteristics and Antibiotic Resistance Profiles of Shiga Toxin-Producing Escherichia coli Isolates from Diverse Sources

Prevalence, Molecular Characterization, and Antimicrobial Resistance Profiles of Shiga Toxin-Producing Escherichia coli Isolated from Raw Beef, Pork, and Chicken Meat in Vietnam

Shiga toxin-producing Escherichia coli (STEC) is one of the most important foodborne pathogens, and the rise of antibiotic resistance to it is a significant threat to global public health. The purpose of this study is to investigate the prevalence, molecular characterization, and antibiotic resistance of STEC isolated from raw meat in Vietnam. The findings in this study showed that the prevalence of STEC in raw beef, pork, and chicken meat was 9.72% (7/72), 5.56% (4/72), and 1.39% (1/72), respectively. The STEC isolates were highly resistant to ampicillin (91.67%) and tetracycline (91.67%), followed by trimethoprim/sulfamethoxazole (83.33%), streptomycin (75%), and florfenicol (66.67%). The incidence of STEC virulence-associated genes, including stx1, stx2, eae, and ehxA, was 8.33% (1/12), 91.67% (11/12), 33.33% (4/12), and 58.33% (7/12), respectively. STEC serogroups O157, O26, and O111 were detected in 3 out of 12 STEC isolates. Two isolates were found to be ESBL producers carrying the blaCTX-M-55 gene, and three isolates were colistin-resistant strains harboring the mcr-1 gene. Notably, a STEC O111 isolate from chicken meat harbored both the blaCTX-M-55 and mcr-1 genes.

Microbiological quality of irrigation water on highly diverse fresh produce smallholder farms: elucidating environmental routes of contamination

AIM

To evaluate the microbiological safety, potential multidrug-resistant bacterial presence and genetic relatedness (DNA fingerprints) of Escherichia coli isolated from the water-soil-plant nexus on highly diverse fresh produce smallholder farms.

METHODS AND RESULTS

Irrigation water (n = 44), soil (n = 85), and fresh produce (n = 95) samples from six smallholder farms with different production systems were analysed for hygiene indicator bacterial counts and the presence of shigatoxigenic E. coli and Salmonella spp. using standard microbiological methods. Identities of isolates were confirmed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and the genetic relatedness of the E. coli isolates determined using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) analysis. Irrigation water E. coli levels ranged between 0 and 3.45 log MPN/100 ml-1 with five farms having acceptable levels according to the World Health Organization limit (3 log MPN/100 ml-1). Fresh produce samples on four farms (n = 65) harboured E. coli at low levels (<1 log CFU/g-1) except for one sample from kale, spring onion, green pepper, onion, and two tomato samples, which exceeded international acceptable limits (100 CFU/g-1). Only one baby carrot fresh produce sample tested positive for Salmonella spp. Of the 224 samples, E. coli isolates were identified in 40% (n = 90) of all water, soil, and fresh produce types after enrichment. Additionally, the DNA fingerprints of E. coli isolates from the water-soil-plant nexus of each respective farm clustered together at high similarity values (>90%), with all phenotypically characterized as multidrug-resistant.

CONCLUSIONS

The clustering of E. coli isolated throughout the water-soil-plant nexus, implicated irrigation water in fresh produce contamination. Highlighting the importance of complying with irrigation water microbiological quality guidelines to limit the spread of potential foodborne pathogens throughout the fresh produce supply chain.

Sanitary status and water quality of some drinking water sources and antibiogram of Shiga toxin-producing Escherichia coli O157:H7 isolated from Shika, Zaria, Nigeria

This study assessed the sanitary condition and quality of selected wells and boreholes in Shika, Zaria Nigeria. Fifty samples each were collected during the dry and wet seasons. This involved sanitary survey, water quality assessment, isolation and characterization of Shiga toxin-producing Escherichia coli O157:H7 (STEC) and, antibiogram assay. Based on the risk of contamination, wells (72%) had a high risk of contamination, while boreholes (44%) had low risk of contamination. Their physicochemical quality varied with season and location, and mean total coliform (TC) and faecal coliform (FC) were significantly lower in the dry season (p < 0.05). STEC were isolated from only wells with a prevalence of 4%, and exhibited a multidrug resistance pattern (amoxicillin, erythromycin and tetracycline). There was a strong positive correlation between sanitary status and water quality. The high- and very high-risk categories (wells) were strongly correlated with TC, FC, BOD, phosphate, turbidity and pH.              .

Study of heavy metal resistance genes in Escherichia coli isolates from a marine ecosystem with a history of environmental pollution (arsenic, cadmium, copper, and mercury)

We analyzed whole genome sequences of 308 Escherichia coli isolates from a marine ecosystem to determine the prevalence and relationships of heavy metal resistance genes (HMRGs) and antibiotic resistance genes (ARGs), as well as the presence of plasmid sequences. We screened all genomes for presence of 18 functional HMRGs conferring resistance to arsenic, cadmium, copper, or cadmium/mercury. In subset analyses, we examined geographic variations of HMRG carriage patterns in 224 isolates from water sources, and sought genetic linkages between HMRGs and ARGs in 25 genomes of isolates resistant to antibiotics. We found high carriage rates of HMRGs in all genomes, with 100% carrying at least one copy of 11 out of 18 HMRGs. A total of 173 (56%) of the isolates carried both HMRGs and plasmid sequences. In the 25 genomes of antibiotic-resistant isolates, 80% (n = 20) carried HMRGs, ARGs, and plasmid sequences, while 40% (n = 10) had linked HMRGs and ARGs on their assembled genomes. We found no evidence of geographic variation in HMRG frequency, nor any association between locational proximity to Superfund sites and co-carriage of HMRGs and ARGs. Our study findings indicate that HMRGs are common among E. coli in marine ecosystems, suggesting widespread heavy metal presence in water sources of a region with history of environmental pollution. Further research is needed to determine the role HMRGs play in driving antimicrobial resistance in human pathogens through genetic linkage and the value their detection in environmental bacterial genomes may offer as an indicator of environmental heavy metal pollution.

CAM-21, a novel lytic phage with high specificity towards Escherichia coli O157:H7 in food products

Escherichia coli O157:H7 is a foodborne pathogen that has become a serious global concern for food safety. Despite the application of different traditional biocontrol methods in the food industry, food borne disease outbreaks linked to this organism remain. Due to their high specificity, lytic bacteriophages are promising antimicrobial agents that could be utilized to control pathogens in foods. In this study, a novel Escherichia phage, CAM-21, was isolated from a dairy farm environment. CAM-21 showed targeted host specificity towards various serotypes of Shiga toxin-producing E. coli, including O157:H7, O26, O103, and O145. Morphological analyses revealed that CAM-21 has a polyhedron capsid and a contractile tail with a diameter of about 92.83 nm, and length of about 129.75 nm, respectively. CAM-21 showed a strong inhibitory effect on the growth of E. coli O157:H7, even at a multiplicity of infection (MOI) of as low as 0.001. Phage adsorption and one-step growth analysis indicated that the target pathogen was rapidly lysed by CAM-21 that exhibited a short latent time (20 min). Electron microscopic and genomic DNA analyses suggested that CAM-21 is a lytic phage, classified as a new species in the Tequatrovirus genus of the Myoviridae Family. Based on whole genome sequencing, CAM-21 has a double-stranded DNA with 166,962 bp, 265 open reading frames and 11 tRNA. The genome of CAM-21 did not encode toxins, virulence factors, antibiotic resistance, lysogeny or allergens. Phylogenetic and genomic comparative analyses suggested that CAM-21 is a T4-like phage species. The growth of E. coli O157:H7 was effectively controlled in milk, ground beef and baby spinach at MOIs of 1000 and 10,000. CAM-21 significantly (P ≤ 0.05) reduced the bacterial counts of the treated foods, ranging from 1.4-2.0 log CFU/mL in milk to 1.3-1.4 log CFU/g in ground beef and baby spinach. These findings suggest that the lytic phage, CAM-21, is a potential candidate for controlling E. coli O157:H7 contamination in foods.

Antimicrobial impacts of zinc oxide nanoparticles on shiga toxin-producing Escherichia coli (serotype O26)

The antibacterial activity of zinc oxide nanoparticles (ZnO NPs) has received significant attention worldwide due to the emergence of multidrug-resistant microorganisms. Shiga toxin-producing Escherichia coli is a major foodborne pathogen that causes gastroenteritis that may be complicated by hemorrhagic colitis or hemolytic uremic syndrome. Therefore, this study aimed to evaluate the antimicrobial effect of ZnO NPs against E. coli O26 and its Shiga toxin type 2 (Stx2). Multidrug resistance phenotype was observed in E. coli O26, with co-resistance to several unrelated families of antimicrobial agents. Different concentrations of ZnO NPs nanoparticles (20 nm) were tested against different cell densities of E. coli O26 (108, 106 and 105 CFU/ml). The minimum inhibitory concentration (MIC) value was 1 mg/ml. Minimum bactericidal concentration (MBC) was 1.5 mg/ml, 2.5 mg/ml and 3 mg/ml, respectively, depending on ZnO NPs concentrations and bacterial cell density. Results showed a significant (P≤0.05) decrease in Stx2 level in a response to ZnO NPs treatment. As detected by quantitative real-time PCR, ZnO NPs down-regulated the expression of the Stx2 gene (P≤0.05). Moreover, various concentrations of ZnO NPs considerably reduced the total protein content in E. coli O26. There was a significant reduction in protein expression with increased ZnO NPs concentration compared to the non-treated control. Scanning electron micrographs (SEM) of the treated bacteria showed severe disruptive effects on E. coli O26 with increasing ZnO NPs concentration. The results revealed a strong correlation between the antibacterial effect and ZnO NPs concentrations. ZnO NPs exert their antibacterial activities through various mechanisms and could be used as a potent antibacterial agent against E. coli O26.

First isolation of verocytotoxin-producing Escherichia coli O157:H7 from sports animals in Southern Thailand

Background and Aim:

Escherichia coli O157:H7 is enterohemorrhagic E. coli, which produces verocytotoxin or Shiga toxin. It is a well-known cause of severe diseases in humans worldwide. Cattle and other ruminants are the main reservoirs of this organism. Sports animals, such as fighting bulls, riding horses, and fighting cocks, are economic animals in Southern Thailand. This study aimed to identify E. coli O157:H7 from the rectal swabs of these sports animals and determine the antimicrobial susceptibility patterns of isolated bacteria.

Materials and Methods:

The rectal swabs were collected from 34 fighting bulls, 32 riding horses, and 31 fighting cocks. The swabs were cultured on MacConkey (MAC) Agar; the suspected colonies were then identified by VITEK^® 2 GN card, and the antimicrobial susceptibility was tested by VITEK^® 2 AST N194 in VITEK^® 2 Compact automation. Escherichia coli O157:H7 was confirmed by culturing on sorbitol MAC agar, the ability to grow at 44°C, and the presence of H7 antigen. In addition, the eaeA (E. coli attaching and effacing), along with stx1 and stx2 (Shiga cytotoxins) genes, were determined using polymerase chain reaction. Finally, the cytotoxicity of Shiga toxin was confirmed using the Vero cytotoxicity test.

Results:

Fifty-five suspected isolates (56.70%), which were collected from 19 fighting bulls (55.88%), 13 riding horses (40.63%), and 23 fighting cocks (71.13%), were identified as E. coli. However, one sample (Bull H9/1) from fighting bulls had an equal confidence level (50%) for E. coli and E. coli O157. The confirmation of this isolate demonstrated that it was sorbitol non-fermenter, could assimilate L-lactate, was unable to grow well at 44°C, and reacted with anti-serum to H7 antigen. In addition, it was positive with stx2 and eaeA genes, and the toxin affected Vero cells by a dose-dependent response. The antimicrobial susceptibility test revealed that five out of 55 (9.09%) E. coli isolates were resistant to antimicrobial agents. All five isolates (21.74%) were collected from fighting cocks. Escherichia coli Cock H4/3 was only one of the five isolates resistant to three antimicrobial agents (ciprofloxacin, moxifloxacin, and trimethoprim/sulfamethoxazole). Fortunately, it was not multidrug-resistant bacteria.

Conclusion:

This is the first report on detection of E. coli O157:H7 in fighting bulls and antibiotic-resistant characteristic of E. coli in fighting cocks in Southern Thailand. This research is beneficial in preventing the dissemination of E. coli O157:H7 or antimicrobial agent-resistant E. coli in sports animals and humans.

Genetic and antimicrobial resistance profiles of non-O157 Shiga toxin-producing Escherichia coli from different sources in Egypt

BACKGROUND

The Shiga toxin-producing Escherichia coli (STEC) represented a great risk to public health. In this study, 60 STEC strains recovered from broiler and duck fecal samples, cow's milk, cattle beef, human urine, and ear discharge were screened for 12 virulence genes, phenotypic and genotypic antimicrobial resistance, and multiple-locus variable-number tandem-repeat analysis (MLVA).

RESULTS

The majority of strains harbored Shiga toxin 1 (stx₁) and stx_1d, stx₂ and stx_2e, and ehxA genes, while a minority harbored stx_2c subtype and eaeA. We identified 10 stx gene combinations; most of strains 31/60 (51.7%) exhibited four copies of stx genes, namely the stx₁, stx_1d, stx₂, and stx_2e, and the strains exhibited a high range of multiple antimicrobial resistance indices. The resistance genes blaCTX-M-1 and blaTEM were detected. For the oxytetracycline resistance genes, most of strains contained tetA, tetB, tetE, and tetG while the tetC was present at low frequency. MLVA genotyping resolved 26 unique genotypes; genotype 21 was highly prevalent. The six highly discriminatory loci DI = 0.9138 are suitable for the preliminary genotyping of STEC from animals and humans.

CONCLUSIONS

The STEC isolated from animals are virulent, resistant to antimicrobials, and genetically diverse, thus demands greater attention for the potential risk to human.

Molecular Detection of Antibiotic Resistance Genes in Shiga Toxin-Producing E. coli Isolated from Different Sources

Shiga toxin-producing Escherichia coli (STEC) is an enteric pathogen associated with human gastroenteritis outbreaks. Extensive use of antibiotics in agriculture selects resistant bacteria that may enter the food chain and potentially causes foodborne illnesses in humans that are less likely to respond to treatment with conventional antibiotics. Due to the importance of antibiotic resistance, this study aimed to investigate the combination of phenotypic and genotypic antibiotic resistance in STEC isolates belonging to serogroups O26, O45, O103, O104, O111, O121, O145, and O157 using disc diffusion and polymerase chain reaction (PCR), respectively. All strains were phenotypically resistant to at least one antibiotic, with 100% resistance to erythromycin, followed by gentamicin (98%), streptomycin (82%), kanamycin (76%), and ampicillin (72%). The distribution of antibiotic resistance genes (ARGs) in the STEC strains was ampC (47%), aadA1 (70%), ere(A) (88%), blaSHV (19%), blaCMY (27%), aac(3)-I (90%), and tet(A) (35%), respectively. The results suggest that most of the strains were multidrug-resistant (MDR) and the most often observed resistant pattern was of aadA1, ere(A), and aac(3)-I genes. These findings indicate the significance of monitoring the prevalence of MDR in both animals and humans around the globe. Hence, with a better understanding of antibiotic genotypes and phenotypes among the diverse STEC strains obtained, this study could guide the administration of antimicrobial drugs in STEC infections when necessary.