Bacterial clustering
The results showed fish-derived
E.
coli isolates were classified into phylogenetic four groups: group A (8%), group B1 (21%), group B2 (59%), group D (12%). The goose-derived isolates were classified into phylogenetic four groups: group A (10%), group B1 (33%), group B2 (48%), group D (9%). The fish-derived and goose-derived
E.
coli isolates were mainly B2+D.
Phylogenetic clustering is an important method for typing
E.
coli. According to previous reports, phylogenetic clustering of
E.
coli can be divided into four groups: A, B1, B2 and D, among which B2 and D are considered to be the main pathogenic groups
(Javed et al., 2021; Lee et al., 2016). Pathogenic strains belonging to group B2 and, to a lesser extent, group D, are known to carry more virulence factor genes than strains of groups A and group B1
(Nowrouzian et al., 2005). More specifically, the B2 phylogenetic group of
E.
coli includes important pathogens such as extraintestinal pathogenic, adherent-invasive and uropathogenic strains
(Deshpande et al., 2015). Zhu Ge et al. (2014) discovered avian pathogenic
E.
coli and human extraintestinal infection of large intestine Most of the bacilli belong to group B2
(Zhu Ge et al., 2014). In this study, it was found that the
E.
coli isolated from goose and fish were dominated by group B2 and D. These data provide a helpful reference about the ecological distribution and genetic evolution of
E.
coli in the area. The results were consistent with the results of dominant evolutionary grouping of avian pathogenic
E.
coli reported by
Wang et al. (2026) (Wang et al., 2016). However, it was different from the research results of other researchers
(Higgins et al., 2007; Kuczkowski et al., 2016), which may be due to the different animal sources, sampling areas and feeding environment.
Biofilm formation ability
The results of this study showed that some strains of
E.
coli isolated from goose and fish could form biofilm. Among the fish-derived
E.
coli isolates, 69% strains had biofilm formation ability, including 36% with strong ability, 33% with weak ability and 31% without biofilm formation ability. Among the goose-derived
E.
coli isolates, 60% strains had biofilm formation ability, including 42% with strong ability, 18% with weak ability and 40% without biofilm formation ability. This indicates that the biofilm formation rate of
E.
coli from goose and fish in Henan, China is high. This may be due to the long-term use of low concentrations of antibiotics in feeding
(Chakraborty et al., 2020; Li et al., 2021). Earlier, other workers also reported biofilm production by
E.
coli from chicken, pig, duck and chicken products
(Li et al., 2021; Wang et al., 2011; Wang et al. 2016). However, no report could be traced in literature on the biofilm forming ability and drug resistance by
E.
coli isolated from goose and fish.
Antibiotic sensitivity
The results of the drug sensitivity test of
E.
coli isolated from fish were shown in Table 2.
All isolates showed a high resistance rate (84% - 100%). The results of the drug sensitivity test of
E.
coli isolated from goose were shown in Table 3.
All isolates also showed a high resistance rate (48% -100%). The drug-resistance rate of the phylogenetic groups B2 and D was higher than the resistance rate of the phylogenetic groups A and B1. This study found that
E.
coli isolated from fish and goose had high multiple drug resistance rates. The reason may be related to different breeding environments. From the point of view of the aquaculture environment when collecting samples, the aquaculture density of fish is highly concentrated and in order to ensure the water quality of fish farming, appropriate amount of fungicides will be regularly put into the water. Long-term use of large amounts of antibacterial drugs can easily lead to high resistance rate of
E.
coli from fish. In the breeding process of geese, some antibacterial drugs will be used regularly, which will increase the resistance of
E.
coli.
At present, most of the drug susceptibility test objects are planktonic bacteria. In this study, the MIC values against planktonic and biofilm
E.
coli were detected and the results showed that the MIC values would increase with the formation of biofilm. Compared with planktonic bacteria, the MIC values of tetracycline, aureomycin, enrofloxacin, doxycycline, TMP trimethoprim, norfloxacin and gentamicin against biofilm fish-derived
E.
coli were increased by 2, 8, 8, 4, 4, 16 and 2 times, respectively. The MIC values of tetracycline, aureomycin, enrofloxacin, doxycycline, TMP trimethoprim and norfloxacin against biofilm goose-derived
E.
coli were increased by 2, 8, 4, 2, 8 and 2 times, respectively (Table 4).
Similarly, Significant differences were observed between MICs of planktonic cells and MICs of UPEC biofilms, indicating a higher level of bacterial tolerance in biofilm form
(Rafaque et al., 2020). (Wang
et al. 2020) found that the
E.
coli minimum biofilm eradication concentrations were generally two times higher than the planktonic minimum inhibitory concentrations
(Wang et al., 2020). They believed that MIC would significantly increase with the formation of biofilm, which further indicated that the formation of biofilm could increase the drug resistance of bacterial strains. Therefore, biofilm is of great significance for the prevention and treatment of clinical
E.
coli. It is necessary to evaluate the bacterial status of infection during clinical medication. Especially when the clinical treatment effect is poor, drug resistance and biofilm factors need to be considered.
Correlation analysis of biofilm formation ability and drug resistance
Table 5 indicated that the isolates showed multidrug-resistance (MDR) (100%).
Among fish-derived
E.
coli isolates, 90 strains were resistant to more than 8 drugs and the biofilm-positive strains accounted for 69% (62/90) and the biofilm-negative strains accounted for 31% (28/90). Among goose-derived
E.
coli isolates, 91 strains were resistant to more than 8 drugs and the biofilm-positive strains accounted for 59% (54/91) and the biofilm-negative strains accounted for 41% (37/91). The antibiotic resistance of biofilm-forming
E.
coli isolates was found to be significantly higher than that of strains unable to form biofilm (p<0.05). The results of this study showed the number of drug resistance of biofilm-positive strains was higher than that of biofilm-negative strains, further proving that the biofilm-forming ability of bacteria is closely related to drug resistance. Similarly,
Qian et al., (2022) revealing that the populations that exhibited more robust biofilm formation likely contained larger proportions of extensively drug-resistant (XDR) isolates.
Dumaru et al., (2019) found that there was strong association between the MDR-status and biofilm-production in gut bacteria
(Dumaru et al., 2019). Katongole et al., (2020) demonstrated a high prevalence of biofilm-forming Uropathogenic
E.
coli strains that are highly associated with the MDR phenotype
(Katongole et al., 2020).