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A total of 126 C. jejuni strains were isolated from samples taken in this study. Multilocus sequence typing and antibacterial susceptibility testing were successfully performed in all isolates.
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The prevalence of C. jejuni from the various sources is shown in Table 1. Statistically, the isolation rate from poultry meat was significantly higher than that from cattle meat (χ2 = 36.222, P < 0.001). However, the isolation rate from poultry cloacal swabs was lower than that from cattle stool (χ2 = 15.950, P < 0.001).
Source No. of Samples No. of Isolates Prevalence of C. jejuni (%) Poultry meat 63 23 36.5 Cattle meat 93 1 1.1 Cattle feces 103 59 57.3 Poultry cloacal swab 74 20 27.0 Patients' feces 437 23 5.3 Table 1. Prevalence of C. jejuni in Poultry, Cattle, and Diarrheal Patients in Shenzhen
The patients with C. jejuni ranged in age from 7 months to 43 years old. Three strains were isolated from 7, 8, and 9 month-old infants. The overall prevalence of C. jejuni in the patients with diarrhea was 5.3% (23/437). Separately, the prevalence of C. jejuni was 4.0% (7/173) in child patients, 6.9% (4/58) in adolescent patients, and 5.8% (12/206) in adult patients (≥ 18 years old). No statistically significant difference was found in the prevalence of C. jejuni between the different age groups (χ2 = 0.955, P = 0.620).
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We identified 62 STs among the 126 isolates (Table 2). Among them, 27 STs were not reported previously, and 10 novel alleles were found in this study: GlyA734, 735, 736, 737, and 738; pgm894, 896, 897, and 898; and tkt699. Isolates from patients with diarrhea had the highest proportion of new STs (12/23, 52%), followed by those isolated from poultry sources (22/43, 51.0%), and those from cattle sources (7/60, 11.7%).
Poultry Source Cattle Source Patients Source ST Clone Complex Number of Isolates ST Clone Complex Number of Isolates ST Clone Complex Number of Isolates 464 464 3 19 21 7 51 443 1 2145 574 1 22 22 13 354 354 1 2895 574 2 45 45 1 403 403 2 4324 NAa 1 51 443 2 1811 21 1 6493 NA 2 61 61 6 1919 52 1 6607 NA 3 113 460 1 2131 NA 1 6909 574 2 257 257 6 2132 NA 1 6913 464 1 354 354 3 2328 NA 1 6962 NA 1 403 403 5 4265 52 1 7456 NA 1 583 45 3 8003 403 1 7866 NA 1 2089 NA 2 8880 574 2 8089 NA 2 5799 443 1 8901 52 1 8847 NA 1 6500 21 1 8904 45 1 8877b 45 2 7469 464 1 8905 354 1 8879 NA 2 7695 21 1 8906 52 1 8880 574 1 8896* NA 2 8907* NA 1 8881* NA 1 8898 21 4 8908 NA 1 8883* NA 2 8934 464 1 8909 NA 1 8884 NA 4 8910 21 1 8886 NA 1 8911* 362 1 8887* NA 2 8935* 403 1 8889* NA 2 8892 NA 1 8893* NA 1 8894* 45 1 8895 NA 1 8936 NA 1 Total 43 60 23 Note. aNA, not assigned; bNew STs are given in bold; *ST contains the new allele unreported previously. Table 2. ST Type of 126 C. jejuni Isolates from Shenzhen
Eighty-six isolates belonged to 13 clonal complexes, while 40 isolates could not be assigned to any known clonal complex. The most frequently observed clonal complexes were ST-21 (11.9%), ST-22 (10.3%), and ST-403 (7.1%).
Separately, 27 STs were obtained from 43 poultry isolates, and 18 STs were obtained from 60 cattle isolates. The calculated Simpson's index of the STs from the poultry isolates was 0.977, versus 0.912 from the cattle isolates.
Moreover, ST-21, ST-45, ST-354, ST-403, and ST-443 overlapped between isolates from patients and cattle, while ST-45 and ST-574 overlapped between isolates from patients and poultry. In addition, ST-45 was the only clonal complex found in all three sources.
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The MICs of the quality control strain (C. jejuni ATCC 33560) were within the reference quality control range. Overall, all the isolates were resistant to at least one antibiotic. The highest resistance rate was detected for ciprofloxacin (89.7%), followed by tetracycline (74.6%), and nalidixic acid (69.0%). The resistance rates of C. jejuni from different sources are shown in Figure 1.
Figure 1. The antibiotic resistance rate of C. jejuni isolated from different sources in Shenzhen. The x-axis represents the antibiotics. The y-axis represents the percentage of resistant isolates. The black area represents the resistance rate of poultry isolates, the white area represents the resistance rate of patient isolates, and the grey area represents the resistance rate of cattle isolates.
The MIC50s of nalidixic acid and tetracycline to all C. jejuni isolates were ≥ 64 μg/mL, while the MIC50s of erythromycin, azithromycin, gentamycin, telithromycin, and clindamycin to all C. jejuni isolates were ≤ 2 μg/mL. For the different sources, C. jejuni from poultry had higher or equal MIC50 s compared with those from patients or cattle against all 11 antibiotics.
For multidrug resistance (MDR), 88.4% of C. jejuni isolated from poultry were resistant to four to nine antibiotics. Among them, one strain was resistant to nine antibiotics, including erythromycin, azithromycin, nalidixic acid, ciprofloxacin, gentamycin, streptomycin, chloromycetin, telithromycin, and clindamycin. This strain was isolated from a chicken cloacal swab from a poultry wholesaler. Similarly, 73.9% of isolates from patients with diarrhea were resistant to four to eight antibiotics. The most prevalent resistance pattern was combined nalidixic acid, ciprofloxacin, florfenicol, and tetracycline resistance (30.4%). In particular, 65.2% of isolates from patients were resistant to florfenicol. In contrast, all C. jejuni from cattle were resistant to less than five antibiotics. None of the isolates from cattle were resistant to erythromycin, azithromycin, gentamycin, telithromycin, or clindamycin.
Statistically, the MDR rate among the isolates from poultry (97.6%, 42/43) was significantly higher than that from cattle (60.0%, 36/60) (χ2 = 19.343, P < 0.001). No statistical significance was observed between the MDR rate of isolates from poultry and patients (91.3%, 21/23) (χ2 = 1.401, P = 0.236).