As shown in
Table 1, a total of 22 different serotypes were divided among 276
Salmonella spp. tested in this study. Somatic (O) antigen groups observed were D (53.5%), B (31.2%), C (12.4%), A (0.7%), and E (0.4%). The major serotype was
S. Enteritidis (116 strains, 42.0%), followed by
S. Typhimurium (60 strains, 21.7%),
S. I 4,[
5],12:i:- (25 strains, 9.1%),
S. Typhi (24 strains, 8.7%), and
S. Thompson (22 strains, 8.0%), accounting for 89.5% of
Salmonella spp. The 17 other serotypes had a low detection rate (10.5% combined).
Antibiotic resistance patterns of
Salmonella spp. strains isolated from Jeollanam-do in Korea during 2004–2014 are shown in
Table 2. The antibiotic resistance test was performed on five major serotypes:
S. Enteritidis,
S. Typhimurium,
S. I 4,[
5],12:i:-,
S. Typhi, and
S. Thompson. The highest resistance was observed in response to nalidixic acid (43.4%), followed by ampicillin (40.5%), tetracycline (31.6%), chloramphenicol (19.8%), cefalothin (11.3%), cefazolin (10.1%), cefoxitin (8.9%), and trimethoprim/sulfame-thoxazole (8.1%). Lower resistance was observed in response to amoxicillin/clavulanic acid (4.9%), cefotaxime (4.0%), and ceftriaxone (4.0%). All strains in this study were susceptible to imipenem and amikacin. As shown in
Table 3, the resistance rate of each antibiotic differed among
Salmonella serotypes. Overall,
S. Enteritidis and
S. Typhimurium showed higher antibiotic resistance than the other tested serotypes. The resistance rates for ampicillin were 70.0, 40.5, and 36.0% in
S. Typhimurium,
S. Enteritidis, and
S. I 4,[
5],12:i:-, respectively. Nalidixic acid showed a resistance rate of 81.0% in
S. Enteritidis. The highest resistance observed was to trimethoprim/sulfamethoxazole, in
S. Typhimurium (85.0%).
The multidrug resistance of
Salmonella serotypes isolated at Jeollanam-do from 2004 to 2014 is presented in
Table 4. Of the 247
Salmonella samples, 51 (20.6%) were susceptible to all of the antibiotics tested in this study. The highest antibiotic susceptibility was observed in
S. Thompson (20 strains, 90.9%), followed by
S. Typhi (18 strains, 75.0%),
S. I 4,[
5],12:i:- (six strains, 24.0%),
S. Typhimurium (five strains, 8.3%), and
S. Enteritidis (two strains, 1.7%). Resistance to one antibiotic was observed in 89 (36.0%) samples, while multidrug resistance, defined as resistance to two or more antibiotics, was detected in 107 (43.3%)
Salmonella samples. Multidrug resistance was observed most frequently in
S. Typhimurium (44 strains, 73.3%), followed by
S. Enteritidis (49 strains, 42.2%),
S. I 4,[
5],12:i:- (nine strains, 36.0%),
S. Typhi (three strains, 12.5%), and
S. Thompson (two strains, 9.0%).
S. Enteritidis and
S. Typhimurium presented the highest resistance (98.3%) and multidrug resistance rates (73.3%), respectively.
Tables 5–
9 present the antibiotic resistance patterns of the
Salmonella serotypes. The most highly observed antibiotic resistance patterns among
Salmonella spp. in this study were against ampicillin-chloramphenicol (14 strains, 5.7%), ampicillin-tetracycline-trimethoprim/sulfamethoxazole (11 strains, 4.5%), and ampicillin-amoxicillin/clavulanic acid-ampicillin/sulbactam-cefalothin-cefazolin-cefoxitin-tetracycline (10 strains, 4.0%). The most frequent antibiotic resistance patterns of
Salmonella serotypes were ampicillin-chloramphenicol (14 strains, 12.1%) in
S. Enteritidis, ampicillin-tetracycline-trimethoprim/sulfamethoxazole (10 strains, 16.7%) in
S. Typhimurium, ampicillin-tetracycline (six strains, 24.0%) in
S. I 4,[
5],12:i:-, cefalothin-cefoxitin-chloramphenicol (three strains, 12.5%) in
S. Typhi, and ampicillin-cefalothin-cefazolin-nalidixic acid (one strain, 4.5%) in
S. Thompson.