Nguyen Thi My Thanh, Nguyen Thi Phuong Lan, Nguyen Thi Kim Hoang,
Nguyen Thi Huong, Nguyen Ngoc Anh Thu
Pasteur Institute of
Typhoid fever has been a common enteric disease in Vietnam since a very long time. In 1998, in the South of Vietnam there were 16 667 typhoid cases, including 7 cases of death. The disease is mainly caused by Salmonella typhi, which is transmitted by food and water. As many other bacteria, Salmonella typhi has developed resistance to common antibiotics and even to those of new generations. So, studying on typhoid fever should not be separated from the surveillance of the antibiotic susceptibility of the pathogen, that can be helpful for the effective treatment and create the foundation for further researches.
- Strains: 167 strains of Salmonella typhi isolated from blood and stool of hospitalized typhoid patients in some southern cities and provinces in 1998.
- Medium for antibiogram: Mueller Hinton agar of Diagnostics Pasteur.
- Antibiotic discs of B.B.L. and Diagnostics Pasteur.
- Methods of enrichment, isolation and identification: After blood culture, subculture on Blood Agar plate, then to Hektoen Enteric Agar (HEA), identification by key biochemical tests (KIA, Indole, Methyl Red, Voges Proskauer, Citrate, Urease, Mannitol fermentation, Motility, Lysine, Malonate, Dulcitol), serotyping by agglutination tests with specific antisera. For stool culture, inoculation the specimen into Selenite before transferring to HEA.
- Antibiogram method: Disk diffusion technique of Kirby-Bauer. Evaluation of antibiotic susceptibility is according to the standards of WHO and of the manufacturer.
- Analysis of antibiogram results: using the WHONET software.
Table 1: Antibiotic susceptibility rates of
Salmonella typhi isolated in 1998.
|
|
Code |
Antibiotic |
Limit |
n |
R% |
I% |
S% |
|
1 |
AMP |
Ampicillin |
14–16 |
108 |
93.5 |
0.0 |
6.5 |
|
2 |
NAL |
Nalidixic acid |
14–18 |
165 |
87.9 |
2.4 |
9.7 |
|
3 |
CHL |
Chloramphenicol |
13–17 |
165 |
92.7 |
0.6 |
6.7 |
|
4 |
OFL |
Ofloxacin |
13–15 |
165 |
0.0 |
0.0 |
100.0 |
|
5 |
CRO |
Ceftriaxone |
14–20 |
135 |
0.0 |
0.0 |
100.0 |
|
6 |
TMP |
Trimethoprim |
11–15 |
114 |
91.2 |
0.9 |
7.9 |
|
7 |
CIP |
Ciprofloxacin |
16–20 |
121 |
0.0 |
15.7 |
84.3 |
|
8 |
NOR |
Norfloxacin |
13–16 |
96 |
0.0 |
17.7 |
82.3 |
|
9 |
FTX |
Cefotaxim |
15–22 |
121 |
0.0 |
2.5 |
97.5 |
|
10 |
TET |
Tetracycline |
15–18 |
47 |
93.6 |
0.0 |
6.4 |
|
11 |
SXT |
Trimethoprim/ |
11–15 |
61 |
91.8 |
0.0 |
8.2 |
|
|
|
Sulfamethoxazol |
|
|
|
|
|
Total of strains: 167
Table 1 shows that Salmonella typhi has no longer sensitivity to commonly used antibiotics as ampicillin, chloramphenicol, tetracycline, co-trimoxazol. The susceptibility to the antibiotics of cephalosporines 3rd generation (ceftriaxone, cefotaxime) and those of quinolones (ciprofloxacin, ofloxacin, norfloxacin) are still high, except nalidixic acid.
Table 2: Comparison of the antibiotic
susceptibility rates of Salmonella typhi in 1997 and 1998:
|
Code |
1997 |
1998 |
||||||
|
n |
R% |
I% |
S% |
n |
R% |
I% |
S% |
|
|
AMP |
101 |
90.1 |
5 |
4.9 |
108 |
93.5 |
0 |
6.5 |
|
NAL |
79 |
19 |
1.3 |
79.9 |
165 |
87.9 |
2.4 |
9.7 |
|
CHL |
101 |
92.1 |
0 |
7.9 |
165 |
92.7 |
0.6 |
6.7 |
|
CRO |
101 |
5.9 |
14.9 |
79.2 |
135 |
0 |
0 |
100 |
|
NOR |
101 |
3 |
5.9 |
91.1 |
96 |
0 |
17.7 |
82.3 |
|
SXT |
99 |
93.9 |
0 |
6.1 |
61 |
91.8 |
0 |
8.2 |
Table 2 shows that there is no remarkable difference between the antibiotic susceptibility of the strains isolated in 1997 and those isolated in 1998, except in case of nalidixic acid, Salmonella typhi increased the resistance to this antibiotic (from 19% to 87.9%).
Table 3: Comparison of the antibiotic
susceptibility rates of Salmonella typhi strains isolated from blood and those
isolated from stools:
|
Code |
S.typhi
isolated from blood, n=90 |
S.typhi
isolated from stool, n=77 |
||||
|
R% |
I% |
S% |
R% |
I% |
S% |
|
|
AMP |
96.8 |
0 |
3.2 |
89.1 |
0 |
10.9 |
|
NAL |
87.6 |
2.2 |
10.1 |
88.2 |
2.6 |
9.2 |
|
CHL |
93.2 |
0 |
6.8 |
92.2 |
1.3 |
6.5 |
|
OFL |
0 |
0 |
100 |
0 |
0 |
100 |
|
CRO |
0 |
0 |
100 |
0 |
0 |
100 |
|
TMP |
93.8 |
0 |
6.2 |
87.8 |
2 |
10.2 |
|
CIP |
0 |
10.1 |
89.9 |
0 |
23.1 |
76.9 |
|
NOR |
0 |
20.4 |
79.6 |
0 |
14.3 |
85.7 |
|
FTX |
0 |
1.4 |
98.6 |
0 |
3.8 |
96.2 |
|
TET |
95.2 |
0 |
4.8 |
92.3 |
0 |
7.7 |
|
SXT |
93.8 |
0 |
6.2 |
89.7 |
0 |
10.3 |
Table 3 shows that
there is no remarkable difference between the antibiotic susceptibility of Salmonella typhi strains isolated from
blood and those isolated from stool. Studies on this aspect
needs to be continued more profoundly because it is related to the
treatment for carriers.
In