CITATION: Lien HT, Long HT, Ha NTT, Lam PD. 1994. Antibiotic resistance of
Shigella isolates during 1990-1992 in Vietnam. APUA Newsletter 12(1): 4-5.


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Antibiotic resistance of Shigella isolates during 1990-1992 in Vietnam
Ha Thi Lien, Hoang Thuy Long, Nguyen Thi Thanh Ha and Phung Dac Lam
National Institute of Hygiene and Epidemiology, Hanoi, Vietnam

Antibiotic resistance is a difficult problem in Vietnam, where infectious diseases are common and often caused by bacteria. Controls on the use of antibiotics are insufficient, as is the understanding in the community of the prudent use of antibiotics. Infections of the intestinal tract are one of the most frequent forms of infectious disease found in Vietnam, predominantly affecting infants under 5 years old.

Shigella is the third most common pathogen isolated in infections of the intestinal tract (1,2). The antibiotic susceptibilities in vitro of 336 Shigella isolated from fecal specimens of patients in Hanoi, Hai Phong, Hue, Nha Trang and Ho Chi Minh city during the period 1990-1992 were determined.

The frequency of resistance to commonly used antibiotics was high (Table 1): tetracycline (79%), chloramphenicol (70%) and sulfisomidine (50%). Trimethoprim in combination with sulfamethoxazole was introduced in 1984. With increasing use of trimethoprim, resistance to this drug increased from 0.7% in 1984 to 10.7% in 1987 (4). In 1985-1986, 23% of Shigella were resistant to trimethoprim (5). We found 58% of Shigella were resistant to trimethoprim and 63% of them resistant to trimethoprim and sulfamethoxazole. We found that ampicillin resistance in Shigella sp. had decreased to 45% from a mean of about 84% between 1986 and 1989. The reason for this decrease may be that ampicillin has not been the drug of choice for treatment of bacterial diarrhea for a long time.

Table 1. Antimicrobial susceptibilities of 336 Shigella isolated during 1990-1992 in Vietnam
Antibiotic

No. of Shigella Isolates

Resistance (%)

Ampicillin

150

45

Tetracycline

265

79

Gentamicin

74

22

Chloramphenicol

235

70

Kanamycin

15

5

Nalidixic

31

12

Trimethoprim

154

58

Trimethoprim & sulfamethoxazole

209

63

Sulfisomidine

128

50

The disc diffusion method was used (3). American Type Tissue Culture Collection strain E. coli 25922 served as a control.

Antibiotics such as tetracycline, chloramphenicol and sulfisomidine, which have been used for many years, are no longer active against Shigella in Vietnam. Similar results have been obtained from Bangladesh, Brazil, Egypt and Thailand (6,7) with the exception of chloramphenicol for which low frequencies of resistance were found in Bangladesh, Brazil and Egypt.

Because relatively few Shigella strains were obtained from Ho Chi Minh city and Hai Phong, we compared the data among the other 3 areas, Hanoi, Hue and Nha Trang. The frequency of resistance to antibiotics varied among the geographical areas (Table 2). kanamycin and nalidixic acid were still relatively active against Shigella isolates from the 3 areas, although resistances were at 10 and 14% respectively in Hue. The frequency of resistance to tetracycline and chloramphenicol was high. Resistance to trimethoprim and trimethoprim and sulfamethoxazole was lower in Hanoi and Nha Trang than in Hue, but all places had resistance frequencies of >50%. Resistance to gentamicin was very high (63%) in Nha Trang, and statistically much lower in Hanoi and Hue. The frequencies of resistance to ampicillin and sulfisomidine were lowest (16% and 2%) in Nha Trang.

Table 2. Frequency of antibiotic resistance in Shigella isolates from three areas in Vietnam.
Antibiotic

Location

Hanoi

Nha Trang

Hue

(n=93)

(n=78)

(n=110)

Ampicillin

59.0

16.0*

47.0

Tetracycline

89.0

47.5

92.0

Gentamicin

0.0

63.0*

3.0

Chloramphenicol

75.0

65.0

72.0

Kanamycin

1.0

4.0

10.0

Nalidixic

6.5

11.0

14.0

Trimethoprim

50.0

52.0

69.0

Trimethoprim & sulfamethoxazole

50.5

47.0

92.0

Sulfisomidine

79.0

2.0*

97.0

*Statistically significant difference P<0.05

The frequency of resistance to antibiotics in groups of Shigella was also significantly different (Table 3). All strains of Shigella were generally more susceptible to kanamycin, nalidixic acid and gentamicin. Strains of S. boydii were still susceptible to almost all antibiotics tested except sulfisomidine and trimethoprim; the frequencies of resistance to sulfisomidine and trimethoprim were 80% and 20%, respectively.

Table 3. Frequency of antibiotic resistance among Shigella spp.

Antibiotic

Species of Shigella

S. dysenteriae

S. flexneri

S. sonnei

S. boydii

(n = 47)

(n = 185)

(n = 44)

(n=5)

Ampicillin

10.5

54.0*

11.5

0

Tetracycline

90.0

71.0

95.5

0

Gentamicin

8.5

26.5

0

0

Chloramphenicol

62.0

77.0

36.5*

0

Kanamycin

23.5

4.5

2.5

0

Nalidixic

19.0

7.0

18.0

0

Trimethoprim

76.0

53.0

73.0

20.0

Trimethoprim & sulfamethoxazole

91.5

56.0

73.0

0

Sulfisomidine

89.0

45.0*

100.0

80.0

*Statistically significant difference P<0.001

Shigella dysenteriae, and S. sonnei were more susceptible to ampicillin than S. flexneri, but resistance to sulfisomidine, trimethoprim and trimethoprim and sulfamethoxazole was lower (45%-56%) in the latter group. Among S. sonnei, resistance to chloramphenicol was lower, 36.5%.

The frequencies of resistance to antibiotics varied among the geographical areas in Vietnam, especially between Nha Trang and the other two areas. The significantly different frequencies of resistance in 4 groups of Shigella calls for accurate routine susceptibility testing in all laboratories in Vietnam. The findings of high frequencies of Shigella resistance to commonly used agents Am, tetracycline, chloramphenicol, sulfisomidine and even trimethoprim, trimethoprim and sulfamethoxazole indicate future problems for antibiotic treatment.

References

  1. Canh DG et al. Symposium "Infections of the gastrointestinal and respiratory tracts" Hanoi, March, p.345-350, 1988.
  2. Qui NP et al. Symposium "Infections of the gastrointestinal and respiratory tracts" Hanoi, March, 232-238, 1988.
  3. Performance standards for antimicrobial disk susceptibility tests -- fourth edition: Approved standard M2 A4 NCCCLS. Villanova, Pa.
  4. Vinh NT, Widemann B: APUA Newsletter VII:2, 1989.
  5. Nguyen TTH, Hoang, TL, Nguyen TH, Nguyen TT, G. Lundstrom, B. Olsson-Liljequist and I Kallings. Inter J of Antimicrob Agents 1:121-126, 1991.
  6. Farrar EW, J. Infect. Dis. 152:1103-1106, 1985.
  7. Murray, BE, Rev. Infect. Dis. Supple.2:172-181, 1986.
 

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