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Changing Sensitivity Pattern of Salmonella typhi in Calicut
Lathi Nair*,Sudarsana J**
*,**Professors of Microbiology,
Medical College, Calicut, India
Address for
Correspondence:
Dr Lathi Nair
Professor of Microbiology
Dept of Microbiology
Calicut Medical College,
Calicut Medical College P.O
Calicut 673008
Kerala,India
E-Mail: drlathi@rediffmail.com
ABSTRACT
A retrospective study of the sensitivity pattern of S.typhi isolated between 1995 and 2003 was done. The strains were tested for susceptibility to Ampicillin, Cotrimoxazole, Chloramphenicol, Furoxone, Ciprofloxacin, Ceftriaxone and Nalidixic acid. Multi drug resistant S.typhi (MDR) was endemic in Calicut from 1989 (68.7%) but since 2002 incidence of MDR isolates decreased substantially (21,05%). 120 (90.22%) S.typhi strains isolated between 1999 and 2003 were resistant to Nalidixic acid, showing treatment failure with Ciprofloxacin. MIC to Ciprofloxacin for 42 strains showed that, 11 Nalidixic acid sensitive S.typhi (NASST) had MIC of 0.015 mg / ml and the rest 31 Nalidixic acid resistant S.typhi (NARST) had MICs ranging 0.25 – 1 mg / ml, showing low-level resistance to Ciprofloxacin. These patients were unresponsive to Ciprofloxacin in the usual therapeutic dose.
Key words: S.typhi, multidrug resistance, Ciprofloxacin resistance
Introduction
Enteric fever is a major public health problem in India accounting for more than 300000 cases per year and S.typhi is the most common etiological agent. (1) Areas with high incidence of typhoid include S.E. Asia, Africa and Latin America. Countries like Indonesia, India and Nigeria report high mortality rate due to typhoid fever ranging from 12 – 32 % in different studies. (2,3,4) These countries seem to share several characteristics including rapid population growth, increased urbanisation, inadequate disposal of human waste, decreased water supply and over burdened health care system.
Chloramphenicol was the drug of choice for Enteric fever since its introduction in 1948. But, in 1970s plasmid mediated resistance to chloramphenicol appeared and has been associated with outbreaks in Latin America (6) and Asia (5.7, 8) . In 1982 less than 15% of the prevalent strains were Chloramphenicol resistant, but by 1988 – 89, multiple drug resistance to Ampicillin, Cotrimoxazole and Chloramphenicol developed in 68.9% of S,typhi isolates in Calicut.(9) Phage types E1 & M1 are usually associated with multiple drug resistance, but others may also be involved. The plasmids conferring resistance are 98 – 120 MDa size and are generally of the H1 incompatibility group (5)
Fluoroquinolones were the drug of choice for MDR S.typhi in Asia for the past decade. But emergence of resistance has become a major problem. The findings in South India were of gradual rise in MIC to Ciproflofloxacin, and similar observations were made in Vietnam (10). So identification of Nalidixic acid resistance by disk diffusion provides a sensitive indicator of low-level resistance to Ciprofloxacin. (11,12)
Material and Methods
A retrospective study was done on the sensitivity pattern of S,typhi isolated from 1995 -2003 in the department of Microbiology Medical college Calicut. The strains were tested for susceptibility to Chloramphenicol 30 mgm, Ampicillin 10 mgm, Trimethoprim-Sulfomethoxazole 1.25 / 23.75 mgm, Ciprofloxacin 5 mgm, Ceftriaxone 30 mgm, and Nalidixic acid 30 mgm by the Kirby-Bauer disc diffusion method. Nalidixic acid screening test was done from 1999 onwards. MIC to Ciprofloxacin was done for 42 strains in 1999 – 2000 by the tube dilution method.
Results
The sensitivity pattern of S.typhi isolates is shown in Table 1& Fig.1. Percentage of MDR S.typhi is shown in Table 2& Fig.2. All the strains were uniformly susceptible to Ceftriaxone. Of the 133 strains subjected to Nalidixic acid screening test 120 strains (90.22%) were resistant to Nalidixic acid (Table 3). MIC of Ciprofloxacin done for 42 strains showed that the 11 strains had MIC of 0.015 mgm / ml and were Nalidixic acid sensitive( NASST). 31 strains had MIC ranging from 0.125 – 1 mgm / ml (Table 4) and were all Nalidixic acid resistant (NARST). Majority of the isolates were sensitive to Chloramphenicol & Cotrimoxazole from the year 2002 unlike the previous years as shown in Table 1.
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Table
1 SENSITIVITY PATTERN OF S.typhi
isolates FROM 1995 - 2003
|
YEAR
|
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1995
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1996
|
1997
|
1998
|
1999
|
2000
|
2001
|
2002
|
2003
|
|
Total
isolates à
|
|
5
|
6
|
23
|
9
|
47
|
19
|
32
|
19
|
16
|
|
Ampicillin
(A)
|
n
|
5
|
6
|
23
|
9
|
47
|
19
|
32
|
19
|
16
|
|
R
|
4
|
4
|
11
|
9
|
34
|
11
|
19
|
14
|
6
|
|
%
|
80
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66.6
|
47.8
|
100
|
72.3
|
57.9
|
59.3
|
73.7
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37.5
|
|
Cotrimoxazole
(Co)
|
n
|
5
|
6
|
23
|
9
|
47
|
19
|
32
|
19
|
16
|
|
R
|
4
|
3
|
9
|
9
|
37
|
12
|
23
|
7
|
6
|
|
%
|
80
|
50
|
39.1
|
100
|
78.7
|
63.2
|
71.8
|
36.8
|
37.5
|
|
Chloramphenicol
(C)
|
n
|
5
|
6
|
23
|
9
|
47
|
19
|
32
|
19
|
16
|
|
R
|
0
|
3
|
6
|
9
|
30
|
10
|
19
|
4
|
2
|
|
%
|
0
|
50
|
26.1
|
100
|
63.8
|
52.6
|
59.3
|
21.1
|
12.5
|
|
Furoxone
(F)
|
n
|
-
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-
|
-
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-
|
13
|
19
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25
|
14
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14
|
|
R
|
-
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-
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-
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-
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1
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4
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4
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1
|
3
|
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%
|
-
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-
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-
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-
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7.7
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21.1
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16
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7.1
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21.4
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Ciprofloxacin
(Cip)
|
n
|
-
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-
|
-
|
9
|
47
|
19
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32
|
19
|
16
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|
R
|
-
|
-
|
-
|
0
|
0
|
2
|
2
|
0
|
2
|
|
%
|
-
|
-
|
-
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