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OJHAS: Vol. 3, Issue
4: (2004 Oct-Dec) |
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| Drug Resistance in Salmonella
typhi: Tip of the Iceberg |
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Shrikala Baliga
Associate Professor of Microbiology,
Kasturba Medical College,
Mangalore-575001, INDIA
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Address For Correspondence |
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Dr. Shrikala Baliga,
Associate Professor of Microbiology,
Kasturba Medical College, Mangalore-575001, INDIA
E-mail: srikalab@yahoo.com
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| Shrikala Baliga. Drug Resistance in Salmonella Typhi: Tip of the
Iceberg
Online J Health Allied Scs.2004;4:1 |
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Submitted: Feb 10,
2005; Accepted: Feb 10, 2005; Published:
Feb 17, 2005 |
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| Abstract: |
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Salmonella typhi is one of the most resistant organisms with
multi-drug resistant strains reported from many countries. Initially, individual plasmids
were known to code for resistance, but since 1988 a single plasmid has been identified to
code for multidrug resistance. It has been found that in certain areas, S. typhi
has lost this acquired resistance.
Key Words:
Drug resistance, Plasmid,
Salmonella typhi
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Salmonella enterica serotype typhi, the etiological agent of typhoid
fever, is known to be amongst some of the most resistant of pathogens.1,2
Typhoid fever causes 20 million cases annually with at least 700,000 deaths. Typhoid fever
is endemic in many countries including India and if not treated appropriately has a
mortality rate of 30%. Appropriate treatment reduces the mortality rate to as low as 0.5%.1
Salmonella enterica serotype
typhi, the etiological agent of typhoid fever, is known to be amongst some of the most
resistant of pathogens.1,2 Typhoid fever causes 20 million cases annually with
at least 700,000 deaths. Typhoid fever is endemic in many countries including India and if
not treated appropriately has a mortality rate of 30%. Appropriate treatment reduces the
mortality rate to as low as 0.5%.1
Chloramphenicol resistance is known in Salmonella
Typhi since 1972, when plasmids of incompatibility group Inc H, coding for
chloramphenicol resistance were found in S. typhi. Multi drug resistance, (defined
as resistance to all the first line antibiotics used to treat typhoid fever, i.e
chloramphenicol, ampicillin, co-trimoxazole and tetracycline) has been endemic in the
Indian Sub continent and South East Asian countries since 1984. Though initially,
individual plasmids were known to code for resistance to each of these antibiotics, since
1988 a single plasmid was known to code for multidrug resistance. This plasmid belongs to
incompatibility group H I1 and is highly transmissible. Chloramphenicol resistance, MDR S.
typhi and now low level fluroquinolone resistance3 have emerged as the
newer challenges to treatment of typhoid fever.
There is still some light at the end of
the tunnel. It has been seen that in certain areas especially Northern India S. typhi
has lost this acquired resistance and Chloramphenicol resistance has reduced from a high
of 18% to only 2%. This has been noticed in our Institutes also where Chloramphenicol
resistance has reduced drastically over the years (unpublished data, presented at National
conference). It has also been seen that chloramphenicol is still being used to treat
typhoid fever in some areas in Indonesia where 96% of strains remain sensitive to
Chloramphenicol. Low level fluroquinolone resistance is due to point mutations in the gene
coding for DNA gyrase enzyme. This thankfully is not transferable on plasmids. Extended
spectrum beta lactamases, coded by transposons and responsible for resistance to third
generation cephalosporins have been identified in S. typhi. Suitable alternatives
to treat MDR S. typhi include azitromycin, third generation cephalosporins and
carbapenems. Though public health, sanitation and vaccines do have a role to play in
control of typhoid fever, it is the antimicrobial therapy which plays a key role in
management of typhoid fever.
It is likely that S. typhi will
continue to acquire genes responsible for antibiotic resistance. The timely detection of
these genes and prevention of their spread is the need of the hour to control antibiotic
resistance among S. typhi. The article by Mandal et al emphasizes the detection of
plasmids encoding for MDR S. typhi and their transmissible nature. More research
could also be directed towards factors responsible for their spread and means to prevent
dissemination of such plasmids so as to limit drug resistance.
- Cooke FJ, Wain J. The Emergence of
Antibiotic Resistance in Typhoid Fever. Travel Medicine and Infectious Disease
2004; 2:67-74
- Parry CM, Hein TT, Dougan G, White NJ,
Farrar JJ. Typhoid Fever. N Eng J Med 2002; 347(22):1770-82
- Shrikala Baliga, Shalini Shenoy,
K.Vidyalakshmi, Prathibha Pereira: Ciprofloxacin resistance in Salmonella typhi: Natl
Med J Ind. 1999; 12(3):138
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