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Year : 2016  |  Volume : 59  |  Issue : 3  |  Page : 327-329
Emerging enteric fever due to switching biotype of Salmonella (paratyphi A) in Eastern Odisha

1 Department of Microbiology, AIIMS, Bhubaneswar, Odisha, India
2 Senior Resident in Microbiology, S.C.B. Medical College, Cuttack, Odisha, India
3 Senior Resident in Microbiology, AIIMS, Bhubaneswar, Odisha, India
4 Department of Pathology, Former Head of Operation, SRL Diagnostics, Bhubaneswar, Odisha, India
5 Department of Anaesthesiology, Chief Consultant ICU, Shanti Memorial Hospital Pvt. Ltd., Cuttack, Odisha, India

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Date of Web Publication10-Aug-2016


Background: Typhoid fever is classically caused by Salmonella enterica serotype typhi.Recently the frequency of isolation of S. paratyphi A (SPA) has been increased in comparison to S. typhi in Indian scenario. Aim: To observe the rate of isolation and antimicrobial susceptibility pattern of SPA from suspected enteric fever cases attending tertiary care centres of Eastern Orissa. Settings and Design: Retrospective study Materials and Methods: 1488 blood samples were collected during different duration of fever and cultured in BACTEC blood culture system and bottles showing signal for growth were subcultured and identified as Salmonella spp. by standard procedure and mini API (Biomeriux) and antimicrobial susceptibility by disc diffusion method. Statistical Analysis: Chi square test. Results: 167 Salmonella spp. were isolated including 83.8% Salmonella paratyphi A and 16.6% S. typhi. Among them 102 were males and 65 were females with mean age of 22.7 yrs. S. paratyphi A was the predominant spp. each year but during 2008 – 2011, there was a dramatic rise (significant P value- 0.034). Multidrug resistance was noticed in 10.2% of the isolates. 98% of S. paratyphi A were resistant to nalidixic acid and 41% to ciprofloxacin, but the MIC of ciprofloxacin was raised between 1-2 μgm/dl showing the relation between nalidixic acid resistance and raised MIC of ciprofloxacin. Conclusion: Nalidixic acid should be tested along with ciprofloxacin disc while testing for susceptibility and MIC of ciprofloxacin is mandatory before advocating therapy to prevent treatment failure.

Keywords: Enteric fever, Salmonella paratyphi A, susceptibility

How to cite this article:
Mahapatra A, Patro S, Choudhury S, Padhee A, Das R. Emerging enteric fever due to switching biotype of Salmonella (paratyphi A) in Eastern Odisha. Indian J Pathol Microbiol 2016;59:327-9

How to cite this URL:
Mahapatra A, Patro S, Choudhury S, Padhee A, Das R. Emerging enteric fever due to switching biotype of Salmonella (paratyphi A) in Eastern Odisha. Indian J Pathol Microbiol [serial online] 2016 [cited 2022 Jan 26];59:327-9. Available from: https://www.ijpmonline.org/text.asp?2016/59/3/327/188124

   Introduction Top

Typhoid fever is the most serious form of enteric fever and humans are the sole reservoir of  Salmonella More Details. Based on a recent survey, the global number of typhoid cases have exceeded 21,000,000 with more than 20,000,000 deaths per year.[1] In India also, this is a major public health problem accounting for more than 300,000 cases per year.[2] It is classically caused by Salmonella enterica serotype typhi.[3]S. enterica serotypeparatyphi A (SPA) causes a milder form of the disease and had been reported less frequently (3.17%) in India. But, since 1996, the frequency of isolation of Salmonella paratyphi has been increased in comparison with Salmonella typhi in Indian scenario.[4] A 5-year retrospective study in New Delhi have documented the rise in proportion of SPA from 6.5% in 1994 to 44.9% in 1998.[5] A similar increase in S. paratyphi isolation has been reported from Rourkela, Odisha, in the year 2007.[6] A variation in antimicrobial susceptibility pattern of SPA has also been reported from different parts of the country. The present study was designed to observe the rate of isolation and antimicrobial susceptibility pattern of SPA from suspected enteric fever cases attending tertiary care centers (SRL Diagnostics, Bhubaneswar, SCB Medical College, Cuttack and Shanti Memorial Hospital, Cuttack) in Odisha.

   Materials and Methods Top

A retrospective study was conducted from April 2006 to March 2011 on blood samples in the Department of Microbiology, SRL diagnostics, Bhubaneswar, which received samples from all over Odisha. A total of 1488 blood samples were collected from suspected enteric fever cases during a period of 5 years. Out of the 1488 blood samples, 72% were collected during the end of 1st week and 28% between 12th and 14th days of fever. About 5–10 ml of blood in case of adults and 1–5 ml in case of children were collected and inoculated to BACTEC blood culture bottles and incubated in the BACT ALERT system at 37°C. The bottles showing signal were immediately removed and subcultured on MacConkey agar and the nonlactose-fermenting translucent colonies were subjected for identification as per the standard procedures.[7]Salmonella spp. was identified as Gram-negative, motile, glucose, mannitol fermenting, sucrose and lactose nonfermenting, catalase positive, oxidase negative, indole negative, MR positive, citrate negative, urease negative, and H2S and lysine positive in S. typhi and negative in SPA. The identified isolates were confirmed by mini API (Biomeriux), which also showed 98.8% probability. Antimicrobial susceptibility patterns were determined using commercially available discs from Himedia – nalidixic acid (30 μg), ciprofloxacin (5 μg), chloramphenicol (30 μg), cefotaxime (30 μg), cotrimoxazole (1.25 + 23.75 μg), and ampicillin (30 μg). Kirby–Bauer disc diffusion method was followed for susceptibility test in Muller–Hinton agar and interpreted according to the zone diameter in the published table. Each set of new antibiotic discs was tested with standard  Escherichia More Details coli NCTC 10418. Minimum inhibitory concentrations (MICs) for ciprofloxacin were tested by agar dilution method.[8] The concentrations tested for MIC were doubling dilutions from 0.25 to 16 μg/dl.

   Results Top

Hundred and sixty-seven isolates of Salmonella spp. were obtained over a period of 5 years. Among those, 102 were from males and 65 were from females with a mean age of 22.7 years. Predominant Salmonella spp. isolated was S. paratyphi A in 140 (83.8%) cases whereas S. typhi accounted for only 27 (16.16%) cases. When the emergence of SPA was taken into account in different years, it was the predominant Salmonella spp. in each year [Table 1], but during the year 2006–7 and 2007–8, the occurrence of SPA in comparison to S. typhi was not statistically significant (P > 1.01 and >0.05). However, during the period of 2008–11, there was a dramatic rise of SPA isolates in all the years with a significant P value. However, the number of S. typhi isolates remained almost unchanged throughout the years. Out of the 27 S. typhi, 13 were sensitive to all the drugs tested. Multiple drug resistance (MDR), that is, resistance to >3 drugs was noticed in 6 isolates and resistance to >5 drugs was noticed in 7 isolates. One isolate was resistant to chloramphenicol (zone of inhibition [ZOI] <12 mm). Regarding the SPA isolates, 98% were resistant to nalidixic acid (ZOI <13 mm) and all were sensitive to ampicillin (ZOI >17), chloramphenicol (ZOI >18), and 93% to cotrimoxazole (ZOI >16). Sensitivity to ciprofloxacin (ZOI ≥31 mm) was 59% and cefotaxime (ZOI >23 mm) was 54%. MDR showing resistance to >3 drugs was noticed only in 10.2% of isolates in SPA. The MIC of ciprofloxacin was found to be 1–2 μg/dl.
Table 1: Year-wise isolation of Salmonella spp. from 2006 April to 2011 March

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   Discussion Top

Salmonella is Gram-negative, motile, nonspore-forming bacilli, and can be differentiated into >2400 serotypes by their somatic “O” antigens. There are six serogroups, namely A, B, C, C2, D, and E. Although any Salmonella serotypes can produce any form of the Salmonella syndromes, each serotype tends to be associated with certain syndromes much more frequently than others. S. typhi and S. paratyphi are more likely to cause enteric fever as well as the chronic carrier state. The species of Salmonella which can cause paratyphoid fever are S. paratyphi A, B, and C.[9] As a result of modern sewage and water treatment facilities, these diseases have become rare in developed countries, but frequent in countries without adequate sanitation and safe water supply. The syndrome of enteric fever is characterized by prolonged sustained fever, relative bradycardia, hepatosplenomegaly, rose spots, leukopenia, and neutropenia. The illness usually resolves by the end of the 4th week in an untreated patient. The differential diagnosis is very broad and depends on the part of the area of the world in which the infection was acquired. In the present study, 167 isolates of Salmonella spp. were obtained over a period of 5 years. A retrospective analysis of laboratory records from April 2006 to 2008 showed an increased rate of isolation of SPA from suspected cases of enteric fever similar to the findings of our prospective analysis during April 2009–11.[3] However, there is a dramatic rise in the number of SPA isolates in the years 2009, 2010, and 2011 [Table 1] as compared to previous years. Again in comparison to the progressive rise in SPA, there was no such change in the isolation of S. typhi in all the 5 years. Various studies have documented S. typhi as the most common serovar isolated over the years.[10],[11] A study at Kasturba Hospital, Sevagram, had reported enteric fever due to SPA (45.45%) as an emerging problem in the year 2004.[12] Nearly, 46.15% of SPA had also been reported from Nagpur during the years 2000–2002.[13] This dramatic switching of biotype SPA from S. typhi could be due to the widespread use of quinolones against S. typhi in the past decades.[4] In our study, 13 isolates of S. typhi were sensitive to nalidixic acid, but 98% of SPA were resistant, similar to the reports during 2009.[3] A report from Calicut also documented 78.6% resistance to nalidixic acid during 2002 and 100% during 2003.[2] As nalidixic acid is a 1st generation quinolone, its resistance is a marker for predicting low-level resistance to ciprofloxacin and an indicator of treatment failure. The cause for this may be a mutation in DNA gyrase, a mechanism for ciprofloxacin resistance which also correlates with resistance to nalidixic acid.[14] However, other mechanisms of resistance such as decreased permeability and active efflux of the antimicrobial agent may be involved.[15] No such mutations have been reported yet in S. typhi, although there are sporadic reports of complete fluoroquinolone-resistant isolates. MDR was noticed in 10.2% of isolates among SPA in our study. Its emergence in other parts of the country (11.1% Nagpur and 13% in New Delhi) warrants the judicious use of antibiotics.[5],[13] Regarding other drugs, 98% of SPA isolates were resistant to nalidixic acid and all were sensitive to ampicillin and chloramphenicol followed by cotrimoxazole (93%). Verma et al. had also reported cefotaxime + sulbactam combination to be highly sensitive in comparison to cefotaxime alone.[16] In our study, sensitivity to ciprofloxacin was 59% and cefotaxime was 54%. The MIC of ciprofloxacin was found to be 1–2 μg/dl. Hence, our study also showed that resistance to nalidixic acid was generally associated with increased MIC of ciprofloxacin as reported by others.[3],[10] Most of the isolates in this study were found sensitive to chloramphenicol, ampicillin, and cotrimoxazole. Hence, the above drugs could be considered for the treatment of typhoid fever. Replacement of ciprofloxacin as the drug of choice for enteric fever would have led to the withdrawal of selective pressure resulting in re-emergence of chloramphenicol susceptibility.[3] Regarding prophylaxis, the typhoid disease is primarily associated with poor hygiene and sanitary condition, so mainly the developed countries bear the brunt of the disease. Around 5 million cases occur annually in India.[16] A major problem in the last 2 decades of the 20th century has been the emergence of plasmid-encoded MDR, especially to the quinolones. As the mode of transmission is via feco-oral route, the best solution would be to provide entire population with treated and bacteriologically monitored water for drinking purpose and proper sanitation of disposal of human waste. However, such principle of hygiene and public health remains at best a distant reality and the only practical viable option is vaccination. The various types of typhoid vaccines available are parenteral whole cell vaccine - initially TAB - a combination of typhoid and paratyphoid A and B. But, subsequently, it was realized that paratyphoid is a less common cause of enteric fever and the vaccines have poor protection, then it became TA and subsequently T vaccine, that is, S. typhi. This may be another cause of emergence of S. paratyphi A in recent years. The widely used live oral vaccine is Ty21a using a mutant strain of S. typhi at gal E gene which results in lacking enzyme uridine diphosphate galactose - 4 epimerase necessary for capsular polysaccharide formation, which is the major virulence factor of S. typhi. Capsular polysaccharide vaccine is a new generation subunit vaccine which stimulates B-cells directly, but not T-cells, so memory cells are not produced and antibody response is not boosted by additional doses.[17]

To conclude, the present study reports SPA to be the predominant cause of enteric fever with higher sensitivity to chloramphenicol, ampicillin, and cotrimoxazole. Moreover, empirical treatment with ciprofloxacin must be avoided. To avoid treatment failure, routine susceptibility testing of ciprofloxacin should be accompanied with nalidixic acid susceptibility even in cases showing ciprofloxacin sensitivity because nalidixic acid resistance is associated with increased MIC of ciprofloxacin, though falling in susceptible range.

Financial support and sponsorship

This study was supported by SRL Diagnostics, Bhubaneswar, Odisha.

Conflicts of interest

There are no conflicts of interest.

   References Top

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Correspondence Address:
Dr. Ashoka Mahapatra
Department of Microbiology, AIIMS, Bhubaneswar - 751 019, Odisha
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.188124

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