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Indian Journal of Medical Microbiology, Vol. 28, No. 1, January-March, 2010, pp. 51-53 Brief Communication Emerging Salmonella Paratyphi A enteric fever and changing trends in antimicrobial resistance pattern of salmonella in Shimla *S Verma, S Thakur, A Kanga, G Singh, P Gupta Department of Microbiology (SV, AK, GS, PG), Medicine (ST), IGMC, Shimla - 171 001, India Correspondence Address: *Department of Microbiology (SV, AK, GS, PG), Medicine (ST), IGMC, Shimla - 171 001, India, drsantwana@gmail.com Date of Submission: 29-Nov-2008 Code Number: mb10013 PMID: 20061765 DOI: 10.4103/0255-0857.58730 Abstract This retrospective study incorporates a six years, six months (January 2000-June 2006) laboratory data comprising 258 isolates of Salmonella. Cultures were identified by standard methods. Salmonella enterica serotype Typhi (S.Typhi) was the more frequent serotype isolated i.e., 61.62% with the remaining 38.37% being Salmonella enterica serotype Paratyphi A (S. Paratyphi A). There was emergence of S. Paratyphi A as the predominant serotype in 2003-2004 with resurgence of serotype Typhi thereon. A total of 66.27% isolates were resistant to one or more antibiotics. MDR S. Typhi was 10.69% and while 13.13% were MDR S. Paratyphi A. There was decrease in resistance to ampicillin, cotrimoxazole in 2004 and nalidixic acid beyond 2005 and increase in resistance to cefuroxime. We also documented a decrease in resistance to ciprofloxacin after 2005.Keywords: Nalidixic acid resistant Salmonella typhi, resistance, Salmonella Introduction Typhoid, a global disease, affects 13.5 million individuals each year. [1] Enteric fever (EF) is endemic in India with S. Typhi predominating. Since 1948, chloramphenicol usage decreased case fatality from 20% in pre antibiotic era to 1%. [2] Resistance was first reported from Britain (1950) and India (Kerala) since 1972. [3],[4] Multi-drug resistant (MDR) EF subsequently emerged with epidemic of MDR S. Typhi in 1972 in Mexico and these strains are prevalent in India since 1989. [3],[5] Quinolones emerged as drug of choice. Regrettably, in late 90s, nalidixic acid resistance was noticed with 100% resistance documented from Mumbai. [6] Gravity of problem is escalating in India. Changing resistance pattern, emergence of MDR and nalidixic acid resistant Salmonella typhi (NARST) and switching serotype spectrum instigated us to communicate our data for documentation and retrieval for clinical use. Material and Methods All strains of Salmonella spp. isolated from samples of blood and bone marrow during January 2000 to June 2006 were considered in the present study. Clinical samples of blood and bone marrow were collected in brain heart infusion broth with sterile precautions and incubated aerobically at 37 C for 18-24 hours. Two subcultures were done on blood agar (BA) and Mac Conkey's agar (MA) after 24 hours and 72 hours, incubated aerobically at 37 C. Growth was identified by using standard methods. [7] Antimicrobial susceptibility testing was performed on Mueller Hinton agar by Kirby Bauer's disc diffusion technique (CLSI standards). [8] Each isolate was tested for a set of antimicrobial drugs. These included ampicillin 10 μg, nalidixic acid 30 μg, cotrimoxazole 25 μg (trimethoprim 1.2 μg/sulphamethoxazole 23.8 μg), gentamicin 10 μg, ciprofloxacin 1 μg, netilmicin 10 μg, ceftazidime 10 μg, cefoperazone 30 μg, cefuroxime 30 μ and ceftriaxone with sulbactum 10 μg. The data was analysed by using the Chi Square test and the Fisher exact test depending whether the sample size was more than or less than five respectively. Results A total of 258 isolates of Salmonella species were obtained over duration of six years and six months. These included 255 isolates from samples of blood and three from bone marrow from patients of EF, pyrexia of unknown origin (PUO) or septicaemia. Out of these, 186 were from male patients and 72 from females. Mean age was 25.7 years. Overall, S. Typhi was the predominant serotype isolated in 159 (61.62%) cases whereas S. Paratyphi A accounted for the remaining 99 (38.37%) isolates. The emergence of S. Paratyphi A as the commonest isolate in 2003 was significant (P value # 0.044) with again a reappearance of S. Typhi in 2005 (P value # 0.01). S. Typhi continues to be the commonest serotype since then. Of the total isolates, 171 (66.27%) were resistant to one or more drugs with 105 and 66 being serotype Typhi and Paratyphi A respectively [Table - 1]. MDR i.e., resistance to three or more antibiotics, was noticed in 17 out of 159 (10.05%) isolates of S. Typhi and 13 out of 99 (13.13%) isolates of S. Paratyphi A [Figure - 1]. Although there was wide variation in the patterns of the MDR strains they were not found to be significant. (P value > 0.05). [Table - 2] shows year wise per cent resistance pattern of S. Typhi and S. Paratyphi A to individual antibiotics. Discussion Typhoid fever remained an important cause of morbidity and mortality in the pre-antibiotic era. The disease is more prevalent in the tropics affecting the young and paediatric age groups. Mean age was 25.7 years with a male to female ratio of 2.5:1 which correlates with other studies. [3] There was a progressive increase in S. Typhi and S. Paratyphi A from 2000-2006 with maximum isolates in 2004. Though endemic throughout the year, cases were concentrated during the rainy season. Various studies document S. Typhi as the commonest serovar isolated over the years. [2,9] Our findings corroborate with this view and 61.62% isolates were serotype Typhi and 38.37% being Paratyphi A. There was a significant change in the occurrence of serotype Paratyphi A in comparison to serotype Typhi in the year 2003 (P value < 0.05). But again there was a significant resurgence of serotype Typhi thereafter. Since then, S. Typhi remains the commonest serotype isolated. Emergence of drug resistance has become a confounding factor in the treatment of EF and is a problem that confronts the medical fraternity. The drug resistance pattern of S. Typhi in Shimla as documented in 1993 denoted resistance to the tune of 48.40% for ampicillin, 40.82% for cotrimoxazole, 13.6 1% for nalidixic acid, 13.38% for gentamicin and 3.67% for ciprofloxacin. [10] The comparative data shows contrasting trends over a decade with decrease in resistance to ampicillin (32.94%) and increase in resistance to nalidixic acid (66.47%) and ciprofloxacin (9.41%) with P value < 0.05. This emphasizes the need for such documentation from time to time. Data analysis for S. Paratyphi A also showed a significant (P value < 0.05) decrease in resistance to ampicillin, cotrimoxazole, nalidixic acid after 2004 and increase in resistance to cefuroxime with minimal resistance to ceftriaxone with sulbactum. The present study revealed a rise in resistance to nalidixic acid and ciprofloxacin for both the serotypes Typhi and Paratyphi A over the years till 2005. Increased resistance to ciprofloxacin may further progress to cross-resistance with other agents of fluoroquinolone group. Beyond 2005, no resistance either to or ciprofloxacin was documented in the present communication as treatment regimens comprising higher doses are being used, accounting for decrease in NARST. The most interesting trends revealed by the present study correlate increasing resistance to ciprofloxacin and the isolates gaining sensitivity to ampicillin. Various surveys have reported 16.1% to 83.3% MDR isolates. [4],[11] In the present study there were 30 MDR strains out of the total of 258 isolates constituting 11.62% with 17 isolates being S. Typhi and 13 of S. Paratyphi A. Out of these MDR strains, 18 showed combined resistance to ampicillin and cotrimoxazole accounting for 60% thus establishing an association between the two antibiotic resistance probably being carried by the same plasmid. Although in [Figure - 1] a sharp rise was seen in the emergence of MDR strains of S. Paratyphi A in comparison to the previous years but statistically this change was not significant (P value $ 0.05) due to paucity of the comparative sample size of the previous year. This communication thereby emphasizes the adverse role of indiscriminate use of antibiotics as the factor of utmost significance in drug resistance. Alternative regimens indicated by changing trends of resistance patterns and changing regimens to avoid development of resistance necessitated by selection pressure on organisms which undergo mutations will go a long way in tackling this problem. In this regard, ampicillin has staged a comeback showing favourable response in-vitro and in-vivo. These recommendations must be incorporated in formulating a hospital antibiotic policy. References
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