Salmonellosis in the systemic form due to multiple drug resistant Salmonella typhimurium.
Salmonellosis, a term often restricted to the gastro-intestinal tract infections caused by salmonellae other than Salmonella typhi and paratyphoid bacilli, is often a self limiting disease. Recently, however, cases of systemic disease due to Salmonella typhimurium and other salmonellae have been reported.,, The present study was undertaken to assess the incidence of Salmonella typhimurium in cases of diarrhoea and to see how often they manifested in a systemic form. It was also intended to study the problem of drug resistance in these salmonellae since antibiotics may be essential for the treatment of systemic diseases.
The study covered a period of 6 months. Faeces, blood, clot, C.S.F. and urine cultures, sent to a large general hospital, were processed following standard procedures for isolation and identification.
The isolates of Salmonella typhimurium were typed biochemically and serologically. Antibiotic disc sensitivity using gentamicin, kanamycin, tetracycline, ampicillin, chloramphenicol and streptomycin was evaluated by the Kirby-Bauer method and the minimum inhibitory concentrations were determined by a standard tube dilution method. The strains of Salmonella typhimurium were sent to The Salmonella Phage Typing Centre, Lady Harding Medical College, New Delhi for phage typing and case histories of patients were noted.
Preliminary studies on the trasferability of resistance were conducted to detect the presence of R plasmid by transfering them directly to Esch. colt K 12 L + Nalr. The conjugation procedure followed was as described by Neu et al.
Over a period of 6 months, 370 faeces and 604 blood and clot cultures were studied. As many as 40 salmonellae were isolated from faeces, of which 39 were Salmonella typhimurium; seventy six of the blood and clot cultures yielded salmonellae of which 14 were identified as Salmonella typhimurium. During the same period, of the 1,058 C.S.F. and 2,240 urine samples studied, there were 3 and 2 isolates of salmonellae respectively, all of which were Salmonella typhimurium.
[Table - 1] shows the age distribution of cases from which Salmonella typhimurium were isolated from faeces and blood. Thirty (76.9%) and 11 (78.6%) of the isolates of Salmonella typhimurium isolated from faeces and blood respectively, were present in children upto 1 year of age.
[Table - 2] illustrates the isolation frequency of Salmonella typhimurium with respect to symptoms. The first 3 cases described in the table are those of salmonella meningitis; Salmonella typhimurium was isolated from faeces, blood and C.S.F. In the next 2 cases, diagnosed as urinary tract infection, only 1 patient gave history of diarrhoea, and Salmonella typhimurium was isolated from faeces, blood and urine.
The other patient gave no history of diarrhoea, and Salmonella typhimurium was isolated only from blood and urine but not from the faeces. The next 7 cases diagnosed as P.U.O. or septicaemia gave a history of diarrhoea but Salmonella typhimurium was isolated only from the blood.
[Table - 3] outlines the resistance pattern of the isolated strains of Salmonella typhimurium to the commonly used antibiotics. The antibiograms of the isolates were confirmed by MIC determination; The MIC of resistant strains was over 128 µg/ml for various antibiotics used.
The Salmonella Phage Typing Centre, New Delhi, reported that all these strains were untypable.
Preliminary genetic studies showed that 21 strains of Salmonella typhimurium had auto transferable R plasmids.
The incidence of diarrhoea due to Salmonella typhimurium is not alarming as it constitutes only about 10% of the total cases of diarrhoea.
The present study reveals that salmonellosis and systemic invasion due to Salmonella typhimurium are more common in children than in adults. Similar findings have been reported by others workers.,
Most of the strains of Salmonella typhimurium isolated, were resistant to drugs like streptomycin, ampicillin, kanamycin and chloramphenicol. This data is very disturbing since the isolates from blood were resistant to the commonly used antibiotics. Similar drug resistance has been observed by Panhotra et al and Koshi.
Strains of Salmonella typhimurium sent for phage typing were reported untypable. R plasmids, besides conferring drug resistance at times, also alter the susceptibility of these bacteria towards indicator phages. This causes a problem in epidemilogical studies.
It is generally accepted that multiple drug resistance is almost invariably due to R plasmids; However, the incidence of auto transferable plasmids in the isolates in the present study was not high. It is possible that drug resistance was conferred by auto transferable plasmids in some and non-auto transferable plasmids in others. It may thus be emphasized that in cases of septicaemias, meningitis or urinary tract infections, the likelihood of multidrug resistant Salmonella typhimurium must be considered, especially when there is a history of diarrhoea.
The authors are thankful to the Dean, L.T.M. Medical College, Sion, for allowing them to publish this paper.