The spectrum of antibiotic resistance in human and veterinary isolates of Escherichia coli collected from 1984-86 in northern India.

This study was undertaken to assess the spectrum of drug resistance prevalent in Escherichia coli isolates from human and animal populations in Northern India. Three hundred and two isolates of Escherichia coli isolated from various infections of humans (47 from diarrhoea; 101 from urinary tract infection) and veterinary animals (17 from poultry septicaemia; 75 from bovine diarrhoea; 14 from ovine diarrhoea and 48 from equine metritis) were studied for their susceptibility to ampicillin, cephaloridine, amoxycillin, cloxacillin, oxytetracycline, doxycycline, chloramphenicol, gentamicin, and trimethoprim-sulphamethoxazole. 63.2% of the isolates (37.7%, human; 25.5%, animal) were resistant to one or more drugs, of which about 41% isolates were multiresistant. Resistant isolates had a wide range of MIC values from 12 to 3200 mg/L, irrespective of origin. Most of the isolates (43.5%) were resistant to ampicillin (MIC greater than 16 mg/L) followed by oxytetracycline (MIC greater than 5 mg/L) (36.4%). Only 9.3% isolates were resistant to trimethoprim-sulphamethoxazole (MIC greater than 21 mg/L). The E. coli isolated from animals tended to be resistant to fewer antibiotics than those isolated from man. 99% of the isolates from human urinary tract infection were resistant compared to only 48.9% of the isolates from diarrhoea. Most of the resistant isolates from animals were recovered from diarrhoea, followed by septicaemia and metritis. This study shows that a high frequency of multiresistant strains are prevalent in both human and animal bacterial populations of Northern India. Since the exchange of these strains among both populations is possible, they pose a great risk in both the selection and the spread of resistance.

Guinea-pig ileal loop assay: a better replacement of the suckling mouse assay for detection of heat-stable enterotoxins of Escherichia coli.

The suitability of guinea-pig ileal loop assay (GILA) for the assay of heat-stable (ST) enterotoxin was confirmed. Secretory response against Escherichia coli heat-stable enterotoxin in this model was determined in terms of dilatation index (DI). DI equal to 0.50 or more was considered as a positive secretory response. Kinetics of fluid accumulation and the titration of toxin in guinea-pig ileal loop suggest uniform secretory response throughout the small intestine and 31.5 microgram of crude ST toxin as the minimum effective dose to induce a DI of 0.5. Guinea-pig intestine was found sensitive to both methanol soluble (STa) and methanol insoluble (STb) toxins of E. coli and so was considered superior to the existing suckling mouse assay (SMA), which is known to be sensitive only to STa toxin. In addition, GILA was also found to be more suitable and economical as at least 10 strains together with the positive and negative controls can be tested in one animal, whereas in SMA, four suckling mice were needed to test a single strain. Hence, in SMA individual susceptibility among mice cannot be ruled out. GILA was considered to be an alternative to the presently available test, SMA, in the determination of ST toxin of E. coli.

Development of Vero cell miniculture assay for detection of heat-labile enterotoxin of Escherichia coli and its significance.

In the present study the Vero cell miniculture assay was developed for the detection of heat-labile enterotoxin of E. coli. The test was found to be reliable and efficient and was comparable with other tissue culture assays. The new cell lines BHK21, MDBK, LM and CK included in the present study did not respond positively to the E. coli toxins.

Drug resistance and colicin production among various serotypes of Escherichia coli of animal origin.

One hundred and twenty two strains of E. coli isolated from clinical conditions of animals were studied for the production of colicins and their sensitivity behaviour towards 16 antibiotics and trimethoprim-sulphamethoxazole. Out of 122 strains, 27 (22.1%) were found colicinogenic and 25 (93%) of these colicinogenic strains were found resistant to one or more of drugs in various combinations. All the 27 colicinogenic strains could be typed into 15 serogroups. Serogroup 084 was found predominant. Transfer of R-plasmids and Col-plasmids were observed in 5 (18.5%) strains individually. In one strain both drug resistance and colicin production determinants were transferred enblock. Such transconjugants will be more invasive and virulent and will create serious chemotherapeutic problems.