Are non-lactose-fermenting Escherichia coli important diarrhoeal pathogens in children and adults?

Abstract

Introduction: Diarrhoeagenic Escherichia coli (DEC) remains one of the major causes of acute diarrhoea episodes in developing countries. The percentage of acute diarrhoea cases caused by DEC is 30-40 % in these countries. Approximately 10% of E. coli isolates obtained from stool specimens have been reported to be non-lactose-fermenting (NLF). The available literature is sparse regarding the pathogenicity of NLF E. coli causing infectious diarrhoea.

Aim: We aimed to elucidate the importance of NLF E. coli in causing diarrhoea in both adults and children by detecting various DEC pathotypes among NLF E. coli in stool samples taken from gastroenteritis cases.

Material and methods: A total of 376 NLF E. coli isolates from 3110 stool samples from diarrhoea/gastroenteritis patients were included in the study. Up to three NLF colonies that were not confirmed as Vibrio cholerae , Aeromonas spp., Salmonella spp. or Shigella spp., but were identified as E. coli using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), were carefully picked up from each MacConkey agar plate and then meticulously streaked onto freshly prepared, sterilized nutrient agar plates, and biochemical reactions were conducted. Multiplex PCR was conducted for the EAEC, EPEC, ETEC and EHEC pathotypes and PCR for the ipaH gene was conducted for EIEC. The disc diffusion method was used for antibiotic sensitivity testing.

Results: Using multiplex PCR and ipaH PCR, a total of 63 pathotypes of DEC were obtained, with EAEC being the most predominant (n=31) followed by EIEC (n=22), EPEC (n=8) and ETEC (n=2). To further differentiate EIEC from Shigella , additional biochemical tests were performed, including acetate utilization, mucate and salicin fermentation, and aesculin hydrolysis. Antimicrobial susceptibility testing (AST) showed that maximum resistance was seen against ciprofloxacin (82.5 %) followed by ampicillin (77.8 %) and cotrimoxazole (68.2 %), and minimum resistance was seen against ertapenem (4.8 %).

Conclusion: In our study two pathotypes (EAEC, EIEC) were predominant among NLF E. coli and these were not only important aetiological agents in children, but also in adults. Our study also sheds light on the epidemiology of EIEC, which is one of the most neglected DEC pathotypes, as hardly any microbiological laboratories process NLF E. coli for EIEC.

Keywords: Escherichia coli; adults; diarrhoea; enteroinvasive Escherichia coli; non-lactose-fermenting.

Fig. 1.

Flow chart showing the scheme of the study.

Fig. 2.

Biochemical reactions for EIEC. (a) Acetate utilization test (green, negative; blue, positive). (b) Mucate fermentation (blue, positive; yellow, negative). (c) Lysine derboxylase (yellow, control; purple, positive). (d) Positive indole test. (e) Salicin fermentation (colourless, negative; pink, positive). (f) Glucose fermentation with gas/without gas. (g) Bile aesculin hydrolysis (yellow, negative; black, positive). (h) Triple sugar iron (K/A with gas formation).

Fig. 3.

A representative gel electrophoresis profile of DEC genes. Lane 1, EPEC (eae); lane 2, EAEC (pCVD432); lane 3, positive control (PC); lane 4, EPEC (eae); lane 5, negative contol (NC); lane 6, DEC gene was not detected; lane 7, EAEC (pCVD432), lane 8, ladder (100 bp).

Fig. 4.

A representative gel electrophoresis profile of the ipaH gene. Lane 1, EIEC (ipaH); lanes 2, 3, 4, 5, ipaH gene was not detected; lane 6, EIEC ; lane 7, 8, ipaH gene was not detected; lane 9, positive control (PC); lane 10, EIEC (ipaH); lanes 11, 12, 13, 14, 15, ipaH gene was not detected; lane 16, negative control (NC); lane 17, ladder (100 bp).