ISRAEL JOURNAL OF
VETERINARY MEDICINE
Vol. 57 (2)
2002
IS ESCHERICHIA COLI O157:H7 AN
ETIOLOGICAL AGENT OF BOVINE MASTITIS?
H. Turutoglu and S. Mudul
Department of Microbiology, Faculty of Veterinary Medicine, Akdeniz
University, 15100 Burdur, Turkey.
Abstract
The presence of Escherichia coli O157:H7 serotype in raw milk raises the question
whether the same serotype is a causative agent of bovine mastitis. For this purpose, E.
coli strains isolated from 382 mastitic bovine milk samples were cultured on Sorbitol
MacConkey (SMAC) agar and tested by latex agglutination assay. None of the strains was
identified as E. coli O157:H7.
Key words: Mastitis, bovine, Escherichia coli O157:H7.
Introduction
Escherichia coli is ubiquitous in the cow’s environment that is contaminated by faeces [1,
2]. It is also a frequent cause of bovine mastitis [1]. Jones [2] reported that the E. coli
serotypes in mastitic milk were similar to faecal isolates. It is known that the O157:H7
serotype of E. coli isolated from raw milk samples [3, 4], was of faecal origin [5, 6]. This
can cause severe diseases such as bloody diarrhea, haemorrhagic colitis, and haemolytic
uraemic syndrome in humans [7, 8]. Although other faecal E. coli serotypes are known to
cause bovine mastitis [2, 9], the role of E. coli O157:H7 is obscure. The purpose of this
study was to investigate whether E.coli O157:H7 is a causative agent of bovine mastitis.
Materials and Methods
Collection of samples: Dairy cows located in 49 different farms of Burdur province were
examined for mastitis clinically and by the California mastitis test. Approximately 10 ml
milk were collected into sterile universal bottles from mastitic quarters of dairy cows.
Bacteriological examinations: A total of 382 mastitic milk samples were cultured on 10
% sheep blood agar and MacConkey agar plates. Plates were incubated in aerobic
conditions at 370C for 24-48 hours. Colonies were identified as E. coli by conventional
methods. A part of a single colony of E. coli isolates was sub-cultured on Sorbitol
MacConkey (SMAC) agar (Oxoid, CM813) and incubated at 350C overnight.
O157 antigen determination: Latex agglutination was performed on all E. coli colonies to
determine whether any of the isolates expressed the O157 antigen (Oxoid, DR620).
Results
Of 382 mastitic milk samples examined, 260 (68 %) yielded aerobic bacteria;
Staphylococcus aureus was present in 26.2 %,
coagulase negative staphylococci in 20.9%, E. coli in 13.0 %, Streptococcus uberis in 10.9
%, Streptococcus dysgalactiae in 6.3%, Streptococcus agalactiae in 1.6 %, Citrobacter
freundii and Candida albicans in 1.0%, Actinomyces pyogenes, Pseudomonas
aeruginosa, Enterobacter aerogenes and Bacillus spp. in 0.5 %. Two organisms (mainly
coagulase negative staphylococci and Streptococcus uberis) were isolated from 50
samples and three organisms from one sample. No pathogens were found in 122 mastitic
milk samples.
It was observed that the sub-cultured 50 E. coli strains that fermented sorbitol in SMAC
agar within 24 hours didn’t produce agglutination in the 0157 latex assay, therefore none
of the strains was serotyped as E.coli O157:H7.
Discussion
E. coli is widely distributed in nature and is frequent cause of bovine mastitis [1, 2]. In this
study of 382 mastitic milk samples taken from dairy cows, E. coli strains were isolated
from 50 of them (13.0 %).
Cattle are suspected to be an important reservoir of E. coli O157:H7 for humans [10, 11,
12, 13]. Although this serotype was associated with severe disease in humans [7, 8, 10],
Orskow et al.[10] reported that E. coli O157: H7 was not a common isolate from sick
animals. In this study, its presence was investigated in 382 mastitic milk samples, while
none of the isolated E. coli strains was identified as O157:H7. This result supports the
findings of Orskow et al. [10], Padhye and Doyle [3] and Rubini et al. [4] who reported that
E. coli was frequently isolated from raw milk samples. In this study, milk samples were
taken under aseptic conditions to reduce contamination of the milk samples with bovine
faeces.
The characteristics that differentiate this organism from most other E. coli strains include
-glucuronidase
activity [5, 14, 15], the expression of O157 and/or H7 antigens [5, 16] and the
ability to produce verotoxins [5, 7]. SMAC agar that was developed originally to isolate E.
coli O157:H7 has been used successfully in similar studies [5, 14, 15] and was
recommended for E. coli O157:H7 isolation by Hammack et al. [15]. In the present study,
the 50 sub-cultured E. coli strains on SMAC agar fermented sorbitol within 24 hours and
did not form white colonies. In addition, it was observed that none of these strains
produced agglutination with the O157 latex assay.
These findings indicate that E. coli O157:H7 does not cause bovine mastitis in samples
from Burdur province. However, we recommend that it is also necessary to examine
whether E. coli O157:H7 is a causative agent of bovine mastitis in clinical trials.
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