Characterization and virulence factors distribution of blaCTX-M and
mcr-1 carrying Escherichia coli isolates from bovine mastitis
Abstract
Escherichia coli is considered as one of the critical pathogens causing
contagious mastitis. The aim of the current study was to investigate the
occurrence of ESBL and colistin resistant E. coli and its genotypic
characterization and identification of virulence determinants in cases
of bovine mastitis in Jiangsu Province, China. Five hundred and
thirty-five (535) milk samples presenting mastitis symptoms were
collected from three dairy farms. Susceptibility testing was identified
by micro-dilution method. E. coli isolates were used to detect ESBL
genes (blaCTX-M, blaSHV and blaTEM) as well as COL-resistant genes
mcr-(1-9). Multiplex PCR approach was used for the detection of major
CTX-M groups, different phylo-groups, and virulence genes. The clonal
relationship of the isolates was then evaluated with MLST, MLSA and
PFGE. Multi-drug resistance (MDR) was found in more than 85% of ESBL
and/or COL resistant E. coli isolates. Genotypic characterization
indicated a dominance of CTX-M-1 group, and the most prevalent alleles
observed in this study were blaCTX-M-28 (38.37%), blaCTX-M-14
(17.44%), blaCTX-M-66 (13.95%), blaCTX-M-55 (10.46%), and blaCTX-M-69
(6.97%), blaCTX-M-15 (4.65%), blaCTX-M-177 (4.65%), and blaCTX-M-148
(3.48%). The results confirmed that group A was the most predominant
group with 54.73%, followed by group B1 and B2 (24.21%, 10.52%)
respectively. The targeted virulence genes were detected in 97.89%
(n=93) isolates. All isolates belong to group A, B1, B2, C, D, and E
showed the presence of virulence factors. Among virulent genes ompC, was
detected in 97.89% (n=93) isolates followed by fimH in 61.05% (n=58),
ECs3703 57.89% (n=55), ompF 50.52% (n=48). MLST and PFGE of the 22 E.
coli isolates were determined for clonal relatedness and yielded clear
fingerprint patterns. Majority of the E. coli isolates carrying ESBL and
mcr-1 isolates were clonally unrelated. Sequence types 58 and ST410 were
the most predominant comprising 2 each (2/20=20%).