Abstract:
The increasing occurrence of multidrug-resistant (MDR) extended-spectrum
b-lactamase- (ESBL) and/or AmpC b-lactamase-producing Enterobacteriaceae in
health care systems, the environment and fresh produce is a serious concern globally.
Production practices, processing and subsequent consumption of contaminated raw
fruit and vegetables represent a possible human transmission route. The purpose of this
study was to determine the presence of ESBL/AmpC-producing Enterobacteriaceae in
complete spinach supply chains and to characterize the isolated strains phenotypically
(antimicrobial resistance profiles) and genotypically (ESBL/AmpC genetic determinants,
detection of class 1, 2, and 3 integrons). Water, soil, fresh produce, and contact
surface samples (n = 288) from two commercial spinach production systems were
screened for ESBL/AmpC-producing Enterobacteriaceae. In total, 14.58% (42/288)
of the samples were found to be contaminated after selective enrichment, plating
onto chromogenic media and matrix-assisted laser desorption ionization time-of-flight
mass spectrometry identity confirmation of presumptive ESBL/AmpC isolates. This
included 15.28% (11/72) water and 12.12% (16/132) harvested- and processed
spinach, while 25% (15/60) retail spinach samples were found to be contaminated with
an increase in isolate abundance and diversity in both scenarios. Dominant species
identified included Serratia fonticola (45.86%), Escherichia coli (20.83%), and Klebsiella
pneumoniae (18.75%). In total, 48 (81.36%) isolates were phenotypically confirmed as
ESBL/AmpC-producing Enterobacteriaceae of which 98% showed a MDR phenotype.
Genotypic characterization (PCR of ESBL/AmpC resistance genes and integrons)
further revealed the domination of the CTX-M Group 1 ESBL type, followed by
TEM and SHV; whilst the CIT-type was the only plasmid-mediated AmpC genetic determinant detected. Integrons were detected in 79.17% (n = 38) of the confirmed ESBL/AmpC-producing isolates, of which we highlight the high prevalence of class 3
integrons, detected in 72.92% (n = 35) of the isolates, mostly in S. fonticola. Class 2
integrons were not detected in this study. This is the first report on the prevalence of
ESBL/AmpC-producing Enterobacteriaceae isolated throughout commercial spinach
production systems harboring class 1 and/or class 3 integrons in Gauteng Province,
South Africa. The results add to the global knowledge base regarding the prevalence
and characteristics of ESBL/AmpC-producing Enterobacteriaceae in fresh vegetables
and the agricultural environment required for future risk analysis.
