A cross-sectional study was conducted to determine the prevalence of and factors associated with Shiga toxin–producing Escherichia coli (STEC) in raw beef and ready-to-eat (RTE) beef products sold in 31 retail outlets in Pretoria, South Africa, and nearby areas. A total of 463 beef and RTE samples were screened for four STEC virulence genes (stx1, stx2, eaeA, and hlyA) and seven O-serogroups (O113, O157, O26, O91, O145, O111, and O103) with a multiplex PCR assay. The total aerobic plate count (TAPC) per gram was also determined. A total of 38 STEC isolates were recovered and characterized by conventional PCR assay and serotyping. The overall prevalence of STEC in the beef and RTE samples tested was 16.4% (76 of 463 samples; 95% confidence interval, 13 to 20%). The prevalence of STEC differed significantly by product type (P < 0.0001), with the highest prevalence (35%) detected in boerewors (spicy sausage). The STEC prevalences in minced beef, brisket, RTE cold beef, and biltong were 18, 13, 9, and 5%, respectively. The most frequently detected stx gene was stx2 (13%), and STEC serogroups from recovered isolates were detected at the following prevalences: O2, 15%; O8, 12%; O13, 15%; O20, 8%; O24, 3%; O39, 3%; O41, 8%; O71, 3%; O76, 3%; O150, 12%; and O174, 3%. A high proportion (77%) of the samples had TAPCs that exceeded the South African microbiological standards for meat export (5.0 log CFU/g). The prevalence of O157 STEC (16%) and the diversity of non-O157 STEC serogroups found in five common beef-based products from retail outlets in South Africa suggest exposure of raw beef and beef products to multiple contamination sources during carcass processing and/or cutting and handling at retail outlets. These data provide direct estimates of the potential health risk to consumers from undercooked contaminated products and indicate the need to improve sanitary practices during slaughter and processing of beef and beef-based RTE products. A risk-based surveillance system for STEC may be needed. HIGHLIGHTS

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In this study, Listeria isolates (214) were characterized as follows: L. innocua (77.10%), L. monocytogenes (11.21%), L. welshimeri (5.61%), L. grayi (1.40%), L. seeligeri (0.93%), and L. species (3.73%) that were not identified at the species level, from beef and beef based products from retail and farms in Mpumalanga and North West provinces of South Africa. MLVA was further used to type Listeria innocua isolates (165) and Listeria monocytogenes isolates (24). The L. monocytogenes isolates were also serogrouped using PCR. The MLVA protocol for L. monocytogenes typing included six tandem repeat primer sets, and the MLVA protocol for L. innocua included the use of three tandem repeats primer sets. The L. monocytogenes serogroups were determined as follows: 4b-4d-4e (IVb) (37.50%), 1/2a-3a (IIa) (29.16%), 1/2b-3b (IIb) (12.50%), 1/2c-3c (IIc) (8.33%), and IVb-1 (4.16%). MLVA could cluster isolates belonging to each specie, L. monocytogenes, and L. innocua isolates, into MLVA-related strains. There were 34 and 10 MLVA types obtained from the MLVA typing of L. innocua and L. monocytogenes, respectively. MLVA clustered the L. monocytogenes isolates irrespective of sample category, serogroups, and geographical origin. Similarly, the L. innocua isolates clustered irrespective of meat category and geographical origin. MLVA was able to cluster isolates based on MLVA relatedness. The clustering of isolates from farms and retailers indicates transmission of Listeria spp. MLVA is an affordable, simple, and discriminatory method that can be used routinely to type L. monocytogenes and L. innocua isolates.

Healthy colonized cattle are the major reservoir of Shiga toxin-producing Escherichia coli (STEC) and play a key role in the entry point of the pathogen into the beef chain. Excretion rates and the concentration of the pathogen in feces influence the epidemiology and transmission of the pathogen within herds and to humans. This study evaluated the prevalence and dynamics of fecal shedding of STEC by cattle in a commercial feedlot in Gauteng, South Africa. An initial cross-sectional survey was conducted; fecal samples were obtained from 106 randomly selected weaned beef calves on arrival at the feedlot using polymerase chain reaction (PCR) to screen by detecting stx 1 and stx 2 genes. Subsequently, a longitudinal study was conducted, and 15 STEC-positive and 11 STEC-negative cattle were sampled monthly and followed to slaughter. STEC O157 and non-O157 were enumerated in samples using commercial chromogenic agar. Initial prevalence of STEC shedding was 27% (29/106; 95% CI [19, 37%]). All 26 cattle shed STEC intermittently or continuously during the study period, all except one were supershedders (≥4 log 10 CFU/g) at one or more samplings, and 19 (73%) were persistent or intermittent super-shedders. Of the 38 STEC isolates recovered, 15 (39%) were serotypeable, representing 11 non-O157 serogroups, including O101, O168, O178, and O68. The most frequent virulence combination profile was stx 1 + eaeA + ehxA (n = 12; 32%). This study confirms the occurrence and variability of STEC super-shedding in feedlot cattle and highlights that super-shedding is not limited to STEC O157. It also shows their public health significance. | INTRODUCTIONShiga toxin-producing Escherichia coli (STEC) has emerged as an important foodborne pathogen globally and has significantly impacted the beef industry and public health (Callaway, Edrington, Loneragan, Carr, & Nisbet, 2013). Healthy colonized cattle, among other ruminants, are the major reservoir of STEC (Munns et al., 2015), and they play a key role in the entry point of the pathogen into the beef chain (Heiman, Mody, Johnson, Griffin, & Gould, 2015). Beef and beef products are frequently identified as a major risk factor for STEC infections and are thus of public health importance, although other sources such as food crops, water, and environment contribute to infection (Heiman et al., 2015). Majowicz et al. (2014) estimated that STEC (O157 and non-O157) is responsible for 2,801,000 acute illnesses annually, resulting in 3,890 cases of hemolytic uremic syndrome (HUS), 270 cases of end-stage renal disease, and 230 deaths globally. E. coli O157:H7 has been recognized as the serotype most commonly associated with severe infections in both large and sporadic outbreaks (Munns