Food Protection Trends - September 2010 - 536

FIGURE 1. Bacterial populations of aerobic bacteria (black bar), total Enterobacteriaceae (dotted bar), coliforms (checked bar), E. coli (striped bar) and presumptive Staphylococcus aureus (white bar) counts obtained from 150 biltong samples (lower detection limit = 1 log CFU/g). {pH ranges associated with samples.}

below the lower detection limit (Fig. 1). The presence of E. coli, an index organism, traditionally highlights the suspected presence of other pathogens, such as Salmonella, as they are capable of surviving in the same environmental niches (17). However, Salmonella was absent from all biltong samples tested in this study. SAC counts showed that convenience stores, followed closely by slaughterhouses and biltong bars, were associated with samples with higher SAC counts than the other points-of-sale; indeed, all SAC counts observed were below 3 log CFU/g (Fig. 1). As Staphylococcus populations are often native to the human nose, throat and skin, high Staphylococcus counts are often indicative of poor human handling practices (15).

Presence of bacterial pathogens in biltong S. aureus
After the screening of 159 presumptive Staphylococcus isolates obtained from biltong samples, 15 isolates were singled out as presumptive S. aureus strains and further identified with 16SrDNA sequencing. Results from molecular analysis showed that of the 15 isolates, only 3 were confirmed as S. aureus (accession numbers

FJ392795, FJ392802 and FJ392805) . The other 12 were identified as S. pasteuri (FJ392791 – FJ392793, FJ392796 – FJ392799, FJ392801, FJ392803 and FJ392804), S. saprophyticus (FJ392800) and Macrococcus caseolyticus (FJ392794). All 15 isolates were also tested for enterotoxin production. Results showed that 3 isolates produced enterotoxin B, including 2 strains (FJ392795 and FJ392802) identified as S. aureus (99% seq-uence similarity to S. aureus ATCC 14458). Enterotoxin B-producing strains are reportedly the serotypes that are the third most common in terms of being, associated with food poisoning events, after enterotoxins A, and D (4). Interestingly, a strain of S. pasteuri (FJ392798) (99% sequence similarity to S. pasteuri AF041361) also produced a positive reaction to enterotoxin B. Although enterotoxin production is often characteristic of coagulase-positive Staphylococcus strains such as S. aureus, it is not limited to these organisms (20, 25). Even though S. pasteuri strains are often associated with food commodities (18), there is no record of this species having been implicated in foodborne illness outbreaks. The presence of enterotoxin producing S. aureus in biltong could potentially be attributed to the high concentration of salts, acidic pH (25) and increased aw

of a moister biltong product, especially since strains of S. aureus are capable of growth and enterotoxin production at aws of 0.85 (24, 25). It is reported that the modern consumer markets favor more moist biltong, which is considered more appealing to the palate (12). Traditionally, dried biltong has a water activity (aw) of 0.77 (12); however, the favored biltong has 40% more moisture than traditional biltong and an aw of between 0.85 and 0.93 (12, 24) which supports the growth of several pathogens.

L. monocytogenes
The findings of this study showed that 2 of the 150 (1.33%) biltong samples tested positive for L. monocytogenes (accession numbers FJ160766 and FJ160767). In comparison, the prevalence of L. monocytogenes observed in this study was 1% higher than that observed in a study on jerky (1). Although the minimum dose of L. monocytogenes cells required to cause foodborne illness is variable, foodborne illness has often been coupled with elevated levels of this pathogen in a consumed food product (22). Biltong would generally be considered a potentially unfavorable environment for L. monocytogenes because of its

536 FOOD PROTECTION TRENDS | SEPTEMBER 2010
Food Protection Trends - September 2010

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