Indicator and Pathogenic Bacteria in Guacamole and Their Behavior in Avocado Pulp

Abstract

The presence of some indicator microorganisms and pathogenic bacteria in guacamole sampled from restaurants and street vendors, and the behavior of Salmonella spp., Staphylococcus aureus, and Escherichia coli O157:H7 were studied in avocado pulp. Coliform, yeast and mold populations showed a wide dispersion, in agreement with the diversity of sanitary conditions observed among places sampled. The frequency of Salmonella spp., Listeria monocytogenes, and E. coli were 1.3, 16.0, and 60.0 %, respectively; with higher numbers among street vendors. Populations of E. coli ranged from 29 to 3800 NMP/g and S. aureus from 2.95 to 5.35 log CFU/g. Thirteen out of 16 hemolytic L. monocytogenes strains were pathogenic for mice. In avocado pulp Salmonella spp. and E. coli O157:H7 showed a lag phase close to 3 h, and a generation time of 54 min and 1.23 h, respectively. No growth of pathogens was observed in avocado pulp stored at 4‐7C.

Microbial Safety of Tropical Fruits

“…Under refrigeration conditions, E. coli O157:H7 and S. aureus survive in avocado pulp at least two weeks, but have not Downloaded by [Northeastern University] at 23:24 19 November 2014 been shown to grow (Arvizu-Medrano et al, 2001). However, Salmonella populations may increase slightly and L. monocytogenes populations grew steadily over two weeks in avocado pulp at refrigeration temperatures (Arvizu-Medrano et al, 2001;Iturriago et al, 2002).…”

“…Population increases in avocado pulp of 6 and 5 log CFU/ml were observed for Salmonella and E. coli O157:H7, respectively, within the first 24 hours when stored at 20-25 • C, independent of inoculums levels (Arvizu-Medrano et al, 2001). Population of S. aureus increase by 2 and 4 log CFU/ml in avocado pulp during a 24-hour storage period at ambient temperatures when initially inoculated at 3.5 and 1.5 log CFU/ml, respectively.…”

“…However, Salmonella populations may increase slightly and L. monocytogenes populations grew steadily over two weeks in avocado pulp at refrigeration temperatures (Arvizu-Medrano et al, 2001;Iturriago et al, 2002). Listeria monocytogenes in avocado pulp held at freezing temperatures was recovered over a 60-week storage period at a consistent level of 3.5 log CFU/g (Iturriaga et al, 2002).…”

“…Population of S. aureus increase by 2 and 4 log CFU/ml in avocado pulp during a 24-hour storage period at ambient temperatures when initially inoculated at 3.5 and 1.5 log CFU/ml, respectively. Although growth S. aureus in avocado pulp was slower than Salmonella and E. coli O157:H7, the potential for S. aureus contamination from food handlers is high, thus avocado pulp should be considered a potential vector of S. aureus (Arvizu-Medrano et al, 2001). Listeria monocytogenes grew in avocado pulp stored at ambient temperatures over a 48 h storage period, with the majority of growth seen in the first 24 hours (Iturriaga et al, 2002).…”

“…The incidence of positive samples was higher in street-vendor guacamole samples than in restaurants. In guacamole samples from street vendors and restaurants, S. aureus was found in 4.3% and 10.3%, E. coli in 54.3% and 69%, Salmonella in 0% and 3.4%, and L. monocytogenes in 15.2% and 17.2%, respectively (Arvizu-Medrano et al, 2001).…”