Inactivation of Escherichia coli O157:H7 in single-strength lemon and lime juices

Control of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated in beetroot or watermelon juice by combined treatments with organic acid or lemon (Citrus limon) extract and mild heat

The study aimed to evaluate the synergistic interaction of organic acids (OAAs) or lemon extract (LE) plus mild heat (MH; 55 °C) against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated in beetroot and watermelon juices. A mixed culture cocktail of E. coli O157:H7, S. Typhimurium or L. monocytogenes was inoculated in beetroot or watermelon juice, followed by treatments with MH, citric acid + MH, malic acid + MH, tartaric acid + MH, and LE + MH. Approximately < 2.0-log reductions in the number of E. coli O157:H7, S. Typhimurium, and L. monocytogenes were observed when these bacteria were heated in juices at 55 °C for 5 min. A combination of 1.0% OAAs or 20% LE and MH (55 °C) for 5 min resulted in an additional log-reduction in the count of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 2.2-5.0, 4.5-5.0, and 1.5-5.0, respectively.

Antibiotic Resistance in Microbes from Street Fruit Drinks and Hygiene Behavior of the Vendors in Delhi, India

Microbial contamination of fruit juices has caused major outbreaks, leading to significant morbidity and mortality in developing countries. The inept hygiene and safety practices followed by the juice vendors are the leading risk factors of the microbial contamination of juices. In this pilot study, the five most crowded markets in urban Delhi, including Kamla Nagar, University of Delhi (north campus), Tilak Nagar, Chandni Chowk, and Rohini, were selected for a questionnaire survey on the fruit juice vendors and the sampling of water used for juice preparation as well as sugarcane, orange, and mix fruit juices collected from these markets for the enumeration of total bacterial count (TBC), Escherichia coli, Salmonella, and Vibrio. Antibiotic susceptibility tests were performed using ampicillin, cefotaxime, chloramphenicol, ciprofloxacin, and imipenem. The results indicated that the majority of the vendors were not following hygiene and safety practices when compared with the recommended standard safety practices. The use of municipal water by 95% of vendors with high TBC counts might have been the major source of microbial contamination in all types of fruit juices. E. coli and Salmonella contaminations were high in sugarcane (2 × 10⁵ colony forming units (CFU)/mL) and mix fruit (2.2 × 10⁵ CFU/mL) juice samples, respectively. On the other hand, Vibrio was found to be absent in almost all juice samples except for orange juice. All strains were found to be susceptible to chloramphenicol, but resistant to ampicillin and cefotaxime. Only a few strains were resistant to ciprofloxacin, and only E. coli strains were resistant to imipenem. Taken together, the overall microbiological standards of fruit juices served by street vendors were not within the acceptable limits, perhaps due to the poor quality of water used to prepare juices and poor hygiene and safety practices followed by the vendors. More importantly, the isolated microbes demonstrated resistance to ampicillin and cefotaxime, which may have pressing public health implications. Post hoc power analyses identified the minimum sample size required for 80% power.

Room Temperature Growth of Salmonella enterica Serovar Saintpaul in Fresh Mexican Salsa

Salsa-associated outbreaks, including the large multistate outbreak in the United States in 2008 caused by jalapeño and serrano peppers contaminated with Salmonella Saintpaul, have raised concerns about salsa as a potential vehicle for transmission. Despite these events, there has been relatively limited research on the potential growth of pathogenic bacteria in salsa. The aim of this study was to characterize the survival and growth of Salmonella, including the outbreak strain of Salmonella Saintpaul (E2003001236), in freshly made salsa and its main ingredients. Chopped tomatoes, jalapeño peppers, cilantro, and onions were tested individually or mixed according to different salsa recipes. Samples were inoculated with five Salmonella serotypes at 3 log CFU/g: Saintpaul (various strains), Typhimurium, Montevideo, Newport, or Enteritidis. Samples were then stored at room temperature (23°C) for up to 12 h or 3 days. The Salmonella Saintpaul levels reached approximately 9 log CFU/g after 2 days in tomato, jalapeño pepper, and cilantro. Growth was slower in onions, reaching 6 log CFU/g by day 3. Salsa recipes, with or without lime juice, supported the growth of Salmonella Saintpaul, and final levels were approximately 7 log CFU/g after 3 days at 23°C. In contrast, the counts of Salmonella Typhimurium, Salmonella Montevideo, Salmonella Newport, and Salmonella Enteritidis increased only 2 log CFU/g after 3 days in any of the salsas. Other Salmonella Saintpaul strains were able to grow in salsas containing 10% lime juice, but their final levels were less than 5 log CFU/g. These findings indicate the enhanced ability of the Salmonella Saintpaul outbreak strain to grow in salsa compared with other Salmonella strains. Recipe modifications including but not limited to adding lime juice (at least 10%) and keeping fresh salsa at room temperature for less than 12 h before consumption are strategies that can help mitigate the growth of Salmonella in salsa.

Citrus fruit extracts with carvacrol and thymol eliminated 7-log acid-adapted Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes: A potential of effective natural antibacterial agents

Despite the widespread belief that citrus fruit extracts (CFEs) are microbiologically safe due to their acidity, limited bactericidal effect results in low applicability as antibacterial agent and outbreaks occurred by acid-adapted pathogens. Here, we examined the antibacterial effects of CFEs [lime (Citrus medica), lemon (Citrus limon), calamansi (Citrus microcarpa)] combined with essential oil components (EOCs; carvacrol and thymol) against non-acid-adapted/acid-adapted Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes under 22 °C for 5 min. CFEs (<20%) alone or small amounts of EOCs (2.0 mM; 0.032%) alone could not inactivate the target bacteria effectively. However, combined treatments exhibited marked synergy: CFE + EOCs eliminated all the bacteria (>6.9 log CFU/ml). Among the CFEs tested, the highest synergism was shown by calamansi, an exotic citrus fruit previously unrecognized as an antibacterial agent. Although acid-adaptation improved bacterial survival, calamansi (<20%) + EOCs (<0.032%) completely inactivated even the most resistant pathogen (E. coli O157:H7). Validation test also showed that all tested commercial juice products also eliminated acid-adapted pathogens when used with EOCs. Physicochemical analysis of tested CFEs (pH measurement and HPLC analysis of components) revealed that low pH and flavanone (hesperidin) did not contribute to the synergistic bactericidal effects. Rather, the high citric acid content is likely to contribute to the strong synergistic effect with EOCs by damaging susceptible bacterial membranes. Sensory scores for CFEs were not altered by addition of EOCs at concentrations up to 1.5 mM. This study provides new insight into the utility of CFEs with EOCs to improve not only the microbiological safety of food products containing CFEs but also their applicability as natural antibacterial complex.

Inactivation by lemon juice of Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes in beef marinating for the ethnic food kelaguen

Lemon juice, a major source of acidulant citric acid, is frequently used in the preparation of ethnic foods. Raw or partially cooked meats are marinated with lemon juice in the preparation of a popular Chamorro dish called kelaguen, which is, unfortunately, strongly associated with foodborne illness outbreaks in Guam. We investigated the efficacy of lemon juice in reducing numbers of Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes at stationary phase during marination. Beef inoculated with a three-strain mixture of E. coli O157:H7, S. Enteritidis, or L. monocytogenes at 10(6)CFU/mL was marinated with lemon juice from 0.2 to 10mL/g for 48h at 28°C. The decline of the pathogens during marination exhibited various degrees of deviation from first-order kinetics. Based on calculations with both linear regression and Weibull models, the decimal reduction time (4-D values) over the range of lemon concentrations was 366-5.1h for E. coli O157:H7, 282-2.4h for S. Enteritidis, and 104-2.4h for L. monocytogenes, indicating that E. coli O157:H7 was the most lemon-juice-resistant of the three. The pathogen reduction time (log 4-D values) plotted against undissociated titratable citric acid exhibited a biphasic pattern. The pathogen reduction time (log 4-D or δ values) was linearly correlated with the pH of the marinating beef (R(2)=0.92 to 0.98). The Z(pH) values (pH dependence of death rate) with beef marination were 1.03 for E. coli O157:H7, 0.92 for S. Enteritidis, and 1.29 for L. monocytogenes, indicating that L. monocytogenes was the most pH resistant of the three. L. monocytogenes exhibited less resistance to lemon juice than S. Enteritidis at pH of 3.5-4.4 but more resistance at pH of 2.6-2.8. In addition, at 4°C, all three pathogens exhibited 4-D values 1.7-4.1 times greater than those at 24°C at 5mL lemon juice/g beef. In conclusion, the usual beef marinating practice for kelaguen preparation (<0.5mL lemon juice/g beef for 1-12h) did not sufficiently inactivate E. coli O157:H7, S. Enteritidis, and L. monocytogenes to meet minimum food-safety requirements. To reduce the risk of kelaguen-associated foodborne illness, kelaguen preparation must include heat treatment in addition to marination with lemon juice.

Validation of Pepperoni Process for Control of Shiga Toxin–Producing Escherichia coli

The objective of this study was to compare the survival of non-O157 Shiga toxin–producing Escherichia coli (STEC) with E. coli O157:H7 during pepperoni production. Pepperoni batter was inoculated with 7 log CFU/g of a seven-strain STEC mixture, including strains of serotypes O26, O45, O103, O111, O121, O145, and O157. Sausages were fermented to pH ≤4.8, heated at 53.3°C for 1 h, and dried for up to 20 days. STEC strains were enumerated at designated intervals on sorbitol MacConkey (SMAC) and Rainbow (RA) agars; enrichments were completed in modified EC (mEC) broth and nonselective tryptic soy broth (TSB). When plated on SMAC, total E. coli populations decreased 2.6 to 3.5 log after the 1-h heating step at 53.3°C, and a 4.9- to 5-log reduction was observed after 7 days of drying. RA was more sensitive in recovering survivors; log reductions on it were 1.9 to 2.6, 3.8 to 4.2, and 4.6 to 5.3 at the end of cook, and at day 7 and day 14 of drying, respectively. When numbers were less than the limit of detection by direct plating on days 14 and 20 of drying (representing a 5-log kill), no more than one of three samples in each experiment was positive by enrichment with mEC broth; however, STEC strains were recovered in TSB enrichment. Freezing the 7-day dried sausage for 2 to 3 weeks generated an additional 1- to 1.5-log kill. Confirmation by PCR revealed that O103 and O157 had the greatest survival during pepperoni productions, but all serotypes except O111 and O121 were occasionally recovered during drying. This study suggests that non-O157 STEC strains have comparable or less ability than E. coli O157 to survive the processing steps involved in the manufacture of pepperoni. Processes suitable for control of E. coli O157 will similarly inactivate the other STEC strains tested in this study.

Inactivation of Shiga toxin-producing Escherichia coli in single-strength lemon and lime juices containing preservatives

The objective of this study was to determine the inactivation of non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes in comparison with O157 STEC in commercially produced, shelf-stable lemon and lime juices. The present validation tests confirmed that storage of the juices containing preservatives at room temperatures (22°C) for 3 days (72 h) ensures a >6-log reduction of O26, O45, O103, O111, O121, O145, and O157 STEC. These results demonstrate that non-O157 STEC had survival abilities comparable to those of E. coli O157:H7 strains in acidic food products such as lemon and lime juices (pH 2.5 ± 0.1); therefore, the storage conditions deemed to inactivate E. coli O157:H7 similarly inactivate the non-O157 serotypes.

Thermal resistance parameters for Shiga toxin-producing Escherichia coli in apple juice

The purpose of the present study was to determine the heat resistance of six non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes in comparison to E. coli O157:H7 in single-strength apple juice without pulp. The thermal parameters for stationary-phase and acid-adapted cells of E. coli strains from serogroups O26, O45, O103, O111, O121, O145, and O157:H7 were determined by using an immersed coil apparatus. The most heat-sensitive serotype in the present study was O26. Stationary-phase cells for serotypes O145, O121, and O45 had the highest D(56°C)-value among the six non-O157 serotypes studied, although all were significantly lower (P < 0.05) than that of E. coli O157:H7. At 60°C E. coli O157:H7 and O103 demonstrated the highest D-values (1.37 ± 0.23 and 1.07 ± 0.03 min, respectively). The D(62°C) for the most heat-resistant strain belonging to the serotype O145 was similar (P > 0.05) to that for the most resistant O157:H7 strain (0.61 ± 0.17 and 0.60 ± 0.09 min, respectively). The heat resistance for stationary-phase cells was generally equal to or higher than that of acid-adapted counterparts. Although E. coli O157:H7 revealed D-values similar to or higher than the individual six non-O157 STEC serotypes in apple juice, the z-values for most non-O157 STEC tested strains were greater than those of E. coli O157:H7. When data were used to calculate heat resistance parameters at a temperature recommended in U.S. Food and Drug Administration guidance to industry, the D(71.1°C) for E. coli O157:H7 and non-O157 STEC serotypes were not significantly different (P > 0.05).