Effects of pH, Sodium Chloride, and Curing Salt on the Infectivity of Toxoplasma gondii Tissue Cysts

Abstract

Toxoplasma gondii is one of the most common zoonotic parasites in the world. The parasite causes no or mild symptoms in immunocompetent humans. However, a high potential hazard exists for seronegative pregnant women and immunocompromised patients. The consumption of meat containing tissue cysts or oocyst-contaminated vegetables and fruits or the handling of cat feces poses a high risk of infection with T. gondii. It is known that raw minced meat, raw fresh sausages, and locally produced raw meat products are possible causes of T. gondii infection. The infectivity of T. gondii tissue cysts in meat products depends, among other factors, on the pH and the salt concentration. Therefore, the impact of these two factors on the tissue cysts was examined. For this purpose, dissected musculature and brain from experimentally infected mice (donor mice) were placed in a cell culture medium (RPMI 1640). The medium was adjusted to different pH values (pH 5, 6, and 7) with lactic acid and to different salt concentrations (2.0, 2.5, and 3.0%) with sodium chloride (NaCl) or nitrite-enriched curing salt (NCS) for the various tests. After storage at 4°C for different time periods, the materials were fed to bioassay mice. Later, the brains were examined for presence of T. gondii to assess the infectivity. The data show that T. gondii tissue cysts have a high pH tolerance. Cysts were infectious in the muscle for up to 26 days (pH 5). In contrast to their tolerance to pH, cysts were very sensitive to salt. Muscle cysts survived at an NaCl concentration of up to 2.0% only, and for no longer than 8 days. At NaCl concentrations of 2.5 and 3.0%, the cysts lost their infectivity after 1 day. When NCS instead of NaCl was used under the same conditions, T. gondii muscle cysts retained infectivity for only 4 days at 2.0%. Consequently, NCS (NaCl plus 0.5% nitrite) has a stronger effect on T. gondii cysts than does common table salt. Sausages produced with low NaCl concentration and short contact times pose a potential risk for susceptible individuals.

Effects of temperature, pH and curing on the viability of <i>Sarcocystis,</i> a Japanese sika deer (<i>Cervus Nippon centralis</i>) parasite, and the inactivation of their diarrheal toxin

“…To examine the effect of curing on the viability of cysts, a 50 g block of meat (5 × 4 × 3 cm) was soaked or rubbed with 2.0 or 6.0% NaCl and/or nitrite-enriched curing salt (NSC, NaCl enriched with 5% sodium nitrite, 10% potassium nitrate; New Shouso, Chiyoda Industry, Tokyo) for up to 7 days according to the study of Pott et al . [ 28 ].…”

Impact of Engineered Expression of Mitochondrial Association Factor 1b onToxoplasma gondiiInfection and the Host Response in a Mouse Model

“…There is likely to be an evolutionary trade-off between the growth-enhancing effects of MAF1b expression and the proinflammatory response that it induces. While induction of higher levels of inflammation may serve to reduce parasite growth and dissemination, it can also lead to death of the host ( 32 ), an endpoint in T. gondii infection that is likely maladaptive given the fact that T. gondii tissue cysts are not environmentally stable ( 33 , 34 ). Type II parasites (which are naturally HMA − ) activate the NF-κB pathway via the secreted protein TgGRA15 ( 35 ), which leads to the activation of inflammatory and antiapoptotic pathways ( 35 ).…”

Risk Assessment of Human Toxoplasmosis Associated with the Consumption of Pork Meat in Italy

“…(47) The negligible risk of infection from salt-cured meat products consumed in Italy is consistent with several in vitro studies that confirmed that, despite the variability of the manufacturing parameters, T. gondii is not able to survive in such products due to a relatively high concentration of NaCl combined with a prolonged curing period. (48)(49)(50) Similarly, some researchers who investigated the viability of T. gondii were not able to isolate the parasite from 6, 12, and 40 dry-cured hams obtained from experimentally infected pigs, and consequently speculated that these products pose a very low risk. (43,51,52) However, these results are in contrast with other studies that reported the finding of viable T. gondii in dry-cured ham sampled at retail level (up to 4.8% of the samples).…”