Acid Resistance of Non-O157 Shiga Toxin-Producing Escherichia coli Adapted in Fruit Juices in Simulated Gastric Fluid

The objectives of this study were I) to compare the acid resistance (AR) of seven non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups, including O26, O45, O103, O111, O121, O145, and O157:H7 STEC isolated from various sources, in 400 mM acetic acid solution (AAS) at pH 3.2 and $30^{\circ}C$ for 25 min with or without glutamic acid and II) to determine strain survival upon exposure to simulated gastric fluid (SGF, pH 1.5) at $37^{\circ}C$ for 2 h after acid adaptation in apple, pineapple, orange, and strawberry juices at pH 3.8, $4^{\circ}C$ and $20^{\circ}C$. Results show that the O111 serogroup strains had the strongest AR (0.12 log reduction CFU/mL) which was very similar to that of O157:H7 STEC (P>0.05), compared to other serogroups in AAS without glutamic acid, whereas O26 serogroup strains showed the most sensitive AR. However, there was no significant (P>0.05) difference of AR among seven serogroups in AAS with glutamic acid. In the SGF study, 05-6545 (O45:H2), 08023 (O121:H19), and 03-4669 (O145:NM) strains adapted in fruit juices at $4^{\circ}C$ and $20^{\circ}C$ displayed enhanced survival with exposure to SGF for 60 min compared to 06E0218 (O157:H7) strains (P<0.05). In addition, 4 STEC strains adapted in pineapple juice at $4^{\circ}C$ showed enhanced survival with exposure to SGF for 60 min compared to those strains acid-adapted in the other fruit juices. Generally, adaptation at $4^{\circ}C$ in fruit juices resulted in significantly enhanced survival levels compared to acid-adapted at $20^{\circ}C$ and non-adapted conditions. The AR caused by adaptation in fruit juices at low temperature may thus increase survival of non-O157 STEC strain in acidic environments such as the gastrointestinal tract. These results suggest that more careful strategies should be provided to protect against risk of foodborne illness by non-O157 STEC.

위합성용액에서 과일주스에 노출한 Non-O157 Shiga Toxin-Producing Escherichia coli의 산 저항성 평가

다양한 환경에서 분리된 시가독소 생산성 대장균(Shiga toxin-producing E. coli, STEC, n=18)을 초산혼합용액(AAS;400 mM, pH 3.2, $30^{\circ}C$)에 노출한 후 산 저항성을 측정하였다. 또한, 선정된 4종류의 non-O157:H7 STEC균을 사과주스, 파인애플주스, 오렌지주스, 딸기주스(pH 3.8)에 정봉하여 $4^{\circ}C$와 $20^{\circ}C$에서 24시간 산 적응시킨 후 위합성용액(SGF, pH 1.5)에서 2시간 동안 생존능력을 평가하였다. Non-O157:H7 STEC를 AAS에 노출했을 때 O111 혈청형의 STEC는 평균 0.12 log CFU/mL 감소하여 다른 혈청형에 비하여 가장 강한 산 저항성을 나타냈고 O157:H7 STEC와 유의적 차이가 없었으며(P>0.05), O26 혈청형의 STEC는 가장 민감한 것으로 나타났다. 반면, AAS에 glutamic acid를 첨가하였을 경우 모든 STEC는 혈청형과 관계없이 초산에 매우 강한 저항성을 나타내었다(P>0.05). SGF에서 생존능력을 측정한 결과, 06E0218(O157:H7)은 다른 non-O157:H7 STEC 균들보다 생존능력이 낮았고 03-4669(O145:NM)가 가장 강한 생존능력을 나타내었다. 한편, 과일주스 중에서는 파인애플주스에 산 적응된 STEC가 SGF에 가장 강한 생존능력을 나타내었다. $4^{\circ}C$의 과일주스에 STEC를 산 적응시켰을 경우 $20^{\circ}C$보다 SGF에 대한 생존능력이 현저하게 높았다(P<0.05). 따라서 과일주스에 의한 non-O157:H7 STEC의 산 적응력 증가는 위장관 내 생존율 및 식중독 발생을 높일 수 있으므로 이에 대한 적절한 연구와 안전관리 옵션을 제공할 필요가 있을 것으로 판단된다.