Molecular Microbiology Research, 2025, Vol.15, No.1, 18-27 http://microbescipublisher.com/index.php/mmr 23 had similar symptoms, which aroused the alert. At that time, 99 cases of EHEC and 48 cases of HUS had already appeared (Mellmann et al., 2011). Studies have found that middle-aged women are most affected. This strain is dangerous because it not only causes severe illness, but is also resistant to many antibiotics, so it spreads very quickly and has a particularly severe condition (Navarro-García, 2014). 6.2 Molecular characterization of the EHEC strain involved The culprit of this epidemic is the O104 strain, which is actually the product of the "combination" of two bacteria - it combines the characteristics of intestinal aggregated E. coli (EAEC) and intestinal hemorrhagic E. coli (EHEC). Not only does it produce Shiga toxin 2 like EHEC, it also carries the virulence genes commonly found in EAEC. These virulence genes are controlled by a regulator called AggR (Mellmann et al., 2011). Gene sequencing shows that this strain is very similar to another EAEC strain 55989, but it has some additional virulence and drug resistance genes, which are obtained through "gene exchange" (Rasko et al., 2011). It sticks firmly to the intestinal cells while releasing toxins. These two points add up to make it very easy to cause serious infections and the patient's symptoms are also very serious. 6.3 Public health response and lessons learned from the outbreak During this epidemic, Germany has taken many countermeasures, such as rapid investigation, strengthening surveillance, and cooperation between various departments. This epidemic shows how important it is to report cases in a timely manner, and also shows that the public health system must be strong in order to respond to emergencies (Tahden et al., 2016). Some post-event studies have pointed out that we also need to improve testing methods and investigation processes, and communication with the public is also particularly important during the epidemic (Köckerling et al., 2019). In addition, during this epidemic, most of the research results were completed by international teams, which also makes people realize the importance of cross-border cooperation. Through this incident, the public health department has gained a lot of experience, which can be used in response to similar sudden outbreaks in the future. 7 Clinical Manifestations of E. coli Infections 7.1 Common diseases caused by pathogenic E. coli Many E. coli strains can cause diseases, the most common of which are urinary tract infections. Urinary tract pathogenic E. coli (UPEC) is the main “culprit”, which can cause simple cystitis and may also rise to the kidneys, causing pyelonephritis, and in severe cases can even develop urinary sepsis (Mobley et al., 2009 ; Alteri and Mobley, 2015 ; Zhou et al., 2023 ). UPEC can cause infection because it has some special “tools” such as pili and toxins. These things can make it stick to the urethral epithelium and even drill into it, causing infection (Terlizzi et al., 2017). In addition to urinary tract infections, E. coli often causes gastroenteritis. In particular, enterotoxin-producing E. coli (ETEC) and enterohemorrhagic E. coli (EHEC), which often cause severe diarrhea (Alteri and Mobley, 2015). 7.2 Complications associated with E. coli infections Some E. coli infections are not just uncomfortable, but can also cause serious or even life-threatening problems. A more typical example is hemolytic uremic syndrome (HUS), which is often associated with EHEC infection. This disease causes anemia, thrombocytopenia, and impaired renal function, and is most likely to occur in children (Alteri and Mobley, 2015). If it is a urinary tract infection, it may also infect the kidneys in severe cases, causing pyelonephritis, and over time, it may even lead to kidney damage or chronic diseases. In addition, if bacteria enter the bloodstream, it may also cause urinary sepsis. This is a very serious systemic infection that can lead to septic shock and even multi-organ failure (Terlizzi et al., 2017). And now some UPEC strains are resistant to many drugs, which makes treatment more difficult and increases the risk of infection becoming severe (Totsika et al., 2012; Zhou et al., 2023). 7.3 Diagnostic approaches for identifying E. coli infections It is very important to diagnose E. coli infection accurately and in a timely manner. If it is suspected that it is a urinary tract infection, doctors will generally ask for a urine culture so that they can find out whether it is UPEC
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