“Is Neisseria gonorrhoeae Initiating a Future Era of Untreatable Gonorrhea?: Detailed Characterization of the First Strain with High-Level Resistance to Ceftriaxone” (2011), by Makoto Ohnishi, Daniel Golparian, Ken Shimuta, Takeshi Saika, et al.

In July 2011, Makoto Ohnishi and colleagues published the article “Is Neisseria gonorrhoeae Initiating a Future Era of Untreatable Gonorrhea?: Detailed Characterization of the First Strain with High-Level Resistance to Ceftriaxone,” hereafter, “Untreatable Gonorrhea,” in the journal Antimicrobial Agents and Chemotherapy. Gonorrhea is a sexually transmitted disease, or STD, caused by the bacterium Neisseria gonorrhoeae. In 2009, Ohnishi and a few of his co-authors found the first ceftriaxone-resistant strain of gonorrhea, called H041. That strain demonstrated resistance to ceftriaxone, one of the last remaining and effective first-line antibiotic treatment drugs for N. gonorrhoeae. In “Untreatable Gonorrhea,” Ohnishi and Colleagues confirm that the H041 strain is resistant to ceftriaxone and analyze the bacterium’s mechanism of resistance. “Untreatable Gonorrhea” was one of the first publications to characterize the H041strain and highlights a need for global public health interventions to prevent the rapid spread of gonorrhea.

1. Background and Context
2. Article Roadmap
3. Detailed Content
4. Impact

Background and Context

The authors of “Untreatable Gonorrhea” hail from multiple academic institutions and laboratories across Japan and Sweden. At the time of the article’s publication in 2011, Ohnishi, the first author, worked as a researcher at the National Institute of Infectious Diseases in Tokyo, Japan. The corresponding author, Magnus Unemo, was a researcher at the Swedish Reference Laboratory for Pathogenic Neisseria of Örebro University in Örebro, Sweden. As of 2024, Unemo is the Director of the World Health Organization Collaborating Centre for Gonorrhea and other Sexually Transmitted Infections. The remaining authors were affiliated with the same research institutions, as well as the Mitsubishi Chemical Medience Corporation in Tokyo and the Hoshina Clinic and Kyoto Prefectural University of Medicine, both located in Kyoto, Japan. Following the publication of “Untreatable Gonorrhea,” the members of the research group continued to research and publish articles about gonorrhea.

“Untreatable Gonorrhea” includes discussion of the STD called gonorrhea, which can infect and cause symptomology in men, women, and babies. Gonorrhea typically is transmitted from one individual to another during sexual intercourse with an infected partner. Gonorrhea can infect the eyes, throat, and rectum, though it primarily affects the female and male reproductive tracts. Symptoms of gonorrhea, or gonococcal infection, typically appear within one to fourteen days after infection, and symptoms vary between men and women. Men are often asymptomatic but can sometimes display symptoms such as abnormal discharge from the urethra, pain and swelling of the testicles, and dysuria or painful urination. Women, like men, are often asymptomatic, but they can experience symptoms such as abnormal vaginal discharge, dysuria, pelvic or abdominal pain, and vaginal bleeding in between periods. Without treatment, women can develop pelvic inflammatory disease, or PID, a condition where the female reproductive organs became inflamed due to infection. Untreated PID can cause scarring of the fallopian tubes, which can lead to infertility. Additionally, a pregnant woman infected with gonorrhea can pass the infection to her child during childbirth, potentially causing severe illness in the infant if untreated.

Prior to the publication of “Untreatable Gonorrhea,” researchers typically treated gonorrhea with a variety of antibiotic drugs, yet various gonococcal strains developed antibiotic resistance to most of those drugs. Antibiotic, or antimicrobial, resistance occurs when pathogens such as bacteria develop the ability to overcome the drug therapies designed to kill them. During the bacterial replication process, mutations arise, and some of those mutations confer traits that allow for antibiotic resistance. Those bacteria with mutations coding for antibiotic resistance typically survive and continue to reproduce. Antibiotic resistance is more likely to occur when people misuse antibiotics by not taking the entire dose of their prescribed antibiotics, taking antibiotics not prescribed to them, or taking antibiotics when they do not have a bacterial infection. 

In the twentieth and twenty-first centuries, researchers observed antibiotic resistance of gonococcal strains to various drugs that previously treated the disease, including sulfonamides, penicillin, tetracycline, spectinomycin, and cefixime. In 1935, researchers developed sulfanilamide, one of the first antibiotics produced and part of the sulfonamide drug class. During the 1930s and 1940s, researchers continued to develop other antimicrobials of the sulfonamide class, and those drugs successfully treated gonorrhea cases. By 1944, over ninety percent of strains in circulation were resistant to the sulfonamide drugs. For the next forty years, physicians continued to treat gonorrhea with different antibiotics, such as penicillin, tetracycline, and spectinomycin, but N. gonorrhoeae repeatedly developed resistance to those treatments. In the late 1960s, the antibiotic drug class of cephalosporins, which includes the drugs cefixime and ceftriaxone, became available as first-line treatments for gonorrhea. By the late 1990s and early 2000s, though, gonorrhea strains evolved resistance to cefixime, which closely resembles ceftriaxone. According to a 2014 publication from Unemo, the resistant strains first appeared in Japan, then spread to the United States, Canada, and multiple countries in Europe. Following that, physicians primarily relied on ceftriaxone as a first-line treatment for gonorrhea, since there were no longer any other antimicrobials effective against the disease.

Prior to the publication of “Untreatable Gonorrhea,” first-line treatment guidelines by the Centers for Disease Control and Prevention, or CDC, recommended dual therapy with a cephalosporin drug and an azithromycin or doxycycline antimicrobial. At that time, researchers had not yet identified clinical cases of ceftriaxone resistance, but cefixime-resistant cases were present. Medical physicians recommended that regimen to patients through 2011.

In 2009, Ohnishi and a few of his coauthors identified the first recorded case of a ceftriaxone-resistant strain of gonorrhea, later called H041, in a thirty-one-year-old female sex worker in Kyoto, Japan, and they reported their findings in the article “Ceftriaxone-Resistant Neisseria gonorrhoeae, Japan.” According to that article, the woman with gonorrhea sought out routine sexually transmitted infection, or STI, testing at a clinic in Kyoto, and physicians found that although the woman was asymptomatic, her throat swab revealed she had a pharyngeal gonorrhea infection, or gonococcal infection of the throat. Two weeks later, she received STI testing again, which yielded another positive result. The authors state that medical providers subsequently treated the woman with one gram of ceftriaxone delivered intravenously. Typically, people treated with ceftriaxone completely clear N. gonorrhoeae from their body within two weeks of receiving treatment, but the woman tested positive again two weeks later. The woman then received further treatment with ceftriaxone, but, according to the article, physicians did not perform an additional test to see if the treatment was successful because of the woman’s high risk of reinfection due to her occupation. A few months later, in April 2009 the woman returned to the clinic for STI testing and she tested negative for gonorrhea. In “Untreatable Gonorrhea,” the authors analyze the strain of gonorrhea found in that woman and relate that strain, which they call H041, to other known strains to quantify its level of resistance and describe its mechanism of resistance.

Article Roadmap

“Untreatable Gonorrhea” contains four sections. In the untitled introductory section, the authors detail that gonorrhea maintains a high global prevalence and many strains have evolved antibiotic resistance to first-line treatments. Thus, they chose to study the recently discovered ceftriaxone-resistant H041 strain and its mechanism. Next, in “Materials and Methods,” the authors explain that they conducted antimicrobial resistance testing as well as a series of additional tests to characterize the H041 strain. In “Results,” the authors emphasize that their test results confirmed that H041 is a strain of gonorrhea and is resistant to multiple drug classes including cephalosporins like ceftriaxone due to specific mutations in its genome. The authors also explain that that H041is a descendant of ST7363, a cefixime-resistant strain previously discovered in Japan. In the final section, “Discussion,” the research group characterizes H041 as four- to eight-times more resistant to ceftriaxone than other strains of gonorrhea and propose that H041 will likely initiate an era of untreatable gonorrhea. Finally, the authors conclude by stating that global public health interventions will be necessary to monitor and control transmission of H041.

Detailed Content

In the unlabeled introduction, Ohnishi and colleagues explain that gonorrhea has developed antibiotic resistance to many previously developed first-line treatments, and thus, the disease continues to infect individuals worldwide. The authors first claim that gonorrhea is the second most common bacterial STI and is a serious global public health problem. They state that since there is no vaccine therapy available for the disease, diagnostic testing and antibiotic treatment are essential for reducing the transmission of gonorrhea as well as preventing severe illness in individuals who do contract the bacteria. The authors elaborate that the use of those treatment options has rapidly decreased because N. gonorrhoeae has achieved antibiotic resistance to many first-line drug therapies, including penicillin and spectinomycin. They explain that physicians can no longer use those therapies to effectively treat gonococcal infections. Then, they assert that gonorrhea has globally become less susceptible to the last few remaining first-line treatments, which are the injectable antibiotic ceftriaxone and the oral cefixime.

Also in the introductory section, the authors discuss that their paper focuses on understanding and treating H041, a newly observed strain of gonorrhea that they explain has high levels of resistance to ceftriaxone. Ohnishi and colleagues explain that physicians previously found the strain in the pharynx, or throat, of a commercial sex worker in Kyoto, Japan. According to the paper, those physicians could not definitively determine if ceftriaxone failed to treat H041 in that woman because they did not have a posttreatment sample of H041 available to test and compare to. However, the authors state that H041 is closely related to ST7363, a common strain of gonorrhea in Japan and Europe that is resistant to the antibiotic cefixime. They elaborate that antibiotic resistance is quite prevalent in Japan and the Western Pacific Region, and previous resistant strains have spread from those regions to other parts of the world, in large part due to sex tourism, migration, and long-distance truck drivers. The researchers predict that ceftriaxone-resistant gonorrhea will follow a similar distribution pattern as its predecessors, thus, they argue that it is essential to study H041 and its mechanism of resistance in detail. Then, the authors describe what researchers already knew about those gonococcal resistance mechanisms, including that it involves alterations in the penA gene. The penA gene codes for the protein that allows N. gonorrhoeae to bind to penicillin and other antibiotics to create resistance. The research team concludes that the aim of the study is to conduct an in-depth characterization of H041 to examine and treat its antibiotic-resistant mechanisms.

In the second section, “Materials and Methods,” the authors explain that in their study, they compared H041 to nine other strains of gonorrhea using the Etest method to quantify its levels of resistance and determine which antibiotics it is resistant to. First, the research group explains that they performed seven species confirmatory tests to verify that is H041 is indeed a strain of gonorrhea. They then detail that they tested ceftriaxone and twenty-nine additional antimicrobials against H041 and the other strains of gonorrhea to discern which antimicrobials each strain was resistant to. They performed that testing using the Etest method, which is a standardized lab test in which researchers place a plastic strip containing antimicrobial agent onto a plate of bacteria and examine if the bacteria grow near the strip. If bacteria grow, then the strain is resistant to that antimicrobial. The Etest measures the minimal inhibitory concentration, or MIC, which is the lowest concentration of an antimicrobial substance required to prevent visible growth of a bacteria in a laboratory setting. MIC can measure how susceptible or resistant a particular bacterial strain is to a specific antimicrobial agent.

At the end of the “Materials and Methods,” section, the research group states that they tested H041 and the other gonorrheal strains to discover that a mutation in the penA gene, called penAH041, causes high ceftriaxone resistance. First, the authors detail that they performed genetic and phylogenetic, or evolutionary, analyses to understand the characteristics of each strain. Then, they explain that they performed transformation assays, or lab tests that clone genetic material, in which they inserted the penAH041 allele, the variation of the penA gene uniquely found in H041, into the other nine strains of gonorrhea to determine how penAH041 affects those strains’ antibiotic susceptibility. They performed the transformation assay three times for each strain to confirm that penAH041 allele caused high levels of ceftriaxone resistance.

In the third section, “Results,” the research group explain that from the tests they ran, they found that H041 is a strain of gonorrhea and is resistant to a majority of the thirty antibiotics they tested, including ceftriaxone. They state that after they performed all seven species confirmatory tests, they were able to confirm that H041 is indeed a strain of gonorrhea. They explain that they found H041 is resistant to seven major antimicrobial classes, including penicillin and other antibiotics that physicians previously used to treat gonorrhea before it acquired widespread resistance to them. The research team then states that H041 was resistant to all cephalosporins, the drug class containing ceftriaxone. The researchers highlight H041’s ceftriaxone MIC, a value between two and four micrograms per milliliter, which was at a level of resistance that they describe as very high. They explain that only one other strain of gonorrhea globally had previously demonstrated a ceftriaxone MIC greater than the threshold 0.25 micrograms per milliliter. They also emphasize that H041 demonstrated a high MIC towards all other cephalosporins when they performed antimicrobial susceptibility testing. However, the authors did disclose that H041 is susceptible to the antibiotics spectinomycin and rifampin, neither of which are typical first-line therapies for the treatment of gonorrhea. They also state that the MIC for the antibiotics tigecycline and those in the aminoglycoside class were low, though as of 2024, doctors consider none of those drugs as first-line therapies. The authors include a table in “Results” that presents information regarding the H041’s MIC for various antibiotics as determined by the Etest method.

Next, Ohnishi and colleagues describe the relationship of H041 to other known gonorrheal strains and explicate that the penAH041 allele confers H041’s high levels of resistance to ceftriaxone. They declare that after conducting phylogenetic analyses, they found that H041 is closely related to other cephalosporin-resistant gonorrhea strains. They elaborate that H041 has the penAH041, which is unique to its strain, and, thus, that allele must be responsible for the strain’s increased resistance to ceftriaxone. They further support that claim by explaining that after they inserted the penAH041 allele into other gonorrheal strains, eight of the nine tested strains had a MIC above the antibiotic resistance threshold of 0.25 micrograms per microliter for ceftriaxone. The authors conclude the “Results” by definitively stating that the penAH041 allele is responsible for high-level ceftriaxone resistance in their study.

In the final section, “Discussion,” the authors explain that the antibiotic resistance of H041 to ceftriaxone and other antimicrobials complicates the available treatment options for gonorrhea and could potentially lead to uncontrollable spread of the disease worldwide. Ohnishi and colleagues begin by reaffirming that ceftriaxone is the last remaining first-line therapy for N. gonorrhoeae, and the discovery and study of the H041 strain has demonstrated that N. gonorrhoeae is able to evolve and lower its susceptibility to that drug. They go on to explain that when medical providers typically treat a gonorrheal infection with ceftriaxone, the treatment eliminates all presence of N. gonorrhoeae genetic material from the host within two weeks. Unlike typical cases of gonorrhea, the female reported to have the first recorded clinical case of H041 retained gonorrheal genetic material after the two-week period. The authors emphasize that based on their results, if a person infected with the H041 strain of gonorrhea receives the standard one-gram dose of ceftriaxone, then the medication will not eradicate the H041 strain in most cases. The authors argue that due to the development of ceftriaxone resistance in the H041 strain, N. gonorrhoeae could potentially become what they define as a superbug, meaning it could initiate an era of untreatable gonorrhea.

The researchers also use the “Discussion” section to emphasize that their study revealed that other alleles, in addition to the penAH041 allele, are responsible for creating ceftriaxone resistance in the H041 strain and demonstrated that the resistance can spread across the N. gonorrhoeae strains. The research team reiterates that the penAH041 allele causes the resistance, and the insertion of the penAH041 allele into the other nine gonococcal strains led those strains to also develop high ceftriaxone MIC. They detail that in order for the other strains to reach the same levels of ceftriaxone MIC as the H041 strain, additional resistance determinants must be present, including the mtrR and penB genes, as well as an unidentified agent, which the authors call factor X. Although high ceftriaxone MIC levels as found in the H041 strain require other determinants, the authors conclude that the penAH041 allele successfully transformed into the other gonococcal strains, and, therefore, ceftriaxone resistance can rapidly spread within the N. gonorrhoeae population.

Next, the authors explain that they theorize that H041 evolved from the previously identified S7363 strain, and that due to the possibility of the spread of H041, they strongly recommend that Japan implement surveillance programs to prevent global transmission. They explain that they suspect that the H041 strain represents a subclone of the ST7363 strain, the gonococcal strain that previously expressed resistance to other drugs in the cephalosporin class and evolved from it. The group explicitly states that they fear H041 may disseminate globally, given that previous strains of antibiotic-resistant pathogens have spread worldwide within one to two decades. The research team asserts that the discovery of H041 is important because experts identified the first clinical case of H041 in a commercial sex worker, a member of a high-risk population that frequently transmits STIs, and the presence of H041 in that population could mean a faster infection rate. Furthermore, Ohnishi and colleagues also emphasize that Japan does not have a national antimicrobial resistance surveillance program. Due to its initial prevalence in the sex work population, where STIs typically rapidly spread, as well as the lack of a national surveillance program, the researchers believe that the H041 strain can rapidly proliferate. The team explains that following the initial discovery of H041 in 2009, experts did create an antibiotic resistance surveillance program in Kyoto, the city where researchers first identified H041, but as of 2011, they had not identified any additional cases of H041 transmission or cases of treatment failure.

The authors conclude “Untreatable Gonorrhea” by arguing for the implementation of global public health interventions to combat the spread of antimicrobial-resistant gonorrhea. They explain that although the survival capacity of the H041 strain remains unknown, there is a possibility that it may lead to a superbug. According to Ohnishi and colleagues, therefore, it is important for countries worldwide to enhance their disease prevention and control activities to reduce the spread of the antibiotic-resistant strains.

Impact

As of 2024, researchers have cited “Untreatable Gonorrhea” 795 times according to Google Scholar, and those studies highlight the importance of understanding antibiotic resistance in gonorrhea and the implementation of global surveillance programs. In 2012, shortly after the team published “Untreatable Gonorrhea,” authors Daniel Golparian and Unemo, among others, published a study about F89, an additional highly cephalosporin-resistant strain of gonorrhea that researchers identified in France in 2010. The authors of that article cite “Untreatable Gonorrhea” to explain that F89 has a similar mechanism of resistance to H041 that involves the penAH041 allele, a penB DNA sequence, as well as the unknown factor X. However, they found that F89 derived from the ST1901 strain, a different strain of gonorrhea from H041. In 2017, a group of researchers, including Unemo, from various research institutions worldwide, published “Antimicrobial Resistance in Neisseria gonorrhoeae: Global surveillance and a Call for International Collaborative Action.” In that article, the authors discuss that many countries in Eastern Europe, Central Asia, parts of Latin, and Africa lack global gonococcal assistance surveillance programs. They explain that many of those setting have high rates of gonorrhea and lack of medical access to microbials, which fosters ideal conditions for gonococcal spread. The researchers cite “Untreatable Gonorrhea” and other studies describing ceftriaxone-resistant strains of gonorrhea as evidence to explain that all documented cases of scientists detecting ceftriaxone-resistant gonorrhea have taken place in well-resourced countries. Thus, the researchers argue that the current documentation does not represent the true global health burden of antimicrobial resistance by gonorrhea, since resource-constrained countries have limited programs and data. The authors state that surveillance resources must be in place in those countries to stop the gonococcal spread.

As of 2024, antibiotic-resistant gonorrhea continues to proliferate worldwide, but the CDC still recommends ceftriaxone as a first-line treatment. Gonorrhea continues to be a public health concern since the publication of “Untreatable Gonorrhea,” with 82 million new occurrences of gonorrhea globally in 2020. As of 2024, the CDC recommends that professionals treat gonorrhea with a 500-milligram single dose intramuscular injection. That is because only a few cases of ceftriaxone resistance have been reported in several countries, including Japan, Australia, France, and Spain, meaning it has not spread wide enough to prohibit the use of the medication. Although the CDC still recommends ceftriaxone as a first-line treatment, they do not advise cefixime as a treatment for gonorrhea. On 10 August 2012, shortly after the publication of “Untreatable Gonorrhea,” the CDC recommended stopping cefixime as a treatment for gonorrhea. As of 2024, researchers are working to develop other antibiotic agents and treatment strategies to address the potential spread of ceftriaxone resistance.

“Untreatable Gonorrhea” was one of the first publications to characterize the H041 strain of gonorrhea. The H041 strain demonstrated a high level of ceftriaxone resistance, thus limiting treatment of ceftriaxone as a first-line treatment drug for gonorrhea. “Untreatable Gonorrhea” allows researchers to understand the mechanism of H041 antimicrobial resistance and create new antibiotic drugs to treat gonorrhea and limit its spread.