by Malak Sadek and Rana Elyamany

Introduction

Neisseria gonorrhoeae is the causative agent of the sexually transmitted infection gonorrhea which is is the second most prevalent bacterial sexually transmitted infection worldwide. Its formal identification was in 1879 by the German bacteriologist Albert Neisser. Gonorrhea grows mainly in the warm, moist areas of the reproductive tract for both men and women. It can also grow in the mouth, throat, eyes, and anus.

Disease

Neisseria gonorrhoeae infections are acquired in humans by sexual contact. It is able to infect the lower genital tract, urethra in men and cervix in women (see Figure 1 and 2). Infected women may be asymptomatic (show no symptoms), but up to 50% show nonspecific symptoms including odorless mucopurulent, vaginal discharge and vaginal bleeding. Even infections without symptoms can also result in severe consequences. On the other hand, 90% of men with urethral infection have symptomatic mucopurulent penile discharge and dysuria. Gonococci can ascend to the upper genital tract, leading to serious diseases, such as epididymitis in men and cervicitis, endometriosis, and pelvic inflammatory disease in women. When N. gonorrhoeae infects the urogenital tract, it interacts with a variety of cells, including Polymorphonuclear leukocytes (PMNs or neutrophils). PMNs are professional cells of the immune system which often serve as the first line of host defense against the bacterial infection. N. gonorrhoeae can survive and replicate inside PMNs and this interactions likely play a critical role in the pathogenesis of infection (see Figure 3).

 

Epidemiology

Gonorrhea is a very common infectious disease. It is the second most prevalent sexually acquired infection in the United States, with more than 300,000 reported cases per year. The Center for Disease Control and Prevention (CDC) estimates that annually more than 700,000 people in the United States get new gonorrhea infections. The most recent data provided by the (CDC) indicate that reported cases have increased by almost 10% over the last 5 years. In 2013, 106.1 cases of N. gonorrhoeae per 100,000 persons were reported, representing an 8.2% increase in incidence from 2009. Approximately 75 percent of all reported cases of gonorrhea are found in younger persons 15 to 29 years of age. The prevalence of this infection has strong economic effects, as in 2008, the total lifetime direct medical cost of N. gonorrhoeae infections in the United States was estimated to be $162.1 million.

Virulence systems

Neisseria gonorrheae express a set of common mechanisms that allow its adaptation to the immune system and immune evasion. .Gonorrheae first attaches itself to the cells and the tissues using a rod shaped protein structure called Type IV pili that recognizes a molecule of the host and bind to it (the host is the human in whom the bacteria live and cause infection). Therefore Type IV pili is essential for virulence in N. gonorrhoeae because it mediates specific attachment to human mucosal cells, initiating the infectious process. It is known that type IV pili is formed from subunits of a protein called pilin, and a gene called pilE in the genome of N. gonorrhoeae, is responsible for encoding the pilin subunit. Notably, Type IV pili in gonorrhoeae is a surface antigen, an antigen is a substance that causes the immune system to produce large proteins called antibodies to identify and neutralize the bacteria. Because N. gonorrhoeae undergoes antigenic variation, the capacity to generate much more diversity in its surface antigens, it has the ability to resist the killing cells in the host. A mechanism called gene shuffling or gene conversion allows N. gonorrhoeae undergoes antigenic variation events.Through DNA recombination (DNA exchange between genes),pilE gene can exchange a part of itself with pilS gene copy. Subsequently a new variant of pilE protein will be produced which is not the same as the original one (see Figure 4). Producing different types of pili increases the chance of evading the immune system especially the antibodies response. Antibodies should bind to adhesions such as typeIV pili and prevent the attachment of the bacteria to the host cells. Furthermore antibodies increase the attachment of the bacteria to phagocytes (immune system cells that pick up and kill the bacteria by a process called phagoctosis) .Therefore, it is assumed that antibodies reacting with pili type IV could block the infection. However, switching of pili expression states alters bacterial interactions with host cells. Thus varying the antigens that are presented to the host immune system prevents antibodies binding to the bacterial surface and subsequently phagocytosis.

Treatment

N. gonorrhoeae has developed resistance to mainly all antibiotics introduced for treatment of gonorrhea. These drugs include: cefixime (an oral cephalosporin), ceftriaxone (an injectable cephalosporin), azithromycin, and tetracycline. N. gonorrhoeae is able to use number of mechanisms for antibiotics resistance including enzymes to degrade antibiotics. Recently, Centers for Disease Control and Prevention (CDC) recommends only ceftriaxone plus either azithromycin or doxycycline as first-line treatment for gonorrhea.

References:

Hill, S. A., & Davies, J. K. (2009). Pilin gene variation in Neisseria gonorrhoeae: reassessing the old paradigms. FEMS Microbiology Reviews, 33(3), 521–530.

JANET A. M. FYFE, C.S.C., AND JOHN K. DAVIES. 1995. The pilE Gene of Neisseria gonorrhoeae MS11 Is Transcribed from a s70 Promoter during Growth In Vitro. JOURNAL OF BACTERIOLOGY 177, No. 13: 3781–3787.

Lancaster et al (2015) Update on Treatment Options for Gonococcal Infections. Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy.

Rotman and seifet (2014) The Genetics of Neisseria Species. Annual Reviews 48: 405-431. doi: 10.1146/annurev-genet-120213-092007.

Seifert, A.K.C.a.H.S. 2012. A bacterial siren song: intimate interactions between Neisseria and neutrophils. Nature Reviews Microbiology 10, 178-190. doi: 10.1038/nrmicro2713.

Unemo, M., & Shafer, W. M. (2011). Antibiotic resistance in Neisseria gonorrhoeae: origin, evolution, and lessons learned for the future. Annals of the New York Academy of Sciences, 1230, E19–E28. http://doi.org/10.1111/j.1749-6632.2011.06215.x

by Rachel Vaughan and Cristina Mastromonaco

It begins…

Anthrax: it’s been plaguing humanity since… well, since the plagues. Bacillus anthracis has been

famously described by the Roman poet Virgil, and is suspected to have popped up as

the Plague of Athens and contributed to the fall of Rome. It brought medicine out of the dark ages: the study of anthrax gave definitive proof that contagious diseases can be attributed to a microorganism from a particular source, or reservoir, and was a pioneer in the field of vaccines [6]. 

Look at me!

So just what is anthrax? To go textbook, it’s an aerobic, gram-positive (Fig 2), spore-forming bacteria that is naturally found worldwide in soil, with a preference for growing in warm, wet climates [1, 2]. That means that when conditions are suboptimal, anthrax can change from an actively replicating, rod shaped bacteria into a dormant endospore form, which can resist drying out, extreme heat, cold temperatures, ultraviolet light and disinfectants [1, 2]. Anthrax is a zoonotic bacteria that mainly affects the hoofed animal, but can be transmitted to humans through contaminated animal products [2].

Anthrax attacks

For someone to get infected with anthrax, the bacteria needs a way in. Cutaneous anthrax, ingestion anthrax and  inhalational anthrax are the three traditional modes of transmission. Your whole body is basically designed to try and fight this kind of thing, but anthrax is a really resourceful attacker. The body’s immune response does its best to protect you from these invaders, but it is no match for the anthrax spore [2].

 

Virulence factors allow a microorganism to cause disease, and anthrax has some good ones. It uses a combination of a capsule and potent exotoxins to evade and destroy. The capsule forms a protective shell around the growing bacteria, allowing it to get into host cells and use them like a taxi cab to travel to your lymph nodes, where it can spread through the blood [2].

 

Stick it to me

So, all of this seems like old news. Blah blah, thousands of years, blah blah different types, blah blah scary disease. But there’s something currently happening with anthrax spores, and it’s worth taking a look at even if the extent of your interaction with animals can be characterized by the words “they’re delicious.”

Just when we thought that anthrax was a thing of the past – the CDC estimates that only about two cases of naturally-occurring anthrax are documented each year [4] – we were given the gift of something new and wonderful to dread instead of sleeping. In their infinite wisdom, illicit drug users found a way to bring an already vicious bacteria to a whole new level: supplies of heroin contaminated with anthrax made their way into the general population, and subsequently into the arms, legs, butts and groins of some very unlucky addicts.

 

Bear with us here: we’re going to look at some numbers, compiled in a 2014 issue of Eurosurveillance. Injectional anthrax has exhibited what’s called a bimodal distribution: it first presented itself en masse in December 2009 (having only cropped up previously in a single case in the year 2000), and was followed by a second cluster of cases in June 2012. From 2009-2010, 126 cases of anthrax contracted by heroin users were reported, 95% of which were diagnosed in bonnie Scotland, which unfortunately doesn’t seem to be able to add “pure, unadulterated narcotics” to its list of tourist attractions. Between 2012 and 2013, 15 more cases have emerged in a half a dozen different European countries A 33% mortality rate was reported the first go-around, but the fatality in this more recent wave is much higher, with an estimated 47% of cases resulting in death (Fig. 4).

 

Looking at an overview of the case studies, we can see the differences in disease characteristics. Despite this anthrax presenting similarly to cutaneous initially, the primary symptom – instead of being something easy-to-spot like an eschar – was disproportionate inflammation. This inflammation is pretty special, because not only are pain, fever and redness uncommon, it doesn’t seem to elicit any of the standard markers for inflammation, like a higher number of white blood cells or elevated levels of C-reactive protein (CRP). It’s pretty weird – they suspect that it’s tied to  the more immediate action of the edema factor within the tissue, as it doesn’t have to cross the regular barriers [7]. So essentially, injectional anthrax presents most frequently as a kind of deep-tissue cutaneous anthrax with skin infection and blistering, but without any of the helpful markers for the disease that doctors look for. This, along with anthrax’s current state of “how on Earth would you get exposed to THAT?” led to some confusion and misdiagnosis, as the symptoms present similarly to a few other diseases.

The most common cause of death was when the infection went systemic instead of being nicely localized in the injection site. Since the bacteria spread all throughout your body, systemic  anthrax often results in one of the most terrifying kinds of inflammation: meningitis (Fig. 5). There are three layers called the meninges wrapped around your brain and spinal cord. Large numbers of bacteria between the layers spells bad news for your brain, and in the case of anthrax, meningitis kills about 96% of the time [5]. Once the bacteria has gone systemic, it’s easy to see why it appeals to strongly to those in the heavy metal profession: the presence of large quantities of anthrax bacilli in your blood stream turns your blood so dark that it appears black.

 

The kicker is that despite the term “injectional anthrax,” at least two patients were likely infected by smoking the drug. That being said, those who smoked only had a much lower risk of developing the disease. That’s actually a pretty interesting development – despite having introduced the spores to their lungs, which would be ripe for colonization, respiratory symptoms were very rare.

 

Where did it come from, where will it go?

So, since anthrax is so uncommon in the modern world, just how did it worm its way into the European heroin supply? It was believed up until last month that all cases of injectional anthrax came from the same contamination in  Turkey, but this is unlikely to be the case. Genetically analyzing all available isolated strains (or isolates) of injectional anthrax suggests that there were at least two separate contamination events – one for each outbreak – as there are two different genetic clusters of anthrax bacilli. They’re not related closely enough on the anthrax family tree to have come from the same source, and according to their genetic makeup, they branched off at completely different times. The evidence does suggest that they come from the same country, but this is not necessarily true [9].

Why do you care? Presumably the grand majority of you aren’t exactly the at-risk population. Sure, it’s scary for heroin users, who may be at risk for another spore contamination event, but what if your drug of choice is caffeine or ethanol? Since we don’t know exactly how the spores got into the heroin supply in the first place – via the smuggling route, from contaminated animal products used to bulk the heroin (like whatever it is they put into hotdogs) or from an intentional dose – there’s no way of predicting where contamination could go next. Anthrax may next find its way into any of the many imported products that you use in your daily life. Sugars, teas, oils or that gorgeous rug that you bought at the local market could easily be the next source of anthrax exposure to the general population.

References

[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523299/

[2] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4073855/?report=classic

[3] http://www.ncbi.nlm.nih.gov/pubmed/19627991

[4] http://www.cdc.gov/nczved/divisions/dfbmd/diseases/anthrax/technical.html#trends

[5] http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(05)70113-4/fulltext

[6] http://www.sciencedirect.com/science/article/pii/S0736467903000799

[7] http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20877

[8] http://www.sciencedirect.com/science/article/pii/S0140673600031330

[9] http://www.sciencedirect.com/science/article/pii/S2352396415301705

 

 

by Bernice Samuel and Jasraj Kaur

Introduction

Vibrio cholerae is a member of the Vibrionaceae family and exists as a facultative anaerobic bacterium characterized by its non-pore forming, Gram-negative behaviour and comma shape. V. cholerae was first isolated as the cause of cholera by an Italian anatomist in 1854 but his research was not broadly recognized until later in 1884. Cholera is an acute state whereby a person suffers from severe watery diarrhea which leads to dehydration and even death if untreated. The main sources of V. cholerae are human faeces and water.

Disease

V. cholerae is transmitted through the ‘fecal – oral route’. In the last phase of causing disease, it escapes into the feces which enables it to enter water. In places where sanitary water is unavailable, the pathogen is quick to be transmitted orally. Once it reaches the stomach, the acidity is a great protective mechanism and destroys V. cholerae almost entirely. However, a small amount makes it to the bowel of the small intestine where it is able to re-establish its population. Through the production of toxins, epithelial cells in the small intestine are induced to secrete vast amounts of electrolytes and water. This excess fluid is excreted from the body in the form of diarrhea and to a lesser extent vomiting. The amount of water loss varies between individuals, depending on the strain they are infected with and the amount that colonizes in the bowel. It is important to note that most strains are ‘free – living’ (can live independently without a host) and only a few such as the O1 and O139 are responsible for causing disease. Individuals accredited with having cholera release life-threatening levels of water (as much as 20L a day) which, in turn, results in hypovolemic shock. In simple terms, the excessive loss of fluid prevents the heart from pumping enough blood to the body, resulting in a weakened pulse. Other symptoms defining the onset of cholera include having muscle cramps, a scaphoid abdomen and loss of skin turgor. In other words, the elasticity of the body’s organs dampen. Furthermore, if the individual is not hospitalized, a new condition called tubular necrosis develops whereby the epithelial cells of the kidney die, immediately resulting in the death of the individual.

 

Epidemiology

There have been many cholera pandemics over the past years with most common cases occurring in tropical and subtropical regions. The World Health Organization (WHO) estimated that 3-5 million cholera cases occur predominantly in Asia and Africa. Most cholera cases occur in children under 5 years old and pregnant women. Epidemics in endemic areas tend to occur during the hot season.

Drinking water contaminated with V. Cholerae or with faeces of an infected person are the most common ways to acquire Cholera. Other hosts range from planktons and zooplankton that have the infectious agent. Environmental factors such as surface change and terrestrial nutrient discharge can lead to production of more hosts. The Haiti cholera is the worst epidemic in recent history that has killed at least 8 534 people and hospitalized hundreds of thousands while spreading to neighbouring countries as well.

Virulence systems

Once the bacteria establishes itself in the bowel, it must penetrate the mucous to reach the epithelial layer. Its long tail allows it to propel itself through this thick layer along while the bacteria also produces mucianlytic enzymes which destroy mucous integrity. Upon reaching the epithelial layer, the bacterium anchors itself onto microvilli by a mechanism yet to be understood. However, the so – called ‘coregulated pilli’ is suggested to be one of the key players. Furthermore, the way by which the bacterium induces excessive leakage of fluid from the cells is described in the following virulence mechanism. It secretes a protein polymer known as cholera toxin which binds to epithelial cells. Subunit B of this polymer binds to the glycolipids exposed on the outside of the host cell, bringing the bacterium and host cell in closer contact. The A subunit can then penetrate the host cell membrane whereby a cascade of intracellular molecular events takes place resulting in higher cAMP (Cycline adenosine monophosphate) levels (figure 1). This, for a reason yet to be understood, causes the secretion of chlorine, bicarbonate and water by the epithelial cells contacted by the toxin. The fluid accumulates to high levels and the body’s only option is to dispense it – mainly through the form of diarrhea. As high as 10⁸ live Vibrio’s are found in 1 ml of diarrhea allowing it to effectively contaminate water that is then consumed by the host.

Treatment

Cholera is curable but because dehydration happens so quickly, it is essential to get antibiotics that kill the bacteria. Antibiotics are mainly used to decrease the diarrhea duration and reduce the bacteria excretion that help avoid the rapid disease spread by 50%. Although there is a vaccine against cholera, drinking water that has been boiled and chemically disinfected is the best way to avoid it.

Reference

Baron, S., & Finkelstein, R. A. (1996). Cholera, Vibrio cholerae O1 and O139, and Other Pathogenic Vibrio.

Collins, C. H., & Kennedy, D. A. (Eds.). (1983). Laboratory-acquired Infections (4th Ed.). Oxford: Butterworth-Heinermann

Harris JB, LaRocque RC, Qadri F, Ryan ET, Calderwood SB (2012) Cholera. Lancet 379: 2466–2476.

Orata FD, Keim PS, Boucher Y (2014). The 2010 Cholera Outbreak in Haiti: How Science Solved a Controversy

Ryan, K. J. and Ray, C. G. (Eds.). (2004.). Sherris Medical Microbiology: An Introduction to Infectious Disease. (Fourth Edition). New York. McGraw-Hill

Wong, C. K, Brown, A. M, Luscombe, G. M, Wong, S. J and Mendis, K. (2015). Antibiotic use for Vibrio infections: important insights from surveillance data.

 

by Sebastien Faucher

Introduction

Legionella pneumophila is the causative agent of Legionnaires’ disease. This bacterium was isolated in 1977 after a large outbreak of pneumonia stroke Philadelphia in 1976. L. pneumophila can be found in almost any man-made or natural water systems. In this environment, L. pneumophila infects and grows inside amoeba, unicellular animals that normally feed on bacteria.

Disease

L. pneumophila is transmitted to humans by inhalation of contaminated aerosols. Once in the lungs, L. pneumophila is able to infect lung macrophages (Figure 1). Macrophages are cells of the immune systems whose role is to take up and digest invading pathogens. L. pneumophila is able to block the normal activity of the macrophage and use it as a bag of food. This results in the death of the infected macrophage. The infection also causes damage to the nearby lung tissues. In healthy individuals, the infection is cleared by the immune system and is usually asymptomatic, but sometimes symptoms similar to a mild cold may appear. In such case the infection is referred to as Pontiac’s fever. When the immune system of the person infected is unable to clear the infection, massive lung damage will result from it. This is what is called Legionnaires’ disease and the symptoms are similar to pneumonia, including headache, chest pain, fever, non-productive cough and diarrhea.

Epidemiology

The rate of confirmed Legionnaires’ disease in Ontario for 2008 is 0.61 per 100,000 people. Since the cause of most pneumonia cases is not investigated, the actual rate of the disease is probably much higher. In some European countries, L. pneumophila is now recognized as one of the most common cause of pneumonia. Elderly, males, heavy smokers, alcohol abusers and immunocompromised individuals are more susceptible to the disease. During outbreaks, the mortality rate is typically around 10%.

Contaminated cooling towers located in densely populated area are usually the cause of outbreaks of Legionnaires’ disease, since many individuals are exposed to the aerosols produced. One notable outbreak is the 2012 Quebec City outbreak, which affected 183 persons, including 13 deaths. Sporadic cases also exist. They are usually caused by an isolated source, such as a contaminated domestic water heater. Therefore, only the members of the household where the contaminated unit is located are exposed to the contaminated aerosols, during showering for example.

Virulence systems

During bacterial lung infection, macrophages are called-in to eat and digest the bacteria. A macrophage picks up L. pneumophila by a process called phagocytosis. At this point L. pneumophila is located in a phagosome, a sort of bag, inside the macrophage (Figure 2a). Normally, bacteria that are taken up by a macrophage will be killed and digested. The macrophage accomplishes this by pumping toxic proteins and chemicals into the phagosome. The macrophage is protected from their toxicity because they are activated only once inside the phagosome.

To the demise of the macrophages, L. pneumophila is able to fight back by inhibiting the digestion process of the macrophage. L. pneumophila uses a secretion system called Icm/Dot to take control of the macrophage. This system acts like a syringe to inject toxins through the wall of the phagososme inside the macrophage (Figure 2b). The toxins then modify the normal properties of the macrophage to stop the digestion process describe above by preventing the pumping of toxic enzymes and chemicals insto the phagosome. Moreover, the toxins stimulate the transport of nutrients into the phagosome to support the multiplication of L. pneumophila (Figure 2c). When the bacteria have consumed all the nutrients inside the macrophage, one of the toxin triggers the destruction of the macrophage allowing L. pneumophila to escape and infect other macrophages (Figure 2d). L. pneumophila also produces a number of proteases, enzymes that degrade proteins, which destroy the nearby tissue causing damage to the lungs.

Treatment

L. pneumophila is usually susceptible to antibiotics normally prescribed to fight pneumonia, such as azithromycin. This antibiotic stops the synthesis of proteins, such as the toxins secreted by the Icm/Dot system, neutralizing the ability of L. pneumophila to inhibit the digestion process of the macrophage. Since L. pneumophila causes damage to the lung tissues, early start of the antibiotic treatment usually means better chance of survival.

References

Albert-Weissenberger, et al. (2006). Legionella pneumophila — a human pathogen that co-evolved with fresh water protozoa. Cell Mol Life Sci 64, 432–448.

Diederen, B. M. W. (2008). Legionella spp. and Legionnaires’ disease. J Infect 56, 1–12.

Fraser, D. W., et al. (1977). Legionnaires’ disease: description of an epidemic of pneumonia. N Engl J Med 297, 1189–1197.

McDade, J. E., et al. (1977). Legionnaires’ disease: isolation of a bacterium and demonstration of its role in other respiratory disease. N Engl J Med 297, 1197–1203.

Ng, V., et al. (2009). Laboratory-based evaluation of legionellosis epidemiology in Ontario, Canada, 1978 to 2006. BMC Infect Dis 9, 68.

Marrie, T. J., Garay, J. R. & Weir, E. (2010). Legionellosis: Why should I test and report? Canadian Medical Association Journal 182, 1538–1542.