Campylobacter, Helicobacter, Bartonella and Rickettsiaceae

Dear students, in this sheet we will mainly go through 4 different types of bacteria (pathogens ) that cause diseases and they are Campylobacter, Helicobacter, Bartonella and Rickettsiaceae. 1- Campylobacter - It is small gram negative rods , motile and curved. - Campylobacter is the most common cause of bacterial gastroenteritis, with (Campylobacter jejuni) being responsible for most infections. So, the pathogen that we are most interested with is Campylobacter jejuni (C. Jejuni), because it cause the most of the damage in the part of the mucosal surface of the intestine called jeujenum. The growth condition of this bacteria are meant to be fastidious. In other words, it needs microaerophilic conditions. (microaerophilic means that this bacteria need different concentraions of oxygen) .The organisms grow best in an atmosphere of reduced oxygen (5% to 7%) and increased carbon dioxide (5% to .10%).C. jejuni grows better at 42° C than at 37° C - These bacteria express lipooligosaccharides ( LOS s) >>> (LOSs lack O-antigen in LPS) - The organisms are killed when exposed to gastric acids, so conditions that decrease or neutralize gastric acid secretion favor disease. Now let's have a look at the following picture 1|Page As you can see, these test tubes represent a certain media to determine the oxygen requirements of microorganisms of the bacteria. This media is called Thioglycolate media. - Obviously. The obligate aerobes grow on the top of this media. However, the obligate anaerobes can be seen grwon at the bottom of the media as they are harmed by thr oxygen or even to avoid the oxygen. Also, the facultative anaerobes which use the oxygen present and sometimes use this oxgen to undergo, for exmaple, fermentaion. Furthermroe, aerotolerant anaerobes don’t use oxygen for growth but are tolerate to its presence, so the absence or the presence of oxygen doesn’t make any difference for them and that's why you may notice them in the tube growing randomly inside it as they like!. Finally, we have microaerophiles which grow at a certain level in the tube forming a band, as at this level, they require a specific concentrations of oxygen. Namely, (microaerophile is a microorganism that requires O2 to survive, but requires environments containing lower levels of oxygen than are present in the atmosphere) ( <21% O2). Remember that C. jejuni referred to as microaerophilic as it better grows at 42° C than at 37° C. Note: As Campylobacter bacteria express (LOSs), they have different toxicity profile from the ones that contain lipopolysaccharides (LPSs). - Campylobacter infections are described as zoonotic infections, which means they can be mostly found in animals serving as reservoirs. Contaminated poultry are responsible for more than half of the Campylobacter infections in developed countries. Also, it is uncommon for the disease to be transmitted by food handlers. - Some of the symptoms that might be caused by (C. Jejuni) are acute enteritis with diarrhea (may may be bloody on gross examination), fever and severe abdominal pain. 2|Page This pictue outlines themicrobiological findings among US emergency department patients presenting with 549 episodes of bloody diarrhea. In other words, these details show the most pathogens that cause bloody diarrhea once isolated, according to those U.S findings. Guillain-Barré syndrome and reactive arthritis are well-recognized complications of Campylobacter infections (although uncommon). Probably through molecular mimicry. Additional information to just understand the concept of Molecular mimicry . Molecular mimicry: is defined as the possibility that sequence similarities between foreign and self-peptides are sufficient to result in the cross-activation of autoreactive T or B cells by pathogen peptides. A presumptive identification of isolates is based on growth under selective conditions, typical microscopic morphology, and positive oxidase and catalase tests -------------------Up to here, Campylobacter has been thoroughly discussed ----------------------- 2- Helicobacter - This species are considered to be spiral gramnegative rods resembling campylobacters. All gastric helicobacters, including H. pylori, are highly motile (corkscrew motility) and strong producers of urease. Additionally, they are catalase positive and oxidase positive. Note that some infections are not necessarily caused due to toxins of bacteria. However, they could also be resulted by the molecular mimicry just like what happens with Rheumatic fever. So, there are some bacterial antigens that can be recognised by the immune system and 3|Page at the same time have similar structure to those antigens found in the body, thus, an immune response will act against them. Guillain-Barre syndrome can also be involved in this type of bacteria. GuillainBarre syndrome is a rare disorder in which your body's immune system attacks your nerve and eventually paralyzing the whole body. Thus, it is considered as a medical emergency. Moreover, in terms of their (H. pylori ) identification conditions, they grow in selective conditions such as increased temperature and microaerophilic environemnt in additoin to the fact that H. pylori adheres to gastric mucosa and is not usually recovered in stool or blood specimens. H. pylori and other helicobacters requires a complex medium in microaerophilic conditions - H.pylori use their motility, chemotaxis, urease production, and other mechanisms to adapt to the acidic conditions of the stomach and colonize a narrow protected region near the surface of epithelial cells. Helicobacter is special in a form that they have the ability to colonize the stomach too, and escape (evade) the gastric acids by their motility and chemotaxis reaching the mucous that lines the gastric epithelium and then using their adhesion tools to bind to this gastric epithelium. Therefore, in this case, while Helicobacter produce an enzyme called urease that breaks down the urea to give ammonia, they are further buffering the gastric acid. H.pylori overlies gastric but NOT intestinal epithelial cells. - So, H.pylori can cause acute gastritis as a gatsrtic epithelial damage and hypochlorhydria ( a case in which, people are ununable to produce enough hydrochloric acid (HCL) in the stomach). H pylori is responsible for 85% of the gastric ulcers and 95% of the duodenal ulcers. Here is a figure down below (form the slide) illustrates the tissue damage caused by urease 4|Page Localized tissue damage is mediated by urease byproducts, mucinase, phospholipases, and the activity of vacuolating cytotoxin A (VacA), a protein that after penetration into epithelial cells damages the cells by producing vacuoles. cytotoxin-associated gene (cagA) interferes with the normal cytoskeletal structure of the epithelial cells - The acute phase of gastritis is characterized by a feeling of fullness, nausea, vomiting, and hypochlorhydria. However, chronic gastritis will progress to develop peptic ulcers. The ulcers develop at the sites of intense inflammation, commonly involving the junction between the corpus and antrum (gastric ulcer) or the proximal duodenum (duodenal ulcer). In addition, chronic gastritis increases the risk of gastric cancer and MALT lymphoma (mucosa-associated lymphoid tissue B-cell lymphomas). - Regarding the diagnosis of the diseases caused by this bacteria, as H. pylori adheres to gastric mucosa , H. pylori can be detected by histological examination of gastric biopsy specimens, but identification is usually done by non-invasive methods. A number of poly-clonal and mono-clonal immunoassays for H. pylori antigens excreted in stool, have been developed and demonstrated to have sensitivities and specificities exceeding 95%. -------------------Up to here, Helicobacter has been thoroughly discussed --------------------- 3- Bartonella with this type of bacteria, we will mainly talk about Bartonella Henselae ( B. Henselae) which causes a disease know as cat-scratch disease (a disease acquired after exposure to cats) such as scratches, bites, contact with the contaminated feces of cat fleas. Furthermore, it develops 1-3 weeks after contact with a cat. 5|Page Bartonella are gram-negative, coccobacillary or bacillary rods with fastidious growth requirements, requiring prolonged incubation (2 to 6 weeks). usually facultative intracellular bacteria. - Bartonella species are transmitted by vectors such as ticks, fleas, sand flies, and mosquitoes. These vectors carry this bacteria with them and then get attached to the cat, so the cat now is carrying this pathogen and transmits it to human body (if the human gets bitted or scratched by the cat). B. henselae is responsible for a disease acquired after exposure to cats (e.g., scratches, bites, contact with the contaminated feces of cat fleas): cat-scratch disease, 1–3 weeks after inoculation. However, symptoms typically include a non-painful bump or blister at the site of injury and painful and swollen lymph nodes. Some of the regional lymph nodes are axiilary, epi-trochlear, or cervical most commonly). Usually, these symptoms emerge with a self-limited disease unless it occurs with immune-compromised patients. Also, there are another diseases that might be caused by Bartonella species. This includes Carrion's disease (by Bartonella Bacilliformis) and trench fever (by Bartonella Quintana). -------------------Up to here, Bartonella has been thoroughly discussed --------------------- 4- Rickettsiaceae - Finally, this is the last pathogen (bacteria) in this sheet being illustrated. This bacteria is obligate intracellular, aerobic, gram-negative rods, and grow only in the cytoplasm of eukaryotic cells. Seen best with Giemsa stain (It can be used to study the adherence of pathogenic bacteria to human cells. It differentially stains human and bacterial cells purple and pink respectively). - Rickettsia can be put into 2 groups depending on the disease they cause. To illustrate, they are subdivided into the spotted fever group and the typhus group. Also, this bacteria can be carried on vectors like fleas, lice, mites, and ticks (remember how cat-scratch disease is caused!) and we should mention that all age groups are at risk for Rickettsial infections during travel to endemic areas (e.g. When you go for hiking). 6|Page - The distribution of Rickettsial diseases is determined by the distribution of the arthropod host/vector . Moreover, the symptoms emerged by this bacteria appear usually after a week from the infection time. So you can be bitten by these species and after a period of time you might be noticing some fever, muscle weakness and maybe tiredness and fatigue. - Most importantly, Rickettsia does NOT cause most of its damage through toxins but via replicating inside the cells then destroying them. So it can be included that the primary clinical manifestations appear to result from the replication of bacteria in endothelial cells, with subsequent damage to the cells and leakage of the blood vessels . cells by Rickettsia (from inside out) can - The destroying either undergo necrosis or apoptosis by the end. Sometimes the immune system can fight this bacteria but often it can't do that leading to tissue destruction as Rickettsia duplicates inside the tissue. The following table had been discussed by the doctor during the last 10 mins. of the lecture. However, you may just focus on the red-marked types in this table. Refer to record 19 on the site if you like. 7|Page Epidemic typhus caused by R. prowazekii infection is rarely reported among tourists but can occur in impoverished communities and refugee populations where body lice are prevalent. Tick-borne spotted fever rickettsioses are the most frequently reported travel-associated Rickettsial infections. 8|Page