GIT Infections PDF

Section Gastrointestinal (GI) Infections 5 Section Outline 39. Gastrointestinal Infective Syndromes 40. Food Poisoning: S. aureus, Bacillus cereus, Cl...

Section Gastrointestinal (GI) Infections 5 Section Outline 39. Gastrointestinal Infective Syndromes 40. Food Poisoning: S. aureus, Bacillus cereus, Clostridium botulinum and Others 41. Gastrointestinal Infections due to Enterobacteriaceae: Diarrheagenic Escherichia coli, Shigellosis, Nontyphoidal Salmonellosis and Yersiniosis 42. Cholera, Halophilic Vibrio and Aeromonas Infections 43. Miscellaneous Bacterial Infections of Gastrointestinal System: Helicobacter, Campylobacter and Clostridioides difficile Infections 44. Viral Gastroenteritis: Rotaviruses and Others 45. Intestinal Protozoan Infections: Intestinal Amoebiasis, Giardiasis, Coccidian Parasitic Infections, Balantidiasis, Blastocystosis, and Others 46. Intestinal Helminthic Infections  Intestinal Cestode Infections: Diphyllobothrium, Taenia, Hymenolepis and Others  Intestinal Trematode Infections: Fasciolopsis buski, Schistosoma mansoni, S. japonicum and Others  Intestinal Nematode Infections: Trichuris, Enterobius, hookworm, Strongyloides, Ascaris and Others  Chapter Gastrointestinal Infective Syndromes 39 Chapter Preview „„Resident Microbial Flora „„Diarrheal Diseases „„Other Infective Syndromes of GIT Gastrointestinal (GI) infections are among the most various vitamins, modulating the immune system, etc., commonly encountered infective syndromes in man (Table (discussed in detail in Chapter 7). 39.1). At the same time, the human gastrointestinal tract (GIT) colonizes a number of resident microbial flora, which Diarrheal Diseases provide several beneficiary effect. The diarrheal diseases are one of the leading cause of illness globally; cause significant morbidity and mortality. Resident Microbial Flora ™™ Worldwide, about 1.7 to 5 billion cases of diarrhea occur Human GIT is colonized by diverse group of normal per year, with 1.26 million deaths; accounting for the resident microbial flora. second leading cause of death globally ™™ Upper GIT contains only sparse flora (streptococci in ™™ It is more common in developing countries, where oral cavity and lactobacilli in stomach) young children get diarrhea on an average three times ™™ Lower GIT: The microbial load gradually increases a year towards lower part of GIT and is highest in the distal ™™ There are various clinical types of diarrheal diseases ileum (1011 to 1012/g). (enlisted in Table 39.1 and described below); caused by „„ The large bowel comprises of both anaerobes and a wide variety of infectious agents including bacteria, aerobes with a ratio of 1,000:1; with Bacteroides viruses, and parasites (Table 39.2). fragilis (most common) and Enterobacteriaceae such as E. coli, Klebsiella present predominantly Diarrhea „„ Normal flora also comprises of yeasts (e.g. Candida) Diarrhea is defined as passage of three or more loose or and parasites (e.g. Entamoeba coli). liquid stools per day, in excess than the usual habit for that Normal GI flora has several benefits such as preventing person (World Health Organization). colonization of pathogens in the intestine, synthesizing ™™ It may be caused by microbial infections, or as a result of other gastrointestinal diseases such as inflammatory Table 39.1: Gastrointestinal infective syndromes. bowel diseases, coeliac disease, etc. Diarrheal diseases ™™ Acute diarrhea usually lasts for 4 America weeks. May result from infections due to various organisms. ™™ Clinical presentation: Most cases begin within the ™™ Parasites (e.g. Cryptosporidium, Cyclospora, Entamoeba first 3–5 days; characterized by a sudden onset of histolytica, Giardia) account for a major cause of chronic abdominal cramps, anorexia, and watery diarrhea. diarrhea The illness is generally self-limited, lasting for 1–5 ™™ Bacteria (e.g. Aeromonas, Campylobacter, Clostridium days difficile, Plesiomonas) ™™ Microbial agents causing traveler’s diarrhea ™™ Viruses such as cytomegalovirus, common in immuno­ are listed in Table 39.3. Overall, enterotoxigenic compromised host Escherichia coli is the most common agent, followed ™™ Fungi such as microsporidia, common in immuno­ by enteroaggregative E. coli. Campylobacter jejuni compromised host. is more common in Asia. Norovirus diarrhea is Chronic diarrhea may also result from various associated with traveling on cruise ships. noninfectious etiologies such as pancreatic disorders,  Chapter 39  Gastrointestinal Infective Syndromes 389 Table 39.3: Agents causing traveler’s diarrhea. Table 39.4: Pathogenic mechanisms of diarrheal agents. Etiologic agent Comments Toxin production Bacteria (50–75%) Enterotoxins Cytotoxins Neurotoxins Enterotoxigenic E. coli Single most important agent Cholera toxin Shigella dysenteriae Staphylococcus (10–45%) Vibrio parahaemolyticus type 1 aureus enterotoxin E. coli Enterohemorrhagic Bacillus cereus Enteroaggregative Emerging enteric pathogen with LT and ST of ETEC E. coli toxin E. coli (5–35%) worldwide distribution EAST of EAEC Clostridioides difficile Clostridium Campylobacter jejuni More common in Asia VT of EHEC (toxin B) botulinum toxin (5–25%) Clostridioides difficile Shigella, Enteroinvasive Major cause of dysentery (toxin A) E.coli Aeromonas Rotavirus (NSP4) Non-typhoidal salmonellae Common agent in India Campylobacter jejuni Others Including Aeromonas, Attachment within or Invasion of intestinal epithelium Plesiomonas, and Vibrio cholerae close to mucosal cells Viruses (17 cases. O139 (Bengal Strain) ™™ El Tor dominance continues, while O139 causes minority It was isolated first from Chennai in 1992. Since it was not of cases agglutinated by any of the antisera available at that time (O1 ™™ NICED: National reference Center for cholera in India to O138), it was designated as a new serogroup O139 or the is located at National Institute of Cholera and Enteric Bengal strain as it spread rapidly along the coastal region of Diseases (NICED), Kolkata. Bay of Bengal up to West Bengal, then to the adjacent areas of Bangladesh. Epidemiological Determinants ‰‰ O139 appears to be a derivative of O1 El Tor, but differs from the latter in having a distinct LPS and being capsulated. ™™ Reservoir: Humans are the only reservoir of infection. As a result, it is invasive, can cause bacteremia and There is no known animal reservoir extraintestinal manifestations ™™ Source: The source of the infection may be either ‰‰ There is no cross-protection between O1 and O139 asymptomatic cases or carriers ‰‰ O139 had caused large-scale outbreaks of clinical cholera ™™ Carriers: Asymptomatic carriers play an important role and spread rapidly across almost 11 Asian countries and in transmitting cholera over long distances became a threat to cause the next pandemic „„ Although carriage usually is short-lived, a few ‰‰ However, by 1994 the fear had come down and once again the O1 El Tor became dominant and largely individuals may excrete the organisms for a prolonged replaced O139 period ‰‰ Currently, O139 still causes a minority of cases in India and „„ In general, biotype El Tor has more carrier rate than Bangladesh. classical. The case–carrier ratio is 1: 50 for the classical biotype and 1:90 for the El Tor biotype Current Situation „„ Patients when effectively treated do not become carriers after they recover, but can be reinfected if In the World exposed again. Cholera is a notifiable disease. However, it is often under ™™ Cholera season: Maximum transmission is associated reported, hence the true incidence is unknown. with high temperatures, heavy rainfall and flooding, but ™™ WHO has estimated that more than 1.3-4 million cases cholera can occur throughout the year of cholera occur every year, resulting in 21,000 to 1.4 ™™ Other factors that promote transmission include Lakh deaths annually poor sanitation, poverty, overcrowding, population ™™ During 2017,12.2 lakh cases were notified to WHO, mobility (as occurs in pilgrimages, fairs, festivals and including 5,654 deaths. The number of cholera cases marriages) decreased globally by 60% in 2018 (4.9 lakh cases and ™™ Factors determining severity of the disease include: 2,990 deaths) „„ Lack of pre-existing immunity ™™ Several outbreaks have been recently reported such as „„ Persons with ‘O’ blood group are at greater risk of from Yemen in the year 2016-2018 (large scale outbreak severe disease if infected, while those with type AB with >6 lakh cases and >2000 deaths reported), Nigeria in blood group are at least risk. The reason is not clear. 2017, Zimbabwe (2018–19), Algeria (2018) and Somalia „„ Malnutrition >10,500 cases in 2017–20 „„ People with low immunity (e.g. HIV infected people). ™™ The majority of cases are due to O1 El Tor. However, ™™ Age: During inter epidemic period, all the age groups occasional cases may occur due to O139 and classical are affected equally, however during epidemics it affects biotype, especially in Bangladesh. more number of children Ending cholera: A Roadmap to 2030—In 2017, WHO ™™ Habitat: V. cholerae is a natural inhabitant of coastal sea launched this strategy for cholera control; which aims to salt water and brackish estuaries, where the organism reduce cholera deaths by 90% and to eliminate cholera in can persist for long periods, particularly in association as many as 20 countries by 2030. with small crustaceans, such as copepods, crabs or plankton In India ™™ Persistence of V. cholerae: The situation has greatly changed in India both geographi- „„ During epidemics, it is maintained by carriers and cally as well as in terms of number of cases and deaths. subclinical cases 414 Section 5  Gastrointestinal (GI) Infections In inter epidemic period, it is maintained in sea water, „„ swabs may be inoculated in 10–20 mL of one of the following crustaceans and planktons. transport media: ™™ Resistance ™™ Venkatraman-Ramakrishnan (VR) medium „„ V. cholerae is acid-labile but stable to alkali ™™ Alkaline salt transport medium „„ It is heat-labile (killed within 30 minutes by heating ™™ Cary-Blair medium: It is also useful for Salmonella and at 56°C or within few seconds by boiling), but stable Shigella to refrigeration and can remain in ice for 4–6 weeks ™™ Autoclaved sea water. „„ Drying and sunshine can kill the bacilli in few hours „„ It is susceptible to disinfectants, such as cresol and Direct Microscopy bleaching powder (6 mg/L) ™™ Gram staining of mucus flakes of feces reveals short „„ In general, biotype El Tor is more resistant than curved comma-shaped gram-negative rods, arranged classical. in parallel rows, which is described by Koch as fish in stream appearance (Fig. 42.3) L aboratory diagnosis Cholera ™™ Motility testing by hanging drop method: They are ‰‰ Specimens: Watery stool or rectal swab (for carriers) actively motile frequently changing their direction, ‰‰ Transport media: VR medium, Cary-Blair medium described as darting motility (dart means a small, ‰‰ Direct microscopy slender, pointed missile which shows sudden, rapid ¾¾ Gram-negative rods, short curved comma-shaped (fish in movement when thrown at a target). It is also described stream appearance) as shooting star or swarming gnats motility. ¾¾ Hanging drop-demonstrates darting motility ‰‰ Culture Culture ¾¾ Enrichment broth: Alkaline peptone water, Monsur’s V. cholerae is strongly aerobic, non-fastidious; grows well taurocholate tellurite peptone water on ordinary media, such as nutrient agar. ¾¾ Selective media: Bile salt agar, Monsur’s GTTT agar, TCBS ™™ However to inhibit the commensals, fecal specimen agar (yellow colonies) ¾¾ MacConkey agar-produces translucent NLF colonies should be inoculated simultaneously onto enrichment ‰‰ Culture smear and motility testing—reveals broth and selective media ¾¾ Short curved gram-negative bacilli and ™™ These media contain salt (0.5–1%), which stimulates its ¾¾ Darting motility growth and have alkaline pH, which allows V. cholerae to ‰‰ Identification grow, while inhibiting the fecal commensals. ¾¾ Catalase and oxidase positive ¾¾ ICUT: Indole (+), Citrate (+/–), Urease (–), TSI:A/A, gas (–), Enrichment Broth H2S (–) Fecal specimen is inoculated onto enrichment broth, ¾¾ String test positive following which they are incubated for 4–6 hours. Thereafter ¾¾ It produces hemodigestion on blood agar a subculture is made onto another selective medium (as ¾¾ Automated systems such as MALDI-TOF and VITEK ‰‰ Biotyping: To differentiate classical and El Tor ‰‰ Serogrouping: To differentiate O1 and O139 ‰‰ Serotyping: To differentiate Ogawa, Inaba and Hikojima serotypes of serogroup O1 ‰‰ Antigen detection by cholera dipstick assay ‰‰ Molecular method—multiplex PCR detecting common diarrheal pathogens ‰‰ Antimicrobial susceptibility testing. Laboratory Diagnosis Specimens ™™ Freshly collected watery stool is the specimen of choice for acute cases. Ideally, it should be collected before starting the antibiotics ™™ Rectal swab is the preferred specimen for convalescent patients or carriers. Fig. 42.3: Vibrio cholerae (Gram stain): Curved comma-shaped Transport/Holding Media gram-negative rods (fish in stream appearance). Specimens should be transported immediately to the Source: Public Health Image Library, ID#:5324/Centers for Disease Control and laboratory. If delay is expected, stool (1–3 mL) or rectal Prevention (CDC) (with permission).  Chapter 42  Cholera, Halophilic Vibrio and Aeromonas Infections 415 listed below). Prolonged incubation of the broths should „„ Urease test—negative be avoided as the commensals may overgrow. „„ TSI (triple sugar iron agar test)—Being sucrose ™™ Alkaline peptone water (APW) fermenter, it shows acid/acid, gas absent, H2S absent. ™™ Monsur’s taurocholate tellurite peptone water. ™™ Hemodigestion: On blood agar, it causes nonspecific lysis of blood cells, seen as greenish clearing around the Selective Media main inoculum (Fig. 42.4A) Stool specimen is directly inoculated on to a selective ™™ String test: When a colony of Vibrio is mixed with a drop medium and the plate is incubated at 37°C for 24 hours. of 0.5% sodium deoxycholate on a slide, the suspension ™™ TCBS agar: It contains thiosulfate, citrate, bile salts (as loses its turbidity, and becomes mucoid. When tried inhibitor), sucrose and has pH of 8.6. This is widely used lifting the suspension with a loop, it forms a string (Fig. at present (Fig. 42.4B). V. cholerae can ferment sucrose 42.4C). and therefore produce large yellow colonies ™™ Alkaline bile salt agar (BSA): V. cholerae produces Biotyping translucent oil drop colonies The classical and El Tor biotypes can be differentiated by ™™ Monsur’s gelatin taurocholate trypticase tellurite agar various biochemical tests, susceptibility to polymyxin B (GTTTA): V. cholerae produces translucent colonies and bacteriophages (refer Table 42.1). with a grayish black center and a turbid halo. Classical biotypes grow better on this medium than on TCBS agar Serogrouping ™™ MacConkey agar: When not sure about the type of Species identification is always confirmed by agglutina- enteric pathogen present in feces, MacConkey agar tion test done on a slide with V. cholerae polyvalent O can be included in the panel. Being a mildly selective antisera: medium, it also supports other enteric pathogens such ™™ Specific serogroups can be identified by using group- as Shigella and Salmonella. Colonies of V. cholerae specific antisera. First the colony is tested with O1 are translucent and pale which may become pink on antisera → If found negative, then tested with O139 prolonged incubation (due to late lactose fermentation). antisera ™™ Serotyping: If agglutinated with O1 antisera, then Culture Smear and Motility Testing the serotyping is done by testing simultaneously with ™™ Culture smear of the colonies reveals short curved gram- Ogawa and Inaba antisera: negative bacilli „„ If agglutinated with Ogawa antisera—it is designated ™™ Hanging drop shows typical darting motility. as Ogawa serotype „„ If agglutinated with Inaba antisera—it is designated Identification as Inaba serotype Identification is made either by automated systems such „„ If agglutinated with both Ogawa and Inaba antisera— as MALDI-TOF or VITEK; or by conventional biochemical it is designated as Hikojima serotype. tests. The key biochemical properties include: ™™ Catalase and oxidase positive Antigen Detection ™™ ICUT test—shows the following reactions: A point-of-care antigen-detection test called—cholera „„ Indole test—positive dipstick assay is commercially available. It is useful in the „„ Citrate test—variable fields, where laboratory facilities are unavailable. A B C Figs 42.4A to C: A. Vibrio cholerae on blood agar (hemodigestion); B. TCBS agar with yellow colored colonies of Vibrio cholerae; C. String test. Source: Department of Microbiology, Pondicherry Institute of Medical Sciences, Puducherry (with permission). 416 Section 5  Gastrointestinal (GI) Infections Molecular Method does not recommend antibiotic prophylaxis against Molecular methods such as PCR can directly detect cholera for travelers coming from or going to cholera V. cholerae specific genes in stool. BioFire FilmArray is an endemic countries. automated multiplexed PCR assay available commercially. Vaccine Its gastrointestinal (GI) Panel can simultaneously detect 22 different enteric pathogens directly from stool specimens Injectable Killed Vaccines including V. cholerae. They are no longer in use, as they provide little protection, cause adverse effects and fail to induce a local intestinal Antimicrobial Susceptibility Testing (AST) mucosal immune response. As there is increasing trend of drug resistance in Vibrio cholerae, AST should be performed for guiding therapy. It Oral Cholera Vaccines is done on Mueller Hinton agar by disk diffusion test. Oral cholera vaccines (OCV) are currently in practice. Two types of oral vaccines are available. T Reatment Cholera 1. Killed whole-cell vaccine: Fluid replacement: It is the most important measure for ™™ Whole-cell (WC) vaccine: It is composed of killed management of the cholera patient. It should be prompt and whole cells of V. cholerae O1 and O139 adequate to correct hypovolemia and thereafter to be maintained „„ Formulations: Two formulations are available: to replace the ongoing fluid losses Shanchol (India) and Euvichol (South Korea) ‰‰ In mild to moderate fluid loss: oral rehydration solution „„ Schedule: Two doses are given orally, with minimum (ORS) should be given ‰‰ In severe cases: Intravenous fluid replacement with Ringer’s of two weeks gap, for all individuals >1 year age lactate (or normal saline) should be carried out till the „„ Protection: It provides protection against cholera for consciousness arrives, thereafter replaced by ORS. 3 years. Antibiotics have a minor role as the pathogenesis is mainly toxin ™™ Whole-cell recombinant B subunit vaccine (WC/rBS): mediated In addition to the composition of WC vaccine, it has ‰‰ Although not necessary for cure, use of antibiotic may recombinant cholera toxin B subunit decrease the duration and volume of fluid loss and hastens „„ Formulation: It is available commercially as Dukoral clearance of the organism from the stool, thus prevents the „„ Schedule: Two doses are given orally, with minimum development of carrier stage ‰‰ The WHO recommends the use of antibiotics to only severely of one week gap. A third dose is given for children dehydrated patients, although wider use is not contraindicated aged 2-5 years. It is given for all individuals >2 year age ‰‰ Drug of choice: Macrolides such as azithromycin or „„ Protection: It provides protection against cholera for erythromycin are the drugs of choice for adults, children 2 years. and also in pregnancy. Alternatively for adults, doxycycline WHO recommends to use vaccine during epidemics and or tetracycline or ciprofloxacin can be given in areas with outbreaks in the community but not during inter epidemic confirmed susceptibility. period. 2. Oral live attenuated vaccines (OCV): They use mutant Prevention strains that lack the gene encoding for cholera toxin. General Measures ™™ CVD 103-HgR : It is commercially available as Vaxchora; General measures include: given as single oral dose ™™ Provision of safe water „„ Indication: It is recommended for adults of age ™™ Improved sanitary disposal of feces 18-64 years, traveling to an area with active cholera ™™ Proper food sanitation transmission. It is also indicated to limit the spread ™™ Prompt outbreak investigation and taking necessary of infection during an outbreak steps to reduce transmission „„ Protection: It gives 90% protection at 10 days after ™™ Notification: Cholera is a notifiable disease locally and vaccination; which lasts for 3-6 months. nationally, hence the cases should be notified ™™ Infection control measures (of contact precaution) Non O1/O139 V. cholerae such as hand hygiene is crucial to limit the spread of the They may resemble biochemically to V. cholerae O1/O139, disease (see Chapter 21). but do not agglutinate with O1 or O139 antisera. Clinically, they differ from O1/O139 strains as follows: Chemoprophylaxis ™™ Gastroenteritis: Several outbreaks of gastroenteritis Tetracycline is the drug of choice; alternative drug includes following sea food consumption (raw oysters) have been doxycycline. It is indicated to household contacts, only reported from Mexico and other places during epidemic. Mass antibiotic prophylaxis may „„ Stool is watery or partly formed, less voluminous and contribute to the emergence of resistance; Hence WHO bloody or mucoid  Chapter 42  Cholera, Halophilic Vibrio and Aeromonas Infections 417 „„ Many cases have abdominal cramps, nausea, T Reatment V. parahaemolyticus infections vomiting and fever „„ However, they never cause epidemic cholera ‰‰ Most of the gastroenteritis is self-limiting and treatment is „„ Treatment is same as that of cholera. Fluid same as that of cholera replacement is the most crucial step. Antibiotics can ‰‰ Indications for antibiotic use: Severe gastroenteritis or extraintestinal manifestations associated with underlying be given in severe dehydration. diseases, such as diabetes, pre-existing liver disease, iron- ™™ Extraintestinal manifestations: Such as otitis media, overload states, or immunosuppression wound infection and bacteremia (in patients with liver ‰‰ Doxycycline or macrolide are the drug of choice disease) have been reported sporadically ‰‰ For proven bacteremia, doxycycline plus ceftriaxone is „„ Most of these infections are acquired by occupational recommended. or recreational exposure to seawater „„ Antibiotics are often indicated. Most strains are Vibrio vulnificus Infections sensitive to tetracycline, ciprofloxacin and third- Though rare, V. vulnificus produces the most severe generation cephalosporins. infection among the Vibrio species. HALOPHILIC VIBRIO INFECTIONS Clinical Manifestations Halophilic vibrios can withstand higher salt concentration It can cause two distinct syndromes: (>6%) in contrast to V. cholerae, which can tolerate up to 1. Primary sepsis: Usually occurs in patients with 6%. They are widespread in marine environments. Cases underlying liver disease and iron overload or rarely in tend to occur during late summer and early rain fall, when renal insufficiency and immunosuppression the bacterial counts are highest in the water. 2. Primary wound infection: It is characterized by painful erythematous swelling or cellulitis or even vesicular, Vibrio parahaemolyticus Infections bullous or necrotic lesions, generally affects people Though V. parahaemolyticus was first reported from Japan without underlying disease (Vulnificus is Latin word for (1953), the incidence of infection has greatly increased in “wound maker”). several countries including Japan since 1993. In India, it has been reported from Kolkata. Laboratory Diagnosis Clinical Manifestations V. vulnificus can be cultured from blood or cutaneous lesions. It ferments lactose, which differentiates it from all ™™ Food-borne gastroenteritis is the most common other vibrios. Identification can also be made by automated presentation, occurs following raw or uncooked sea methods such as MALDI-TOF and VITEK. food (e.g. oyster) intake. It commonly presents as watery diarrhea or rarely as dysentery with abdominal cramps T Reatment Vibrio vulnificus infections ™™ Extraintestinal manifestations such as wound infection, otitis and sepsis are rare. Early antibiotic institution, wound debridement, and gen- eral supportive care are the keys to recovery. V. vulnificus Laboratory Diagnosis is sensitive in vitro to a number of antibiotics, including tetracycline, fluoroquinolones, and third-generation cepha- Laboratory diagnosis of V. parahaemolyticus is carried losporins. out similar to that followed for V. cholerae. The distinct properties are as follows: Vibrio alginolyticus Infections ™™ Morphology: It is capsulated, shows bipolar staining in fresh isolates and pleomorphism in older cultures V. alginolyticus can occasionally cause eye, ear and wound ™™ Motile by peritrichous flagella (but it does not show infections. darting motility) ™™ Few cases of otitis externa, otitis media and conjunctivitis ™™ On TCBS, agar it produces green colonies (sucrose non- have been reported fermenter) ™™ It rarely causes bacteremia in immunocompromised ™™ Kanagawa phenomenon: It causes β-hemolysis on hosts Wagatsuma agar (a special type of high salt blood agar) ™™ It is the most salt-tolerant Vibrio and can grow at salt ™™ Swarming: It swarms on blood agar concentrations of more than 10% ™™ Urease test is positive in few strains ™™ Identification can also be made by automated methods ™™ Salt tolerance test: It can resist maximum of 8% NaCl such as MALDI-TOF and VITEK ™™ Identification can also be made by automated methods ™™ Disease is usually self-limiting. Severe infections such as MALDI-TOF and VITEK. respond well to antibiotics (tetracycline) and drainage. 418 Section 5  Gastrointestinal (GI) Infections ™™ Gastroenteritis (watery diarrhea, vomiting, fever and AEROMONAS INFECTIONS rarely dysentery) and peritonitis Aeromonas was earlier placed in the family Vibrionaceae; ™™ Musculoskeletal and wound infections however, it has now been assigned to a separate family, ™™ Bacteremia in immunocompromised adults and Aeromonadaceae. A. hydrophila causes red leg disease infants in frog. ™™ Respiratory tract infections, such as epiglottitis, Pathogenicity of Aeromonas in humans is mainly related to: pharyngitis and pneumonia. ™™ Tissue adherence mediated by adhesions such as S-layer Laboratory diagnosis: Identification of Aeromonas up to and fimbriae species level from colonies is made either by automated ™™ Capsular polysaccharide (prevents the bacilli from identification systems such as MALDI-TOF and VITEK or phagocytosis) by various conventional biochemical tests (e.g. oxidase and ™™ Exotoxins, such as aerolysin, phospholipases, hemolysins, catalase positive). enterotoxin and cytotoxin similar to Shiga toxin ™™ Endotoxin or LPS. T Reatment Aeromonas infections Clinical manifestations: over 85% of the human infections Aeromonas is susceptible to ciprofloxacin and levofloxacin. are caused by A. hydrophila, A. caviae and A. veronii. Most Alternatively, cotrimoxazole and cefepime can be given. However, of the other species are mainly isolated from environmental the plasmid mediated drug resistance has been reported sources and animals. Various manifestations include: including β-lactamase production. EXPECTED QUESTIONS I. Write essay on: c. Robertson cooked meat medium 1. A 4-year-old boy developed severe watery diarrhea d. Modified Thayer Martin medium and vomiting. The stool collected has a rice water 5. All of the following Vibrio species are halophilic, type of appearance. It was sent for bacteriological except: analysis. a. V. cholerae a. What is the probable etiological diagnosis of this b. V. parahaemolyticus condition? c. V. alginolyticus b. Describe in detail the pathogenesis of this d. V. vulnificus condition. 6. Gardner and Venkatraman classification—which c. Add a note on its laboratory diagnosis. of the following is a biotype of Vibrio? II. Write short notes on: a. Ogawa b. Inaba 1. Prophylaxis against cholera. c. Hikojima d. El Tor 2. Halophilic vibrios. 7. O139 (Bengal strain)—all are true, except: a. Capsulated III. Multiple Choice Questions (MCQs): b. Toxigenic 1. Which of the following media can be used as c. Clinically similar to El Tor transport medium for vibrios? d. More common than El Tor a. Selenite F broth 8. V. cholerae—all are true, except: b. Nutrient broth a. Acid-labile but stable to alkali c. Tetrathionate broth b. Heat-labile d. Venkatraman–Ramakrishnan medium c. Classical is more resistant than El Tor 2. All of the following tests can differentiate between d. ‘O’ blood group are affected more frequently classical and El Tor biotypes of V. cholerae, except: 9. All are selective media for V. cholerae, except: a. β-hemolysis on sheep blood agar a. Alkaline peptone water b. Chick erythrocyte agglutination b. Alkaline bile salt agar c. Growth on TCBS agar c. TCBS agar d. Polymyxin B (50 IU) d. Monsur’s agar (GTTTA) medium 3. Pathogenesis of V. cholerae involves one of the 10. Which of the following confirms the isolate of following second messenger systems: V. cholerae as Hikojima serotype? a. cGMP b. cAMP a. If agglutinated with Ogawa antisera c. Ca2+ d. IP3 b. If agglutinated with Inaba antisera 4. Selective media for Vibrio cholerae: c. If agglutinated with Hikojima antisera a. TCBS d. If agglutinated with both Ogawa and Inaba b. Mannitol salt agar antisera Answers 1. d 2. c 3. b 4. a 5. a 6. d 7. d 8. c 9. a 10. d  Chapter 43 Miscellaneous Bacterial Infections of Gastrointestinal System Chapter Preview „„Campylobacteriosis „„Helicobacter Infections „„Clostridioides difficile Infection This chapter covers various bacterial infections of „„ In developed countries, Campylobacter is the leading gastrointestinal system caused by Campylobacter, bacterial cause of diarrheal disease, more common Helicobacter and Clostridioides difficile. than Shigella and Salmonella. ™™ Seasonality: Incidence peaks during summer and early CAMPYLOBACTERIOSIS autumn. Campylobacter species cause both diarrheal and systemic Pathogenesis diseases. They are motile, nonsporing, microaerophilic, Pathogenesis of C. jejuni is due to expression of the curved gram-negative rods. following virulence factors: Human pathogens fall into two major groups: ™™ Motility of the strain (possesses single polar flagellum 1. Primarily diarrheal disease: It is caused by C. jejuni (accounting for 80–90% of total cases), and others and exhibits darting motility) ™™ Capacity to adhere to host tissues such as C. coli, C. upsaliensis, C. lari, C. hyointestinalis, ™™ Produce toxins, which play a minor role: C. fetus „„ Enterotoxin (heat-labile, similar to cholera toxin) 2. Extraintestinal infection: Caused by C. fetus. „„ Cytotoxins (cytolethal distending toxin, or CDT). Epidemiology ™™ Proteinaceous capsule-like structure (S-layer) expressed ™™ Source: Campylobacter species are zoonotic, found in by C. fetus. the intestine of many animals (poultry, cattle, sheep and Clinical Manifestations swine) and household pets (including birds, dogs and cats). However, animals are asymptomatic Incubation period of campylobacteriosis varies from 2–4 ™™ Mode of transmission: Campylobacter is transmitted by days. The clinical manifestations seen are as follows: the following routes: ™™ Intestinal infection: It is characterized by inflammatory „„ By raw or undercooked food products: Ingestion diarrhea, abdominal pain and fever. Degree of diarrhea of contaminated poultry (most common), raw varies from several loose stools to grossly bloody stools. (unpasteurized) milk or untreated water It is self-limiting; however, relapse is seen in 5–10% of „„ Through direct contact with the infected household untreated cases pets ™™ Complications: It is mainly due to C. fetus developing „„ Oral-anal sexual contact. mostly in immunocompromised hosts and at the ™™ Infective dose: The infective dose is small;