Medical Bacteriology Gram Negative PDF

Medical Bacteriology Gram negative  SPIROCHETES The bacteria in the order Spirochaetales are : o helically coiled Gram negative o 5-20 μm in length and 0.1-0.6 μm in diameter o flexible outer cell membrane o mobile for the presence of endoflagella → t...

Medical Bacteriology Gram negative  SPIROCHETES The bacteria in the order Spirochaetales are : o helically coiled Gram negative o 5-20 μm in length and 0.1-0.6 μm in diameter o flexible outer cell membrane o mobile for the presence of endoflagella → the contraction of endoflagella imparts the motions to the spirochaetes 5-20 µm 0.1-0.6 µm The locomotor system consists of one or more endoflagella anchored to one pole of the cell and inserted longitudinally in the periplasmic space  Why a corkscrew shape? The flagella cause the cells to rotate like a corkscrew (spiral motion). This enables spirochetes to: o invade tissues o travel through highly viscous media, like mucus and the host connective tissue matrix  SPIROCHAETALES Treponema pallidum Borrelia burgdorferi Leptospira interrogans Treponemes are thin, tightly coiled spirochetes with pointed, straight ends Borreliae are larger than other spirochetes, with irregular, wide, open coils Leptospires are thin, coiled spirochetes with a hook at one or both pointed ends  Treponemes General feature of Treponemes: o long, thin, tightly coiled spirochetes (0.1 to 0.2 × 6 to 20 µm) with pointed, straight ends o corkcrew motility (endoflagella) o obligate human pathogen o poorly resistant in the environment and die quickly out of the human body o anaerobic or microaerophilic bacteria o very difficult to grow in culture T. pallidum is the etiologic agent of the venereal disease syphilis  Treponema pallidum ssp. pallidum The bacteria is the etiological agent of syphilis, a systemic, sexually transmitted disease Other transmission routes are: o close muco-cutaneous contact with skin lesions o parenteral (blood transfusions) o vertical transmission from mother to fetus at any time during pregnancy (congenital infection) Clinical disease The clinical course of syphilis evolves through three phases: Primary syphilis o the initial phase is characterized by one or more skin lesions (chancre) at the site where the spirochetes penetrated (localized stage in penis, glans in man and vulva, vagina, cervix in woman) o the lesion develops 10-90 days after infection and starts as a papule and becomes a painless ulcer with raised borders o the lesion is highly infectious o this ulcer heals spontaneously within 2 months giving the patient a false sense of relief  Treponema pallidum ssp. pallidum Secondary syphilis o this is the dissemination stage occurring 6-12 weeks after infection o the clinical signs of disseminated disease are prominent skin lesions (generalized mucocutaneous rash) dispersed over the entire body surface, including mucosal surfaces, and flu-like syndrome (sore throat, headache, fever, myalgias, anorexia, generalized lymphadenopathy). Rarely, meningitis. o the mucocutaneous lesions are highly infectious o within a few weeks rash and symptoms resolve spontaneously, and patients may undergo spontaneous remission, enter the latent or clinically inactive stage of disease, or progress to the late phase of disease. Latent syphilis o patients are asymptomatic and after the second year after infection they are not infectious o patients can remain asymptomatic or progress to…  Treponema pallidum ssp. pallidum Tertiary syphilis o the late stage of the disease is characterized by a diffuse chronic inflammation, with involvement of all tissues. Classic clinical signs are gummas, granulomatous lesions that may form in virtually any organ or tissue. o the disease may include cardiovascular syphilis (aortic disease), neurosyphilis, and gummas (granulomatous lesions).  Congenital syphilis In utero infections can lead to serious fetal disease, resulting in multiorgan malformations, or death of the fetus. Most infected infants are born without clinical evidence of the disease, but rhinitis can develop followed by a widespread desquamating maculopapular rash. Teeth and bone malformations, blindness, deafness, and cardiovascular syphilis are common in untreated infants who survive the initial phase of disease. Vertical transmission occurs: o 70-100% in primary or secondary syphilis Syphilitic rhinitis o 20% in early latent syphilis o 10% in late latent syphilis Hutchinson teeth Saddle nose  Treponema pallidum ssp. pallidum Pathogenesis is related to: o adherence to host cells by means of the outer membrane proteins o corkscrew motility for invasion o production of hemolysins → it is unclear if they mediate tissue damage o production of hyaluronidase → it has been proposed that this facilitates perivascular infiltration, but this remains to be demonstrated The disease occurs primarily because of the host immune response to the treponemal infection, with both humoral and cell-mediated immune systems playing a role  Diagnosis and Therapy of syphilis MICROSCOPY & CULTURE T. pallidum is too thin to be seen by light microscopy and do not grow in cell-free cultures. NUCLEIC ACID–BASED TESTS They have been developed for detecting T. pallidum in genital lesions, infant blood, and cerebrospinal fluid → currently not widely available SEROLOGY is the gold standard o VDRL (Venereal Disease Reference Laboratory): the nontreponemal screening test identifies Ab directed against lipoid Ag (cardiolipin) [positive starting from the 8th day after the appearance of chancre] o TPHA (Treponema Pallidum Hemoagglutination Assay): the treponemal specific test identifies Ab against the endoflagellar proteins of Treponema [positive starting from the 10th week, little use in identifying the early stages of the disease] THERAPY. Penicillin is the drug of choice for treating T. pallidum infections.  FAMILY ENTEROBACTERIACEAE  ENTEROBACTERIACEAE Members of the family Enterobacteriaceae are: o moderate-sized, non-spore forming Gram negative rods o if motile, motility is by peritrichous flagella o aerobes and facultative anaerobes, they ferment glucose, reduce nitrate o catalase positive and oxidase negative o some have fimbriae, some produce exotoxins o normal inhabitants of the intestinal tracts of humans and animals Members of the family share common surface antigens: o O antigen = somatic antigen (LPS) o H antigen = flagellar antigen o K antigen = capsular antigen  Pathogenesis of infections caused by Enterobacteriaceae Endogenous infections: o urinary tract infections (>70% caused by Enterobacteriaceae) o increased replication of bacteria normally present in intestinal microbiota Exogenous infections: o intestinal infections Incidence of Enterobacteriaceae associated with bacteremia Bacteria (either exogenous or opportunistic/endogenous) can invade the gut or urinary tract mucosa → systemic infection  Escherichia coli E. coli is the most common and important member of the genus Escherichia. It is a normal inhabitant of gut microbial flora but it can turn out to be pathogenic causing: o endogenous urinary tract infections (UTIs) o gastroenteritis (contaminated food) o meningitis and sepsis in newborns (K1 serogroup) It posses a broad range of specialized virulence factors, including adhesins and exotoxins:  Escherichia coli - Pathogenesis of urinary tract infections (UTI) UroPathogenic Escherichia coli (UPEC) are characterized by: o flagella motility favors the «ascension» of microorganisms towards the upper urinary tract o pili and fimbriae → adhesion to the urethral/bladder epithelium o production of hemolysins (damage of the epithelium promotes invasion) o production of iron-acquisition systems  Escherichia coli - Pathogenesis of intestinal infections The strains of E. coli that cause gastroenteritis are subdivided into 5 groups: o enterotoxigenic E. coli → ETEC o enteropathogenic E. coli → EPEC o enteroaggregative E. coli → EAEC o enteroinvasive E. coli → EIEC o enterohaemorragic E. coli → EHEC  Enterotoxigenic E. coli → ETEC These bacteria are the most common cause of traveler's diarrhea and infant diarrhea in developing countries. Symptoms are watery diarrhea, vomiting, low-grade fever. Pathogenesis is related to two plasmid-mediated, heat-stable (ST) and heat-labile (LT) enterotoxins that stimulate hypersecretion of electrolytes and fluids.  Enteropathogenic E. coli → EPEC These bacteria are the cause of infant diarrhea in developing countries. Symptoms are severe and protracted watery diarrhea, fever and vomiting. Pathogenesis is related to the disruption of normal microvillus structure resulting in malabsorption and diarrhea.  Enteroaggregative E. coli → EAEC These bacteria are the cause of infant diarrhea in developing and probably developed countries, and traveler's diarrhea. Symptoms are persistent watery/secretory diarrhea with fever, vomiting. Pathogenesis is related to adherence to the epithelium, cytokine release is stimulated, which results in neutrophil recruitment and progression to an inflammatory diarrhea. (1) Agglutination of planktonic EAEC bacteria. (2) Adherence to the intestinal epithelium and colonization of the gut. (3) Formation of biofilm. (4) Release of bacterial toxins, inducing damage to the epithelium and increased secretion. (5) Establishment of additional biofilm  Enteroinvasive E. coli → EIEC These bacteria are able to invade and destroy the colonic epithelium, producing a disease characterized initially by watery diarrhea. They lyse the phagocytic vacuole and replicate in the cell cytoplasm of intestinal cells. Thereafter they move to adjacent epithelial cells. This process of epithelial cell destruction with inflammatory infiltration can progress to colonic ulceration (dysenteric form). EIEC is not toxigenic, but invasive.  Enterohaemorragic E. coli → EHEC (STEC) These bacteria cause an initial watery diarrhea followed by bloody diarrhea (hemorrhagic colitis) with abdominal cramps, little or no fever. Symptoms may progress to Hemolytic Uremic Syndrome (HUS: acute renal failure, thrombocytopenia, and hemolytic anemia). Pathogenesis is mediated by cytotoxic Shiga toxins (Stx1, Stx2), which disrupt protein synthesis, leading to destruction of intestinal microvilli. Stx1 and Stx2 have one A subunit and five B subunits, with the B subunits binding to a specific glycolipid on the host cell. After the A subunit is internalized, it is cleaved into two molecules, and the A1 fragment binds to 28S rRNA and causes a cessation of protein synthesis → cell death.  SALMONELLA, SHIGELLA, KLEBSIELLA, ENTEROBACTER, SERRATIA, PROTEUS, CITROBACTER o Salmonella Thyphi is a primary pathogen responsible for gastroenteritis and disseminated diseases (enteric fever) o Shigella spp. is a primary pathogen responsible for the bacillary dysentery o Klebsiella pneumoniae is a commensal of the upper airways and human intestine, can cause community- or hospital acquired primary lobar pneumonia, urinary tract infections and bacteremia in immunocompromised subjects (opportunistic infections) o Enterobacter aerogenes is an intestinal commensal or environmental saprophyte, and causes sepsis and urinary tract infections o Serratia marcescens is a common opportunist in hospitalized patients responsible for pneumonia, bacteremia o Proteus mirabilis and vulgaris cause urinary tract infections, bacteremia, pneumonia in hospitalized patients o Citrobacter freundii is responsible for urinary tract infections and sepsis Klebsiella pneumoniae Proteus mirabilis Salmonella spp. Shigella spp. ENTEROTUBE TEST FOR ENTEROBACTERIACEAE IDENTIFICATION  VIBRIO Vibrio species are: o motile (a single polar flagella), curved, Gram negative bacilli → comma-shaped rods (vibrions) o facultative anaerobic organisms Their natural environment is saltwater where they can multiply freely, and they have been find in shellfish and plankton. The major human pathogens are: V. cholera O1 and O139 produce the cholera enterotoxin and are associated with epidemics of cholera  V. cholera pathogenesis Virulence factors: o pili/adhesin factors o flagellum o hemagglutinin-protease (mucinase) for colonization o neuraminidase o siderophores o cholera toxin enterotoxin produce its effect by stimulating adenyl-cyclase activity in mucosal cells V. cholera pathogenesis o abrupt onset of watery diarrhea and vomiting, “rice- water” stools (severly infected patients can lose up to 15 liters of fluid per day) o fluid and electrolyte loss → dehydration, muscle cramps, metabolic acidosis (bicarbonate loss), hypokalemia, hypovolemic shock and renal failure o mortality rate: 70% in untreated patients, < 1% in patients who are treated with replacement of fluids and electrolytes  Diagnosis and therapy of V. cholerae infection Clinical diagnosis Laboratory diagnosis o Microscopic examination (Gram stain) of stool specimens o Culture: bacteria grow in TCBS (thiosulfate-citrate-bile salts-sucrose agar), a selective medium that inhibits gram-positive bacteria and Enterobacteria Therapy o fluid and electrolyte replacement o oral antibiotics: azithromycin or doxycycline or ciprofloxacin  Helicobacter pylori o Curved, Gram-negative bacilli that requires microaerophilic environments to grow o highly motile (corkscrew motility) through 5 to 6 polar flagella o urease-producer → urease allows the bacteria to survive the harsh gastric environment Humans are the primary resevoir for the bacteria, and no animal resevoir has been identified at the present time. Infections are ubiquitous and worldwide, commonly clustered in families or among close contacts as transmission is person-to-person, and by fecal-oral and oral-oral routes. H. pylori has been implicated in the development of multiple gastrointestinal diseases: o type B gastritis o gastric ulcers o gastric cancers: gastric adenocarcinoma of the body and antrum and gastric mucosa- associated lymphoid tissue (MALT) B-cell lymphomas  Pathogenesis of H. pylori infection Lytic enzimes (mucinases) Flagella Pathogenesis of H. pylori infection GASTRITIS PEPTIC ULCERS GASTRIC CANCER  Diagnosis and Therapy of H. pylori infection o urea test on gastric biopsy (invasive) o urea breath test (non-invasive) o detection of H. pylori antigens in stool samples (poor sensitivity) o detection of IgG in serum samples (screening test) TRIPLE THERAPY: Combination of a proton pump inhibitor (e.g., omeprazole), a macrolide (clarithromycin), and a β-lactam (amoxicillin), with administration for 7 to 10 days