module 11: other gram negative rods

those not in the enterobacteriaceae family

vibrio cholerae

causes epidemic Asiatic cholera. human is the only host and source as they shed this bacteria in feces, contaminating food & water supplies. 2 strains/biotypes distinguished by phenotypic markers & O (somatic) antigens (both have O1).

vibrio cholerae: strain El Tor

milder form of the disease, patient can be asymptomatic. bacteria survives in the body longer than the other strain; allows carriers to infect more people in the population. responsible for most global cholera cases. biotype that caused cholera in Haiti after earthquake

vibrio cholerae: classical

cholera that’s relatively rare globally except in India & Bangladesh

convalescent carriers

those recovering from disease who shed bacteria for up to a year

chronic carriers

those who no longer have disease but still carry bacteria for years. store bacteria in the gall bladder → gallbladder intermittently sheds bacteria, which can make ID of individuals difficult

how is vibrio cholerae transmitted?

fecal-oral route: ingestion of contaminated food or water. ex: fruits & vegetables grown in sewage-rich soil that are ingested without prior cooking, eating raw oysters. after ingestion, bacteria multiply rapidly in the intestine

pathogenesis of vibrio cholerae

bacteria produce enterotoxin that acts on intestinal lining, causing massive fluid & electrolyte loss (up to 20 L/day). voided fluid contains high electrolytes. onset of symptoms abrupt with severe vomiting & diarrhea: “rice-water stools”

complications from vibrio cholerae

result from massive loss of essential electrolytes. hypovolemic shock & metabolic acidosis. untreated mortality rate ~50%. good news: immunity is long-lasting for most people after resolution

how to prevent vibrio cholerae?

desiccation, sunlight, & acid kill this, but microbial dose is so great that losing some bacteria to stomach acid is not sufficient. single dose vaccines available. oral cholera vaccine (OCV), but limited protection in children. proper sanitation & hygiene

how to treat vibrio cholerae?

fluid & electrolyte management: rehydration 1st priority. antibiotics such as tetracycline, which lower bacteria load → lowers enterotoxin released. also eliminates [bacteria] in gall bladder bile → eliminating carrier state

laboratory diagnosis of vibrio cholerae

gram negative rod, comma-shaped. growth on simple culture/agar; media specific for this is also available. oxidase positive (enterics are negative). lactose negative

campylobacter

causes 5-11% of all diarrhea cases in the USA. most human illness caused by jejuni. all cases occur as isolated, sporadic events (not large outbreaks). many causes undiagnosed or unreported. affects 1M people annually

campylobacter jejuni

source is lower animals (dogs, cats), but birds carry it without getting sick; people acquire this from infected stool of sick pet. invasive & infiltrates lining of intestine: causes fever, cramps, bloody diarrhea, ulceration at mucosal surface of intestine. self-limiting, treated with erythromycin

how is campylobacter jejuni transmitted?

handling raw poultry or eating raw/undercooked poultry meat, unpasteurized dairy products, contaminated water. freezing reduces bacteria present on raw meat. very small amount of organisms can cause illness in humans (one drop of raw chicken juice)

environmental reservoirs that can lead to human infection of C. jejuni

colonization of GI tract of chickens: bacteria passes through chicks in a flock through fecal-oral route → humans consume contaminated animal products. can enter water supply & infect humans via drinking water. invades epithelium of human intestine: inflammation, diarrhea follow

helicobacter pylori

leading cause of peptic ulcers and chronic gastritis in the USA. pathogenesis mechanisms include motility, urease activity, & association with gastric mucosal cells (important virulence factors). long-term infection leads to risk of gastric cancer & MALT lymphoma

source of helicobacter pylori

more than 50% of the population globally harbors this in upper GI tract. most infected people asymptomatic. many people infected as children. transmitted person-to-person with direct contact (saliva, vomit, feces) or fecal contamination of food/water

endoscopy & associated biopsy for H. pylori

reference method for diagnosis. specimens of stomach & duodenum obtained. use urease test on tissue (this bacteria is urease positive). use histologic stain of tissue & culture to ID bacteria in tissue (gold standard of diagnostic tests)

urea breath test for H. pylori

patient given ¹⁴C-labeled urea to drink. the bacteria metabolizes urea rapidly & labeled carbon is released. labeled carbon measured in patient’s breath to determine whether bacteria is present

serum antibody test for H. pylori

measure specific IgG antibodies having reactivity against this bacteria. if antibodies present, then patient has or had the infection

stool antigen test for H. pylori

accurate, noninvasive test for direct detection of this bacteria in stools. antigen detection = active infection. definitive test of choice for diagnosis & treatment monitoring

helicobacter pylori treatments

antibiotics like amoxicillin & tetracycline. antacid or proton pump inhibitor: help alleviate ulcer-related symptoms, heal gastric mucosal inflammation

laboratory diagnosis for campylobacter & helicobacter

gram negative rods, curved & S-shaped. no growth on blood or MacConkey agars. microaerophilic: requires high CO2 (killed by O₂ content in air). temp preference 42C (higher than most bacteria). nonfermentative, oxidase positive, catalase positive

pseudomonas

found in soil, water as natural habitat. most don’t infect man, but those that do cause severe infections and are difficult to treat.

pseudomonas aeruginosa

found nearly everywhere and may be harbored in nearly any site in medical environment (water systems): contaminated equipment like IV fluids & water. easily spread from patient to patient via hospital personnel. infections usually occur in people with altered host defenses. resistant to many antibiotics

pseudomonas aeruginosa laboratory diagnosis

aerobic gram negative rods. nonfermentative, don’t utilize glucose by fermentation. most frequently isolated nonfermenter in clinical setting. produces pigments pyocyanin & fluorescein: blue-green, fluorescent under UV light, occurs in virtro & in vivo

pyocyanin

kills competing microbes. generates reactive oxygen species such as H₂O₂ & superoxide anion. inactivates catalase. interferes with electron transport chain

clinical infections of P. aeruginosa

lesions may spread via bloodstream causing septicemia. localized lesions may occur in burns, wounds, corneal tissue, lungs, urinary tract. eye infections. highly susceptible states: leukemia patients, burn patients, cystic fibrosis patients (lung infections). can be prevented by heptavalent vaccine

treatment of P. aeruginosa

topical antimicrobics for burns, wounds, eyes; systemic by ingestion (enteral) or injection (parenteral → not thru GI tract). systemic consists of combination strategy. aminoglycosides & penicillins

burkholderia pseudomallei

responsible for meliodosis (Whitmore’s disease), which is characterized by pneumonia & multiple abscesses. mortality rate 40%. found in soil & water in tropical areas of Southeast Asia. 5-20% agricultural workers have antibody to it. can remain latent for a long time: relapse known to occur

burkholderia pseudomallei disease presentation

ingestion or inhalation of contaminated dust, soil contamination of abraded skin. infection where abscess forms and leads to aggressive granulomatous disease. further abscess forms in lungs & other viscera. overwhelming & rapidly fatal septicemia can occur

hemophilus

small gram negative rods (coccobacilli). characterized by a requirement for specific growth factors that are found in blood. species of importance: influenzae, aegyptius, ducreyi, gardnerella vaginalis (vaginale)

hemophilus influenzae

source: humans, 30% of adults have it in upper respiratory tract. transmitted human to human by inhalation of infected droplets from active cases or carriers. causes upper & lower respiratory tract infections (pneumonia), meningitis (most serious), & acute bacterial epiglottitis (lead to closed off airways, sepicemia)

laboratory diagnostics for hemophilus influenzae

chocolate agar: V factor (NAD) & X factor (hemin). serotyped into 6 groups utilizing capsular antigens A → F. type B is most common cause of acute bacterial meningitis in infants/children. non-epidemic

treatment & prevention of H. influenzae

antibiotics: ampicillin & chloramphenicol. since it’s resistant to phagocytosis by alveolar macrophages, several vaccines are available (part of routine childhood vaccination)

hemophilus aegypitus: Koch-Weeks Bacillus

needs to be differentiated serologically from H. influenzae. causes conjunctivitis (pink eye), which can be epidemic in kids. treated with local administration of ophthalmic antibiotic solution

hemophilus ducreyi: Chancroid Bacillus

venereal disease. initial infection causes formation of soft chancre, a painful ulcerative sore on genitalia that bleeds easily if scraped. transmitted by direct contact, highly contagious

hemophilus vaginale (gardnerella vaginalis)

venereal transmission that is associated with vaginitis. does not invade tissue, but grows in vaginal secretions. ID by clue cells, which are squamous epithelial cells with adhered masses of gram negative pleomorphic rods

bordetella pertussis

causative agent of whooping cough in humans. usually children with disease. healthy adults are reservoirs. can be misdiagnosed. transmitted by inhalation or direct contact with discharges from respiratory mucous membranes of people infected. coughing aerosolizes bacteria, transmitting it to susceptible individuals

laboratory diagnosis of bordetella pertussis 

strict aerobe. requires bordet-gengou medium (potato blood agar). slow grower, so use PCR or fluorescent antibody test. contains capsular K antigens, but serologic testing is difficult to interpret

pertussis (whooping cough)

organism aggregates on bronchial & tracheal lining and toxins are released: exotoxin causes bacteria to adhere to cells, cytotoxicity & cell necrosis. 3 stages: catarrhal, paroxysmal, & convalescence. can lead to CNS disorders and secondary infections in ears, sinuses, respiratory tract

catarrhal (stage 1)

most highly infectious period. upper respiratory involvement. mild cold-like symptoms like coughing, sneezing, slight fever, runny nose.

paroxysmal (stage 2)

cough described as paroxysmal (sudden intensification of symptoms) or spasmodic (sudden but transitory airway construction). coughs so forceful & close that patient can’t breath. at the end of spasm, gasp for air which sounds like a whoop. young infants don’t whoop, which is bad 

convalescence (stage 3)

less severe and less frequent paroxysms

treatment & prevention of bordetella pertussis

antibiotic erythromycin. fluid & electrolyte management, oxygen therapy to avoid anoxia. DTap vaccine and TDap booster (for diptheria, tentanus, pertussis)

brucella

bacteria that are intracellular parasites that infect lower animals and are transmissible to man. causes contagious abortion in lower animals (abortus). causes brucellosis (undulant fever) in humans, which rises & falls like a wave (melitensis). worldwide, concentrated in Mexico, Africa, India, & Europe

brucella melitensis

from infected animals or secretions (milk), animals may recover quickly but excrete this for varying lengths of time. transmitted by ingestion of contaminated milk, consumption of undercooked meat, direct contact with sick animals, or inhalation (rare)

how does brucella melitensis initiate infection?

it enters through skin (direct contact) or are ingested. disseminate through lymphatics & bloodstream. remain intact within phagocytes (especially macrophages) where they’re protected from antibiotics. may cause abscess formation in infected tissue. localize in spleen, bone marrow

symptoms of brucella melitensis 

nonspecific manifestations like weakness, chills, malaise, headache. intermittent (undulant) fever due to endotoxin release. sometimes mental depression & increased nervousness. can last a while. complications: arthritis, endocarditis, neurologic disorders

laboratory diagnosis of brucella melitensis

found intracellular in phagocytes or tissue. slow growing. BSL-3. serological test for antibody is recommended. febrile agglutination rapid results. panel of tests that rule in/out different diseases. specific agglutination tests for this. acute & convalescent serum samples are norm for diagnosis

treatment & prevention of brucellosis (malta, crimean, gibraltar fever)

antibiotics: tetracycline &/or rifampin, chloramphenicol. intracellular localization of bacteria may contribute to antimicrobic inefficiency/ineffectiveness. control animal infections (& meat from infected animals), pasteurize milk & milk products

francisella tularensis 

found intracellular in macrophages. causative agent of tularemia (rabbit fever). acute infectious disease of wild animals, especially rabbits & ground squirrels. direct contact is most common mode of transmission, also bites of insect vectors. febrile disease, chills, headaches, back pain, progressive weakness, exhaustion

disease progression of F. tularensis

sequesters in phagosome of macrophages, breaks out into cytosol where it rapidly proliferates. infected macrophages undergoes apoptosis, releasing bacteria that initiate more infections. infected lymph glands drain into lymph nodes where bacteria enters blood stream. cycle starts again: phagocytes in bloodstream ingest bacteria

clinical forms of tularemia

ulceroglandular (direct contact), oropharyngeal infection (can be due to ingestion), oculoglandular (direct contact), glandular (direct contact, no ulcers), pneumonic (aerosol inhalation), septicemic, typhoidal

ulceroglandular tularemia

most cases. direct contact. cutaneous ulcer at site of infection. regional lymph nodes become swollen & painful (lymphadenopathy) due to bacterial transport by macrophages

occuloglandular tularemia

purulent conjunctivitis. similar to ulceroglandular except conjunctiva is primary site of infection. usually results from rubbing eyes with contaminated fingers

typhodial tularemia

focus of infection is mouth, throat, GI tract. systemic illness with fever with toxemia in liver, spleen. can be due to ingestion of bacteria

laboratory diagnosis of F. tularensis

PCR. growth on blood & chocolate agar (fastidious). specimen is symptom-dependent. serological tests most common. elevated antibody titer to antigen in patient w/o history of vaccination in conjunction with symptoms. ELISA or agglutination rxns

treatment & prevention of F. tularensis

antibiotics: streptomycin. avoid infected animals, wash hands, cook food thoroughly, drink safe water, insect repellent, vaccinated if high exposure

pasteurella multocida

transmitted from animal to man via animal licks, bites, or scratches (dogs/cats). cellulitis & abscess formation at the site. complications: sepsis, meningitis, osteomyelitis. specimen: exudate from lesion, blood if fever. culture & biochem ID. clean wound, avoid suturing. initiate antibiotics (penicillin, tetracycline) ASAP

legionella pneumophila

from water supplies (water holding vats), especially with biofilms, has tolerance for chlorine. inhalation of infected water droplets (aerosolized particles). upper respiratory tract infections. can be asymptomatic. associated with legionnaires disease (fever, pneumonia) & pontiac fever (milder w/ no pneumonia)

laboratory diagnosis of legionella pneumophila 

gram negative rods. able to enter, survive, & multiply within host cells, especially macrophages & neutrophils. treated with erythromycin or erythromycin/rifampin combo.