Aerobic Gram-Negative Nonenteric Bacilli

• Large, diverse group of non-spore-forming bacteria

• Wide range of habitats – large intestines (enteric), zoonotic, respiratory, soil, water

• Most are not medically important; some are true pathogens, some are opportunists

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Aerobic Gram-Negative Nonenteric Bacilli

• Pseudomonas and Burkholderia – an opportunistic pathogen

• Brucella and Francisella – zoonotic pathogens

• Bordetella and Legionella – mainly human pathogens

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Pseudomonas: The Pseudomonads• Small gram-negative rods with a single polar flagellum• Free living

– Primarily in soil, sea water, and fresh water; also colonize plants and animals

• Important decomposers and bioremediators• Frequent contaminants in homes and clinical settings• Aerobic; do not ferment carbohydrates • Produce oxidase and catalase• Many produce water soluble pigments

Pseudomonas aeruginosa

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Pseudomonas Aeruginosa

• Common inhabitant of soil and water

• Intestinal resident in 10% normal people

• Resistant to soaps, dyes, quaternary ammonium disinfectants, drugs, drying

• Frequent contaminant of ventilators, IV solutions, anesthesia equipment

• Opportunistic pathogen

Skin rash from Pseudomonas

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Pseudomonas Aeruginosa

• Common cause of nosocomial infections in hosts with burns, neoplastic disease, cystic fibrosis

• Complications include pneumonia, UTI, abscesses, otitis, and corneal disease

• Endocarditis, meningitis, bronchopneumonia• Grapelike odor• Greenish-blue pigment (pyocyanin)• Multidrug resistant• Cephalosporins, aminoglycosides, carbenicillin,

polymixin, quinolones, and monobactams

Pseudomonas (left) and Staphylococcus (right)

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Related Gram-Negative Aerobic Rods

• Genera Burkholderia, Acinetobacter,

Stenotrophomonas• Similar to pseudomonads• Wide variety of habitats in soil, water, and related

environments• Obligate aerobes; do not ferment sugars• Motile, oxidase positive• Opportunistic

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Burkholderia

• Burkholderia cepacia – active in biodegradation of a variety of substances; opportunistic agent in respiratory tract, urinary tract, and occasionally skin infections; drug resistant

• B. pseudomallei – generally acquired through penetrating injury or inhalation from environmental reservoir; wound infections, bronchitis and pneumonia, septicemia

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Acinetobacter and Stenotrophomonas

• Acinetobacter baumanii – nosocomial and community acquired infections; wounds, lungs, urinary tract, burns, blood; extremely resistant – treatment with combination antimicrobials

• Stenotrophomonas maltophilia – forms biofilms; contaminant of disinfectants dialysis equipment, respiratory equipment, water dispensers, and catheters; clinical isolate in respiratory soft tissue, blood, CSF; high resistance to multidrugs

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Brucella and Brucellosis• Tiny gram-negative coccobacilli• 2 species:

– Brucella abortus (cattle)– Brucella suis (pigs)

• Brucellosis, malta fever, undulant fever, and Bang disease – a zoonosis transmitted to humans from infected animals

• Fluctuating pattern of fever – weeks to a year• Combination of tetracycline and rifampin or

streptomycin• Animal vaccine available• Potential bioweapon

Agglutination titer test for brucellosis

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Francisella Tularensis and Tularemia

• Causes tularemia, a zoonotic disease of mammals endemic to the northern hemisphere, particularly rabbits

• Transmitted by contact with infected animals, water and dust or bites by vectors

• Headache, backache, fever, chills, malaise, and weakness

• 10% death rate in systemic and pulmonic forms• Intracellular persistence can lead to relapse• Gentamicin or tetracycline• Attenuated vaccine• Potential bioterrorism agent

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Bordetella Pertussis

• Minute, encapsulated coccobacillus• Causes pertussis or whooping cough, a communicable

childhood affliction • Acute respiratory syndrome• Often severe, life-threatening complications in babies• Reservoir – apparently healthy carriers• Transmission by direct contact or inhalation of

aerosols

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Bordetella Pertussis

• Virulence factors– Receptors that recognize and bind to ciliated

respiratory epithelial cells– Toxins that destroy and dislodge ciliated cells

• Loss of ciliary mechanism leads to buildup of mucus and blockage of the airways

• Vaccine – DTaP – acellular vaccine contains toxoid and other Ags

Prevalence of pertussis in the United States

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Alcaligenes

• Live primarily in soil and water

• May become normal flora

• A. faecalis – most common clinical species– Isolated from feces, sputum, and urine– Occasionally associated with opportunistic

infections – pneumonia, septicemia, and meningitis

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Legionella Pneumophila and Legionellosis

• Widely distributed in water• Live in close association with amoebas• 1976 epidemic of pneumonia afflicted 200 American

Legion members attending a convention in Philadelphia and killed 29

• Legionnaires disease and Pontiac fever• Prevalent in males over 50• Nosocomial disease in elderly patients• Fever, cough, diarrhea, abdominal pain, pneumonia

fatality rate of 3-30%• Azithromycin

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Appearance of Legionella pneumophila

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Enterobacteriaceae Family• Enterics• Large family of small, non-spore-forming

gram-negative rods• Many members inhabit soil, water, decaying

matter, and are common occupants of large bowel of animals including humans

• Most frequent cause of diarrhea through enterotoxins

• Enterics, along with Pseudomonas sp., account for almost 50% of nosocomial infections

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Bacteria that account for the majority of hospital infections

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• Facultative anaerobes, grow best with O2

• All ferment glucose, reduce nitrates to nitrites, oxidase negative, and catalase positive

• Divided into coliforms (lactose fermenters) and non-coliforms (non-lactose fermenters)

• Enrichment, selective and differential media utilized for screening samples for pathogens

Biochemical traits for separating enteric genera

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Isolation media for enterics

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Antigenic Structures and Virulence Factors

Complex surface antigens contribute to pathogenicity and trigger immune response:

• H – flagellar Ag

• K – capsule and/or fimbrial Ag

• O – somatic or cell wall Ag – all have

• Endotoxin

• Exotoxins

Antigenic structures in gram-negative enteric rods

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Escherichia Coli: The Most Prevalent Enteric Bacillus

• Most common aerobic and non-fastidious bacterium in gut

• 150 strains

• Some have developed virulence through plasmid transfer, others are opportunists

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Pathogenic Strains of E. Coli

• Enterotoxigenic E. coli causes severe diarrhea due to heat-labile toxin and heat-stable toxin – stimulate secretion and fluid loss; also has fimbriae

• Enteroinvasive E. coli causes inflammatory disease of the large intestine

• Enteropathogenic E. coli linked to wasting form infantile diarrhea

• Enterohemorrhagic E. coli, O157:H7 strain, causes hemorrhagic syndrome and kidney damage

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Escherichia coli

• Pathogenic strains frequent agents of infantile diarrhea – greatest cause of mortality among babies

• Causes ~70% of traveler’s diarrhea

• Causes 50-80% UTI

• Coliform count – indicator of fecal contamination in water

Rapid identification of E. coli O157:H7

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Other ColiformsClinically important mainly as opportunists• Klebsiella pneumoniae – normal inhabitant of

respiratory tract, has large capsule, cause of nosocomial pneumonia, meningitis, bacteremia, wound infections, and UTIs

• Enterobacter sp. – UTIs, surgical wounds• Citrobacter sp. – opportunistic UTIs and

bacteremia• Serratia marcescens – produces a red pigment;

causes pneumonia, burn and wound infections, septicemia and meningitis

A capsule stain of Klebsiella pneumoniae

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Serratia marcescens

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Noncoliform Lactose-Negative Enterics

• Proteus, Morganella, Providencia

• Salmonella and Shigella

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Opportunists: Proteus and Its Relatives

Proteus, Morganella, Providencia – ordinarily harmless saprobes in soil, manure, sewage, polluted water, commensals of humans and animals– Proteus sp. – swarm on surface of moist agar in a concentric

pattern

– Involved in UTI, wound infections, pneumonia, septicemia, and infant diarrhea

– Morganella morganii and Providencia sp. involved in similar infections

• All demonstrate resistance to several antimicrobials

Wavelike, swarming pattern of Proteus vulgaris

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Salmonella and Shigella

• Well-developed virulence factors, primary pathogens, not normal human flora

• Salmonelloses and Shigelloses– Some gastrointestinal involvement and diarrhea

but often affect other systems

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Typhoid Fever and Other Salmonelloses

• Salmonella typhi – most serious pathogen of the genus; cause of typhoid fever; human host

• S. cholerae-suis – zoonosis of swine• S. enteritidis – includes 1,700 different

serotypes based on variation on O, H, and Vi

• Flagellated; survive outside the host• Resistant to chemicals – bile and dyes

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Typhoid Fever

• Bacillus enters with ingestion of fecally contaminated food or water; occasionally spread by close personal contact; ID 1,000-10,000 cells

• Asymptomatic carriers; some chronic carriers shed bacilli from gallbladder

• Bacilli adhere to small intestine, cause invasive diarrhea that leads to septicemia

• Treat chronic infections with chloramphenicol or sulfatrimethoprim

• 2 vaccines for temporary protection

Prevalence of salmonelloses

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The phases of typhoid fever

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Animal Salmonelloses

• Salmonelloses other than typhoid fever are called enteric fevers, Salmonella food poisoning, and gastroenteritis

• Usually less severe than typhoid fever but more prevalent

• Caused by one of many serotypes of Salmonella enteritidis; all zoonotic in origin but humans can become carriers– Cattle, poultry, rodents, reptiles, animal, and dairy

products– Fomites contaminated with animal intestinal flora

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Shigella and Bacillary Dysentery

• Shigellosis – incapacitating dysentery• S. dysenteriae, S. sonnei, S. flexneri, and S. boydii• Human parasites• Invades villus of large intestine, does not perforate

intestine or invade blood• Enters Peyer’s patches instigate inflammatory

response; endotoxin and exotoxins• Treatment – fluid replacement and ciprofloxacin and

sulfatrimethoprim

The appearance of the large intestinal mucosa in Shigella

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The Enteric Yersinia Pathogens

• Yersinia enterocolitica – domestic and wild animals, fish, fruits, vegetables, and water– Bacteria enter small intestinal mucosa, some enter

lymphatic and survive in phagocytes; inflammation of ileum can mimic appendicitis

• Y. pseudotuberculosis – infection similar to

Y. enterocolitica, more lymph node inflammation

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Nonenteric Yersinia Pestis - the Plague

• Nonenteric

• Tiny, gram-negative rod, unusual bipolar staining and capsules

• Virulence factors – capsular and envelope proteins protect against phagocytosis and foster intracellular growth– Coagulase, endotoxin, murine toxin

Gram-stain of Yersinia pestis

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Yersinia Pestis• Humans develop plague through contact with wild

animals (sylvatic plague) or domestic or semidomestic animals (urban plague) or infected humans

• Found in 200 species of mammals – rodents, without causing disease

• Flea vectors – bacteria replicates in gut, coagulase causes blood clotting that blocks the esophagus; flea becomes ravenous

Infection cycle of Yersinia pestis

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Pathology of Plague• ID 3-50 bacilli• Bubonic – bacillus multiplies in flea bite, enters lymph,

causes necrosis and swelling called a bubo in groin or axilla

• Septicemic – progression to massive bacterial growth; virulence factors cause intravascular coagulation subcutaneous hemorrhage and purpura – black plague

• Pneumonic – infection localized to lungs, highly contagious; fatal without treatment

The bubo, classic sign of bubonic plague

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• Diagnosis depends on history, symptoms, and lab findings from aspiration of buboes

• Treatment: streptomycin, tetracycline, or chloramphenicol

• Killed or attenuated vaccine available

• Prevention by quarantine and control of rodent population in human habitats

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Oxidase-Positive Nonenteric Pathogens

• Pasteurella multocida

• Haemophilus influenzae

• H. aegyptius

• H. ducreyi

• H. parainfluenzae

• H. aphrophilus

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Pasteurella Multocida

• Zoonotic genus; normal flora in animals• Opportunistic infections• Animal bites or scratches cause local

abscess that can spread to joints, bones, and lymph nodes

• Immunocompromised are at risk for septicemia and complications

• Treatment: penicillin and tetracycline

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Haemophilus

• Tiny gram-negative pleomorphic rods• Fastidious, sensitive to drying, temperature

extremes, and disinfectants• None can grow on blood agar without special

techniques – chocolate agar• Require hemin, NAD, or NADP• Some species are normal colonists of upper

respiratory tract or vagina (H. parainfluenzae, H. ducreyi)

• Others are virulent species responsible for childhood meningitis, and chancroid

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Haemophilus

• H. influenzae – acute bacterial meningitis, epiglottitis, otitis media, sinusitis, pneumonia, and bronchitis

– Subunit vaccine Hib

• H. aegyptius – conjunctivitis, pink eye

• H. ducreyi – chancroid STD

• H. parainfluenzae and H. aphrophilus – normal oral and nasopharyngeal flora; infective endocarditis

Meningitis in the United States

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Acute conjunctivitis

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