Gram Negative Bacteria - Microbiology - Lecture Slides, Slides for Microbiology. Aliah University
jojy30 January 2013

Gram Negative Bacteria - Microbiology - Lecture Slides, Slides for Microbiology. Aliah University

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Gram Negative Bacteria, Medical Importance, Cocci, Family Neisseriaceae, Blooded Animals, Acinetobacter, Neisseria Gonorrhoeae, Neisseria Meningitidis, Primary Human Pathogens, Pili are some points from these slides of M...
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Foundations in Microbiology

The Gram-Negative Bacteria of Medical Importance

1 Chapter 20

Gram Negative Bacteria


Family Neisseriaceae

• Gram-negative cocci • Residents of mucous membranes of warm-

blooded animals • Genera include Neisseria, Moraxella,

Acinetobacter • 2 primary human pathogens

Neisseria gonorrhoeae Neisseria meningitidis


Neisseria • Gram-negative, bean-shaped, diplococci • No flagella or spores • capsules on pathogens • pili • Strict parasites, do not survive long outside of

the host • Aerobic or microaerophilic • Pathogenic species require enriched complex

media and CO2 4

Neisseria gonorrhoeae • Causes gonorrhea, an STD • Virulence factors: pili, other surface molecules, IgA

protease • Strictly a human infection • In top 5 STDs • Does not survive more than 1-2 hours on fomites • Infection is asymptomatic in 10% of males and 50%

of females


Neisseria gonorrhoeae



• Males – urethritis, yellowish discharge, scarring & infertility

• Females – vaginitis, urethritis, salpingitis (PID), common cause of sterility & ectopic tubal pregnancies

• Extragenital infections – anal, pharygeal, conjunctivitis, septicemia, arthritis




Potential scar tissue blockage infertility



Potential for PID (pelvic inflammatory disease)

Gonorrhea in newborns • Infected as they pass through birth canal • Eye inflammation, blindness • Prevented by prophylaxis after birth


Gonorrhea diagnosis


Neisseria meningitidis

• Virulence factors – capsule, pili, IgA protease • Many strains exist • Prevalent cause of meningitis • Disease begins when bacteria enter bloodstream,

pass into cranial circulation, multiply in meninges; very rapid onset; endotoxin causes hemorrhage and shock; can be fatal

• Treated with penicillin, chloramphenicol • Vaccines exist


Neisseria meningitidis


Spread of bacteria from a nasopharyngeal infection to blood and CSF

The Gram-Negative Bacilli of Medical Importance

14 Chapter 20

Septic Shock-Endotoxic shock • LPS (lipopolysacchardide)

Component of Gram negative cell wall is a potent immune stimulant.

• May lead to circulatory failure, tissue damage and death


Release of LPS as bacteria breaks apart

Aerobic Gram-Negative Bacilli

Pseudomonas – an opportunistic pathogen • Brucella & Francisella – zoonotic pathogens • Bordetella & Legionella – mainly human

pathogens • Alcaligenes – opportunistic pathogen



• small gram-negative rods with a single polar flagellum, produce oxidase & catalase

• highly versatile metabolism


Pseudomonas aeruginosa

18 Single polar flagellum

Pseudomonas aeruginosa • common inhabitant of soil & water (ubiquitous-wide spread) • intestinal resident in 10% normal people • grapelike odor • greenish-blue pigment (pyocyanin) • resistant to soaps, dyes, quaternary ammonium

disinfectants, drugs, drying • frequent contaminant of ventilators, IV solutions,

anesthesia equipment • opportunistic pathogen


Pseudomonas aeruginosa • common cause of nosocomial infections

in hosts with burns, neoplastic disease, cystic fibrosis

• Can cause: pneumonia, UTI, abscesses • Septicemia can lead to: endocarditis,

meningitis, bronchopneumonia • Corneal ulcers from contaminated lens

solutions • Ear infections (Otitis) “swimmer’s ear” • Skin rash (contaminated hot tubs,

saunas, swimming pools) • multidrug resistant


Pseudomonas aeruginosa

21 Skin rash/eruption

Pseudomonas aeruginosa

22 Pseudomonas aeruginosa Staphylococcus aureus

Multiple drug resistance

Brucella • tiny gram-negative coccobacilli • 2 species

Brucella abortus (cattle) – Brucella suis (pigs)

• Brucellosis (synonyms=malta fever, undulant fever, & Bang disease) – a zoonosis transmitted to humans from infected animals

• fluctuating pattern of fever –weeks to a year • combination of tetracycline & rifampin or streptomycin • animal vaccine available (efforts underway to eradicate

from cattle herds and swine) • potential bioweapon



24 Undulating fever

Francisella tularensis • causes tularemia, a zoonotic disease of mammals

endemic to the northern hemisphere, particularly rabbits

• transmitted by contact with infected animals, water & dust or bites by vectors

• headache, backache, fever, chills, malaise & weakness • 10% death rate in systemic & pulmonic forms • intracellular persistence can lead to relapse • gentamicin or tetracycline • attenuated vaccine available • potential bioterrorism agent


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 • May be relatively common in adults (as chronic

cough) and be misdiagnosed as a cold or the flu


Bordetella pertussis

• virulence factors – receptors that recognize & bind to ciliated respiratory

epithelial cells – toxins that destroy & dislodge ciliated cells

• loss of ciliary mechanism leads to buildup of mucus & blockage of the airways

• Hacking coughs followed by abrupt deep inhalation (whoop)

• Vaccine does not give long-term immunity so adults and older children can have a recurrence




Prevalence increasing due to decrease in vaccination rate in children as a result of concern over its publicised vaccine side effects


• live primarily in soil & water • may become normal flora • A. faecalis – most common clinical species

– isolated from feces, sputum, & urine – occasionally associated with opportunistic

infections – pneumonia, septicemia, & meningitis


Legionella pneumophilia


Legionella pneumophila

• widely distributed in water • 1976 epidemic of pneumonia afflicted 200

American Legion members attending a convention in Philadelphia & killed 29 (source was a contaminated air-conditioning system) Legionnaires disease

• Most prevalent in males over 50 • nosocomial disease in elderly patients • Symptoms: fever, cough, diarrhea, abdominal pain,

pneumonia fatality rate of 3-30% • azithromycin


Enterobacteriaceae Family

• enterics • large family of gram-negative bacteria • many members inhabit soil, water, & decaying matter

& common occupants of large bowel of humans & animals

• all members are small, non-sporing rods • facultative anaerobes, grow best in air • cause diarrhea through enterotoxins • divided into coliforms (lactose fermenters) and non-

coliforms (non lactose fermenters)


Dichotomous Key for the Enterobacteriaceae


Diarrheal Disease • Two Mechanisms

– Toxigenic • Organism itself does not invade the tissue • Enterotoxins released which cause cells to increase secretion

secretory diarrhea

– Invasive • Microbes breakdown epithelial cells and form ulcerations. May see


• Fluid and electrolyte loss may result in dehydration…death. • Diarrheal disease = 40% of infectious diseases

– 18% of death worldwide



Nosocomial Infections

Nosocomial infections from Gram negative enterics


Coliforms- Ferment lactose. (normal enteric flora but may cause infections)

Noncoliforms- Do not ferment lactose. (some are normal enteric flora others are true pathogens…Salmonella, Shigella)

Escherichia coli

• most common aerobic & non-fastidious bacterium in gut

• enterotoxigenic E. coli causes severe diarrhea due to heat-labile toxin & heat-stable toxin – stimulate secretion & fluid loss; also has fimbrae

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

• enteropathogenic E. coli linked to wasting from infantile diarrhea; O157:H7 strain causes hemorrhagic syndrome & kidney damage


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 • indicator of fecal contamination in water


Escherichia coli O157:H7

The Ready-To- Eat Spinach outbreak of ‘06

E. Coli 0157:H7 outbreak

• September 28, 2006 : 187 people infected in 26 states (97 hospitalized…29 developed HUS)




15 +

2006 Spinach- associated outbreak

Newer Outbreaks

• Nestle Toll House cookie dough (E. coli) June 2009) (72 cases in 30 states)

• Ground beef (E. coli) ( July 2008) (49 cases in 7 states)

• Pepperoni pizza (E.coli) (Oct-Nov 2007) 7.html (21 cases in 10 states)

Other coliforms

Klebsiella pneumoniae– normal inhabitant of respiratory tract, has large capsule, cause of nosocomial pneumonia, mennigitis, bacteremia, wound infections & UTIs

Enterobacter – UTIs, surgical wounds • Serratiamarcescens – produces a red pigment;

causes pneumonia, burn & wound infections, septicemia & meningitis

Citrobacter – opportunistic UTIs & bacteremia


43 Capsule of Klebsiella pneumoniare

Noncoliform lactose-negative enterics

Proteus Salmonella & Shigella


Proteus • Swarm on surface of moist agar in a concentric pattern • Cause UTI, wound infections, pneumonia, septicemia, &

infant diarrhea



S. typhi – typhoid fever – ingested bacilli adhere to small intestine, cause invasive diarrhea that leads to septicemia. Asymptomatic carriers perpetuate and spread the bacteria.

S. enteritidis – 1,700 serotypes (varieties)- salmonellosis – can be zoonotic (fecal contamination of food products) (1/3 of all chickens have Salmonella)

– Food Poisoning-gastroenteritis for 2-5 days


A recent Salmonella in peanut butter outbreak

(Late 2008 through 2009)


Phases of Typhoid Fever




50 Patches of mucus and blood

Shigellosis – bacillary dysentery •S. dysenteriae, S. sonnei, S. flexneri & S. boydii •Invades large intestine, can perforate intestine or invade blood (septicemia) •Virulence factors: endotoxin & exotoxins •Treatment – fluid replacement & ciprofloxacin & sulfa- trimethoprim


Yersinia pestis

• Nonenteric…tiny, gram-negative rod • virulence factors – *capsular & envelope proteins that

protect against phagocytosis & foster intracellular growth

*coagulase *endotoxin


Yersinia pestis


Yersia pestis in blood

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 53


Yersinia pestis


Infection cycle

Pathology of plague

• bubonic – bacillus multiplies in flea bite, enters lymph, causes necrosis & swelling called a bubo in groin or axilla

• septicemic – progression to massive bacterial growth; virulence factors cause intravascular coagulation & subcutaneous hemorrhage. Necrosis and skin blackening occur – black plague

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

• treatment: streptomycin, tetracycline or chloramphenicol

• Killed or attenuated vaccine that gives a short-term protection exists


57 Classic bubo (painful nodule that can rupture to the surface)

Pasteruella multocida

• zoonotic genus • opportunistic infections • animal bites or scratches cause local abscess

that can spread to joints, bones, & lymph nodes (septicemia)

• treatment: penicillin & tetracycline


Hemophilus • tiny gram-negative pleomorphic rods • Fastidious. can’t grow on blood agar without special

techniques. • some species are normal colonists of upper

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

• others are virulent species responsible of conjunctivitis, childhood meningitis, & chancroid



H. influenzae – acute bacterial meningitis, epiglottitis, otitis media, sinusitis, pneumonia, & bronchitis – meningitis symptoms: fever, vomiting stiff neck neurological

impairment. High fatality is untreated – subunit vaccine Hib

H. aegyptius –conjunctivitis, pink eye • H. ducreyi – chancroid STD • H. parainfluenzae & H. aphrophilus – normal oral &

nasopharyngeal flora; infective endocarditis


61 Bacterial meningitis from H. influenzae

62 Pinkeye (infectious conjunctivitis) H. aegyptius

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