Microbiol Rev w Cases

REVIEW OF MEDICAL MICROBIOLOGY

Infections of

Respiratory tract

Cardiovascular system

Gastrointestinal tract

Skin and soft tissue

Central nervous system

Genitourinary tract

THE RESPIRATORY TRACT

Upper Respiratory Tract

Pharyngitis (mostly 2 years through adolescence)

Adenoviruses

Group A Streptococci ( S. pyogenes )

Potential for rheumatic fever

Chlamydophila pneumoniae

Neisseria gonorrhoeae

Corynebacterium diphtheriae

Mycoplasma pneumoniae


Otitis media (infants and young children)

Streptococcus pneumoniae

Haemophilus influenzae

Staphylococcus aureus

Group A streptococcus

Moraxella catarrhalis

Formerly “Branhamella”

Gram-negative cocci

Opportunistic pathogen


Otitis externa


Pseudomonas aeruginosa

Group A Streptococcus

Malignant otitis externa

• In diabetics, elderly & immunocompromised

• Can lead to osteomyelitis and meningitis


Sinusitis




Chlamydophila pneumoniae




Viruses

Oral anaerobic bacteria


Conjunctivitis


Group B Streptococcus

Viridans Streptococcus





Conjunctivitis (contd)


Corynebacterium species

Francisella tularensis

Adenoviruses

Chlamydia trachomatis


Rhinocerebral mucormycosis

• Life-threatening

• Most common in diabetics

• The fungi Mucor and Rhizopus invade blood vessels, resulting in necrosis of bone and thrombosis of the cavernous sinus and internal carotid artery


Bacterial epiglottitis

Life-threatening

Haemophilus influenzae type b




Diphtheria


Whooping cough

Bordetella pertussis


“Common colds”

Rhinoviruses

Adenoviruses

Influenza C

Coronaviruses

Coxsackie viruses


“Croup”

Respiratory syncytial virus

Influenza virus

Parainfluenza virus


Lower Respiratory Tract

Community acquired infections

Streptococcus pneumoniae (elderly)

Klebsiella pneumoniae (alcoholics)

Mycoplasma pneumoniae (school-age children)

Mycobacterium tuberculosis

RSV (infants and young children)

Influenza virus



Community acquired infections

Bronchitis or pneumonia secondary to viral pneumonia




Moraxella cararrhalis



Nosocomial infections

Mycobacterium tuberculosis

RSV in pediatric patients

Methicillin-resistant S. aureus (pneumonia)


Legionella spp.



Patients with underlying lung infections

Chronic obstructive pulmonary disease

P. aeruginosa

S. pneumoniae

H. influenzae

Moraxella cararrhalis

Allergic bronchopulmonary aspergillosis




Cystic fibrosis

S. aureus

P. aeruginosa

Allergic bronchopulmonary aspergillosis




Cavitary lung disease (due to prior MTB infection)

Aspergillus spp (Aspergilloma or fungus ball)



Immunocompromised individuals

At risk for all recognized respiratory tract pathogens

AIDS patients

Pneumocystis carinii

S. pneumoniae

MDR M. tuberculosis




Neutropenic patients

Invasive aspergillosis

Mucormycosis




Transplant patients

Invasive fungi

CMV

HSV

Legionella spp.

Pneumocystis carinii

A 40-year-old male with multisystem failure secondary to bilateral pneumonia was transferred to our hospital via helicopter.

He had presented to his local physician 3 days previously complaining of fever, malaise, and vague respiratory symptoms.

He was given amantadine for suspected influenza. His condition became progressively worse, with shortness of breath and a fever to 40.5˚C.

From: “Cases in Medical Microbiology and Infectious Disease”

He was admitted to an outside hospital 24 h prior to transfer.

A laboratory examination revealed abnormal liver and kidney function.

Therapy with Timentin (ticarcillin-clavulanic acid) and trimethoprim-sulfamethoxazole was begun.

He underwent pronchoscopic examination which revealed mildly inflamed airways containing thin, watery secretions.

A Gram-stain of bronchial washings and culture results are shown in the figure.

Based on these findings, he was begun on appropriate antimicrobial therapy.

Which organisms are common causes of communityacquired bacterial pneumonia?

Streptococcus pneumoniae

Haemophilus influenzae

Mycoplasma pneumoniae

Staphylococcus aureus

(frequently following an influenza infection)

Klebsiella pneumoniae

(elderly & alcoholics)

Legionella pneumophila

Chlamydophila pneumoniae

On the basis of the Gram-stain of bronchial washings, and the patient’s presentation, what is the most likely cause of this patient’s catastrophic infection?

Why must the laboratory be notified if this organism is considered in the differential diagnosis?

The patient has Legionella pneumophila.

Renal and hepatic dysfunction and thin watery secretions are characteristic of this infection.

Patients with bacterial pneumonia due to most other bacterial agents have thick, purulent secretions.

The laboratory needs to be informed because the organism requires a specific growth medium, buffered charcoal yeast extract (BCYE) agar.

What techniques other than culture can be used to detect this organism within 24 h?

DFA

What is the appropriate antimicrobial agent for the treatment of this infection?

Which other Gram-negative respiratory pathogen is treated with this antibiotic?

Erythromycin

Can penetrate into white blood cells

Legionella multiplies in macrophages

Bordetella pertussis

THE CARDIOVASCULAR SYSTEM

Septicemia: Predisposing factors and agents

Abdominal sepsis

Enterobacteria

Bacteroides fragilis

Enterococcus faecalis

Enterococcus faecium

Infected wounds


Streptococcus pyogenes

Enterobacteria



Osteomyelitis


Pneumonia

Streptococcus pyogenes

Food poisoning

Salmonella spp.

Campylobacter spp.



Intravascular devices


Staphylococcus epidermidis

Enterobacteria

Meningitis


Neisseria meningitidis




Immunocompromised patients


Enterobacteria


Infective endocarditis

> 80% of cases caused by streptococci or staphylococci

Total streptococci

Viridans group anginosus group mitis group mutans group salivarius group

60%

35%


Infective endocarditis

Total streptococci

Total staphylococci

S. aureus

S. epidermidis

60%

25%

20%

5%


Myocarditis


Clostridium perfringens


Borrelia burgdorferi

Neisseria meningitidis

Staphylocccus aureus

The patient was a 4-month-old female who was admitted to the hospital in March with sever respiratory distress.

Five days prior to admission she had developed a cough and rhinitis.

Two days later she began wheezing and was noted to have a fever.

She was brought to the emergency room when she became lethargic.

From: “Cases in Medical Microbiology and Infectious Disease”

One sibling was reported to be coughing, and her father had a “cold”.

On examination she had a fever of 38.9˚C tachycardia with a pulse of 220/min tachypnea with respirations of 80/min

Her throat was clear.

A chest X-ray revealed interstitial infiltrates.

She was put in respiratory isolation in the pediatric intensive care unit, and was subsequently intubated.

Blood and nasopharyngeal cultures were sent to the bacteriology and virology laboratories.

A rapid diagnostic test was positive and specific antiviral therapy was begun.

She was also given a bronchodilator (aminophylline) to treat the bronchospasm which was resulting in her wheezing.

She was extubated 5 days later and discharged home on day 8.

1. What are the possible causes for this patient’s pneumonia?

Parainfluenza virus

Influenza A and B

Respiratory syncytial virus

Mycoplasma pneumoniae

Bordetella pertussis

Membrane-enzyme immunoassay

2. What other techniques could one use to identify this microorganism?

Direct Fluorescence Antibody

“Shell Vial Assay”

Fibroblasts grown on coverslips in a shell vial

Clinical specimens a centrifuged onto the cell monolayer

Incubation for 1-2 days

The monolayer is stained with a fluorescent monoclonal antibody specific for an RSV antigen

2. What is the epidemiology of the disease?

RSV is spread by large droplets and on fomites

Can be spread via contaminated hands

Occurs primarily in winter months

3. What is the pathophysiologic basis for wheezing?

RSV is tropic for bronchial epithelium

Edema and necrosis can lead to collapse and obstruction of a child’s small bronchioles

4. What specific therapy should be given after the antigen test gives the diagnosis?

Only one antiviral agent is available for treatment of RSV in infants

Aerosolized ribavirin

(oral administration can result in hepatic or bone marrow toxicity)

The American Academy of Pediatrics recommends its use in children with congenital heart disease, cystic fibrosis, immunodeficiency or severe illness.

5. What infection control measures should be taken?

Patients should be put on respiratory isolation

Gowns and gloves should be used during contact

6. What can be done to prevent the disease?

Inactivated RSV vaccine did not work and exacerbated the disease

Immune globulin can be used in children at greatest risk

THE GASTROINTESTINAL SYSTEM

Two basic mechanisms of diarrheal disease:

Enterotoxin-induced fluid loss

Cholera toxin

Direct damage to the intestinal epithelium

Cytotoxin

Entamoeba histolytica

Invasion of epithelium

Salmonella spp.

Shigella spp.


Yersinia enterocolitica


Infectious doses

Hundreds of thousands to millions

Salmonella spp.

Vibrio cholerae

Less than 100

Shigella spp.


Bacteria

Invasive diarrhea


Salmonella spp.

Shigella spp.


Large-volume watery diarrhea

Vibrio spp.


Bacteria

Watery diarrhea

Enterotoxigenic E. coli


Typhoid fever

Salmonella spp.


Bacteria

Traveler’s diarrhea

Enterotoxigenic E. coli

Dysentery

Shigella spp.


Bacteria

Antibiotic-associated diarrhea

Pseudomembranous colitis

Clostridium difficile

Food poisoning



Bacillus cereus

Salmonella spp.


Bacteria

Abdominal abscess

Bacteroides fragilis

Gangrenous lesions of bowel or gall bladder


Enterohemorrhagic colitis

Enterohemorrhagic E. coli


Viruses

Acute, self-limited hepatitis

Hepatitis A

Acute and chronic hepatitis

Hepatitis B

Hepatitis C


Viruses

Diarrhea

Enterovirus

Rotavirus

Norwalk agent (calicivirus)

Vomiting

Rotavirus

Norwalk agent (“24-hour flu”)


Viruses

Infants

Rotavirus A (most common cause)

Adenovirus 40, 41

Coxsackie A24 virus

Infants, children, and adults

Norwalk agent (“24-hour flu”)

Calicivirus

Reovirus

SKIN AND SOFT TISSUE

Diffuse erythematous macular rash may be a manifestation of systemic disease

Rocky Mountain spotted fever

Meningococcemia

Entereoviral infection

Toxic shock syndrome

Scarlet fever

Measles

German measles


Erythema migrans

Lyme diseases

Vesicular skin lesions

Varicella Zoster virus

Macular, papular or pustular, but not vesicular, skin lesions

Secondary syphilis


Important to treat superficial skin infections

Folliculitis caused by Staphylococcus aureus

Cellulitis caused by Streptococcus pyogenes

Delay in treatment may result in invasion of the deeper structures (e.g necrotizing fasciitis)


Cat scratch disease, bacillary angiomatosis

Bartonella henselae

Lyme disease

Borrelia burgdorferi

Gas gangrene


Tetanus

Clostridium tetani


Diphtheria and wound diphtheria


Cellulitis

Group A streptococci (S. pyogenes)

Group B streptococci (S. agalactiae)

Pasteurella multocida


Cryptococcus neoformans


Skin infection in burn patients


Thrush

Candida albicans

Candida spp.

Cutaneous infection

Blastomyces dermatitidis


Infection of keratinized tissue

Epidermophyton floccosum

Microsporum spp.

Trichophyton spp.

Ulcerative skin lesions

Leishmania tropica


Exanthem subitum

Human herpesvirus type 6

Oral infections

Herpes simplex virus

Warts

Human papillomavirus

CENTRAL NERVOUS SYSTEM

The most frequent infections are

Meningitis

Encephalitis

Abscess

Meningitis

Septic: caused by bacteria

CSF cloudy (>1,000 white blood cells/µl)

Aseptic: Viruses, fungi, MTB

CSF clear (100500 cells/µl)


Neonatal meningitis (newborn - 2 months)

Group B streptococci (most common cause)

Listeria monocytogenes

E. coli

Klebsiella pneumoniae

Citrobacter diversus Citrobacter koseri

Treponema pallidum


Meningitis (2 months - 5 years)

Haemophilus influenzae type b


Neisseria meningitidis (all ages)

Meningitis (Patients with head trauma)

Coagulase-negative staphylococci




Aseptic meningitis

Echovirus

Coxsackievirus

Herpes simplex virus

Fungal meningitis

(primarily in the immunocompromised)

Cryptococcus neoformans (in AIDS patients)


Viral encephalitis

Herpes simplex virus (most common)

(necrotizing; necrotizing hemorrhagic)

Eastern equine encephalitis virus

Western equine encephalitis virus

St. Louis encephalitis virus

La Crosse encephalitis virus


Encephalitis

Toxoplasma gondii

Taenia solium (“cysticercosis”; from pork)

Meningoencephalitis

Cerebral malaria

Naegleria fowleri (an amoeba)

Citrobacter diversus


Brain abscesses

Extension from a contiguous site

Hematogenous spread from another site

(endocarditis or lung abscess)

Septic emboli (blood clots containing an infectious agent)

In immunocompetent individuals

S. aureus viridans streptococci

Actinomyces spp.

Anaerobic bacteria


Brain abscesses

In immunocompromised individuals

Aspergillus

Mucor

Rhizopus

Nocardia spp.

In diabetic patients

Rhinocerebral mucormycosis

GENITOURINARY TRACT

Urinary tract infections

Endogenous infections

Nosocomial (catheterization)

Sexually transmitted diseases

Exogenous infections


Urinary tract infections

Enterobacter

Enterococcus

Klebsiella pneumoniae

Proteus mirabilis


Staphylococcus saprophyticus

Candida spp.


Pelvic inflammatory disease

Chlamydia trachomatis (PID)

Neisseria gonorrhoeae (PID)

Actinomyces spp. (endogenous; IUD usage)

Vaginitis

Candida spp. (endogenous)

Trichomonas vaginalis


Sexually transmitted diseases

Chlamydia trachomatis (PID)

Neisseria gonorrhoeae (PID)

Treponema pallidum (fetal loss or perinatal infect.)

Herpes simplex virus (fetal loss or perinatal infect.)

HIV

Human papilloma virus

Trichomonas vaginalis

Microbiol Rev w Cases

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