Lecture 1: Atypical Bacteria: Mycobacteria, mycoplasma, legionella

Atypical bacteria

lacking a typical cell wall or being intracellular, which makes them resistant to certain antibiotics like penicillin

what are types of atypical bacteria ?

Mycobacterium and Atypical pneumonias

Mycobacteria characteristics

Slow growing bacilli, mycolic acid, and is acid fast bacilli (AFB)

Mycobacteria: Slow growing bacilli

aerobic to microaerophilic so it needs oxygen or little oxygens and doubling time is 18-24 hours so its slow growing

Mycobacteria: Mycolic Acid

Key virulence factor, its a rich cell wall with thick hydrophobic waxy long fatty acid that prevents gram staining

Mycobacteria Species

M. tuberculosis complex (MTC)

M. leprae and M. lepromatosis

Mycobacteria Tuberculosis (Mtb)

Human respiratory tract bacterial pathogen and causes 2 diseases: Pulmonary TB and Extrapulmonary TB

Pulmonary Tuberculosis

most common disease but can disseminate from lung to other parts of the body

Extrapulmonary Tuberculosis

infections outside the respiratory tract in the gastrointestinal tract, bones, joints, nervous system, lymph nodes, genitourinary tract, and skin

Mycobacteria Tuberculosis Reservoir

Humans are the only known b/c its a obligate human parasite, “white plague”, and deadliest infectious disease worldwide now

Obligate human parasite

requires a living host to survive and complete its life cycle

Mycobacteria: Pulmonary Tuberculosis transmission

via inhalation of infectious air droplets emitted from a person

After infection, 3 possible clinical outcomes of Mycobacteria Tuberculosis 

infection is eliminated, it turns out to latent tuberculosis, or active tuberculosis disease

Tuberculosis

disease caused by the bacterium Mycobacterium tuberculosis

Once in the body tuberculosis (TB) can be

Inactive tuberculosis - Latent tuberculosis infection (LTBI)

Active tuberculosis - Tuberculosis disease

Tuberculosis occurs more often

In people with weakened immune systems like very young, very old, and immunocompromised HIV

Symptoms of Active TB

Chronic, productive coughing, or bloody sputum

Other common symptoms are fever, weight loss, fatigue, and can disseminate from lungs to other body parts

AIDS

Active TB number one killer for people with

Risk Factors for TB Today for Mtb

Recent airborne exposure to mycobacteria tuberculosis like close contact with a person with active tuberculosis or works/lives in a area with high tuberculosis rates or weakened immune systems

Mycobacteria Tuberculosis Detection

Tuberculin skin test by injection (of PPD) and evaluation of injection site but it cant distinguish between latent or active infections

Diagnosis of active Tuberculosis based on

Abnormal chest radiograph, acid fast bacilli in sputum, and DNA detection tests (NAATs)

Treatment of tuberculosis

Both Active Tuberculosis and Latent Tuberculosis infection are curable with multi-drug antimicrobial therapy

Active Tuberculosis treatment

6 – 9 months of 4-drug regimen (isoniazid, rifampin, pyrazinamide and ethambutol); more added if multidrug resistant (MDR-TB)

Latent Tuberculosis infection Treatment

3 – 6 mon prophylactic preventable antibiotics (TST Positive (+PPD) w/no signs or symptoms of active TB)

Multidrug-Resistant Tuberculosis (MDR-TB) 

a form of tuberculosis infection caused by bacteria that are resistant to at least two of the first-line drugs used to treat TB: isoniazid (INH) and rifampin. 

Mycobacteria tuberculosis – Prevention

BCG Vaccination but only works for kids

Infection control

Bacille Calmette-Guérin (BCG) Vaccination

derived from a live strain of Mycobacterium bovis that is used to protect against tuberculosis

Mycobacterium leprae characteristics

Slow growing obligate intracellular AFB and invades skin macrophages and schwann cells (found in pns)

Mycobacterium leprae: Slow growing obligate intracellular AFB

Longest doubling time of all known bacteria but grows optimally at cooler temps (30-35C) and strictly depends on living inside a host to survive

Hansen disease aka leprosy

Caused by the organism Mycobacterium leprae and needs cooler temps (30-35) for growth

Mycobacterium Leprae – Hansen’s Disease

Chronic, granulomatous disease (like TB), chronic infection results in inflammatory nodules (granulomas) in the skins and peripheral nerves

Hansen’s Disease results in

inflammatory damage to the peripheral nerves and skin tissues of the extremities, eyes, nose, respiratory mucosa

M. leprae - Transmission

Used to be spread person to person by inhalation of infectious respiratory droplets but recently shows zoonotic origin by armadillos

Mycobacterium leprae infects

~95% of people have a natural immunity to the disease (large genetic component to susceptibility)

M. leprae – treatment

Antibiotics is %100 cure, without antibiotic can lead to chronic inflammation

Mycobacterium Leprae – Risk Factors

Living near leprosy endemics, close contact with infected humans/animals, and having specific immune system defects

Mycobacterium leprae – Disease Signs/Symptoms

subtle, occur slowly (usually over years), begin in cooler areas of the body (e.g., hands, feet, face, and knees)

Mycobacterium leprae – Diagnosis 3 criteria

Hypopigmented or reddish skin patches

thickened peripheral nerves

AFB detected on skin smears or biopsy

Mycobacterium leprae – Prevention

Avoid contact infected untreated people and avoid armadillos zoonotic and no vaccines yet

Pneumonia

 infection of the lung/lower respiratory tract

Atypical

distinguished from classical bacterial pneumonia by clinical findings and lack of response to typical antibiotics used for classical pneumonia

Atypical pneumonia (AKA walking pneumonia)

Symptoms often milder, slower to develop 1 – 4 weeks after infection, and more persistent than those of typical pneumonia

Species of Atypical Pneumonia

Mycoplasma pneumoniae

Chlamydia pneumoniae

Legionella pneumophila 

Mycoplasma pneumoniae characteristics

One of the smallest free-living bacteria, no cell wall, and limited metabolic and biosynthetic capabilities

Mycoplasma pneumoniae: No cell wall

able to do cellular polymorphism, prevents gram stain, is naturally resistant to many, and is susceptible to desiccation

Mycoplasma pneumoniae: Limited metabolic and biosynthetic capabilities

Small genomes so depends on tight adherence to human respiratory epithelium and escapes host immune response by intracellular localization

Mycoplasma pneumoniae virulence factor

Produces hydrogen peroxide which causes cytopathic effect to airway epithelium and results in persistent cough

Mycoplasma pneumoniae Infected

Community-acquired upper and lower respiratory tract disease in children and adults worldwide

Mycoplasma pneumoniae – Transmission

person to person through respiratory droplets and incubation period is 2-3 weeks

Mycoplasma pneumoniae – Signs and Symptom

Illness is typically mild with symptoms that get worse over a period of 1 to 4 weeks

Fatigue, headache, low grade fever, sore throat, cough, and chest pain

Mycoplasma pneumoniae – Treatment

Most people recover from mild disease without treatment (or diagnosis)

can be treated with antibiotics

Mycoplasma pneumoniae – prevention

There is no vaccine and infection is not protective against re-infection

Legionella pneumophila characteristic

Non-encapsulated, motile, environmental gram negative bacilli

Legionella pneumophila location

Widespread in nature; reside in surface and drinking water

Legionella pneumophila: Facultative intracellular parasite

Able to live and reproduce inside or outside cells, they invade and replicate inside amoebae in environment and macrophages in humans - intracellular lifestyle

Legionella pneumophila is most

important atypical pneumonia pathogen in terms of disease severity and primarily respiratory infections

Legionella pneumophila – Transmission

By inhalation of contaminated aerosols like water

Person to person transmission is rare

Legionella pneumophila – Infection

Begins in lower respiratory tract where bacteria multiply intracellularly in alveolar macrophages

Can be sporadic or epidemic

Legionnaire’s disease caused by

Organism Legionella Pneumophila

Legionnaire’s disease

Most severe type of atypical pneumonia, most people exposed don’t become ill, and risk factors are old, lung disease, and smoking history

Two diseases caused by Legionella infection

Legionnaire’s disease (most common)

Pontiac fever

Legionellosis: Pontiac Fever

Less common and milder respiratory infection and symptoms resemble acute influenza (fever, headache, severe muscle aches)

Legionella pneumophila – Diagnosis

Chest X-ray exam, urine test for legionella antigens, NAATs, and analysis of blood samples

Legionella pneumophila – Treatment and prevention

Antibiotics and avoid smoking

4 Atypical Bacterial Pathogen

1.Mycobacteria: Mycobacterium tuberculosis and Mycobacterium leprae

2.Atypical pneumonias: Mycoplasma pneumoniae and Legionella pneumophila