Lecture 1: Atypical Bacteria: Mycobacteria, mycoplasma, legionella

Mycobacteria characteristics

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

Mycobacteria: Slow growing bacilli

aerobic to microaerophilic, 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 Subspecies

Mycobacterium tuberculosis complex (MTC)

Mycobacterium leprae and Mycobacterium lepromatosis

Nontuberculous Mycobacteria (NTM) (Mycobacteria Other Than Tuberculosis (MOTT))

Mycobacteria Tuberculosis (Mtb)

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

Pulmonary TB

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

Extrapulmonary TB

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

Mycobacteria Tuberculosis (Mtb) Resevoir

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

Mtb – Pulmonary Tuberculosis

Transmitted via inhalation of infectious air droplets emitted from a person

Tuberculosis (TB)

disease caused by the bacterium Mycobacterium tuberculosis (Mtb)

Once in the body tuberculosis (TB) can be

Inactive tuberculosis - Latent TB infection (LTBI)

Active tuberculosis - TB disease

TB 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 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 (Mtb)

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

Mtb Detection

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

Diagnosis of active TB based on

Clinical manifestation, abnormal chest radiograph, acid fast bacilli in sputum, and DNA detection tests (NAATs)

Mtb Treatment of tuberculosis

Both Active TB and LTBI are curable with multi-drug antimicrobial therapy

Active TB treatment

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

LTBI Treatment

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

Mtb – Prevention

BCG (Bacille Calmette-Guerin) Vaccination (M. bovis) but only works for kids

Infection control

Mycobacterium leprae characteristics

Slow growing obligate intracellular AFB and invades skin macrophages and schwann cells

Mycobacterium leprae: Slow growing obligate intracellular AFB

Longest doubling time of all known bacteria but grows optimally at cooler temps (30-35C)

Obligate intracellular

an organism is strictly dependent on living inside a host cell to survive and reproduce

Ex: Mycobacterium leprae

Mycobacterium leprae causes

Hansen disease aka leprosy

M. 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 result of

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 (armadilos)

M. leprae – Infection

~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

M. leprae – Risk Factors

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

M. leprae – Disease Signs/Symptoms

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

M. leprae – Diagnosis 3 criteria

Hypopigmented or reddish skin patches, thickened peripheral nerves, and AFB detected on skin smears or biopsy

M. leprae – Prevention

Avoid contact infected untreated people and avoid armadillos (zoonotic)

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

Causes 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

M. 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

M. pneumoniae: virulence factor

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

M. pneumoniae – Infection

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

M. pneumoniae – Transmission

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

M. 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

M. pneumoniae – Treatment

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

Pneumonia treated with antibiotics

M. pneumoniae – prevention

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

Legionella pneumophila characteristic

Non-encapsulated, motile, environmental gram - bacilli

Legionella pneumophila location

Widespread in nature; reside in surface and drinking water

L. 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

L. pneumophila – Transmission

By inhalation of contaminated aerosols and person to person transmission is rare

L. pneumophila – Infection

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

Can be sporadic or epidemic

L. Pneumophila causes 

Legionnaire’s disease

Legionnaire’s disease

Most severe type of atypical pneumonia, most people exposed don’t become ill, and risk factors are old or immunocomprised people

Two diseases caused by Legionella infection

Legionnaire’s disease and Pontiac fever

Legionellosis: Legionnaire’s Disease

Most common type,  varies in severity from mild illness that does not require hospitalization (walking pneumonia) to fatal multi-lobar pneumonia

Legionellosis: Pontiac Fever

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

L. pneumophila – Diagnosis

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

L. 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