Air Microbiology

Saad Farooqi

Department of Environmental Sciences

University of Swat

Saad.luck57@gmail.com

Air Microbiology

• Aerobiology is defined as the study of life present in the air. • Aeromicrobiology relates to the study of

environmentally relevant microorganisms. • Microorganisms exist within 300-1000 feet of earth’s

surface that have become attached to fragments of dried leaves, straw or dust particles light enough to be blown by wind. • In dry whether the microbial load of air is high while in

wet weather the rain washes the microorganisms from the air.

• Air is a poor medium for microbial growth – too dry and no nutrients

• Spore forming and Gram-positive bacteria are resistant to drying

• Dust, water droplets in air carry microbial populations from one place to another

• Sneezing, coughing, talking are efficient methods of transferring microbes from one respiratory tract to another

100 m/sec, 10000 – 100000 bacteria

• Liquid and dust particles settle in the respiratory tract depending on their velocity and size

• Microorganisms colonize specific locations in the respiratory tract

Streptococcal diseases • S. pyogenes, S. pneumoniae •Nonsporulating, fermentive, anaerobic gram-positive cocci• S. pyogenes accounts for about half of sore throat cases, causes ‘Strep throat’ – enlarged tonsils, mild fever, tender cervical lymph nodes• S. pyogenes lysogenized with bacteriophage produce an erythrotoxin – small blood vessels are damaged, diffuse rash and fever called ‘scarlet fever’• Systemic infection leads to necrotizing fasciitis – ‘flesh eating disease’

Streptococcus pyogenes

Hemolysis of blood agar

• Diagnosis of S. pyogenes infection from throat swab includes fluorescent Ab staining, or culturing on blood agar for hemolysis

• S. pneumoniae causes difficult lung infections (pneumonia) due to the bacterial capsule

• Infection can spread to inner ear,, heart with mortality rate around 10%

• Vaccination is possible with capsule polysaccharide, treatment with antibiotics

Diptheria • Childhood respiratory illness caused by

Cornyebacterium diptheriae infection.• Gram-positive non-motile aerobic rods• Spread via fluid droplets entering the lung• Bacterial enzyme called neuraminidase

interacts with epithelial glycoproteins for successful invasion

• Inflammatory response in throat tissues causes characteristic ‘pseudomembrane’ of damaged host cells, leukocytes and C. diptheriae.

• Death can occur from obstructed breathing and the effects of the diptheria exotoxin

pseudomembrane

• Treatment includes antibiotic therapy in conjunction with diptheria antitoxin – neutralizing antibodies against the toxin

•Diptheria toxoid (formalin treated exotoxin) is part of the Diptheria/Tetanus/Pertussis vaccine

Whooping cough (pertussis)

• Infection by Bordetella pertussis •Small, gram-negative, aerobic coccobacillus• Attaches to epithelial cells of upper respiratory tract using an adherence protein called filamentous hemagglutinin antigen•Produces an exotoxin that induces cAMP production, and an endotoxin that may induce the cough•Recurring spasmodic coughing that lasts up to 6 weeks• Nasopharyngeal aspirate is plated on blood-glycerol-potato extract agar to diagnose

• Vaccine consists of killed whole cells or purified proteins derived from Bortedella pertussis

• Rise in the incidence of whooping cough. Why?

Tuberculosis (consumption)

Lung tubercles

• Infection by gram-positive bacillus Mycobacterium tuberculosis

• Extremely contagious by respiration• Primary infection usually occurs by

inhalation – bacteria are usually engulfed but survive within activated macrophages of the lung – structures called tubercles

• Primary infection is diagnosed using the tuberculin test, and usually provides cell-based immunity

• Secondary infection or reactivation of dormant bacteria can cause extensive lung tissue damage

• Pathology most often occurs in very young, elderly, malnourished, immune-compromised people

1.5 million deaths annually

Treatment includes streptomycin antibiotic, as wellas the growth factor analog isoniazid

Isoniazid is an analogue of nicotinimide, requiredFor mycolic acid synthesis in Mycobacterium

Leprosy (Hansen’s disease)

lepromatous lesion

tubercular lesion

• Infection by Mycobacterium leprae, can not be cultured in the lab

• Intracellular parasite grows in macrophages

• Folded, bulblike lesions on the body containing a billion bacteria/gram of tissue

• Severe form is lepromatous leprosy which can also affect peripheral nerves and motor function

• Milder form is tubercular leprosy, in which fewer bacteria can be recovered

• As, many as 12 million cases worldwide

Meningitis and meningococcemia

• Infection by Neisseria meningitidis • Gram-negative, aerobic encapsulated• Infection starts via the airborne route, spreads to blood and can cause 1) meningococcemia – sepsis, coagulation, shock, 17% mortality2) meningitis – inflammation of membranes lining the central nervous system, sudden headache, vomiting, stiff neck• Treated by penicillin G or chloramphenicol

Measles, Mumps, Rubella

• Measles caused by a paramyxovirus, nasal discharge, sore throat, fever, characteristic rash. Now occurs in isolated outbreaks

• Mumps caused by a different paramyxovirus, inflammation of salivary glands, can spread through bloodstream to testis and brain

• Rubella caused by a togavirus, generally milder than measles but can be transmitted congenitally

• All three are effectively managed by the MMR vaccine

Chickenpox and shingles

• Both caused by the same herpes virus• Chickenpox is transmitted by respiration and disseminated in bloodstream causing characteristic rash• Dormant virus in nerve cells can migrate to surface skin causing shingles (zoster). Usually strikes elderly and immune-compromised•Decreased incidence due to new vaccine

Common cold

rhinovirus

adenovirus

• 85% caused by ssRNA viruses, especially rhinovirus and coronavirus, 15% caused by DNA viruses such as adenovirus

• Average person gets 3/year• Nasal inflammation and obstruction,

general malaise but no fever• Aerosol transmission• Vaccination is extremely unlikely. Why?• Specific anti-rhinoviral drugs are under

development: Block viral coat protein to prevent virus-cell recognition

Influenza• ssRNA orhomyxovirus, types

A,B,C• Low grade fever, chills, fatigue,

headache• Segmented RNA genome –

infection by more than one strain leads to gene reassortment called antigenic shift

• Mutations in important genes encoding the haemagglutinin and neuraminidase result in antigenic drift

• Immunity generally comes from IgA to Ha and Neu antigens

• Severe localized epidemics occur every 2-3 years due to antigenic drift

• Worldwide pandemics occur every 10-40 years due to antigenic shift

• Vaccines are created using mixed population of strains from the previous year

Staphylococcus infections

• gram-positive and nonsporulating, but resistant to drying. Therefore found on skin and mucus membranes

• Infection often occurs at wound sites – especially nosocomial (hospital) infections

• S. aureus produces a hemolysin exotoxin – lyses red blood cells, an enterotoxin - causing food poisoning, coagulase – blood clots around bacteria mask it from immune system, leukocydin – kills white blood cells

• Toxic shock syndrome can be caused by inadequate feminine hygiene

Gastric ulcers and cancers

• Infection by Helicobacter pylori in the non acid secreting mucosa of stomach

• gram-negative motile, polar flagella• 80% of gastric ulcer patients are

infected• Perhaps transmitted from contaminated

food or water, or person-to person contact in unknown fashion

• Mucosal layer protects from stomach acid, how it causes ulcers is unknown

•Treated with a combination of antibiotics

Hepatitis

• Infection of hepatocytes (liver cells) leading to inflammation, cirrhosis and sometimes cancer

• Jaundice, hepatomegaly • Caused by a number of unrelated viruses:• A – person to person, vaccine• B – parenteral, vaccine, fatal, vaccine• D – defective virus requires B coat• C – parenteral, chronic• E – enteric, acute • G - perhaps asymptomatic• Universal precaution against blood-borne

and sexually transmitted infections

Sexually transmitted infections

• Fallacy – there is a technological solution to every problem

• “The sex drive in some individuals is so strong that it will suppress the fear of disease, even AIDS”

Acquired immunodeficiency syndrome (AIDS)

• Suite of disorders as a secondary consequence to infection by human immunodeficiency virus (HIV)

• First recognized in 1981, now 50 million infected

•HIV is a ssRNA retrovirus: reverse transcriptase enzyme generates a cDNA that integrates into host cell genome

• HIV infects macrophages and TH cells

• An individual has AIDS if:1) Tests positive for HIVAND2) Has a drastically reduced number of TH cellsOR3) At least one unusual opportunistic infection or cancer

such as Pneumocystis carinii pneumonia, toxoplasmosis, or Kaposi’s sarcoma (cancer of blood vessel endothelium)

• HIV first infects macrophages expressing CD4 and CCR5 coreceptors

• HIV next infects T cells expressing CD4 and CXCR4 coreceptors

• HIV can exist in latent state as a provirus for long periods

• Infected T cells express gp120 on their surface and fuse with uninfected T cells

• Death of CD4 T cells leads to complete loss of cytokine production, cellular and humoral immunity is destroyed

• Typical course of a poor-prognosis HIV infection• Presence of HIV in the blood is routinely done by

screening for anti-HIV antibodies• More sensitive technique is reverse-transcription PCR

(RTPCR)• Blood products are screened using enzyme-linked

immunosorbent assay (ELISA)

• Pharmaceutical therapy for AIDS:

• 1) Nucleoside analogs such as AZT inhibit reverse transcription

• 2) Non-nucleoside Rt inhibitors

• 3) Protease inhibitors specifically inhibit maturation of HIV proteins

• Intensive vaccination research

• Majority of HIV infections are in people who can not afford treatment

• Is this an ethical problem?

Bacteria Disease Streptococcus pyogenes Sore throat Corynebacterium diphtheriae Diphtheria Mycobacterium tuberculosis Tuberculosis Streptococcus pneumoniae Pneumococcal pneumonia Klebsiella pneumoniae atypical pneumonia Neisseria meningitidis Meningococcal meningitis Yersinia pestis Bubonic plaque Bordetella pertussis Whooping cough Haemophilus influenzae Influenza Nocardia asteroids Nocardiosis

Air-borne human diseases of importance and their causative agent

Virus Disease Influenza virus Influenza Hantavirus Pulmonary syndrome Hepatitis virus Hepatitis Herpes virus Chicken pox Picorna virus Common cold Flavivirus Dengue fever Rubella virus Rubella Measles virus Measles Influenza virus Influenza Hantavirus pulmonary syndrome

Fungi Disease Aspergillus fumigatus Aspergillosis Blastomyces dermatiridi Blastomycosis Coccidioides immitis Coccidioidomyosis Cryptococcus neoformans Cryptococcosis Histoplasma capsulatum Histoplasmosis Pneumocystis carinii Pneumocystitis