Microbiology Lecture: Bacteria 1 - Respiratory Pathogens 1 - Nov. 2023 PDF

PPOM 2: Lecture #136: Microbiology: Bacteria 1 – Respiratory Pathogens 1 Nov. 2023 Charles Pavia, Ph.D. Professor, Dept. of Biomedical Sciences [email protected] Office of Academic Affairs  Session Objectives Differentiate & describe the key roles that epidemiology, microbial vir...

PPOM 2: Lecture #136: Microbiology: Bacteria 1 – Respiratory Pathogens 1 Nov. 2023 Charles Pavia, Ph.D. Professor, Dept. of Biomedical Sciences [email protected] Office of Academic Affairs  Session Objectives Differentiate & describe the key roles that epidemiology, microbial virulence factors and host-defense mechanisms play in the prevention, or as causative factors, in the development of respiratory infections. Differentiate and describe based on unique microbiologic features, the medically important bacterial pathogens that cause disease in the human respiratory tract, with the emphasis being on the causes of pneumonia. Differentiate and describe the various test procedures that are often used in a clinical microbiology lab for the purpose of identifying the key disease-causing bacterial agent(s) and for aiding the clinician in making the correct Dx. Source: Course Syllabus  Classification of Pneumonia or Pneumonia-like Syndromes caused by Bacteria A. Acute / Community-acquired: 1. Person-to-person or autologous [these are the most common ones] – Strept. pneumoniae (the pneumococcus); Mycoplasma pneumoniae Hemophilus influenzae Strept. pyogenes (aka Group A strept.) Staph. aureus Klebsiella pneumoniae Chlamydophila pneumoniae 3  Pneumonia Classification continued: Acute / Community-acquired: 2. Animal / Environmental Exposure [these are somewhat less common causes] – Legionella pneumophila (from old heating & cooling systems / cooling towers); Francisella tularensis** (from mostly rabbits & ticks); Coxiella burnetii** (from exposure to farm animals); Chlamydophila psittaci (mostly from exotic pet birds or illegally imported birds); Yersinia pestis** [the plague] (from fleas & rats). **Considered to be potential agents of bioterrorism 4  Pneumonia Classification continued: A. Acute / Nosocomial Enteric Bacteria (e.g. Klebsiella) (gram-) Pseudomonas (-) Acinetobacter (-) Staph. aureus (+) 5  Pneumonia Classification continued: B. Subacute or Chronic: Tuberculosis (Mtb) & atypical Mycobacteria; Various fungi. *C. Immunocompromised pts: Atypical Mycobacteria (and also Mtb); Various fungi (such as Pneumocystis jiroveci - formerly called P. carinii [agent of PCP]). 6  Natural Defense Mechanisms: Vibrissae filter out large particles; Epiglottal and cough reflexes; Ciliated respiratory epithelium; Mucus-producing cells lining the bronchi; Natural anti-microbial substances: 1. lysozyme 2. lactoferrin 3. secretory IgA & complement Pulmonary Macrophages. 7 Arrow points to a large pulmonary macrophage 8  Predisposing Factors to Serious Infection/Pneumonia: Previous viral respiratory disease; Allergies [e.g., dust, pollen]; Chronic pulmonary disease (emphysema); Alcoholism & cigarette smoking; Diabetes, cancer & other illnesses; Immunosuppressive disorders & therapy; Age extremes; Debility (from certain developmental or congenital anomalies; pts recovering from invasive surgical procedures; anaesthesia; stroke; intoxication). 9 Normal Microbial Flora in the Respiratory Tract A. Mouth and oropharynx: ☻ various streptococcal bacteria (mostly viridans): 1. Strept. mitus [viridans group]; 2. Strept. salivarius [viridans group]; 3. Strept. pneumoniae; 4. Strept. pyogenes (aka group A strept.). ☻ some yeasts (esp. Candida albicans). 10  Normal Microbial Flora in the Respiratory Tract continued Lung: NONE – it is considered to be sterile, but it may not always be germ-free, even in healthy people free of any respiratory disease; some studies suggest possible transient colonization, but that is okay, so long as the microbial numbers stay low and we are not immunocompromised. 11 EM Microscopic view of some of the oral microflora found in the human mouth 12  Types of Upper Resp. Tract Infections Sinusitis = inflamed sinuses caused by infection; Otitis media = inflamed middle ear; Otitis externa = inflamed outer ear; Pharyngitis or sore throat; Epiglottitis = inflamed epiglottis; very serious – can be life-threatening, but now controlled due to a vaccine (Hib) given during early childhood. 13  Pneumonia  A severe complication of bronchitis; Bronchioles & alveoli become filled with pus; Pus consists of dead microbes, host inflammatory cells (PMNs) and some fluid exudate; Diagnosed by chest x-ray: “shadow” or opaque area is present over a portion of the lung; Caused mostly by various bacteria; Especially life-threatening if caused by certain types of bacteria or fungi. 14  Common & Less common Causes of Bacterial Pneumonia / Pneumonia-like syndromes by Age Group  Young Adults: Strept. pneumo. & Mycoplasma [both are common] Adults: Strept. pneumo. & Legionella [both common] Older Adults: Strept. pneumo.; H. influenzae; & Legionella [all 3 are common]. Less common: TB; Mycoplasma; 15  Pneumonia continued So-called “Typical pneumonia”: Strept. pneumoniae (pneumococcus) Haemophilus influenzae So-called “Atypical pneumonia”: Mycoplasma pneumoniae Chlamydophila pneumoniae Certain enteric bacteria (esp. Klebsiella) Other rare or unusual bacteria and some viruses (flu) 16  Pneumonia continued Epidemiology: About 2 million cases per year in USA; 40-70K die per year; 6th most common disease causing death; 1st most common lethal hospital- acquired infection; 17  Pneumonia continued The More Common Bacterial Respiratory Pathogens 18  Streptococcus pneumoniae Gram+ cocci, arranged in pairs / chains; have unique lancet-shaped appearance (elongated with a slightly pointed outer curvature) Catalase neg. [very important – all strept. bacteria are catalase neg.] 19  Streptococcus pneumoniae continued Grows readily on agar & causes alpha-hemolysis. What is α-hemolysis? Capsule – important virulence factor; – 84 known serotypes [polysaccharide]; – basis for the pneumococcal vaccine: “PNEUMOVAX” (a polyvalent vaccine); there is also another vaccine (a conjugate vaccine: “PREVNAR”) It produces an IgA protease and a pneumolysism [2 other virulence factors] 20  Pneumococcal pneumonia Caused by S. pneumo. / classic lobar form; Common in young-to-middle age adults; Somewhat rare in infants and elderly – but lethal; Common in oncology pts & ETOH pts; Sudden onset with fever, chest pain & thick sputum. 21 Pneumococcal pneumonia continued: Diagnosis: - gram stain & culture sputum sample; - on agar plate look for alpha hemolysis and optochin-disk sensitivity; also, bile soluble (bile-solubility test); - alternative: urine antigen test [detects pneumococcal capsular antigens that are excreted in the urine]. 22 Pneumococcal pneumonia cont’d: Optochin-sensitivity 23 Pneumococcal Pneumonia cont’d: Pathogenesis Aerosolized bacteria are inhaled into alveoli or Already colonized bacteria are aspirated into lungs; Inflammatory response begins & alveoli become filled with edema fluid; Peri-alveolar capillary congestion occurs; Massive infiltration of PMNs; Intra-alveolar hemorrhage (red hepatization); PMNs & other inflammatory debris are phagocytized by macrophages (grey hepatization); Bacteremia may follow; depending on the pt’s over- all condition, this could lead to a life-threatening situation. 24  Other Pneumococcal Diseases Meningitis – very common cause; Otitis Media – most common cause; Sinusitis – a major cause; Bacteremia – gives rise to meningitis, endocarditis and pneumonia (if respiratory route is not the primary source). 25  Haemophilus influenzae AKA “H. flu” & not to be confused with viral influenza; Gram-negative coccobacillus (or short rod) ; It is a fastidious grower [needs chocolate agar in order to be cultured; what is chocolate agar?] 26  Haemophilus influenzae continued: May be part of our “normal” nasopharynx flora; Produces an IgA protease: may facilitate mucosal surface colonization mediated by pili; Outer capsule – key virulence factor: consists of polyribitol phosphate; Six capsular antigenic** types: a,b,c,d,e,f; **Serotype b is associated with most infections & forms the basis for an effective vaccine (Hib). ** the terms “antigenic” &“serotype” are often used interchangeably. 27 Haemophilus influenzae continued: Gram stain H. influenzae: appears as pleomorphic gram-negative rods 28 H. influenzae continued: H. flu infections: Pneumonia – esp. in the elderly and those with underlying pulmonary disease; Meningitis – esp. in pediatric cases; Epiglotittis – sole cause, but very, very rare now because of the vaccine; Otitis media – mostly in those < 8 years of age; Sinusitis & Conjunctivitis; Bacteremia; Cellulitis & Arthritis. 29  Mycoplasma pneumoniae AKA as the cause of “Walking or Viral pneumonia”; Occurs mostly in older children & young adults; Relatively long incubation period (10 -14 days); It is the smallest free-living bacteria; Has NO cell wall – thus, cannot be gram-stained; Difficult to grow on agar or in culture media; Originally thought to be a virus; why is it not a virus? Electron micrograph of M. pneumoniae 30  Mycoplasma pneumoniae continued Pneumonia – Most cases are asymptomatic to mild; Even severe cases are almost never fatal; Readily treatable with non-beta-lactam antibiotics [Ex??]; 2nd complications include otitis media, erythema multiforme, hemolytic anemia, myo/peri-carditis & neurologic complications. Tracheobronchitis Pharyngitis Diagnosis by : clinical presentation & serology (ELISA; cold hemagglutinins: what are these?) or molecular techniques (PCR) 31 Cold hemagglutinins: reacting with RBCs in a test tube (A) and no reaction in tube B (control) A B  Cold hemagglutinins: microscopic view reveals clumping of RBCs Office of Academic Affairs  Bordetella pertussis The cause of “whooping cough” / pertussis; A fragile gram-negative coccobacillus; Bacteria grow only on a special type of media called Bordet-Gengou; Disease is very rare because of a vaccine; Part of the DPT vaccine: a possible link to autism with the pertussis component was recently shown to be bogus; Periodic outbreaks due to laxity in vaccinations or to “waning” immunity in “older vaccinees” or possibly to the emergence of new genetic variants; Disease has 3 stages: catarrhal; paroxysmal; & convalescent [there can be complications]. 34  Klebsiella pneumoniae A member of the enteric family of bacteria Gram-negative, bacillus [stains what color?]; also, non-motile Grows on most agars (blood; MacConkey) It’s a lactose-fermenter [what else is?] It has endotoxin and a capsule Endotoxin (or LPS) is toxic & life-threatening Capsule makes treatment with antibiotics difficult Bacteria are aspirated from the g.i. tract and then reach the respiratory tract It causes pneumonia in mostly alcoholics, diabetics & cancer / immunocompromised pts 35 36 Klebsiella [gram stain]: showing plump gram-negative bacilli or rods (arrows) ↓ Culture on MacConkey agar ↓ ← ← 37 Pseudomonas aeruginosa A gram-negative rod; found virtually everywhere, but esp. in moist environments (“hot” tubs); Bacteria are oxidase-positive, but lactose-negative; Colonies on MacConkey agar appear colorless; Grow readily on agar & produce a bluish-green pigment (pyocyanin): see below; Causes otitis media & otitis externa; Big problem for cystic fibrosis pts. Pseudomonas growing on an agar plate showing pigment formation → 38 Clinical Case: A 59-yr-old man with emphysema presents with fever, chills, chest pain, and a cough. He had a “cold” with mild cough and congestion for about 3 days but then had the abrupt onset of more severe symptoms. His temperature has been as high as 103oF, and he’s had shaking chills. His cough is productive of sputum that is “rust”-colored. When he coughs or takes deep breaths, he gets a sharp stabbing pain in his left lower chest. On exam, he appears quite ill and has a temp. of 102F, pulse of 110, BP 110/60, and RR 28. His pulmonary exam is significant for the presence of crackles and rhonchi in the left lower fields and expiratory wheezing heard in all other fields. His heart is tachycardic but otherwise normal on auscultation. His WBC count is markedly elevated. An EKG is normal. A chest x-ray shows a dense infiltration of the left lower lobe along with a pleural effusion on the left side. A Gram stain of a sputum sample suggests the Dx.  Clinical Case continued What is this patient most likely suffering from? What would you expect to see on a gram stain of a sputum sample? What is the likely pathogen given this pt’s scenario? What are some of the unique microbiologic features of this organism? Our patient → 39  Summary Slide 1. A vast array of microbes can cause respiratory disease. 2. The most common causes of serious respiratory infections are bacteria. 3. The most serious form of respiratory disease is pneumonia. 4. The major bacterial causes of pneumonia are: Strept. pneumoniae, H. influenzae, Mycoplasma pneumoniae, and Legionella pneumophila [under certain conditions]. 40  Summary Slide continued: 5. M. tuberculosis causes the most serious form of a chronic respiratory infection. 6. Key virulence factors for these pathogens are: - outer capsule; - LPS [ found only in gram-negative bacteria ]; - IgA protease [ found in some bacteria ]; - mycolic acids [ found only in Mycobacteria ]. 41  Lecture Feedback Form: https://comresearchdata.nyit.edu/redcap/surveys/?s=HRCY448 FWYXREL4R