KICK THE BOARDS USMLE STEP 1MICROBIOLOGY Prepared by Dr. Irfan Mir

KICK THE BOARDS.USMLE STEP 1 MICROBIOLOGYPrepared by Dr. IRFAN MIR ONLY FOR EDUCATIIONAL PURPOSE.1NOT FOR COMMERCIAL USE OR SALE. BACTERIOLOGY * Growth of Anaerobes inhibit by O2 because anaerobes lack Catalase & Superoxide Dismutase which detoxifyH2O2 and super oxide which is toxic to bacteria. (O2 also cause oxidation of sulfahydryl group of enz). * Outer membrane found in Gram - ve bacteria where as Gram +ve lacks it. * Difference b/w ---- Clostridium Spore forming BacteroidsNon spore forming and lactamase +ve. * Anaerobic infection characterize by :Abscess formation / Foul smelling discharg / Gas in tissue / Necrotic tissue. ----------------------------------------------------------------------- GRAM + ve COCCI :(Streptococcus & Staphylococcus) Gram + ve Cocci are divided on the basis of Catalase + ve & Catalase - ve Groups.

Catalase + ve:1. Staph Aureus produce yellow colonies. Protein A (virulence factor). Hemolytic. Coagulase & lactamase +ve. 2. Staph Epidermidis produce white colonies. Non hemolytic. Coagulase - ve. 3. Staph Saprophyticus are coagulase - ve. Catalase ve: 1. Strep Pyogens ------- group A Hemolytic.----- Bacitracin sensitive. 2. Strep Agalactae ------ group B Hemolytic.----- Bacitracin resistant.Hydrolyze hippurate. 3. Strep Fecalis -- (Enterococcus) group D & Hemolytic or non. It grow in 6.5 Nacl.Habitat is Colon. 4. Strep Bovis (Non enterococcus) ------ group D hemolytic or non.Lancet shaped5. Strep Pneumoniae (Pneumococcus) -- Hemolytic or non. --Bile soluble.---Optochin sensitive. 6. Strep Viridian ( S mitis, S mutans, S sanguis) -- Hemolytic or non -- Bile insoluble -- Optochin resistant. GRAM + ve RELATED INFECTIONS : 1. Staph Aureus ----------------------------- Endocarditis in prosthetic heart valve, Food poisoning, Carbuncle. 2. Staph Epidermidis ---------------------- Endocarditis in IV Drug addict and Pt with prosthetic heart valve. 3. Staph Saprophyticus ------------------ Osteomylitis and lower UTI. 1. Strep Pyogenes --------------------------- Pyoderma, RF, Pharyngitis, Glomerulonephritis. 2. Strep Agalactae -------------------------- Neonatal sepsis. 3. Strep Fecalis ------------------------------ UTI, Infective Endocarditis in 10 % of cases. (S fecalis is penicillin G resistant) 4. Strep Bovis -------------------------------- Colon Carcinoma. 5. Strep Pneumoniae ----------------------- Meningitis in very young and old person. Pneumonia (lung consolidation). 6. Strep Viridians ---------------------------- Infective endocarditis in 90 % of cases. * Pathogenesis of Staph Aureus food poisoning is by stimulation of IL1 and IL2 release. * Virulence factor of Staph Aureus is protein A which binds to Fc portion of IgG thus preventing complement binding. * Staph Aureus produce lactamase. Drug of choice is lactamase resistant penicillin or vancomycin or both inresistant case. * Hemolysins cause hemolysis when colonies grow on blood agar plate, Streptococcus produce 2 type of hemolysins. 1. Streptolysin O is O2 labile ( inactivated by O2 )2. Streptolysin S is O2 Stabile ( cannot inactivated by O2 ).

* Strep Pyogenes contain 3 virulence factor :-1. M protein ---- determine group A Hemolytic infection and interfere with phagocytic ingestion. 2. Hyaluronidase ---- Hydrolyze the ground substance of the connective tissue. 3. Erythrogenic Toxin ---- Cause rash of scarlet fever (lysogenised by bactriophage carrying the gene for Toxin).Dx by Dick test * Rheumatic fever occur due to cross reaction b/w streptococcal Ag and Ag of joint & heart tissue. Usually 2 weekafter the pharyngitis with Sterp Pyogenes. * Glumerolunonephritis is initiated by AgAb complex on glomerular basement mem and Soluble Ag (M protein) mayKICK THE BOARDS.USMLE STEP 1 MICROBIOLOGYPrepared by Dr. IRFAN MIR ONLY FOR EDUCATIIONAL PURPOSE.2NOT FOR COMMERCIAL USE OR SALE. be the inciting factor. It occur 2 - 3 week after skin infection with Strep Pyogens . * Pneumococci (Strep Pneumonie) cause meningitis in very young and old. It is identify by Quellung Reaction. It can be prevent from 23 type vaccine or penicillin. Pnemococcal virulence factor is polysacharide capsule which interfere with Phagocytes by IgA protease and elicit primary B cell response (i.e T cell dependant).Pneumococci produce no toxins and are lactamase - ve. GRAM - ve COCCI ( Gonococcus & Meningiococcus) : * Are Neisseria Gonococcus (Gonococcus) & Neisseria Meningitides (Meningiococcus). * Both are Oxidase +ve (ie Enz cytochrome c) & produce Endotoxins (Lipooligosaccharide LOS, & Lipopolysaccharide LPS). 1. N Gonococcus: Oxidase + ve. Produce Endotoxin LOS & Glucose, Contain Pilli, IgA protease. It contain no capsule.vs. 2. N Meningitides: Oxidase + ve. Produce Endotoxin LPS, glucose & maltose. Contain IgA protease & polysacchrideCapsule. * Remember endotoxins are produce by only Gram - ve Bacterias.* Role of Endotoxins LOS, LPS is to cause fever, and provoke reaction that lead to shock.* Enz Oxidase (ie Enz cytochrome c) turn colonies black when expose to Phenylalanine as a result of oxidation. * Remember Meningococci ferment maltose where as gonococci does not. Both ferment Glucose. * Gonococci culture on Thayer Martin medium which is chocolate agar (contain Blood heated at 80 which inhibittoxic metal and fatty acid to promote bacterial growth, also Antibiotics to suppress normal flora). It can also beidentified by glucose fermentation by fluorescent Ab stainig. * Complements are imp defense. C6 - C9 deficiency incidence of incidence of meningococcal & gonococcalbacteremia. * N Gonorrhea does not have capsule but it does have IgA protease and pili (virulence factor) both mediateattachment to mucosal surface and are antiphagocytic. Where as N Meningitides has polysaccharide capsule(virulence factor) which is antiphagocytic and induce protective Ab. (remember pili mediate attachmentnonpiliated strains are avirulent). * IgA protease hydrolyze secretory IgA to promote attachment. * Meningiococci colonize the Oropharynx than enter the blood stream & spread to meninges and joints. (sp inimmunodeficient pt). * Meningiococcal meningitis can be prevente by Rifampin (Rifampin secrete in saliva), and vaccine (containA,C,Y,W135 strain but does not contain B strain). * Gonococci is resistant to penicillin due to plasmid mediated penicillinase production.TX of choice is ceftriaxone IM single dose. * N meningitides is most likely cause of meningitis epidemic. * Common organism cause meningitis in new born ( < 1 month of age ). 1. Listeria Monocytogenes (Gram + ve Rod) 2. E- coli ( because 25% of women have organism in vagina ). Gram - ve Rod * Common organism cause meningitis over 2 months of age. 1. H Influenza. ( also rank # 1 in 6 month to 6 yr age group) 2. Sterp Pneumonie ( it rank # 1 in adult ) 3. N meningitidis( it rank 2nd to H influenza in causing meningitis, in children age 6 months to 6 years) * Gonococci cause Gonorrhea (STD) characterize by urethral exudates, TX of choice is Ceftriaxone, and Ophthalmia Neonatrum which can be treated with Erythromycin or silver nitrate. GRAM + ve RODSKICK THE BOARDS.USMLE STEP 1 MICROBIOLOGYPrepared by Dr. IRFAN MIR ONLY FOR EDUCATIIONAL PURPOSE.3NOT FOR COMMERCIAL USE OR SALE. * It is divided on the bases of Spore forming and Non spore forming. SPORE FORMING: 1. Bacillus:* B. Anthracis -- Motile, Capsule (composed of D - glutamate). Habitat is soil. cause Anthrax. (Aerobes)* B. Cereus -- spores present on grain of rice.-- cause Food poisoning. 2. Clostridium -- * C. Tetani -- Toxin Tetanspasmin (protease) -- cause Tetanus (Anaerobes) * C. Botulinum -- Toxin Botulinin (protease) -- cause Botulism (food, wound, infantile type) * C. Perfringines -- Toxin (lecithinase) Gas Gangrene, food poisoning, septic abortion. * C. Dificile -- Exotoxin A & B (enterotoxin, cytotoxin) -- cause PM enterocolitis.

NON SPORE FORMING: 1. Cornybacterium Diptheriae --- Club shape, Non motile, Cell appear blue & granule red. EF2. (Aerobes) 2. Listeria monocytogenes --- Motile, Toxin listeriolysin O, hemolytic-- cause Meningitis, sepsisin new born & immunocompromised adult. * Mostly bacterias has Polysaccharide capsule but B. Anthracis capsule is composed of D - glutamate which isunique to it. * B. Anthracis invade host skin, mucous mem, Resp tract & produce Anthrax Toxins which contain 3 components, 1. Protective Ag 2. Lethal factor 3. Edema factor (Exotoxin) is adenylate cyclase, dependent of protective Ag for its binding & gain entry into the cell. * Tetanspasmin (Tetanus toxin) is protease which cleave the protein involved in mediator release. It reach to CNS inretrograde fashion via axon where it bind to ganglion side receptor & block release of inhibitory mediator Glycine atspinal synapses. * Tetanus can be prevented by cleaning the wound, Tetanus toxoids (vaccine), Tetanus Ig (in gross contamination ofwound), Penicilllin * C. Botulinum acquired by contaminated food sp cane food, smoked fish. It Can be prevented by discarding swollen canes. * Botulinum can be occur in two more clinical forms. 1. Wound botulism 2. Infantile Botulism -- by ingestion of honey contaminated with spores (recover spontaneously). * Botulism toxin is Botulinin, it absorbed from gut reach to peripheral nerve synapse via blood where it block therelease of Ach.It is isoprotease which cleave the protein involved in Ach release. * C. Perferingenes cause Gas gangrene associated with war wounds, road side accidents, septic abortion. \\ Vegetative cells are normal flora of colon and vagina. Penicillin is prophylactic. * C. Perferingenes produce toxin (lecithinase) which damage the cell wall including erythrocytes. Degenerativeenz produce gas in tissue. Exudate culture anaerobically shows Gram + ve Rods, spores are not seen, organism canbe identified by sugar fermentation and organic acid production. * C. Perferingenes also cause food poisoning mechanism is unknown. * C. Dificile produce exotoxin A (enterotoxin) -- cause out pouring of fluid exotoxin B (cytotoxin) -- cause damage to colonic mucosa by ADP ribosylate, it is GDP binding protein that regulates actin in cytoskeleton. (results into pseudo membranous formation & diarrhea). * PM enterocolitis can also caused by antibiotics. Treatment of choice is Metronidazole or vancomycin. * Cornybacterium Diptheriae appear club shaped on gram stain arranged in palisade or in V or L shaped formation.Rod have beaded appearance. (Bead contain granule of polyphosphate, Remember Dye stains the cell blue and granule red). * Diphtheria toxin inhibit syn of ADP ribosylation of EF2 (elongation factor). Toxin is a single polypeptide with twodomain one mediate binding and other possess enzymatic activity which cleave nicotinamide from NAD andtransfer the remaining ADP ribose to EF2 thereby inactivating it. It effect all eukaryotes. * Diphtheria shows whitish gray adherent mem over the tonsils and pharynx. KICK THE BOARDS.USMLE STEP 1 MICROBIOLOGYPrepared by Dr. IRFAN MIR ONLY FOR EDUCATIIONAL PURPOSE.4NOT FOR COMMERCIAL USE OR SALE. * DNA that encodes Diphtheria toxin is part of genetic material of temperate Bacteriophage (bacteria infected byvirus). Remember only lysogenized bacteria (the viral infected bacteria) produce toxins and cause dis. * Diphtheria vaccine contain diphtheria toxin, tetanus toxin & killed pertussis (on 2,4,6, month, than 1, 6 yr booster,than every 10 yrs booster). * Diphtheria once bound irreversibly to cell mem can not be neutralized so antibiotics should be given immediately. * Listeria monocytogenes Cause meningitis and sepsis in newborn and in immunocompromised adult. * Listeria transmitted by contact with animal feces, unsaturated milk, contaminated vegetable, unpasturized cheese(in USA), across the placenta in new born (1 - 4 week cause acute meningitis). * L monocytogenes toxin is Listeriolysin O which is similar to streptolysin O. it acts by producing holes in cell mem hemolysis. * Cell mediated immunity is imp in host defense. TX is Ampicillin in high doses. * Diphtheria confirmed by growth on Loflers Blood agar. GRAM - ve RODS * Gram - ve Rods are divided in 3 groups Enteric tract related, Respiratory tract related and zoonotics. * Remember Endotoxins are produce by Gram - ve bacterias. ? GRAM - ve RODS: 1. Lactose Fermenter: Slow Fermenter -- Serratia Opportunistic infection(Enteric tract. Contain O Ag)Fast Fermenter -- Enterobacter Opportunistic infection E. Coli -- H Agmeningitis, sepsis, UTI, travelers diarrhea. Klebsiella -- K Ag (identified by Quellung reaction) Pneumonia

2. Lactose Non Fermenter: Oxidase - ve -- Shigella Bloody Dysentery (diarrhea). Salmonella -- H Ag,Widal test Enter colitis (Enteric fever), Typhoid. Proteus mirabilis -- (urease +ve), Weil Felix test UTI Providencia Morganella Oxidase + ve -- Pseudomonas Aerogenosa Nosocomial infection.

3. Other Gram - ve Rods : Vibrio -- comma shape, Exotoxin Choleragen (A & B subunit) Cholera. Campylobacter jejuni -- comma or S shape diarrhea (USA) Helicobacter Pylori -- Gastric ulcer. DX. urea breath test, serum Ab, biopsy. Bacteroids -- sepsis.

* All Enteric tract Gram - ve Rods are facultative Anaerobes, ferment glucose (sugar varies), reduce nitrate to nitrite(as energy generation), Except Pseudomonas which is strictly aerobe and donot ferment glucose or reduce nitrate.They are oxidase + ve (enz cytochrome c)which derived energy from oxidation. Where as all Enteric tract gram ve contain O Ag. * Enterobacteriaceae Ag ---- 1. O Ag is a cell wall Ag (outer polysaccharide portion of Lipopolysaccharide)2. H Ag is a Flagellar Ag (protein) present in E. Coli and Salmonella only. * Lactose Fermentation is imp criterion for the identification of organism, that is 1. Non Fermenters form colorless colonies, it includes Shigella, salmonella, proteus, pseudomonas. 2. Lactose Fermenter form colored colonies, it includes E. coli, Klebsiella, Enterobacter, and Serratia (slow Fermenter). * E. Coli is the major cause of neonatal meningitis along with streptococci (Agalacteae). It occur during birth due of vaginal colonization of E coli in 25% of pregnant women. * Certain E. coli donot produce Toxin but are invasive and can cause diarrhea. * E. Coli adhere by mean of pili once attached synthesize enterotoxin to produce diarrhea. It include Enterotoxins KICK THE BOARDS.USMLE STEP 1 MICROBIOLOGYPrepared by Dr. IRFAN MIR ONLY FOR EDUCATIIONAL PURPOSE.5NOT FOR COMMERCIAL USE OR SALE. 1. Heat Labile Toxin ( LT) ---- it stimulate Adenylate cyclase which results into outpouring of K+cl- (diarrhea). 2. Heat stabile Toxin ( ST) ---- it stimulate Guanylate cyclase. * E. Coli strain that cause neonatal meningitis contain specific capsular Ag called K1 Ag. * E Coli endotoxin is cell wall LPS cause sepsis, fever.1. O serotype of E. coli preferentially cause UTI 2. K1 erotype of E. coli preferentially cause meningitis, sepsis, DIC * E. Coli 0157: H7 identify on sorbitol agar Afebrile hemorrhagic colitis & Hemolytic uremic $ due to sheiga like toxin. * Salmonella change its flagellar H Ag by DNA rearrangement (reversibly alternate two type of H Ag) to evadeimmune response. * Enter colitis (Enteric fever) by salmonella is caused by invasion to epithelial and sub epithelial tissue of small andlarge intestine with resultant inflammation and diarrhea with or without blood. * Typhoid infection cause by Salmonella Typhi begins in small intestine, organism enter and multiply in non nuclearphagocytes of Payers Patches and spread to liver, gallbladder and spleen with resultant bacteremia and fever. * Gall Bladder inflammationcarrier state for long time ( excrete bacteria in feces ). * Salmonella transmitted by ingestion of food and water contaminated by human feces and animal waste speciallypoultry & eggs. * Salmonella Typhi is transmitted by human only. * Salmonella Enteric fever DX by Widal test ( Ab titer in pts serum) and Slide Agglutinin test (can isolate salmonella). * Salmonella vaccines are 1. Acetone killed S typhi ( IM ).2. Live attenuated S Typhi ( orally ). * TX of Enteric fever / septicemia is Ceftriaxone where as Typhoid can be treated with Ampicillin, or ciprofloxacin inchronic cases. * Shigella are transmitted by 4 Fs Finger, Flies, Food, Feces. Out breaks are food and water borne. * Shigella invades distal colon mucosa surface cause ulceration but rarely penetrate the gut wall or enter in blood.(unlike salmonella). * Shigella that does not produce enterotoxin still cause dis. Where as non invasive are non pathogenic. * Shegella dysentery is watery first and than bloody with mucous, also presents PMNs. TX is hydration, Ampicillin, TMP-SMX. * Serratia & Enterobacter are group together because they are similar in motility and several biochemical reactionboth cause opportunistic infection, usually inIV catheterization, respiratory intubation, UT manipulation. * Serratia and nitrobacteria are highly resistant. TX of choice is Ceftriaxone and gentamicin combination. * Klebsiella cause pneumonia. Its capsule is K polysaccharide Ag which has antiphagocytic activity. * K Ag are identified by Quellung reaction. (Strep Pneumoniae have polysaccharide capsule is antiphagocytic and also identified by Quellung reaction) * Proteus distinguished by Urease production on TSI agar which form ammonia NH3 & CO2. Some Proteus are motile.* Urease from Proteus hydrolyze urea in urine to form NH3 which the PH of urine and encourage the formation ofStruvite calculi composed of magnesium hydroxide Mg(NH4OH)2. Alkaline urine favor growth of proteus thats why txalso include Low urinary PH. * The O Ag of proteus (OX2, OX9, OXK) cross react with Rekittsial Ag. So Ag can be used to detect Ab againstRekittseas. This test called Weil Felix test or reaction. * Proteus can cause extensive renal damage. TX of choice is Ampicillin. For severe infection ampicillin & gentamicin. * P Aerogenosa are strictly aerobes, non fermenter, donot reduce nitrate and is oxidase + ve (cytochrome c) that itproduce energy from oxidation. * Pseudomonas cause nosocomial infection produce characteristic blue green pus due to pigment Pyocyanin. Thepigment pyoverdin under UV rays (fluorescent). * In Pseudomonas grow in water containing traces (humid environment). It remarkably stands disinfectant, grow inhexachloroprene soap solution, anti septic, and detergents.* Pseudomonas cause opportunistic infection in person with Neutrophil counts