Microbiology Lecture Notes PDF

MICROBIOLOGY 1 Topics Routes of bacterial entry Role of bacteria in pulp & periapical diseases Endodontic flora Culturing technique Measures of Infection control in RCT 2 Apical periodontitis : A P is an inflammatory disease of microbial...

MICROBIOLOGY 1 Topics Routes of bacterial entry Role of bacteria in pulp & periapical diseases Endodontic flora Culturing technique Measures of Infection control in RCT 2 Apical periodontitis : A P is an inflammatory disease of microbial etiology primarily Caused by infection of root canal system. Chemical and physical factors can also induce periradicular inflammation. Most scientific evidence suggest that endodontic infection is the main cause of different forms of apical periodontitis 3 Types of microorganisms in association with endodontic infection are: Bacteria : most implicated Fungi Viruses The ultimate goal of endodontic treatment is either to prevent the development of apical periodontitis or, in case where the disease is already present ,to create favorable conditions for periradicular tissue healing. 4 Role of bacteria in pulp and periapical diseases: The direct relationship between bacteria and pulp/periapical diseases was clearly demonstrated by a classic study in 1965(Kakehashi et al). In this specific research pulp exposures were done in two groups of animals one group had normal microbial flora while the other were germ free animals (their saliva is free from any microorganisms). Abscesses and pulpal necrosis and periapical pathosis developed in animals with normal flora and not in germ free animals. 5 Routes of bacterial entry Dental caries : most common Periodontal diseases Traumatic exposure Traumatic injuries Anachoresis : is the positive attraction of blood-borne microorganisms to inflamed or necrotic tissue during bacteremia. This process is considered another route of entry of bacteria to the pulp space. 6 Microbial ecology and root canal ecosystem Root canal system is considered to be an ideal media for bacterial growth as it is Moist Warm Nutrition Anaerobic environment The Major ecological factors that determine the composition of root canal microbiota include : Oxygen tension Types and amount of variable nutrients Bacterial interaction 7  In the initial phases of the pulpal infectious process facultative bacteria predominant After few days or weeks , O2 is depleted within the root canal due to its consumption by facultative bacteria ,consequently obligate anaerobes predominate. The main source of bacterial nutrition to colonized in root canal system : 1.Necrotic pulp tissue. 2.Proteins and glycoproteins from tissue fluids and exudate. 3.Componant of saliva that may coronally penetrate into root canal. 4.product of bacterial metabolism. 8 Mechanism of microbial pathogenicity and virulence factors Pathogenicity : the ability of microorganism to cause diseases Virulence : Degree of pathogenicity of microorganism Virulence factor : Factors that contribute pathogenicity Example : microbial product ( enzyme , toxins) bacterial structure component (lipopolysaccharide , lipoteichoic acid) These virulence factors have ability not only stimulating the host immune reaction but also causing sever tissue destruction. 9 Endodontic flora Out of the 350 species of microorganisms present in the oral cavity only a small group of organisms are commonly isolated from root canals. Prior to 1970, very few strains of strict anaerobes were isolated because of inadequate anaerobic culturing methods. Nowadays, it is agreed that strictly anaerobic bacteria (obligate) dominates, with some facultative anaerobic and aerobic species. 10 Aerobic bacteria Streptococcus Mutans is the commonly present aerobic species because it is always associated with smooth and pit and fissure caries. Actinomyces associated with root caries is another aerobic species present. 11 Anaerobic bacteria These comprise the dominant organism of the endodontic flora. Averages of 5-8 different species harbor the root canal. These include: Peptostreptococcus Actinomyces Lactobacillus Fusobacterium Black pigmented Bacteroides (BPB) 12  Black pigmented Bacteroides : an important organism due to its proposed role in acute infections symptomatic cases being associated with flare-ups. The recent classification for subdivisions of BPB : Asaccharolytic Bacteroides (Porphyromonas)- Porphyromonas asaccharolyticus Porphyromonas gingivalis Porphyromonas endodontalis Saccharolytic Bacteroides (Prevotella) Prevotella melaninogenica Prevotella intermedia 13 Culturing in endodontic Culturing is the procedure of Detecting Isolating identifying different microbes. At a time, one of the criteria for obturation was to obtain two negative cultures from inside of the prepared canal before obturation (negative culture = absence of microorganisms). This does not appear to stand still nowadays. We do believe that culturing before obturation does not have a place in modern endodontics, however, it is required in special cases as: Medically compromised patients Cases with persistent infection Cases with progressive 14 Culturing technique A microbial sample is taken from the root canal follows: Tooth isolation and disinfection. Access preparation using sterile burs Canal flooded with culturing medium. Sample to be collected on a paper point introduced inside the canal Paper point should be placed in a sterile test tube containing a transfer medium. Test tube should be send immediately to the lab for culturing. 15 Measures for control in pulp and periapical diseases infection Infection control include both local and systemic measures. (A) Systemic measures (antibiotics): The vast majority of infections of endodontic origin can be effectively managed without the use of antibiotics. Antibiotics can never be considered a substitute for proper local measures (proper cleaning and shaping). An antibiotic regimen is prescribed in conjunction with appropriate endodontic procedure when there is signs of systemic involvement. These signs include fever, malaise, cellulitis or progressive swelling. 16 The recommended regimen includes: Penicillin remains the drug of choice being effective against obligate and facultative anaerobes commonly present in endodontic infections. Erythromycin is the drug of choice with penicillin allergic patients, however, it is not active against obligate anaerobes. Cephalosporins can be another choice of broad-spectrum antibiotics, but again they are not effective against anaerobes. Clindamycin and metronidizole are effective drugs against anaerobes and can be used in conjunction with penicillin in case of serious infections. 17 Prophylactic antibiotics for medically compromised patients: Medically compromised patients who are at increased risk of secondary infection following bacteremia should be premeditated with a special antibiotic regimen (prophylactic). These cases include: Patients with rheumatic heart or congenital heart diseases. Patients with Prosthetic cardiac valves. Patients with uncontrolled Diabetes. Patients having mitral valve prolapse. Patients under immunosuppresant drugs. Patients with any organ transplant. 18 The exact dose for these patient as listed by the American Heart Association (AHA 1998) is: 2 gms of Amoxicillin one hour before the procedure. Incase of patients who are allergic to penicillins, erythromycin or clindamycin can be used. 19 (B) Local measures : These involve both chemical and mechanical measures. Mechanically, microorganisms are eliminated by the process of canal enlargement. Chemically, the use of antibacterial agents during instrumentation (irrigants) or sealing antibacterial drugs inside the canal between visits (intracanal medicaments), both contribute to the fight against bacteria. 20 Sodium hypochlorite ( NaOcl) Chloramination Saponification PH=11 Oxidation effect reaction effect Cytopl With Lipid Bacteri asmic protei degra al memb n A.A. dation. enyme rane s Cell Cell Cell wall Enzymes integrity metabolism Endotoxins inactivation Calcium hydroxide (Ca(OH)2) Ionic dissociation Ca +2 OH- Cell wall destruction 22