Veterinary Bacteriology and Mycology PJL:2011 Bacterial Overview: Morphology, Structure, Jargon General Features Domain Bacteria Proteobacteria Spirochaetes Firmicutes Actinobacteria No nuclear membrane Generally 1 chromosome Extrachromosomal DNA Oil- immersion (1000x) Cocci : ~ 0.5 1.5 Rods: ~ Spirochaetes : 0.5 x 10-20 m Firmicutes, Actinobacteria http://www.cdc.gov/ncidod/eid/vol4no3/relmang.htm PJL:2011 1
Bacterial Cell Morphology Staphylocci Streptococci curved rod Branching filamentous Bacillus sp. Spiral/coiled - spirochetes PJL:2011
Overview of Bacterial Envelope Structure Why is Envelope important? For the bug: Facilitates a controlled interaction with environment (including host) For us: Important diagnostic tool : Gram stain (Christian Gram, 1884) This stain allows us to determine: Size, morphology and Gram reaction facilitate presumptive identification and early treatment decisions Gram stain variations Old /Anaerobic /antibiotics - gram-positives appear gram-negative Gram-variable organisms Number of Genera that require special stains PJL:2011
Classic Bacterial Envelopes PJL:2011
Corynebacterium-Nocardia-Mycobacterium Group Gram +ves with a Gramnegative like OM NO LPS Mycolic acid +/- porin-like OMPs Niederweis et. al., 2010 Figure 3: Corynebacterium-Nocardia-Mycobacterium Group Envelope Porin-like proteins? Capsule Mycolic acids Mycolic acid rich Outer-membrane Peptidoglycan With arabinose and galactose Inner Membrane PJL:2011
Pathogen-Host Interactions Therapeutic - treatment of disease (antimicrobials, quarantine, culling and destroying) A medical strategy limited to diagnosis and treatment (therapy) there is virtually not possibility of large scale control or eradication of infectious disease Prophylactic - prevention of disease (management, vaccination, antimicrobials, identification and eradication) Infection is a complex interaction between the host, the pathogen and the environment. Dr. Mike Collins referred to this as the Beast: The Bug: The Business Definitions and Concepts Pathogen - organism that can cause disease Commensalism: a state of infection that results in either no damage or clinically apparent damage to host. Obligate pathogen - organism that almost always causes disease when present in host (Bacillus anthracis) Primary pathogen - organism that generally causes disease Opportunistic pathogen: often commensals which can cause disease when they gain access to a different tissue type (non-enterotoxin producing E. coli gain access to urinary tract). Often these infections arise when host immune defenses are impaired (immunosuppression, stress) Shipping fever in feedlot cattle. 1
Definitions and Concepts Facultative Intracellular - can replicate within host cells as well as extracellular spaces (classically this group included; Listeria, Salmonella, Mycobacteria, Brucella, etc.). There is an expanding list of bacteria that fall into this category Obligate intracellular - must access host intracellular space to replicate and survive (Chlamydiales, Rickettsiales, Coxiella burnetti, Lawsonia sp.) Virulence - degree of pathogenicity that is typically multifactorial (tissue invasion factors, immune escape, toxins, biofilms). Infection presence of potentially pathogenic organisms in a host. Acute, chronic, subclinical Carrier - an animal which harbours a disease organism without manifesting clinical signs and appears healthy Bacterial Interaction with Host Attachment/Tissue Invasion Factors Allow attachment and subsequently colonization of the host pili/fimbriae, capsules, and non-pilus type adhesins (ie. Mycoplasma adhesins) Hyaluronidase (many bacteria) and collagenase (some strains of Clostridium perfringens) breakdown host intercellular materials and aid in further spread of extracellular pathogens Acquisition of critical nutrients (Fe) siderophores (gram-negatives) 2
Virulence Factors Cont d Immune Escape: Utilize a variety of mechanisms to escape detection by the host s immune surveillance system Extracellular/secreted products: antiphagocytotic capsules, coagulase, superantigens, cytotoxins Possess specific virulence factors to evade the phagolysosome and thereby spread from cell to cell. Surface Antigenic Variation (ie.mycoplasma spp.) foil antibody recognition. Induce apoptosis of host cells involved in immune response (e.g. Salmonella, Histophilus somni) Virulence Factors Cont d Toxins Exotoxins Produced by a variety of gram-positive and gram-negative bacteria Kill host phagocytic cells, acquire nutrients Endotoxins Lipid A component of LPS 3
Biofilms and Quorum Sensing Biofilms an immune escape strategy Sessile, structured community of bacteria cells Inherently resistant to Abx persistent infections A growing number of gram-positive and gram-negative pathogens demonstrate this capability. Disease manifestations include: tooth decay and periodontal disease, otitis media (humans), medical devices Quorum Sensing: cell-to-cell communication between bacteria of the same species (e.g. P. aeruginosa and S. aureus). Mechanisms of Host Resistance A. Natural or Innate Immunity Rapid response that involves the recognition of unique components of bacterial cells (Pathogen- Associated Molecular Patterns - PAMPs) by a variety of host cell receptors (Pattern Recognition Receptors - PRRs). Activation and recruitment of neutrophils and macrophages to the site of infection. Frequently influences acquired immunity 4
Host Adhesins/Receptors Acute Phase Proteins Complement C3 - binds bacterial CHO s C-reactive protein (CRP) and Serum amyloid protein (SAP) binds bacterial surfaces and activates complement Ferritin binds iron to restrict essential nutrient Lipopolysaccharides (LPS) binding protein (LBP) Mannan-binding protein (MBL) binds terminal mannose on bacteria and activates complement Macrophage Scavenger Receptors Binds peptidoglycan (PGN), LPS and lipoteichoic acid (LTA) Host Receptors Cont d Toll-like Receptors (TLRs) These are PRRs that bind a variety of PAMPs Expressed by different cell types TLR -2 (with the aid of TLR-1 and 6) recognize PGN, LTA, LAM, bacterial lipoproteins, LPS (Leptospira) TLR - 4 binds LPS (LBP-LPS-CD14 complex) TLR - 5 receptor for bacterial flagellin TLR - 6 Mycoplasma lipopeptides TLR - 9 recognizes DNA with unmethylated CpG-motifs, abundant in bacterial DNA 5
Cationic Antimicrobial Peptides Over 500 hundred small peptides (15-20 aa) identified in virtually all species Some inducible, some constitutively expressed As a group they have very broad spectrum of activity that includes: Gram-positive, gram-negative, fungi, parasites Found in ears, on eyes, skin and mucosal epithelial surfaces etc. Granules of polymorphonuclear leukocytes (PMN s) Mechanisms of Host Resistance B. Acquired Immunity Passive immunity antibody-mediated protection in neonates provided by placental or colostral transfer of pathogen specific antibodies can protect offspring weeks - months interfere with the development of active immunity following vaccination 6
Acquired Immunity Cont d Active Immunity Humoral (Antibodies)- bacterins and subunit vaccines typically induce this type of immune response Cell mediated - critical arm of immune response for clearance of intracellular pathogens Components include T-cells and T-cell activated phagocytic cells 7