Bacterial Pathogens, Virulence Factors, and Clinical Pathology

Vocabulary flashcards covering Gram-negative and spiral bacterial pathogens, their morphology, metabolic properties, key virulence factors, and associated clinical pathologies.

Gram-negative Bacteria

Prokaryotic cells characterized by a thin peptidoglycan layer between two membranes that stain pink/red on Gram stain and possess an outer membrane containing LPS or LOS acting as an endotoxin source.

Coccobacilli

Oval-shaped bacterial cells representing an intermediate morphological form between cocci and bacilli, identifiable by a distinctive shortened, oval-shaped geometry under microscopy.

Diplococci

Spherical or coffee-bean-shaped bacteria that typically aggregate, grow, and arrange in pairs.

Haemophilus influenzae, type b (Hib)

A coccobacillus causing severe invasive infections including meningitis and bacteremia primarily in infants and toddlers; protected by a phagocytosis-resistant PRP capsule targeted by a conjugate vaccine.

Haemophilus influenzae, non-typeable (NTHi)

Unencapsulated coccobacilli lacking a PRP capsule that cause localized mucosal infections like pneumonia, otitis media, and sinusitis by forming resilient biofilms along respiratory surfaces.

Bordetella pertussis

A coccobacillus causing whooping cough (pertussis) with paroxysmal coughing; uses fimbriae to bind ciliated respiratory epithelium and elevates cAMP via Pertussis Toxin (blocks $G_i$ inhibitor) and Adenylate Cyclase Toxin.

Neisseria meningitidis

A Gram-negative diplococcus causing life-threatening meningitis with a petechial rash and rapid endotoxic shock; features a facultative intracellular lifestyle, sheds outer membrane vesicles (OMVs) containing LOS, and is targeted by a capsule vaccine.

Neisseria gonorrhoeae

A Gram-negative diplococcus causing gonorrhea and neonatal ophthalmia neonatorum; evades adaptive immunity via extensive antigenic variation of pili and Opa proteins, lacks a capsule, and expresses LOS.

Pseudomonas aeruginosa

An opportunistic, lactose non-fermenting Gram-negative rod (non-Enterobacteriaceae) that infects burn wounds, indwelling catheters, and cystic fibrosis lungs; produces green-pigmented colonies, a sweet fruity odor, and dense biofilms.

ETEC (Enterotoxigenic E. coli)

A lactose-fermenting rod spread via the fecal-oral route causing watery Traveler’s diarrhea; produces Heat-Labile (LT) and Heat-Stable (ST) toxins that surge cAMP/cGMP, driving chloride ($\text{Cl}^-$) and water secretion.

EPEC (Enteropathogenic E. coli)

A lactose-fermenting rod spread via the fecal-oral route that causes watery secretory diarrhea in infants (Weanling diarrhea); encodes the LEE pathogenicity island and a Type III Secretion System (T3SS) to form Attaching and Effacing (A/E) lesions with actin pedestals.

EHEC (Enterohemorrhagic E. coli)

A zoonotic lactose-fermenting rod causing watery to bloody diarrhea and hemolytic uremic syndrome (HUS); utilizes a LEE-encoded T3SS for actin pedestals (A/E lesions) and carries a prophage encoding Shiga Toxin (STx) that shuts down ribosomes in blood vessels.

Shigella

A human-restricted, lactose non-fermenting, $H_2S$-negative rod causing painful, bloody inflammatory diarrhea (dysentery) and colonic ulcers; uses a T3SS to invade colonic epithelium and replicate intracellularly, with some strains carrying phage-encoded STx.

Salmonella enterica (non-typhoidal)

A zoonotic, lactose non-fermenting, $H_2S$-positive rod causing localized inflammatory diarrhea; triggers a massive neutrophil influx via PAMPs and uses SPI1 (T3SS-1) for epithelial invasion and SPI2 (T3SS-2) for survival in a Salmonella-Containing Vacuole (SCV).

Salmonella enterica serovar Typhi

A human-restricted, lactose non-fermenting, $H_2S$-positive rod causing systemic Typhoid fever and chronic gallbladder carriage; uses T3SS-1 and T3SS-2 and evades neutrophil recruitment via a Vi capsular polysaccharide that masks surface PAMPs.

Vibrio cholerae

A motile curved rod causing profuse, watery "rice-water stools" (secretory diarrhea); secretes Cholera Toxin (CTx) to ribosylate G proteins, locking adenylate cyclase on and surging cAMP to force massive $\text{Cl}^-$ and osmotic water efflux.

Campylobacter jejuni

A microaerophilic, motile spiral/comma rod causing inflammatory, bloody diarrhea; triggers Guillain-Barré syndrome through molecular mimicry between its surface lipooligosaccharides (LOS) and human peripheral nerve gangliosides.

Borrelia burgdorferi

A microaerophilic spirochete motile via axial filaments (periplasmic flagella) and transmitted by Ixodes ticks; causes Lyme disease across early localized, early disseminated, and late disseminated stages, utilizing VlsE surface protein antigenic variation.

Erythema migrans

An expanding, painless, non-itchy red rash with central clearing displaying a characteristic bullseye appearance; diagnostic of early localized Lyme disease following an Ixodes tick bite.

Treponema pallidum

An obligate intracellular/microaerophilic spirochete causing syphilis; lacks standard LPS, exhibits a low-protein outer membrane ("stealth pathogenicity"), and utilizes hyaluronidase to degrade host extracellular matrix for perivascular invasion.

Chancre

A firm, painless, crater-like ulcer developing at the initial inoculation site during the primary stage of syphilis caused by Treponema pallidum.

Gumma

A destructive, chronic granulomatous lesion occurring in the skin, bones, or viscera during the tertiary stage of untreated Treponema pallidum infection.