BioSci: Bacteriology I

Normal flora

bacteria and fungi that are permanent residents of certain body sites; can be commensal or human microbiome

___, ____, and sometimes ____ can be found in individuals but are not part of the normal flora; they can be found in asymptomatic individuals

Viruses, parasites, mites

Commensal bacteria

Bacteria that derive benefit from another host, but do not damage that host

Normal flora vary in

number and kind from one site to another

Major sites of colonization are the

skin, oropharynx, colon, and vagina

Areas that are normally sterile are

CNS, blood, lower bronchi/alveoli, liver, spleen, kidneys, and bladder

A carrier state is

different than normal flora

A carrier state is an individual that

carries a pathogenic organism and can be source of infection or reservoir for others, but is asymptomatic

A carrier state individual is an individual that would be considered

colonized by a new microorganism; ex. Typhoid Mary (Mary Mallon) carried Salmonella typhi

Normal flora function to…

• act as protective host mechanism

• produce compounds to inhibit pathogenic bacteria

• regulate mucosal immunity

• serve nutritional function

Normal flora act as host defense systems by..

occupying attachment sites on the skin/mucosa that interfere with colonization by pathogenic bacteria: colonization resistance

Normal flora produce ______ like bacteriocins, lactic acids, etc.

compounds to inhibit pathogenic bacteria

Normal flora regulate mucosal immunity by… (3)

•IgA production against pathogens and induction of tolerance to flora

•Important in development of GALT

•Regulate levels of T helper cells (Th1, Th2, and Th17) in gut

Normal flora have nutritional functions such as… (3)

•Intestinal bacteria produce B vitamins (folate and biotin) and a type of vitamin K

•Help us absorb iron

•Digest what we cannot: indigestible plant fibers = short-chain fatty acids

Antibiotic usage can induce alterations in our normal flora by

suppressing our normal flora, allowing for pathogens may grow and cause disease

Ex) C. diff causing pseudomembranous colitis

Alterations in our normal flora can arise in poorly nourished people treated with antibiotics due to

vitamin deficiencies = disrupted since intestinal flora are not present (B vitamins and vitamin K)

Alterations in normal flora can play a role/be observed in ___

obese individuals

Alterations in normal flora can induce disease in ____

immunocompromised or debilitated individuals

Normal flora may also become ____, especially if seen in different locations of the body than usual

pathogenic

Staphylococcus epidermidis and Staphylococcus aureus are ______, but can live in hair follicles —they are resistant to ____

predominate on surface of skin, hand washing

Staphylococcus epidermidis can cause disease if ___

it reaches artificial heart valves or prosthetic joints

Deeper skin follicles/pores have ____

Propionibacterium and Peptococcus

Propionibacterium acnes causes __

acne

Candida albicans can also be part of normal flora that can cause ____, as well as cause ______ if it gets into the bloodstream

systemic infections in patients with reduced cell-mediated immunity, sepsis (via IVDU, IV catheters)

Sometimes ___ like Demodex species can be apart of the normal flora

mites

Mites, like the Demodex species, serve to..

help clean out our hair follicles (like eyelashes and eyebrows)

Mites can also be considered ___ and most people have them

obligate ectoparasites

If mites multiply too much, they can ___

cause blepharitis

S. aureus and some S. epidermidis are found mainly in the _____

nose

S. epidermidis inhibits

S. aureus

Nasopharynx typically houses … (6)

• Corynebacterium species

• Haemophilus species

• Neisseria species

• Moraxella catarrhalis

• Viridans streptococci

• Strep. pneumoniae

Viridans streptococci inhibits ___ and Neisseria species inhibits ____ N. meningitidis

Strep. pyogenes, N. meningitidis

Bacterioides and Fusobacterium are more often found in the __

throat

Mouth has.. (4)

• Candida albicans

• Lactobacillus

• Neisseria species

• Viridans streptococci

In dental plaque, ___ is found as the main agent of caries (cavities)

Strep. mutans, a type of Viridans Streptococci

Strep. mutans, a type of Viridans Streptococci, induces caries/cavities by..

demineralizing enamel with acid production

_____ can cause bacterial endocarditis if it ____

Strep. sanguinis (a type of Viridans streptocci), enters bloodstream during dental surgery (attaches to damaged/prosthetic heart valves)

•Eikenella corrodens can cause skin/soft tissue infections associated with

human bites and “clenched fist” injuries

____ live in gingival crevices

Anaerobic bacteria

Dysbiosis causes ____, which can be aspirated and cause ___

periodontal disease, lung abscesses

Actinomyces israelii can cause abscesses in ___

jaw, lungs, or abdomen

There are few organisms in the stomach due to

low pH

Small intestine has small numbers of ___ and larger numbers are found in the __

streptococci, lactobacilli, and yeasts   (Candida albicans, terminal ileum

The colon is the ___

major location of bacteria in the body

20% of feces is _____, with _____

bacteria, 90% of those being anaerobes

Human healthy gut is predominately good microbes (_____) versus bad microbes (____) and if they become unbalanced, dysbiosis occurs

Bacteriodetes and Firmicutes, Proteobacteria and Actinobacteria

Main Bacteriodetes in the gut are ___

Bacteriodes and Prevotella, specifically B. fragilis as the main one

Main Firmicutes in the gut are __

Clostridium and Faecalibacterium, specifically C. perfrigens =

Proteobacteria includes ____ and Salmonella

Actinobacteria includes ___

Escherichia coli, Actinomyces

What are some bacterial causes of UTIs and endocarditis?

• E. coli is the leading cause of UTIs.

• Enterococcus faecalis can cause UTIs and endocarditis

Which bacteria are associated with GI-related infections or complications?

• Bacteroides fragilis causes peritonitis after intestinal wall perforation (e.g., trauma, appendicitis, diverticulitis).

• Clostridium difficile causes pseudomembranous colitis, especially after antibiotic use (e.g., clindamycin)

Neomycin is used ___

pre-GI surgery to reduce gut flora

What infections are associated with Pseudomonas aeruginosa?

P. aeruginosa can cause a wide range of infections, especially in immunocompromised patients (e.g., wound, lung, urinary tract infections)

What role do Lactobacillus species play in the vaginal microbiome?

Lactobacillus species produce acid that keeps vaginal pH low, helping prevent growth of pathogens like Candida

How do estrogen levels affect Lactobacillus and vaginal pH?

Low estrogen (e.g., pre-puberty, post-menopause) reduces Lactobacillus presence, raises vaginal pH, and increases risk of Candida overgrowth

How can antibiotics lead to vaginitis?

Antibiotics may deplete Lactobacillus, allowing Candida albicans to overgrow, leading to vaginitis

Why can fecal flora colonize the vagina?

Due to the close proximity of the anus to the vagina, fecal flora like E. coli and Enterobacter can colonize the vaginal introitus

How can vaginal colonization by coliforms lead to infection?

Colonization by E. coli, Enterobacter, and other coliforms can cause frequent urinary tract infections (UTIs)

What hygiene practices help prevent UTIs?

Wipe front to back and urinate after sexual activity to reduce UTI risk

Which additional microbes may colonize the vagina?

Bacteroides spp., Corynebacterium spp., Gardnerella vaginalis, and Staphylococcus epidermidis

What risks are associated with Group B Streptococcus in pregnancy?

Carried by ~20% of women; can cause neonatal sepsis and meningitis during birth. Prophylactic antibiotics are given before delivery to prevent this

What conditions can S. aureus and Gardnerella vaginalis cause?

• S. aureus (in ~5% of women) can predispose to toxic shock syndrome

• Gardnerella vaginalis overgrowth can lead to bacterial vaginosis

Is urine normally sterile, and when can it become contaminated?

Urine is sterile in the bladder but may become contaminated by Staph. epidermidis, coliforms, diphtheroids, and nonhemolytic streptococci as it passes through the distal urethra

What bacteria can be found around the urethral area in women and uncircumcised men?

Mycobacterium smegmatis, an acid-fast bacterium, can colonize secretions near the urethra in these individuals

Which skin bacterium near the GU tract can cause UTIs in women?

Staphylococcus saprophyticus, found on the skin around the genitourinary tract, can cause UTIs in women

Quorum sensing allows bacteria to detect when a _____, triggering the production of _______

critical population density is reached, virulence factors and biofilm formation

Biofilms commonly form on which foreign bodies?

Prosthetic joints, prosthetic heart valves, IV catheters, and urethral catheters

Biofilms can also form on native __________ and __________

heart valves; teeth

What structure allows Staph. epidermidis and Viridans streptococci to strongly adhere to heart valves?

Their glycocalyx

__________ mediate the adherence of bacteria to cell surfaces

Adhesions

What is the composition of the biofilm matrix after bacterial attachment?

Polysaccharides and proteins

How do biofilms impact wound healing and chronic infections?

Biofilms slow wound healing, causing chronic infections—especially in diabetics—and contribute to persistent Pseudomonas infections in cystic fibrosis lungs

Biofilms form __________, which leads to dental caries

dental plaque

Why are biofilms resistant to immune responses and antibiotics?

They block access by antibiotics and immune defenses like antibodies and neutrophils; phagocytes can't adhere due to lack of selectins or binding proteins on the biofilm surface

What is virulence and how is it measured?

Virulence is a quantitative measure of pathogenicity, often measured by LD₅₀ or ID₅₀

LD₅₀ refers to the number of organisms or toxin required to cause death in _____% of hosts

50

What does ID₅₀ measure?

The number of organisms required to cause infection in 50% of hosts

A lower LD₅₀ or ID₅₀ indicates a more __________ pathogen

virulent

Which is more infectious based on ID₅₀—Shigella (<100 organisms) or Salmonella (100,000 organisms)?

Shigella is more infectious

What are pathogenicity islands?

Clusters of genes on bacterial chromosomes that encode virulence factors like adhesins, invasins, and exotoxins

Mutations in bacteria can increase ____

virulence and antibiotic resistance

Which process involves transfer of F plasmids between bacteria?

Conjugation (via sex pilus)

Transfer of genes by bacteriophages that can result in toxin production is called __________

transduction

What is lysogenic conversion?

When a bacteriophage inserts its DNA into a host bacterium, causing it to express new virulence factors like toxins

Which of the following can transfer virulence genes?

transposons

Horizontal gene transfer of __________ can enhance bacterial pathogenicity

pathogenicity islands

What bacterial structure helps resist heat, dehydration, chemicals, and radiation?

Spores

Why can't spores be killed with antibiotics?

Because they are metabolically inactive and highly resistant

What structure limits phagocytosis and enhances bacterial adhesion to tissues?

Capsule

Which structure helps bacteria form biofilms on surfaces like catheters or heart valves?

Glycocalyx

Which bacterial appendage enables motility and movement to deeper tissues?

Flagella

What helps bacteria attach to human cells or mucous membranes?

Pili (fimbriae)

What are endotoxins (LPS), and what effects can they cause in the human body?

Endotoxins are lipopolysaccharides in Gram-negative cell walls that trigger excessive immune responses, such as fever, septic shock, and DIC (disseminated intravascular coagulation)

Which of the following is ONLY found in Gram-negative bacteria?
A. LTA
B. Capsule
C. LPS
D. Pili

LPS

Recognition of LPS by white blood cells triggers __________ production, leading to tissue damage from inflammation

proinflammatory compound

What are key signs of septic shock (SIRS)?

Hypotension, fever, tachycardia, tachypnea, and leukocytosis

Why can septic shock continue even after bacteria are killed?
A. White blood cells stop functioning
B. The bacteria reappear
C. Proinflammatory compounds continue to act
D. The immune system becomes inactive

C. Proinflammatory compounds continue to act

In DIC, tissue factor released from damaged endothelial cells activates the __________ cascade, leading to thrombosis and organ failure

coagulation

What are exotoxins and what do they do?

Exotoxins are polypeptides secreted by Gram-positive and Gram-negative bacteria that cause cellular dysfunction, damage, and death

Which of the following bacterial toxins are encoded by bacteriophages?
A. Diphtheria, Botulinum, Cholera, Strep. pyogenes
B. Tetanus, Anthrax, Shiga
C. Pertussis, TB, MRSA
D. LPS, LTA, TLR

A. Diphtheria, Botulinum, Cholera, Strep. pyogenes