Clinical Laboratory - Microbiology


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Microbiologic Testing

Role of Healthcare Providers in Hospital Epidemiology

Nosocomial Infections, which are defined as those infections that are acquired during one's stay in a healthcare facility, may be acquired through a variety of vectors. Common vectors of disease include the hands of health care workers, non-sterile devices and procedures, and hospital food. Measures such as thorough hand washing and the practice of sterile technique must be employed to limit the risk of infection.

Health care departments of governmental institutions adopt rules for reporting of infectious diseases that are likely to be of importance for the population as a whole, such as infectious agents that could cause epidemics or have a high morbidity/mortality. Reportable diseases MUST be reported to the health department by YOU, the health care worker.

Statistics can be compiled in regard to incidence and distribution (age, geography, season, etc) retrospectively: medical records can be reviewed, laboratory reports analyzed, patients followed up, or anatomic pathology material (surgical pathology, autopsy records) reviewed.

Epidemiologists and public health department workers can collect additional data: interview infected persons to determine how, when, and where they became infected; follow up contacts of infected persons (such as sexual partners of persons with sexually transmitted diseases (STD's) such as gonorrhea, syphilis, and HIV); test food and water, or test animal vectors, for presence of infectious agents.

A course of action is taken (quarantine, immunization program, closure of a business or facility, specific treatment of contacts or a subset of the population, etc.).

Antimicrobial Resistance

Bacterial organisms can acquire genetic material that gives them survival advantages in adverse environments, such as antibiotic therapy. There are multiple resistance mechanisms:

  • Plasmids are usually a circular portion of double-stranded DNA within bacteria. Plasmids may carry genetic material that gives the bacteria an advantage, such as genes encoding for virulence factors or resistance factors. Many gram-negative bacteria have these factors.

  • Transposons are portions of genetic material that can move within the bacterial genome or between bacteria. They may carry genes for resistance, such as those for vancomycin resistance by gram-positive cocci.

  • Integrons are units of genetic material that can recognize and capture mobile gene cassettes that may code for proteins involved in resistance to antibiotics. An example is a gene cassette encoding for beta-lactamase that confers resistance to beta-lactam antibiotics such as the penicillins and cephalosporins.

  • Pathogenicity islands are chromosomal elements within bacteria that can carry genes for virulence, such as superantigens for toxic shock syndrome (TSS-1) or staphylococcal food poisoning enterotoxin, or resistance in methicillin resistant Staphylococcus aureus.

When patients harboring microorganisms are clustered in health care facilities, those organisms can spread to heath care workers and onto environmental surfaces, from where they can infect others. This concentration of organisms provides opportunities for spread of resistance genes. The commensal bacteria of humans serve as a reservoir for bacteria harboring resistance genes that can spread to other humans. Increasing and indiscriminant usage of antibiotics speeds evolutionary pressure to select for resistant strains.

A health care facility can monitor infections to detect potential patterns of spread or development of resistance by microorganisms. Infection control measures can be instituted. Sanitize your hands before and after every patient contact. The usage of antibiotics can be modified.


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