General Classification of Surgical Infections
Surgical infection is divided into two broad categories depending on the nature of the pathogen:
- Nonspecific infection. Caused by classic pyogenic flora and can develop along purulent, putrid, or anaerobic pathways.
- Specific infection. Caused by strictly defined microorganisms. This includes tuberculosis, tetanus, gas gangrene, actinomycosis, anthrax, and wound diphtheria.
When considering the disease by etiology (type of microorganism), staphylococcal, streptococcal, pneumococcal, colibacillary, gonococcal, anaerobic (spore-forming and non-spore-forming), as well as fungal and polymicrobial forms are distinguished.
Staphylococcal Infection (Staphylococcus)
Staphylococcus is the absolute leader among causative agents of purulent surgical pathology. Its primary route of transmission is contact. Sources of infection are either other patients with active inflammation (exogenous route) or the patient's own dormant foci and saprophytic flora colonizing the skin, mucous membranes of the nasopharynx, respiratory tract, and genital organs (endogenous route).
The microorganism possesses potent pathogenicity factors: it secretes destructive exotoxins (staphylolysin/staphylohemolysin, leukocidin, coagulase) and exhibits high resistance to antibiotics and chemical antiseptics.
It causes two types of lesions:
- Localized: furuncles, carbuncles, hidradenitis, phlegmons, lung abscesses, and osteomyelitis.
- Generalized: sepsis. A distinctive feature of staphylococcal sepsis is the formation of metastatic purulent foci in various organs.
Streptococcal Infection (Streptococcus)
Among streptococci, the most significant are group A, B, and D $\beta$-hemolytic strains. They are responsible for erysipelas, bacterial endocarditis, cholecystitis, and pyelonephritis.
Streptococci also frequently trigger severe pediatric infections: pneumonia, osteomyelitis, meningitis, and neonatal sepsis.
The clinical presentation of streptococcal infection is characterized by pronounced, extremely severe systemic intoxication. Meanwhile, unlike staphylococcus, generalized purulent infection (sepsis) occurs without the formation of metastatic purulent foci.
Pseudomonas aeruginosa (Pseudomonas aeruginosa)
Pseudomonas aeruginosa normally lives as a saprophyte on human skin, primarily localized in sweat gland regions. In clinical practice, however, it is one of the main and most dangerous pathogens of nosocomial infections.
It actively colonizes wounds against the background of a sharp decline in the patient's immune defenses; therefore, it is most often encountered in burn units and intensive care units (ICUs). The presence of Pseudomonas aeruginosa in a wound critically impairs natural tissue regeneration.
The pathogen exhibits extremely high resistance to most antibiotics and chemical antiseptics. Only a few agents retain efficacy against it: polymyxin, amikacin, carbenicillin, and among topical agents, boric acid.
Non-Spore-Forming Anaerobes
This is a broad group of microorganisms that proliferate in an oxygen-free (anaerobic) environment yet do not form spores. They include:
- Gram-positive cocci: Peptococcus, Peptostreptococcus;
- Gram-negative bacteria: Bacteroides, Fusobacterium.
They cause severe purulent-inflammatory complications following abdominal surgical interventions, form intrapelvic suppurations, and lung abscesses. A key feature of these pathogens is that they can initiate a pathological process either independently or in polymicrobial synergy with aerobic bacteria, significantly complicating treatment.
Mnemonic to remember sepsis differences: STAPH leaves "STA-ff" (metastatic foci) behind in organs. STREP is RAMPANT with toxicity, but causes no metastases.
Class and exam questions
Which microorganism most frequently causes nosocomial infections in burn centers?
Pseudomonas aeruginosa, as it easily affects a weakened organism and suppresses the regeneration of damaged tissues.
What is the main clinical difference between staphylococcal and streptococcal sepsis?
Staphylococcal sepsis is characterized by the emergence of metastatic purulent foci in various organs. Streptococcal sepsis presents with severe systemic intoxication, but without metastatic dissemination.
Which bacteria are classified as non-spore-forming anaerobes?
These include Gram-positive (Peptococcus, Peptostreptococcus) and Gram-negative (Bacteroides, Fusobacterium) microorganisms that thrive in an oxygen-free environment.
What else to study on this topic
- Mechanism of action of staphylococcal exotoxins (coagulase, leukocidin)
- Pathogenesis of tissue regeneration impairment by Pseudomonas aeruginosa
- Clinical features of mixed infections (aerobes + anaerobes)
- Pathogens of specific surgical infection (tuberculosis, actinomycosis)
- Clostridial spore-forming anaerobic infection
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Other topics from the section "CHAPTER 11. SURGICAL INFECTION (PURULENT-INFLAMMATORY DISEASES)"
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