The document discusses nosocomial (hospital-acquired) infections. It notes that the most common sites of nosocomial infections are the urinary tract, surgical/soft tissue sites, gastrointestinal tract, and respiratory system. Bacteria cause about 90% of nosocomial infections, with common genera being Streptococcus, Acinetobacter, Enterococcus, Pseudomonas, Staphylococcus. Excessive and improper antibiotic use has led to many drug-resistant strains causing nosocomial infections. The distribution of bacteria causing nosocomial infections has changed over time.

1. B Y D R . S R E E R E M Y A . S
F A C U L T Y O F B I O L O G Y
Nosocomial Agents-An
Overview

2.  Types of nosocomial infections
 National Healthcare Safety Network with Centre for Disease Control
(CDC) for the surveillance has categorized nosocomial infection
sites into 13 types, with 50 infection sites, which are specific on the
basis of the biological and clinical criteria. The sites which are
common encompass urinary tract infections (UTI), surgical and soft
tissue infections, gastroenteritis, meningitis and also respiratory
infection. A change regarding nosocomial infection sites can be
easily detected with time due to the aggrandized use of cancer
chemotherapy, advancement in organ transplantation,
immunotherapy and the invasive techniques for diagnostic and for
the therapeutic purposes. The perfect example of this can be
observed in the case of pneumonia as prevalence of nosocomial
pneumonia increased from 17% to 31% during five
years(Dzupova,2008).

3.  Bacteria are mainly responsible for about ninety
percent infections, whereas protozoans, fungi,
viruses and the mycobacteria are less contributing
compared to bacterial infections. The agents that are
generally involved in hospital-acquired infections
encompass Streptococcus spp., Acinetobacter spp.,
enterococci, Pseudomonas aeruginosa (P.
aeruginosa), the coagulase-negative staphylococci,
Staphylococcus aureus (S. aureus),

4.  Bacillus cereus (B. cereus), Legionella and the
Enterobacteriaceae family members encompassing
Proteus mirablis, Klebsiella pneumonia (K.
pneumonia), Escherichia coli (E. coli),
Serratiamarcescens. Out of these enterococci species,
P. aeruginosa, S. aureus and E. coli have the major
role. UTI usually contain E. coli, while it is
uncommon in other infection sites. Contrarily, S.
aureus is quiet frequent at other body sites and
rarely causes UTI(Fumagalli,2005). In blood-borne
infections, the coagulase-negative S. aureus is the
main causative agent.

5.  Surgical-site infestations contain Enterococcus spp. which is less prevalent
at respiratory tract. One tenth of all the infections are caused by P.
aeruginosa, which is evenly distributed to the entire body
organs(Folkehelseinstituttets,2009) .Mycobacterium kansasii is also a
chronic pathogenic organism(Sreeremya,2018)
 Excessive and improper use of wide -spectrum antibiotics, especially in
healthcare settings, are elevating nosocomial infections. Penicillin-resistant
pneumococci, the multi-drug-resistant tuberculosis, the methicillin-
resistant S. aureus (MRSA), vancomycin-resistant S. aureus are common
examples of drug-resistant bacteria. The distribution of the bacteria in
nosocomial infections is changing over time. For example,the Proteus spp.,
Klebsiella spp. and Escherichia spp. were responsible for nosocomial
infections in the 1960s, but from 1974 to 1980s, Acinetobacter spp. with P.
aeruginosa created much clinical difficulties. During the recent years,
streptococci along with the coagulase-negative staphylococci and
coagulase-positive staphylococci reemerged and the incidence level of K.
pneumonia and E. coli declined from 7% to 5% and 23%–17%,
respectively(Ducel,2002).

6.  BACTERIOLOGY OF COMMONLY ISOLATED
NOSOCOMIAL PATHOGENS A multicenter research was
conducted in Japan to isolate bacteria from surgical infections
during 2011–2012. About 784 strains including 31 of Candida
spp. were isolated from 204 out of 259 surgical patients.
About 524 strains were isolated from primary infections and
231 from surgical site infection. From primary infections, the
anaerobic Gram-negative bacteria were prevalent.
Enterococcus spp. was the highest among the Gram-positive
aerobic bacteria followed by Streptococcus and
Staphylococcus spp. E. coli was the dominant form among the
Gram-negative aerobic bacteria followed by the K.
pneumonia, P. aeruginosa and Enterobacter
cloacae(Debaroti,2005). S. aureus

7.  Out of many species of Staphylococcus genus, S. aureus is
considered one of the major important pathogens, responsible for
the nosocomial infections. It is Gram-positive cocci, non-spore
forming, catalase- and coagulase-positive, immotile, and the
facultative anaerobe. It is not only the disease-causing organism but
also plays its role as commensal. It mainly colonizes in nasal
passages. About 21% individuals have persistent colonization of S.
aureus, whereas 31% are intermittent. Hospitalized patients with
decreased immunity and immunocompetent people in the
community are more prone to S. aureus infections. S. aureus infects
not only the superficial but also the deep tissues and the local
abscess lesion. Toxin-mediated diseases of S. aureus encompass
food poisoning, due to ingestion of enterotoxins, while toxic shock
syndrome toxin 1 is responsible for the toxic shock syndrome and
exfoliative toxins causes the staphylococcal scalded skin syndrome.
Virulence mechanisms of S. aureus encompass toxins, enzymes and
immune modulators (Darouiche,2007). E. coli

8. REFERNCE
 Journal of General Nursing and Community Health,
Nosocomial Agents -An Overview, Dr.S.Sreeremya ,
2019.Vol 1(2):1-9.