Infections, their causative microorganisms and the antibiotics

Written by Dr.Md.Redwanul Huq (Masum)
Friday, 24 June 2011 09:34

Definition of Antibiotic

An antibiotic is a natural substance or derivative of a natural substance, which if taken in small doses, will either kill or prevent the growth of a microorganism, but will not seriously harm the person taking it.

Prescription of Antibiotic(s)-

Many of the infections are viral and self limiting. So, antibiotic for infection is not all time essential. Therefore, while prescribing antibiotic(s) you should follow the “General principles of antibiotic prescribing” given here:

*Prescribe antibiotics only for bacterial infections where-

  •  Symptoms of the disease are severe or significant
  • The infection is not resolving itself
  • There is a high chance of arising complications

* Choose the most appropriate antibiotic on the basis of the identification of the microorganism causing the infection.
* Provide prescription of antibiotic(s) with as narrow a range of effectiveness as possible
* Reserve broad spectrum antibiotics for indicated conditions only
* Prescribe a dosage to cure the infection, but use the antibiotic for the shortest possible time which will effect a cure.

Here a tableis given for the practicing doctors, which contains some common Infections, their causative organisms & the antibiotics (according to chronology of efficacy) for those infections.

(Note: For Immunosuppressed patients and those who had splenectomy the choice of antibiotics are a combination of Aminoglycoside with an antipseudomonal Penicillin or Cephalosporin).

Table : Some Infections, their causative microorganisms & the antibiotics (according to chronology of efficacy) for those infections-

Infections Microorganisms Antibiotics(according to chronology of efficacy)

Bone infection

Acute osteomyelitis Staphylococcus, Streptococcus,Escherichia coli,Proteus spp, P aeruginosa. Cefotaxime,Ampicillin,Amoxicillin, Cephalexin, Cephaloridine, Flucloxacillin plus Fusidic acid,Gentamicin, Kanamycin,Clindamycin.
Chronic osteomyelitis Staphylococcus, Streptococcus,Escherichia coli,Proteus spp. Ampicillin,Amoxicilliin,Cephalexin, Flucloxacillin, Cephaloridine, Gentamicin, Kanamycin, Clindamycin.
Fungal Infection of Bone Aspergillus, Cryptococcus, Histoplasma etc. Nystatin,Amphotericin B,Fluconazole, Ketoconazole
Septic arthritis Streptococci, Staphylococcus aureus, Enterobacteriaceae. Cefotaxime.

Central Nervous System

Bacterial meningitis Neisseria eningitides, Streptococcus pneumoniae,Listeria monocytogenes, Haemophilus influenzae For Newborns: Ampicillin + Cefotaxime, Ampicillin +Gentamicin.For patients having age of 2 months-60 years: Ceftriaxone/ Cefotaxime with or without Vancomycin, Meropenem with or without Vancomycin.
Fungal meningitis Cryptococcus Amphotericin plus Flucytosine
Viral meningo-encephalitis Herpes simplex Aciclovir.

Ear infection

Antibiotic for Ear infection
Acute Otitis Externa Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, polymicrobial infections Clioquinol + flumethasone Ear Dropor Dexamethasone + framycetin + gramicidinEarDrop or Ciprofloxacin + hydrocortisone Ear Drop, Oral flucloxacillin (If there is spreading cellulites).
Acute Otitis Media Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis Amoxicillin, Azithromycin or Clarithromycin or Erythromycin, Cefuroxime, Cefpodoxime, Amoxicillin with Clavulanate, Clindamycin, Ceftriaxone.


Acute Native Valve Endocarditis (NVE) -Staphylococcus aureus and group B streptococci.

Subacute Native Valve Endocarditis (NVE)- Alpha-hemolytic streptococci or enterococci.


Early Prosthetic valve Endocarditis (PVE)- Coagulase-negative staphylococci, gram-negative bacilli, and Candida species.

Late Prosthetic valve Endocarditis (PVE)- Staphylococci, alpha-hemolytic streptococci, and enterococci.

Intravenous Drug Abuse (IVDA) Endocarditis- S aureus.

Pacemaker IE- Staphylococci (both coagulase-negative and coagulase-positive).

Nosocomial IE (NIE)- S aureus. Enterococci.

Antibiotic for Endocarditis Penicillin G or Ampicillin + Gentamicin, IV Vancomycin+ Gentamicin.

Eye infection

Antibiotic for Eye infection
Conjunctivitis(Infectious) Viruses, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Chlamydia trachomatis or Neisseria gonorrhoeae Antibiotic for Conjunctivitis Topical Chloramphenicol, Topical Fusidic acid or topical Framycetin.

Gall bladder

Acute cholecystitis Coliforms Cefuroxime plus Metronidazole, Amoxicillin with Clavulanate, Ciprofloxacin plus Metronidazole.



Campylobacteriosis Campylobacter jejuni Azithromycin or Clarithromycin or Erythromycin, Ciprofloxacin.
Clostridium difficile colitis Clostridium difficile Metronidazole, IV Vancomycin (hospital treatment).
Giardiasis Giardia lamblia Ornidazole or Metronidazole
Salmonellosis Salmonella enteritidis, Salmonella typhimurium Ciprofloxacin,Co-trimoxazole.
Travellers’ diarrhoea Escherichia coli, Campylobacter jejuni, Salmonella and Shigella species Ciprofloxacin, Azithromycin.

Genito- Urinary system

Acute non-specific urethritis Ureaplasma urealyticum, Mycoplasma genitalium, Trichomonas vaginalis Azithromycin plus Ceftriaxone , Doxycycline plus Ceftriaxone, Azithromycin plus Cefixime or Ciprofloxacin, Ofloxacin.
Acute prostatitis Escherichia coli,
Klebsiella pneumoniae, Chlamydia trachomatis.
Trimethoprim plus Doxycycline,Ciprofloxacin.
Acute pyelonephritis

Escherichia coli, Proteus, Pseudomonas, Staphylococcus aureus, and Enterococcus faecalis (formerly Streptococcus faecalis)

For ambulatory patients: Fluroquinolones: Ciprofloxacin or Levofloxacin or Gatifloxacin or Norfloxacin, 1st generation Cephalosporins (Cephradine,Cephalexin etc), Amoxycillin with Clavulanic acid, Co-trimoxazole.For hospitalized patients: Fluroquinolones: Levofloxacin or Gatifloxacin, Ampicillin/Sulbactam + Gentamycin, Imipenem/Meropenem.
Bacterial vaginosis Gardnerella vaginalis, Bacteroides, Peptostreptococci, Mobilunculus Antibiotic for Bacterial vaginosisMetronidazole or Ornidazole or Secnidazole.
Cervicitis Chlamydia trachomatis, Neisseria gonorrhoeae, Ureaplasma urealyticum, Mycoplasma genitalium, Trichomonas vaginalis Azithromycin plus Ceftriaxone , Doxycycline plus Ceftriaxone, Azithromycin plus Cefixime or Ciprofloxacin, Ofloxacin.
Chlamydia Chlamydia trachomatis Antibiotic for ChlamydiaAzithromycin,Doxycyclineor Amoxicillin.
Cystitis Escherichia coli, Staphylococcus saprophyticus, Proteus sp., Klebsiella sp., Enterococcus sp. Antibiotic for CystitisFluroquinolones: Ciprofloxacin or Levofloxacin or Gatifloxacin or Norfloxacin, Trimethoprim/ Sulfamethoxazole, Nitrofurantoin, 1st generation Cephalosporins (Cephradine,Cephalexin etc),
Epidiymo-orchitis Mainly due to Chlamydia trachomatis or Neisseria gonorrhoeae. Also due to E. coli, Bacteroides species, Gardnerella vaginalis, Mycoplasma hominis, Ureaplasma urealyticum, Trichomonas vaginalis, Streptococcus agalactiae If STI is suspected:Ceftriaxone and Azithromycin, Ciprofloxacin.If UTI is suspected: Amoxicillin clavulanate or Ciprofloxacin.
Gonorrhoea Neisseria gonorrhoeae Antibiotic for GonorrhoeaCeftriaxone or cefixime and Azithromycin, Cefotaxime, Cefpodoxime, Cefuroxime, Ciprofloxacin.
Lower UTI Escherichia coli
Staphylococcus saprophyticus
Proteus mirabilis
Klebsiella pneumoniae
Newborn<2 weeks: Ampicillin + Gentamycin.Newborn 2weeks-2months: Ampicillin+ Cefotaxime.Children>2months:For ambulatory Children : Cephalexin, Co-trimoxazole,Cefixime,Nitrofurantoin.

For hospitalized Children : Cefotaxime, Ceftriaxone.

For adults: Ciprofloxacin or Levofloxacin, 1st generation Cephalosporins (Cephradine,Cephalexin etc), Amoxycillin with Clavulanic acid, Co-trimoxazole.

Pelvic inflammatory disease Chlamydia trachomatis, Neisseria gonorrhoeae and others For ambulatory patients: Ceftriaxoneand Doxycycline and Metronidazole, Ofloxacin and Levofloxacin and Metronidazole, Azithromycin.For hospitalized patients: Cefoxitin plus Doxycycline, Clindamycin plus Gentamicin plus Doxycycline, Ofloxacjn plus Metronidazole, Ciprofloxacin and Doxycycline and Metronidazole, Azithromycin and Metronidazole.
Syphilis Treponema pallidium Antibiotic for Syphilis Benzathine penicillin or Procaine penicillin, Ceftriaxone, Tetracycline or Doxycycline.
Trichomoniasis Trichomonas vaginalis Metronidazole or Ornidazole or Secnidazole.
Vulvovaginal Candidiasis Candida albicans Fluconazole, Nystatin, Terconazole, Clotrimazole, or Miconazole.


Intra-abdominal Infections & Peritonitis

E. coli, Enterococci, Klebsiella species,Bacteroides, Peptococcus, Fusobacterium and Clostridium species, staphylococci, P. aeruginosa, Candida species, Pneumococcal and streptococcal species,Listeria monocytogenes, Campylobacter coli, and Aeromonas species. Ampicillin/Sulbactam with or without Aminoglycoside,Cefotetan/Cefoxitin with or without Aminoglycoside,3rd generation Cephalosporins(Ceftriaxone,Cefotaxime) plus Metronidazole/Clindamycin with or without Aminoglycoside, Ciprofloxacin plus Metronidazole/Clindamycin, Imipenem/Meropenem with or without Aminoglycoside.


Acute Sinusitis Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, anaerobic bacteria Amoxycillin or Amoxycillin with Clavulanic acid, Ciprofloxacin or Levofloxacin, Azithromycin, Doxycycline, Co-trimoxazole, Cefaclor.



Acute exacerbation of chronic bronchitis or COPD Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis Azithromycin, Levofloxacin, Gatifloxacin, Amoxicillin or Amoxycillin with Clavulanic acid, Doxycycline, 2nd or 3rd generation Cephalosporins(Cefixime,Cefpodoxime, Cefaclor), Co-trimoxazole
Aspiration pneumonia Community-acquired aspiration pneumonia- Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Enterobacteriaceae.Hospital-acquired aspiration pneumonia- Gram-negative organisms including Pseudomonas aeruginosa, Staphylococci. Coamoxiclav or Amoxicillin+Metronidazole
Atypical or Legionella likey Legionella pneumophila,Chlamydia pneumoniae, Chlamydia psittaci,Coxiella burnetii,Francisella tularensis,Mycoplasma pneumoniae, Fungus, Protozoa,Virus. Erythromycin or Tetracycline
Antibiotic for Bronchitis Acute bronchitis-Mycoplasma pneumoniae and Chlamydia trachomatis.Virus.Chronic bronchitis-Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Virus. Amoxicillin, Oxytetracycline or Doxycycline.
Community acquired pneumonia (In adult) Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydophilia pneumonia, Legionella pneumophila, Staphylococcus aureus For ambulatory patients: Azithromycin or Clarithromycin, Doxycycline, Levofloxacin or Gatifloxacin, Amoxycillin or Amoxycillin with Clavulanic acid, 2nd generation Cephalosporins(Cefuroxime axetil,Cefpodoxime proxetil, Cefdinir,)For hospitalized patients: Ceftriaxone or Cefotaxime with or without Azithromycin or Clarithromycin, Levofloxacin or Gatifloxacin, Cefuroxime axetil with or without Azithromycin or Clarithromycin.
Community acquired pneumonia (In child) Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae Amoxycillin or Amoxycillin with Clavulanic acid, Erythromycin
Hospital acquired pneumonia/Post operative P. aeruginosa, A.baumanii, Methicillin-resistant S. aureus [MRSA], Stenotrophomonas maltophilia, S. aureus, Haemophilus influenzae, and Streptococcus pneumoniae. Ceftazidime/Ciprofloxacin+Metronidazole, IV Gentamicin and Ticarcillin with Clavulanic acid.
Pertussis Bordetella pertussis Antibiotic for PertussisErythromycin.
Uncomplicated Chest Infection Respiratory viruses, Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus. Amoxicillin, Erythromycin.

Septicaemia and Septic Shock

Septic Shockdue to lower respiratory tract infection by- Streptococcus pneumoniae,Klebsiella pneumoniae,Staphylococcus aureus,Escherichia coli,Legionella species,Haemophilus species,Anaerobes,Gram-negative bacteria,Fungi.Septic Shockdue to urinary tract infection by- E coli,Proteus species,Klebsiella species,Pseudomonas species,Enterobacterspecies,Serratia species.Septic Shockdue to soft tissue infection by- S aureus,Staphylococcus epidermidis,Streptococci,Clostridia,Gram-negative bacteria,Anaerobes.Septic Shockdue to GI tract infection by- E coli,Streptococcus faecalis,Bacteroides fragilis,Acinetobacter species,Pseudomonas species,Enterobacter species,Salmonella species.

Septic Shockdue to reproductive system infection by- Neisseria gonorrhoeae,Gram-negative bacteria, Streptococci, Anaerobes.

Septic Shockdue to foreign body infection by- S aureus, S epidermidis, and fungi / yeasts (eg, Candida species).

Septic Shockdue to miscellaneous infection by- Neisseria meningitides.

Antibiotic for Septicaemia and Septic ShockFor Neonates: Ampicillin plus Cefotaxime, Ampicillin plus Ceftriaxone, Ampicillin plus Genatamicin.For Children: 3rd generation Cephalosporins(Ceftriaxone,Cefotaxime).For Adults: 3rd or 4th generation Cephalosporins(Ceftriaxone,Cefotaxime, Ceftizoxime,Cefepime), Piperacillin/Tazobactam, Imipenem/Meropenem, Vancomycin with Aminoglycoside.

Skin & Soft Tissue Infections

Bites and clenched fist infections Polymicrobial infection, Pasteurella multocida, Capnocytophaga canimorsus (bites by cat or dog), Eikenella corrodens (fist injury), Staphylococcus aureus, Streptococci and anaerobes Amoxycillin or Amoxycillin with Clavulanic acid, Clindamycin/Metronidazole plus Doxycycline or Co-trimoxazole.
Boils Staphylococcus aureus Antibiotic for BoilsFlucloxacillin, Cephalosporins (Cephradine, Cephalexin, Cefazolin etc).
Cellulitis Group A streptococci, Staphylococcus aureus. Antibiotic for CellulitisFor ambulatory patients: Amoxycillin with Clavulanic acid, Flucloxacillin, Azithromycin, 1st generation Cephalosporins (Cephradine,Cephalexin etc), Aminopenicillins or Quinolones.For hospitalized patients: Imipenem/Meropenem, IV Cephalosporins (Ceftazidime, Ceftriaxone), Fluroquinolone + Clindamycin/ Metronidazole.
Diabetic Foot Infections Gram-positive organisms include Enterococcus faecalis, S aureus(specially Methicillin-resistant S aureus (MRSA), S epidermidis,and groupB streptococci.Gram-negative organisms include Proteus species, E coli, Klebsiella species, and Pseudomonas species.Anaerobesinclude Peptococcus species and Bacteroides fragilis Mild infection: Amoxycillin with Clavulanic acid, Cephalosporins (Cephalexin, Cephradine, Cefazolin etc) plus Clindamycin/Metronidazole,Severe infection: Ampicillin/Sulbactam, Cefotetan/Cefoxitin, Fluroquinolone + Clindamycin/ Metronidazole, Imipenem/Meropenem. IV Vancomycin (If caused by MRSA ).
Erysipelas Streptococcus pyogenes. Phenoxymethylpenicillin, Ciprofloxacin plus Clindamycin.
Foot infections S. aureus, S. epidermidis, and Streptococcus sp. First-generation Cephalosporins, Clindamycin (for patients allergic to Penicillin), Amoxicillin and Cavulanate, Levofloxacin.
Impetigo Streptococcus pyogenes, Staphylococcus aureus Fusidic acid cream, Flucloxacillin.
Mastitis Staphylococcus aureus for lactating women, anaerobes for non-lactating women or men Antibiotic for Mastitis Flucloxacillin,Cephalosporins (Cephalexin, Cefazolin etc), Amoxycillin with Clavulanic acid.
Necrotizing fasciitis Bacteroides species, staphylococci, and enterococci, Aerobic streptococci, E coli and Proteus species

Piperacillin and Tazobactam,Ticarcillin and Clavulanate, Ceftazidime and Clindamycin.

Severe limb- threatening foot infections S. aureus, S. epidermidis, and Streptococcus sp. Ampicillin and Sulbactam, Ticarcillin and Clavulanate or Piperacillin and Tazobactam. IV Clindamycin in combination with oral Ciprofloxacin (for patients allergic to Penicillin), Levofloxacin or Gatifloxacin, Aminoglycoside should be added if wounds are suspected of having very aggressive gram-negative organisms.


Acute Epiglottitis H. influenzae Cefotaxime.
Pharyngitis Respiratory viruses, Streptococcus pyogenes Phenoxymethylpenicillin, Azithromycin or Clarithromycin or Erythromycin,1st or 2nd generation Cephalosporin (Cefuroxime axetil,Cefpodoxime proxetil, Cefdinir), Clindamycin.
Quinsy Beta haemolytic Streptococci, Anaerobes of mouth cavity. Phenoxymethylpenicillin with Metronidazole.
Tonsillitis Streptococci pneumoniae (commonest), Staphylococcus, Pneumococcus, H. Influenzae,Diphtheroids,
Antibiotic for TonsillitisPenicillin V
Vincent’s Angina Anaerobes of mouth cavity Phenoxymethylpenicillin with Metronidazole.

Wound Infections

Abdominal and Pelvic wound infection Anaerobic streptococci, E. coli, Klebsiella, Proteus, Bacteroides species, Staphylococcus aureus, Pseudornonas and the Group B haemolytic streptococci. Metronidazole with 2nd or 3rd generation Cephalosporin or Benzyl Penicillin & Genatmycin.
Burn wounds P aeruginosa, S aureus, Escherichia coli, Klebsiella and Enterococcus species Piperacillin-tazobactam, Imipenem, Meropenem, Ceftazidime or Piperacillin with Gentamicin, Oxacillin, Cefuroxime, Cefepime, Flucloxacillin, Ciprofloxacin, Levofloxacin, Trimethoprim + Sulfamethoxazole.
Crush injuries P aeruginosa, S aureus, Escherichia coli, Klebsiella and Enterococcus species,anaerobic organisms Piperacillin-tazobactam, Imipenem, Meropenem, Ceftazidime or Piperacillin with Gentamicin, Oxacillin, Cefuroxime, Cefepime, Flucloxacillin,Ciprofloxacin, Levofloxacin, Trimethoprim + Sulfamethoxazole.
Gas gangrene Clostridium perfringens & other species of Clostridium Benzyl Penicillin,Metronidazole,Chloramphenicol (for patients allergic to Penicillin).
Infection at the site of amputation Clostridium perfringens,coliforms, anaerobes,gram positive bacteria. Amoxycillin with Clavulanic acid,Benzyl Penicillin,Metronidazole.
Penetrating/Puncture wounds S aureus, beta-hemolytic streptococci, and various anaerobic bacteria,Pseudomonas aeruginosa, Flucloxacillin, Ciprofloxacin, Levofloxacin, Trimethoprim + Sulfamethoxazole, Piperacillin-tazobactam, Imipenem, Meropenem, Ceftazidime or Piperacillin with Gentamicin, Oxacillin, Cefuroxime, Cefepime.

To know the Generic and Trade names of the above mentioned drugs and their available formulations in Bangladesh click here.


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