Postoperative wound infections, also known as surgical site infections (SSIs), complicate the recovery course of many patients. As defined by the Centers for Disease Control and Prevention (CDC), these infections typically occur within 30 days of an operation at the site or part of the body where the surgery took place, or within a year if an implant is left in place and the infection is thought to be secondary to surgery (1). The organism most often isolated is Staphylococcus aureus (2). Overall, it is estimated that SSIs occur following 1-3.1% of all surgical procedures and account for approximately 2.0% of deaths due to health care-associated infections (HAIs) (3). With regard to abdominal surgery, the rate of wound infection may be much higher, with several prospective studies reporting an incidence of 15-25% depending on the level of contamination (4-6). Knowledge of the bacterial species responsible for these infections and knowledge of their sensitivity to antibiotics are important to improve patient management.

Thus, the objectives of this study are to identify the bacteria responsible for postoperative wound infections and to describe these antibiotic resistances in order to improve the management of these infections.

This study has shown the isolation of staphylococci in 50% of postoperative wound infections. Other studies have also found that the most commonly implicated pathogens in superficial SSIs include gram-positive bacteria, mainly S. aureus, and coagulase-negative staphylococci (1,8). Concerning the antibiotic resistance, these isolates were highly resistant to penicillin G, tetracycline and cotrimoxazole. Indeed, these 3 classes of antibiotics are used frequently by the population. Tetracycline and cotrimoxazole are sold in small grocery stores. Misuse of these antibiotics increases antibiotic resistance. Similarly, self-medication reinforces this high resistance. Fortunately, MRSA isolates are uncommon in this study. Antimicrobial therapy should target these organisms as well as MRSA in patients with specific risk factors (eg, presence of non-penetrating trauma, MRSA infection elsewhere, and history of intravenous drug abuse). First line empiric therapy consists of a first-generation cephalosporin (eg, cefazolin). Vancomycin, daptomycin, linezolid, or an equivalent antibiotic are appropriate when targeting MRSA (3). Indeed, all isolates of staphylococci were sensitive to vancomycin in this study.

Concerning other bacteria, this study found 32.6% of enterobacteria isolated in postoperative wounds. Other studies have also found these bacteria in SSIs (1,9). These isolates are also highly resistant to cotrimoxazole like the staphylococci isolates because of the misuse of this antibiotic. Likewise, they are highly resistant to beta-lactams like amoxicillin, AMC and 3CG. The high consumption of beta-lactams by the population may be responsible for this antibiotic resistance (10) 41.2% of enterobacteria isolated were represented by ESBL-producing enterobacteria. Therefore, broad-spectrum antimicrobial coverage active against gram-negatives should be used in these cases. Indeed, all enterobacteria isolates tested in this study were susceptible to amikacin and imipenem. Another study in Douala also found that imipenem (1.3% of resistance) and amikacin (12.9% of resistance) are the most effective antibiotics against enterobacteria (11). These data suggest that penems (imipenem, meropenem) and aminoglycosides especially amikacin could be an effective alternative choice in enterobacteria infections especially in SSIs. The other aminoglycosides like gentamicin and tobramycin are less effective because they are used frequently in the hospital resulting in the antibiotic resistance of enterobacteria.

Concerning the streptococci isolates, this study has shown 11.5% isolates in postoperative wounds. Other studies have also found streptococci in SSIs (1,12). These isolates are also highly resistant to cotrimoxazole and penicillin G like the staphylococci isolates because of the misuse of these antibiotics. Macrolides, lincosamides, and streptogramins (MLS) are recommended as alternate antibiotics for the treatment of S. pyogenes infections in patients who are allergic to β-lactams or in cases of penicillin failure (13). However, the streptococci isolated in this study were highly resistant to macrolide (erythromycin) and lincosamide (lincomycin). Therefore, broad-spectrum antimicrobial coverage active against streptococci should be used in these cases. In this study, all streptococci isolates tested were susceptible to vancomycin. These data suggest that glycopeptides (teicoplanin and vancomycin) could be an effective alternative choice in streptococci infections especially in SSIs.

Concerning other bacteria, this study found 5.7% of NFGNB isolated in postoperative wounds. Other studies have also found these bacteria in SSIs (1,14). The importance of isolation of NFGNB has increased in last decade, after more and more reports are correlating them with the either infection outbreaks in hospitals, or healthcare-associated infections (15). Concerning antibiotic resistance, this study showed a high resistance of isolates of NFGNB to antibiotics. It is 100% for cotrimoxazole. As mentioned previously, this antibiotic is improperly prescribed in Madagascar and is sold in small grocery stores. Thus, self-medication reinforces this high resistance. Moreover, the molecules of choice, such as penemes and aminoglycosides, are becoming less and less effective, showing 33% (imipenem) and 33% (amikacin) of resistance. These NFGNBs are represented essentially by the species A. baumannii and P. aeruginosa. Similarly, another study in Iran showed resistance A. baumannii with cefixime (99%), ceftazidime (99%), ciprofloxacin (98%), meropenem (99%), trimethoprim-sulfamethoxazole (99%), imipenem (91.5%), ceftriaxone (99%), levofloxacin (96.5%), amikacin (70%) and gentamycin (85%) (16). The emerging challenges of multidrug resistance, both intrinsic and acquired, among NFGNB, are of serious concern to the treating physician. Improved antibiotic stewardship and infection control measures will be needed to prevent or slow down the emergence and spread of multidrug-resistant NFGNB in the healthcare setting. Identification of NFGNB and monitoring their susceptibility patterns will help in improving the empirical therapy (17).

In brief, the bacteria responsible for postoperative wound infections or SSIs have been represented by staphylococci, enterobacteria, streptococci and NFGNB. The majority of these bacteria are resistant to penicillins and cotrimoxazole due to the misuse of these antibiotics and self-medication in the population. All streptococci and staphylococci isolates tested were susceptible to vancomycin. Similarly, all enterobacteria isolates were susceptible to imipenem and amikacin. Among these bacteria, NFGNB were the most resistant to antibiotics. Thus, In view of the antimicrobial resistance of NFGNB, detection in a patient must be the subject of an official declaration of the circulation of this strain at Coordination Center for the Fight against Nosocomial Infections.